CIGRE Green Books
CIGRE
Study Committee B1: Insulated Cables
Accessories for
HV and EHV
Extruded Cables
Volume 1: Components
CIGRE Green Books
Series Editor
CIGRE
International Council on Large Electric Systems (CIGRE)
Paris, France
CIGRE presents their expertise in unique reference books on electrical power
networks. These books are of a self-contained handbook character covering the
entire knowledge of the subject within power engineering. The books are created
by CIGRE experts within their study committees and are recognized by the engineering community as the top reference books in their fields.
More information about this series at http://www.springer.com/series/15209
Pierre Argaut
Editor
Accessories for HV and
EHV Extruded Cables
Volume 1: Components
With 217 Figures and 111 Tables
Editor
Pierre Argaut
Héricy, France
ISSN 2367-2625
ISSN 2367-2633 (electronic)
ISBN 978-3-030-39465-3
ISBN 978-3-030-39466-0 (eBook)
ISBN 978-3-030-39467-7 (print and electronic bundle)
https://doi.org/10.1007/978-3-030-39466-0
© Springer Nature Switzerland AG 2021
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Message from the President
CIGRE is the global expert community for electric power systems. It is a nonprofit
organization based in Paris. It consists of members from over 100 countries
representing 61 national committees. It functions as a virtual organization with
members who are experts in their technical field, forming working groups dealing
with issues facing the power delivery industry. In 2019, 230 working groups
including more than 3000 experts were working together to resolve the identified
issues. The output of the working groups is technical brochures. There are over 700
technical brochures, which contain the combined knowledge and practice of engineering experts from all over the world. The brochures are practical in nature
enabling the engineer to plan, design, construct, operate, and maintain the power
delivery systems as required. CIGRE has over 10,000 reference papers and other
documents supporting the brochures and dealing with other relevant technical
matters.
This Green Book on Accessories for HV and EHV Cable Systems, compiled by
Study Committee (SC) B1, “Insulated Cables” provides state of the art in the design
and application of Accessories in HV and EHV Cable Systems. The book comprises
material from published technical peer-reviewed publications and technical experts
in the field. CIGRE is a source of unbiased technical information. Engineers can
refer this book without fear of favoring one supplier or country. It is a compilation of
the combined expertise of many international experts.
Like other CIGRE Green Books this book contains input from several tens of
experts; not only one or two. These international experts have provided technical
information relevant to readers irrespective of where the readers reside. The views
expressed and suggestions made are unbiased objective statements. These can be
used as references for engineers to develop standards such as IEC Standards and
guidelines within their organizations. This book is a reference book for academia,
power transmission engineers, consultants, and users. For each of the chapters of this
book, a tutorial has been prepared by the members of the Working Group who
published the content of the chapter as a technical brochure or a report in Electra to
disseminate this unbiased information.
By collecting the knowledge and experience gained over time in the field of cable
accessories and systems, this book not only explains the know-how but also the
know why.
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Message from the President
I would like to congratulate those involved from SC B1 who have compiled this
book. Many of them have had to work in their spare time for hours to complete this
task, for which they worked as volunteers. I specifically want to address on behalf of
Cigre all my thanks and gratitude to Pierre Argaut, Past Chair of Study Committee
B1 for leading this formidable task. I would recommend this book in forming the
basis for Underground Transmission System design activities now and in the future.
December 2020
Michel Augonnet
Michel Augonnet is a graduate electrical engineer from
Centrale Supelec (1973).
Forty-two years of his career was related to Alstom
Group in the field of power generation, transmission,
and distribution, with a focus on electrical systems,
control and instrumentation, project management, and
sales.
Michel is currently the president of SuperGrid Institute
(an electrical research and testing laboratory in Lyon,
France); a board member of AEG Power Systems,
Mastergrid SA; and an alternate board director for
ACTOM (PTY) South Africa.
Michel is president of CIGRE, and outgoing treasurer
and former president of the French NC.
Message from the Chairman of the Technical
Council of CIGRE
This Green Book on Accessories for HV and EHV cable systems aims at describing
the cumulated experience gained by CIGRE experts in the domain of accessories for
transmission underground systems.
It is well known that the reliability and performance of a cable circuit is dependent
in equal measures on the design of the cable and accessories and on the skill and
experience of the person who is assembling the accessory. The cable insulation is
manufactured in the factory under controlled process conditions using selected
materials of high quality. It is equally important that the same quality measures are
employed for the manufacture of the accessories in the factory and for their assembly
on site onto the specially prepared cable.
It is essential to select the design of accessory to be exactly compatible with the
particular cable type and the particular service application. Compatibility should be
validated by electrical type approval tests and be supported by prequalification tests,
and satisfactory service experience. In particular, the performance of the accessory is
dependent on the quality, skill, and training of the jointing personnel and on the use
of the specialized tools required for a particular accessory.
The chapters of this book form the basis of the information that is needed by the
manufacturer and installer of the cable and accessories. For many applications the
cable manufacturer also manufactures, supplies, and installs the accessories as part
of the complete cable circuit. In the event that the user purchases the accessories
separately from the cable, the Green Book will also provide the basis of the
information (including tests reports) that should be needed to obtain the appropriate
performance of the system, both in the case of a new underground line of “the Power
System of the Future” or in the upgrading process of an existing line “to make the
best use of the existing power system”.
This Green Book has been authored by leading industry, research, and academic
professionals, acting as members of Working Groups within Study Committee B1,
who published technical brochures and prepared tutorials, providing all stakeholders
with high quality and unbiased information.
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Message from the Chairman of the Technical Council of CIGRE
I take the opportunity to acknowledge the editor, the chapters’ authors, and all the
numerous contributors in working bodies for this contribution from which the entire
global power systems will benefit. Also, I especially acknowledge the leading role of
Study Committee B1 – Marco Marelli on the realization of this Green Book.
Marcio Szechtman
CIGRE Technical Council Chair
Marcio Szechtman graduated and received his Ms. Sc.
degree in Electrical Engineering from the University of
Sao Paulo – Brazil, in 1971 and 1976, respectively.
He joined CIGRE in 1981 and became the Study Committee Chair of B4 (DC Systems and Power Electronics) between 2002 and 2008. He received the CIGRE
Medal in 2014 and was elected as Technical Council
Chair in 2018.
Marcio has a long career in R&D Power Systems
Centers and since April 2019 was appointed as
Eletrobras Chief Transmission Officer.
Message from the Secretary General
In 2014, I had the pleasure to comment on the launching of a new CIGRE publication collection in an introductory message about the first CIGRE Green Book, the
one on Overhead Lines, the second one being on Accessories for HV Extruded
Cables.
The idea to valorise the collective work of the study committees accumulated
over many decades, by putting together all the technical brochures of a given field in
a single book, was first proposed by Dr. Konstantin Papailiou to the Technical
Committee (now Council) in 2011.
In 2015, cooperation with Springer allowed CIGRE to publish the Green Book on
Overhead Lines again as a “Major Reference Work” distributed through the vast
network of this well-known international publisher. In 2016, the collection was
enriched with a new category of Green Books, the CIGRE “Compact Series,” to
satisfy the needs of the study committees when they want to publish shorter, concise
volumes. The first CIGRE compact Book was prepared by Study Committee D2,
under the title Utility Communication Networks and Services.
The concept of the CIGRE Green Books series has continued to evolve, with the
introduction of a third subcategory of the series, the “CIGRE Green Book Technical
Brochures” (GBTB). CIGRE has published more than 720 technical brochures since
1969, and it is interesting to note that in the first one, on tele-protection, the first
reference was a Springer publication of 1963.
A CIGRE Technical Brochure produced by a CIGRE working group, following
specific Terms of Reference, is published by the CIGRE Central Office and is
available from the CIGRE online library, e-cigre, one of the most comprehensive,
accessible databases of relevant technical literature on power engineering. Between
40 and 50 new technical brochures are published yearly, and these brochures are
announced in Electra, CIGRE’s bimonthly journal, and are available for downloading from e-cigre.
In the future, the Technical Council of CIGRE may decide to publish a technical
brochure as a Green Book in addition to the traditional CIGRE Technical Brochure.
The motivation of the Technical Council to make such a decision is to disseminate
the related information beyond the CIGRE community, through the Springer
network.
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Message from the Secretary General
All CIGRE Green Books, are available from e-cigre in electronic format free of
charge for the co-authors of the Book. CIGRE plans to co-publish new Green Books
edited by the different study committees, and the series will grow progressively at a
pace of about one or two volumes per year.
This new Green Book, a Major Reference Work prepared by Study Committee
B1 on Insulated Cables, is an updated version of the Green Book published in 2014,
and is the seventh of this subcategory.
This new edition comprises two additional chapters related to the most recent
work of SC B1. A second volume of the book will address Accessories in submarine
and DC applications. Some chapters will also cover distribution cable systems.
It is important to know that each of the chapters of this book is the topic of a
dedicated Tutorial prepared by the members of the WG who published the content of
the chapter as a Technical Brochure or an Electra Report.
I want to congratulate all the authors, contributors, and reviewers of this book,
which gives the reader a clear, comprehensive, and unbiased vision of the past,
recent, and future developments of Accessories for HV and EHV Cable Systems.
Secretary General
Philippe Adam
Philippe Adam was appointed secretary general of
CIGRE in March 2014. Graduate of the École Centrale
de Paris, he began his career in EDF in 1980 as a
research engineer in the field of HVDC and was
involved in the studies and tests of outstanding projects
like the Cross Channel 2000 MW link and the first
multiterminal DC link between Sardinia, Corsica, and
Italy. After this pioneering period, he managed the team
of engineers in charge of HVDC and FACTS studies of
the R&D division of EDF. In this period, his CIGRE
membership as a working group expert and then as a
working group convener in Study Committee 14 was a
genuine support to his professional activities. Then,
Philippe held several management positions in the
EDF Generation and Transmission division in the fields
of substation engineering, network planning, transmission asset management, and international consulting
until 2000. When RTE, the French TSO, was created
in 2000, he was appointed manager of the Financial and
Management Control Department, in order to install
this corporate function and the necessary tools. In
2004, Philippe contributed to the creation of RTE international activities first as project director and then
Message from the Secretary General
xi
deputy head of the International Relations Department.
From 2011 to 2014, he has been the strategy director of
Infrastructures and Technologies of the Medgrid industrial initiative. In the meantime, between 2002 and
2012, he served CIGRE as the technical committee
secretary and as the secretary and treasurer of the
French National Committee from 2009 to 2014.
Philippe was appointed secretary general of CIGRE in
March 2014.
Preface
Dear Reader,
This CIGRE Reference Book on Accessories for HV and EHV Extruded Cables is
the first in a series of Reference Books regarding High and Extra High Voltages
Cable Systems.
This first volume of the Book provides information regarding Recommendations
and Guidelines from CIGRE for Design, Installation, and Testing of Accessories for
AC extruded cables. Accessories for HVDC extruded cables will be introduced in a
second volume together with accessories for submarine applications.
The Book compiles the results of the work by several Working Groups and Task
Forces of CIGRE Study Committee 21/B1 and Joint Working Groups and Joint Task
Forces with other Study Committees. Many experts from Study Committees 21/B1
(HV Cables), 15/D1 (Materials and Emerging Test Techniques) and 33/B3 (Substations) have participated in this work in the last 30 years in order to offer
comprehensive, continuous, and consistent outputs. I would like to express my
deepest thanks to these WG members who made all this possible.
This volume is divided into 11 chapters as follows:
▶ Chapter 1, “Compendium of Accessory Types Used for AC HV Extruded Cables”
is the output of WG 21.06, published as TB 177 in 2001 and convened by
Z. IWATA (Japan). This chapter is a compendium of accessory types made in
1995. Of course ▶ Chap. 1, “Compendium of Accessory Types Used for AC HV
Extruded Cables”, which was written by WG 21.06 around 20 years ago, does not
describe some designs of accessories currently offered in the market. Since 2001
new designs of accessories (plug-in connectors, cold shrinkable premoulded
accessories) have been introduced in the market. Nevertheless, they are still of
the same type as the family of accessories inventoried in 2001. It is thus possible
to manage the extension of qualification of the “classical” designs towards the
newer innovative designs through the functional analysis described in ▶ Chap. 4,
“Qualification Procedures for HV and EHV AC Extruded Underground Cable
Systems” and since the basics of interfaces in accessories have been carefully
studied and explained in ▶ Chap. 3, “Interfaces in Accessories for Extruded HV
and EHV Cables”.
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Preface
▶ Chapter 2, “A Guide to the Selection of Accessories” contains further outputs of
WG 21.06, (published in TB 177) and proposes a Guide for the Selection of
Accessories. The goal was to establish and recommend good practice to obtain
the expected performance from accessories.
▶ Chapter 3, “Interfaces in Accessories for Extruded HV and EHV Cables” is the
output of TF 21.15, published as TB 210 in 2002 and convened by H. GEENE
(Netherlands). This chapter deals with the many interface aspects both electrical
and mechanical between cables and joints/sealing ends.
▶ Chapter 4, “Qualification Procedures for HV and EHV AC Extruded Underground
Cable Systems” is the output of WG B1.03, published as TB 303 in 2006 and
convened by J. BECKER (Belgium). This chapter deals with the Prequalification,
Type, Sample, and Routine Testing of Extruded Cables and Joints/Sealing Ends
in the range of 170 to 550 kV.
▶ Chapter 5, “Cable Accessory Workmanship on Extruded High Voltage Cables” is
the output of WG B1.22, published as TB 476 in 2011 and convened by
K. LEEBURN (South Africa). This chapter contains Guidelines with
recommended practices in Workmanship. As the continuous increase in voltage
levels also resulted in increase of electrical stresses at the interface of cables and
accessories, it was necessary to produce Guidelines with recommended practices
in Workmanship to ensure reliable installation of joints and sealing ends.
▶ Chapter 6, “Guidelines for Maintaining the Integrity of Extruded Cable Accessories” is the output of WG B1.29, published as TB 560 in 2013 and convened by
E. BERGIN (Ireland). This chapter deals with how to maintain the Integrity of
Accessories for Extruded Cables and is one of the most important issues, both for
new and existing installations. It takes into account the recommendations for a
better workmanship as proposed in ▶ Chap. 5, “Cable Accessory Workmanship
on Extruded High Voltage Cables” and indicates new ways and procedures to
obtain higher reliability from joints and sealing ends.
▶ Chapter 7, “Feasibility of a Common, Dry Type Plug-in Interface for GIS and
Power Cables above 52 kV” is the output of JWG B1.B3.33, published as TB
605 in 2014 and convened by P. MIREBEAU (France). This chapter is dedicated
to the design and testing of dry type/plug-in GIS terminations. In the conclusion
of this report, a new work is recommended to propose a standard design of a GIS
termination at voltages up to 145 kV.
▶ Chapter 8, “Test Procedures for HV Transition Joints for Rated Voltages 30 kV up
to 500 kV” is the output of WG B1.24, published as TB 415 in 2010 and
convened by M. MARELLI (Italy). This chapter gives recommendations for
testing AC transition joints. Transitioning from old Cable Technology (LPOF)
to New Cable Technology (Extruded) is one of the ways to prepare the Network
of the Future while making the Best Use of the Existing Equipment. For DC
systems this is also achieved by means of transition joints. A chapter in the second
volume of the book will deal with DC Transition joints.
▶ Chapter 9, “Thermal Ratings of HV Cable Accessories” is the output of TF 21.10,
published in Electra 212 in 2004, and convened by R. SCHROTH (Germany) and
later on by H. GEENE (Netherlands) and is mainly of historical value. It is very
Preface
xv
useful to help the reader to better understand how to match the thermal performance of an accessory with the thermal performance of the cable. This has been
taken into account in the existing IEC Standards (IEC 60840 and 62067) and also
in Chap. ▶ 4, “Qualification Procedures for HV and EHV AC Extruded Underground Cable Systems”.
▶ Chapter 10, “Test Regimes for HV and EHV Cable Connectors” deals with Cable
Connectors. It is the output of TB 758, published in 2019 by WG B1.46 and
convened by M. UZELAC (USA) to cover Test regimes for HV and EHV various
types of cable conductors, both in Copper or Aluminum.
▶ Chapter 11, “Standard Design of a Common, Dry Type Plug-in Interface for GIS
and Power Cables up to 145 kV” is the output of TB 784, published by JWG B1.
B3.49 in 2019 to propose a “Standard Design of a Common, Dry type, Plug-in
Interface for GIS and Power Cable up to 145 kV” as recommended in ▶ Chap. 7,
“Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power Cables
above 52 kV”. This JWG was convened by P. MIREBEAU (France) as JWG B1.
B3.33.
As immediate past Chairman of SC B1, as well as being a Member of several of
the Working Groups, I have reviewed these chapters. I can confirm that all of them
give unbiased information, which will be useful for those involved in new cable
systems’ projects or in upgrading old systems.
In this task of reviewing and with the help of the Conveners of the Working
Groups, I have been assisted by Mrs. LIU Ying (CN). I would like to express my
deepest thanks to all of them.
Among all these experts and co-authors, a special mention should be made to two
of them who are sadly missed by our community: Jean BECKER (▶ Chap. 4,
“Qualification Procedures for HV and EHV AC Extruded Underground Cable
Systems”) and Eugene BERGIN (▶ Chap. 6, “Guidelines for Maintaining the
Integrity of Extruded Cable Accessories”). This book is dedicated to their memory.
We will never forget how good friends and colleagues they were for all of us.
Of course, this first volume of the Book will be updated, as soon as new relevant
official documents from B1 are available.
Contents
1
Compendium of Accessory Types Used for AC HV Extruded
Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Zensuke Iwata
1
2
A Guide to the Selection of Accessories
Zensuke Iwata
.....................
59
3
Interfaces in Accessories for Extruded HV and EHV Cables . . . . .
Henk Geene
81
4
Qualification Procedures for HV and EHV AC Extruded
Underground Cable Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Jean Becker
97
Cable Accessory Workmanship on Extruded High Voltage
Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Kieron Leeburn
191
Guidelines for Maintaining the Integrity of Extruded Cable
Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Eugene Bergin
257
Feasibility of a Common, Dry Type Plug-in Interface for GIS
and Power Cables above 52 kV . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pierre Mirebeau
317
Test Procedures for HV Transition Joints for Rated Voltages
30 kV up to 500 kV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Marco Marelli
369
5
6
7
8
9
Thermal Ratings of HV Cable Accessories . . . . . . . . . . . . . . . . . . .
Henk Geene and Reinhard Schroth
401
xvii
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Contents
10
Test Regimes for HV and EHV Cable Connectors . . . . . . . . . . . . .
Milan Uzelac
11
Standard Design of a Common, Dry Type Plug-in Interface
for GIS and Power Cables up to 145 kV . . . . . . . . . . . . . . . . . . . .
Pierre Mirebeau
421
529
About the Editor
Pierre Argaut was graduated as electrical engineer
from the “Institut d’Electrotechnique de Grenoble” in
1971. He joined Delle-Alsthom (HV Switchgear Manufacturer) in November 1971 and took several positions
before heading the R&D Department on GIS. After
being operation manager of South European Pipeline,
he joined SILEC in 1988 and retired at the end of 2010.
His last position with SILEC was senior vice president.
In Study Committee B1 (Insulated Cables), Pierre
has held position of working group member
(21.09;21.06;21.07;21.17), French SC member, working group convener (B1.19), special reporter (2010),
advisory group convener (Tutorial Advisory Group till
2010), and chairman of SC B1 from August 2010 to
August 2016. He received the Technical Committee
Award in 2000, the Distinguished Member Award in
2002, and the title of Honorary Member of CIGRE in
2016.
xix
Contributors
Jean Becker Charleroi, Belgium
Eugene Bergin Dublin, Ireland
Henk Geene Prysmian Group, Product Management HV Accessories, The Hague
Area, Netherlands
Zensuke Iwata Kamakura, Japan
Kieron Leeburn CBI Electric African Cables, Chief Engineer Process and Product
in HV, Vereeniging, South Africa
Marco Marelli Prysmian Group, System Engineering, Land and Submarine HV
and EHV AC/DC Power Cable Systems and Telecom Cable Systems, Milano, Italy
Pierre Mirebeau Villebon sur Yvette, France
Reinhard Schroth Berlin, Germany
Milan Uzelac G&W Electric Co, R&D, HV Cable Accessories, Bolingbrook, USA
Jean Becker: deceased.
Eugene Bergin: deceased.
Zensuke Iwata has retired.
Pierre Mirebeau has retired.
Reinhard Schroth has retired.
xxi
1
Compendium of Accessory Types Used
for AC HV Extruded Cables
Zensuke Iwata
Contents
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Types of Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2.1 Types of Straight Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2.2 Types of Transition Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2.3 Types of Y Branch Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3 Types of Terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3.1 Types of Metal Enclosed GIS Terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3.2 Types of “Oil Immersed Transformer” Terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3.3 Types of Outdoor Terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3.4 Types of Indoor Terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3.5 Types of Temporary Terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Appendix: Glossary of Component Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Glossary of Names for Components Used in Accessories for Extruded Cables . . . . . . . . . . .
1.1
1
2
5
12
15
16
17
21
22
28
33
34
34
Introduction
Chapter 1 categorises the types of accessory designs available for use on HV cables
with extruded insulation for ac transmission voltages of 60 kV (75.5 kV) and above.
The typical types of extruded cable insulation being low density polyethylene
(LDPE), high density polyethylene (HDPE), cross-linked polyethylene (XLPE)
and ethylene propylene rubber (EPR).
Zensuke Iwata has retired.
Z. Iwata (*)
Kamakura, Japan
e-mail: z.iwata@kamakuranet.ne.jp
© Springer Nature Switzerland AG 2021
P. Argaut (ed.), Accessories for HV and EHV Extruded Cables, CIGRE Green Books,
https://doi.org/10.1007/978-3-030-39466-0_1
1
2
Z. Iwata
The contents were compiled by Cigré Working Group 21-06, as part of a survey
into the world-wide usage of accessories up to the year 1992. The purpose of
Chapter 1 is twofold;
• To organise the designs into logical categories based upon their function and
principle of design and
• To provide a glossary of the names of their component parts.
The collection of accessory designs has been compiled from those known to have
been used in service applications or to have been developed in the first thirty year
period since the emergence of the extruded type of HV cable. It is important to note
that the inclusion of an accessory design does not imply that it has technical merit or
is preferred for any particular voltage category, nor does the exclusion of a design
imply any censure. Similarly the details of the designs shown are typical and it is
acknowledged that design variations exist of equal utility.
The Chapter 1 is divided into two parts:
Sections 1.2 to 1.3.5:
Appendix:
“COMPENDIUM OF ACCESSORY TYPES”
“GLOSSARY OF COMPONENT NAMES”
The work has been published as Cigré TB 89 (also included in TB 177) in both
English and French versions, these being the dual languages of Cigré. It has been
additionally translated into the German language for reference. The dual language
versions of the Glossary, cross reference each other, for example, the English version
lists each component name together with its French counterpart.
Sections 1.2 to 1.3.5 is a compendium of the generic types of accessories. The
accessory designs are divided firstly into the main categories of joints and terminations and secondly into sub-categories. For example Type 1.2.1.2, Fig 1.6, is a
“straight joint” of the “prefabricated” type, employing “composite” insulation. A
diagram is provided for each category of design, together with a description of the
accessory and its function. The preferred names of components have been used.
Appendix is a glossary in alphabetic order of the preferred names of the component parts. Each preferred name is accompanied by a definition and a list of
alternative names. For completeness the list of each type of accessory name have
been included under the headings for “straight joint”, “transition joint”, “Y joint”,
“metal enclosed GIS termination”, “oil immersed transformer termination”, “outdoor termination”, “indoor termination” and “temporary termination”, together with
a cross reference by item number to the Compendium of Accessory Types in Sects. 1.2
to 1.3.5. For example under the heading of “outdoor termination” can be found the
“stress cone and insulator” type together with its Part I item number 1.3.3.4.
1.2
Types of Joints
A joint is the insulated and fully protected connection between two or more cables.
Also termed “splice”. The following types exist:
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Compendium of Accessory Types Used for AC HV Extruded Cables
•
•
•
•
Straight Joint
Transition Joint
Screen Interruption Joint
Y Branch Joint.
3
Each of the above joint designs is illustrated by a diagram to show the type of
insulation. For the purpose of clarity other important design details have been
omitted. The design requirements common to each type of joint are:
• A high current connection between conductors.
• A joint insulation which meets the same performance standard as the cable.
• A high current connection to permit the flow of short circuit current between the
two cable sheaths or screen wires.
• A metallic joint shell or screen wire connection electrically insulated from earth
potential to match the insulating integrity of the cable oversheath.
• A protection of the joint and cable insulation against the ingress of water.
• A protection against corrosion of the joint metal work.
In the HV voltage class of greater than 60 kV the majority of extruded cables are of
single core construction, thus straight joints of the single core type have been illustrated.
Three core joints employ the same types of insulation and are grouped together in one
housing as illustrated in Sect. 1.2.2 for transition joints to three core paper insulated cable.
Single core joints with screen interruption, Fig. 1.1, have:
• A gap in the insulation screen.
• An insulated flange in the joint shell.
• Bonding leads to permit the adjacent cable sheaths to be connected in the
configuration necessary for a specially bonded cable system.
Fig. 1.1 “Taped” straight joint with screen interruption
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The insulated flange can be electrically shorted to make the joint suitable for a
solidly bonded cable system.
Joints without screen interruption have an electrically continuous insulation
screen and continuous joint shell; such joints are used for solidly bonded single
core and three core cable systems (Figs. 1.2, 1.3, 1.4, and 1.5 are examples of taped
joints without screen interruption).
For the purpose of comparison the diagram for each type of joint shows the
insulation contained within a metallic joint shell which is plumbed to the cable
sheaths, as shown in Fig. 1.1. This provides a complete water barrier and a connection between the cable sheaths. For buried direct installations it is usual to protect
and to insulate the metallic shell within a compound filled joint box as shown in
Fig. 1.3. For indoor installations, such as tunnels, the joint shell can be insulated by
either a) a polymeric sleeve or wrapping, or b) by pedestal insulators as shown in
Fig. 1.4. For cables which do not have a metallic sheath an alternative design of joint
protection is shown in Fig. 1.5. The cable screen wires are connected across the joint
and the joint is protected within either a compound filled waterproof joint box as
shown, by a heat shrink sleeve or by a wrapping of elastomeric or adhesive tape.
Fig. 1.2 “Taped” straight joint without screen interruption
Fig. 1.3 Typical protection for a joint with metallic shells for direct burial
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5
Fig. 1.4 Typical protection for a joint with metallic shells for indoor installations
Fig. 1.5 Typical protection for a joint without metallic shells for direct burial and for indoor
installations
1.2.1
Types of Straight Joints
A straight joint connects two cables of the same type. Also termed “straight splice”.
•
•
•
•
•
“Taped” Joint
“Prefabricated” Joint
“Field Moulded” Joint
“Heat Shrink Sleeve” Joint
“Back-to-back” Joint.
1.2.1.1 “Taped” Joints
“Self Amalgamating Tape” Type
Elastomeric semi-conducting and insulating tapes are wound onto the cable to form the
conductor screen, the insulation, the stress control profile screens, the insulation screen
and the screen interruption insulation, Figs. 1.1 and 1.2. Stretching the tape during
application activates amalgamation between the layers of tape to form a solid mass.
“Adhesive Tape” Type
Semi-conducting and insulating tapes which have been pre-coated with an adhesive
layer are wound onto the cable as described for the “self amalgamating tape” type.
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1.2.1.2 “Prefabricated” Joints
Prefabricated straight joints employ insulation that has been preformed and tested in
the factory. The usual methods of manufacture are to mould elastomeric insulation
and to cast thermoset resin insulation.
“Composite” Type
Two factory premoulded elastomeric stress cones are inserted into a central insulator
of cast thermoset resin, Fig. 1.6. Pressure at the stress cone to central insulator
interface and at the cable core interface is maintained by a compression device which
is usually comprised of metallic springs.
“Premoulded One-Piece” Type
A single premoulded elastomeric sleeve forms the insulation as shown in Fig. 1.7, it
is complete with insulation, connector screen, stress control profile screens, insulation screens and, where applicable, screen interruption. Interfacial pressure at the
sleeve to cable core interface is maintained by the elastic memory of the sleeve.
Fig. 1.6 “Prefabricated composite” joint
Fig. 1.7 “Premoulded one-piece” joint
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Fig. 1.8 “Premoulded two-piece” joint
Fig. 1.9 “Premoulded three-piece” joint
“Premoulded Two-Piece” Type
A two-piece joint, Fig. 1.8, is similar to the one-piece type, but the elastomeric
insulation is comprised of a large diameter premoulded sleeve which is stretched to
fit on top of a smaller diameter elastomeric adaptor moulding.
“Premoulded Three-Piece” Type
The three-piece joint, Fig. 1.9, has insulation comprised of a large diameter, cylindrical sleeve, elastomeric moulding which is stretched to fit onto two elastomeric
adaptor mouldings.
1.2.1.3 “Field Moulded” Joints
Field moulded joints employ insulation that is melted, moulded and consolidated to
the prepared cable insulation in situ ie. “in the field”.
The following types of joints differ in the processes used to form the insulation, these
are summarised in Table 1.1. The completed joints all have a similar design as shown in
Fig. 1.10.
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Table 1.1 The Typical Methods Used to Form the Insulation of Field Moulded Joints
Types of Joint
Tape moulded
Crosslinked tape
moulded
Forming Process of Joint
Insulation
Taping ! Moulding
Taping ! Moulding !
Crosslinking
Extrusion moulded
Extrusion ! Moulding
Crosslinked
extrusion moulded
Extrusion ! Moulding !
Crosslinking
Injection moulded
Pellets ! Injection
Crosslinked
injection moulded
Pellets ! Injection !
Crosslinking
Block moulded
Premoulded block ! Moulding
Crosslinked block
moulded
Premoulded block ! Moulding
! Crosslinking
Diagram
“Tape Moulded” Type
The insulation is applied in the form of layers of elastomeric or polymeric tape. A
heated mould is fitted around the insulation. The insulation is softened and melted by
the heat. Pressure which is generated by the thermal expansion consolidates the
melted insulation both to itself and to the cable insulation. The connector screens and
insulation screens are usually applied separately to the insulating process.
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9
Fig. 1.10 “Field moulded” joint
“Crosslinked Tape Moulded” Type
As above, but with the addition of a prolonged heating process at elevated temperature, which activates a chemical agent within the tapes to crosslink the insulation.
External pressure (hydraulic, pneumatic or mechanical) is applied to prevent the
formation of voids.
“Extrusion Moulded” Type
The prepared cable core is housed within a mould. An extruder containing a rotating
screw is used to heat and soften the insulating material before injection into the mould.
The insulation is allowed to cool under pressure to consolidate the insulation to the
prepared cable core.
“Crosslinked Extrusion Moulded” Type
As above, but with the addition of a prolonged heating process at elevated temperature
to activate the chemical agent within the insulation material after the insulation has been
formed around the cable. External pressure is applied to prevent the formation of voids.
“Injection Moulded” Type
As for the extrusion moulded type, but the insulating material is heated and melted in
a cylinder or pot, it is then injected into the mould, either mechanically by a piston,
or by the direct application of gas or liquid pressure.
“Crosslinked Injection Moulded” Type
As above, but with the addition of a prolonged heating process at elevated temperature
to activate the chemical agent within the insulation material after the insulation has been
formed around the cable. External pressure is applied to prevent the formation of voids.
“Block Moulded” Type
The insulation is premoulded in the form of two mouldings which are divided
longitudinally. These half mouldings are fitted to the prepared cable core and are
themselves encased in a heated mould tool to consolidate them to the cable.
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Fig. 1.11 “Heat shrink sleeve” joint
“Crosslinked Block Moulded” Type
As above, but with the addition of a prolonged heating process at elevated temperature
to activate the chemical agent within the insulation material once the insulation
material has been formed around the cable. External pressure is applied to prevent
the formation of voids.
1.2.1.4 “Heat Shrink Sleeve” Joint
A crosslinked polyolefin sleeve is heated to above its crystalline melting point and is
expanded to a large diameter in a factory process. It is then allowed to cool and freeze at
the larger diameter. During assembly of the joint the sleeve is positioned over the
conductor connector and is again heated to above the crystalline melting point such that
the sleeve contracts to form an intimate fit with the cable. The insulation and screens
may be supplied as one integral sleeve or as several individual sleeves. Stress control
sleeves which are pre-loaded with either a resistive or high permittivity filler may also
be applied over the joint to control the stress distribution as shown in Fig. 1.11.
1.2.1.5 “Back-to-Back” Joint
These joint designs are derived from certain types of cable terminations and as such
are part insulated with either a dielectric liquid or pressurised SF6 gas. Provision is
made in the design to withstand the effects of the thermal expansion of these fluid
insulants (see item 1.3).
“Back-to-Back” Joint with Two Insulators
The joint, as shown in Fig. 1.12, is comprised of either a) two metal enclosed GIS
terminations which are connected with a short length of SF6 gas insulated busbar
trunking, as described in item 1.3.1, or b) two oil immersed terminations which are
connected with a short length of liquid insulated busbar trunking, as described in
item 1.3.2. These joints can be single phase or three phase. For the latter type, three
termination insulators are mounted on a barrier plate. The insulators anchor the
conductors and segregate the SF6 gas or insulating liquid from each cable. Some
designs employ a mixture of SF6 and N2 gas.
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11
Fig. 1.12 “Back-to-Back” joint with two insulators
Fig. 1.13 (a) “Back-to-Back” joint with one insulator and fluid insulation. (b) “Back-to-Back”
joint with one insulator and solid insulation
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“Back-to-Back” Joint with One Insulator
One half of the joint employs an insulator as described in item 1.2.1.5 for the “backto-back” joint with two insulators. In the second half of the joint, Fig. 1.13a, the
cable termination is “open”, that is it is terminated as in a “directly immersed” GIS or
oil immersed transformer termination. Alternatively, as shown in Fig. 1.13b, the
second half of the joint can be insulated by solid insulation formed from tape or an
elastomeric sleeve. The single insulator anchors the conductors and centralises the
corona shield within the SF6 gas or liquid filled joint shell. It is necessary to seal the
“open” cable to prevent ingress of the SF6 gas or liquid into it.
“Back-to-Back” Joint Without Insulator
Both of the cable terminations are “open” as shown in Fig. 1.14, that is they are terminated
as in a “directly immersed” GIS or oil immersed transformer termination. It is necessary to
seal both of the “open” cables to prevent ingress of the SF6 gas or liquid into them.
1.2.2
Types of Transition Joints
A transition joint connects two cables of different types, for example a polymeric
extruded cable to a self-contained oil filled cable. Transition joints are sometimes
employed to connect cables of the same type, but with different conductor sizes. In
the latter application they are designed to withstand imbalanced conductor thermomechanical force.
• “Polymeric extruded cable to mass impregnated cable” transition joint.
• “Polymeric extruded cable to oil filled paper cable” transition joint.
• “Polymeric extruded cable to gas pressurised paper cable” transition Joint.
▶ Chapter 8, “Test Procedures for HV Transition Joints for Rated Voltages
30 kV up to 500 kV” of this book is dedicated to tests procedures for HV
Transition Joints for Rated Voltages 30 kV to 500 kV.
Fig. 1.14 “Back-to-Back” joint without insulator
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13
Fig. 1.15 “Polymeric extruded cable to mass impregnated cable” transition joint
Fig. 1.16 “Polymeric extruded cable to oil or gas filled paper cable” transition joint, three core type
1.2.2.1 “Polymeric Extruded Cable to Mass Impregnated Cable”
Transition Joint
The hydrocarbon compound impregnant in the paper cable is segregated from the
polymeric cable by a) a stop ferrule which contains a solid barrier and b) a barrier
tape or sleeve which is usually applied over the core of the paper cable to seal onto
the ferrule. The joint, as shown in Fig. 1.15, is then insulated with tape or sleeves in
the conventional manner.
Alternatively the two cables can be segregated using a solid central barrier as
described in 1.2.2.2.
1.2.2.2 “Polymeric Extruded Cable to Oil or Gas Filled Paper Cable”
Transition Joint, Three Core Type
The two cables are segregated by a solid central barrier comprised of three insulated
conducting rods in the form of bushings, Fig. 1.16. The barrier is usually premoulded
in thermoset resin and is designed to withstand the pressure in the oil or gas filled
cable. The joint insulation on the polymeric cable side may be formed of any of the
types described for the straight joint (i.e. taped, premoulded elastomeric sleeve, heat
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shrink sleeve etc.). The joint on the paper cable side is usually insulated with either
impregnated plain or crepe paper tapes.
The solid barrier can also be formed, as shown in Figs. 1.12 and 1.13a, by either a)
two sets of three back-to-back GIS terminations, which are connected within a short
length of SF6 gas or oil insulated busbar trunking, or b) one set of three back-to-back
oil immersed terminations within a short length of oil insulated busbar trunking.
For the “oil immersed termination” design of joint, one set of insulators can be
omitted and the cable oil can be used to insulate both the busbar trunking and the
paper insulated cable, as shown in Fig. 1.13a (but with each paper cable termination
of the “open” unscreened type).
1.2.2.3 “Polymeric Extruded Cable to Oil or Gas Filled Paper Cable”
Transition Joint, Single Core “Non-Fed” Type
The solid barrier contains one bushing, Fig. 1.17, of the type described for the three
core cable. With this design of joint it is not possible to feed the oil or gas directly
into the central conductor duct of the paper cable. The oil or gas is fed indirectly via
the annular gap between the cable core and the metallic sheath.
1.2.2.4 “Polymeric Extruded Cable to Oil or Gas Filled Paper Cable”
Transition Joint, Single Core “Fed” Type
The joint in Fig. 1.18 employs a central barrier, usually of cast thermoset resin, which
closely resembles the stop joint employed to segregate pressure between two single
core oil filled cables. The barrier is cylindrical and contains an embedded metallic HV
electrode, which is bolted to the conductor connection to form the oil seal. Paper
insulation is hand applied onto the paper cable, often with the addition of a stress
cone cast in thermoset resin, such that a thin annular channel is formed to permit oil or
gas to be fed to the central conductor duct. The insulation on the polymeric cable side
can be in the form of the “prefabricated composite” design, as shown in Fig. 1.18, in
which an elastomeric stress cone is compressed by springs into the bore of the barrier, or
in the form of tape or premoulded elastomeric sleeves, as shown in Figs. 1.7 and 1.17.
Alternatively the “back-to-back” type of straight joint, Figs. 1.12, 1.13a, b, can be
used to permit gas or oil to be fed directly to the conductor central duct.
Fig. 1.17 “Polymeric extruded cable to oil or gas filled paper cable” transition joint, single core,
‘non-fed’ type
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15
Fig. 1.18 “Polymeric extruded cable to oil or gas filled paper cable” transition joint, single core,
“fed” type
1.2.3
Types of Y Branch Joints
A Y branch joint joins together three cables. In principle any of the types of
insulation employed for the straight joint can be considered, however in practice
this is a specialised application in which the “prefabricated composite” design,
Fig. 1.19, has been the most frequently employed. The three conductor connectors
are plugged into an HV electrode. The HV electrode is embedded in a factory cast
Fig. 1.19 “Prefabricated composite” Y branch joint
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thermoset resin barrier from which protrude three half joints of the “composite type”,
described in 1.2.1.2.
1.3
Types of Terminations
A termination is the connection between a cable and other electrical equipment. Also
termed “pot-head”.
•
•
•
•
•
Metal or Sealing End enclosed GIS termination
Oil immersed transformer termination
Outdoor termination
Indoor termination
Temporary termination.
Each of the above termination designs is illustrated by a diagram to show the type
of insulation. For the purpose of clarity other important design details have been
omitted. The design requirements common to each type of termination are:
•
•
•
•
A high current connection from the cable conductor to an external busbar.
Insulation to the same performance standard as the cable.
Provision of support to the cable.
Ability to withstand cable thermomechanical loads and external forces such as
wind, ice and busbar loading.
• A high current connection to permit the flow of short circuit current from the
cable metallic sheath or shield wires via a bonding lead to the system earth.
• A connection to the cable metallic sheath or earth wires which is electrically insulated
from earth potential to match the insulating integrity of the cable oversheath.
• Protection to the cable insulation and sheath against the ingress of atmospheric
water and the ingress of pressurised dielectric liquid or gas from adjacent metalclad busbar trunking.
Some termination designs are filled with either a dielectric liquid or pressurised
SF6 gas to provide insulation. Provision is required in such designs to withstand the
effects of the thermal expansion of these insulants. The incompressible nature of a
dielectric liquid requires that an expansion volume be provided. The expansion
volume can be formed by an air or gas filled space, usually at the HV end of the
insulator, or by either a) an external header tank, b) an external pressurised feed tank,
or c) an internal flexible accumulator containing gas usually at the LV end of the
termination. In the case of an internal air volume these terminations are only suitable
for vertical installation or for max inclined angle or 30 . If they are to be installed
inclined, horizontally or inverted then it is usual to fill the termination completely
with insulating liquid and to provide either external compensation or an internal
flexible accumulator containing gas. An expansion volume is not necessary for
gaseous insulation because of its compressible nature, however the termination
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Compendium of Accessory Types Used for AC HV Extruded Cables
17
must either be designed to withstand the increased pressure or an external gas
cylinder must be connected to limit the pressure to an acceptable level.
1.3.1
Types of Metal Enclosed GIS Terminations
This is a cable termination which connects to a busbar within metal trunking,
insulated with gas. The gas is usually pressurised SF6. The busbar is usually
connected to switchgear.
This type is also termed an “SF6 termination” or “metal enclosed pothead”
•
•
•
•
•
“Stress cone and insulator” termination
“Deflector and insulator” termination
“Prefabricated composite dry type” termination
“Capacitor cone and insulator” termination
“Directly immersed” termination.
1.3.1.1 “Stress Cone and Insulator” Metal Enclosed GIS Termination
A hand taped or premoulded one or two-piece moulded elastomeric stress cone or
moulded plastic stress cone, is fitted to the prepared cable core, as shown in
Fig. 1.20. The cable core can be wrapped with polymeric or paper rolls to a
predetermined diameter before the stress cone is fitted.
Alternatively the stress cone can be field moulded using one of the methods
described for the straight joint (item 1.2.1.3).
The prepared cable is housed within an insulator, which is filled with either
insulating fluid or SF6 gas. The SF6 gas inside the insulator is usually at a significantly lower pressure than the SF6 gas within the GIS busbar trunking. In some
designs either a passageway through the insulator or an external pipe is used to
permit the SF6 gas from the GIS to also provide the insulation for the cable
termination. It is necessary to seal the cable to prevent ingress of SF6 gas or
insulating fluid. In some designs employing a moulded elastomeric stress cone, the
stress cone is sealed to the insulator baseplate by a tube to segregate the dielectric
fluid or gas from the cable. Some designs employ a mixture of SF6 and N2 gas.
The insulator both centralises the conductor within the trunking and anchors it to
prevent longitudinal movement due to thermomechanical conductor force. The
insulator is usually formed from a cast thermoset resin. Porcelain is also employed.
1.3.1.2 “Deflector and Insulator” Metal Enclosed GIS Termination
This is similar to that described in item 1.3.1.1, Fig. 1.20, but has the stress cone
replaced by a deflector cone, which is directly insulated by either the dielectric fluid
or the SF6 gas contained within the termination. Additional stress control can be
employed in the form of a high permittivity layer applied over the cable insulation
adjacent to the insulation screen termination. A typical “deflector” cone is shown
within an outdoor termination in Fig. 1.29.
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Fig. 1.20 “Stress cone and insulator” metal enclosed GIS termination
1.3.1.3 Prefabricated Composite “Dry” Metal Enclosed GIS Termination
A premoulded elastomeric stress cone is inserted into a cast thermoset insulator,
Fig. 1.21. Pressure at the stress cone to insulator interface and at the stress cone to
cable core interface is maintained by metallic springs or similar compressing device.
It is not necessary to fill the insulator with either gas or insulating liquid, thereby
dispensing with the need to provide equipment for pressure monitoring, pressure
compensation and/or a thermal expansion reservoir. This design is now more and
more used. ▶ Chapters 7, “Feasibility of a Common, Dry Type Plug-in Interface for
GIS and Power Cables above 52 kV” and ▶ 11, “Standard Design of a Common,
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19
Fig. 1.21 Prefabricated composite “dry” metal enclosed GIS termination
Dry Type Plug-in Interface for GIS and Power Cables up to 145 kV” of this book
which are dedicated to this design.
1.3.1.4 “Capacitor Cone and Insulator” Metal Enclosed GIS Termination
This is similar to the “stress cone and insulator” type (item 1.3.1.1) in general layout,
but with capacitor stress control instead of geometric stress control.
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Fig. 1.22 “Capacitor cone and insulator” metal enclosed GIS termination
Pre-shaped rolls of polymeric film are wound onto the cable, with sheets of
conducting film interleaved in the rolls to form a linear longitudinal voltage distribution, Fig. 1.22. Alternatively a) the capacitor cone can be assembled onto a tubular
insulator in the factory and then loosely fitted over the prepared cable core on site, or
b) the capacitor cone can be formed from individual toroidal capacitors as shown in
Fig. 1.32. The prepared cable is housed in an insulator which is filled with either
insulating liquid or SF6 gas.
1.3.1.5 “Directly Immersed” Metal Enclosed GIS Termination
The insulator is not employed in this design. The pressurised SF6 gas from the
GIS provides the electrical insulation. The stress cone method of stress control
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21
Fig. 1.23 “Directly Immersed” metal enclosed GIS Termination
is usually employed in this design, Fig. 1.23. It is necessary to seal the
conductor and sheath of the cable to prevent ingress of the SF6 gas. It is
also necessary for the busbar adaptor to centralise the conductor within the
trunking and to prevent or contain longitudinal movement due to conductor
thermomechanical force.
1.3.2
Types of “Oil Immersed Transformer” Terminations
This is a termination into oil insulated metalclad busbar trunking, which is usually
part of the transformer housing. These closely resemble the types of metal enclosed
GIS terminations shown in Figs. 1.20, 1.21, 1.22 and 1.23. A corona shield larger
than the one of GIS Termination is usually fitted on HV side of Oil Immersed
Transformer Terminations.
Also termed “oil immersed transformer potheads”.
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1.3.2.1 “Stress Cone and Insulator” Oil Immersed Transformer
Termination
See item 1.3.1.1 and Fig. 1.20.
1.3.2.2 “Deflector and Insulator” Oil Immersed Transformer
Termination
See item 1.3.1.2 and Figs. 1.20 and 1.29.
1.3.2.3 Prefabricated Composite “Dry” Oil Immersed Transformer
Termination
See item 1.3.1.3 and Fig. 1.21.
1.3.2.4 “Capacitor Cone and Insulator” Oil Immersed Transformer
Termination
See item 1.3.1.4 and Figs. 1.22 and 1.32.
1.3.2.5 “Directly immersed” Oil Immersed Transformer Termination
See item 1.3.1.5 and Fig. 1.23.
1.3.3
Types of Outdoor Terminations
This is a cable termination which interfaces with air insulated equipment and which
is subjected to full climatic conditions.
Also termed “outdoor pothead” or Outdoor Sealing End.
•
•
•
•
•
•
•
•
“Prefabricated” elastomeric sheds and stress cone outdoor termination
“Heat shrink sleeve” outdoor termination
“Elastomeric sleeve” outdoor termination
“Stress cone and insulator” outdoor termination
“Deflector and insulator” outdoor termination
“Prefabricated composite and insulator” outdoor termination
“Capacitor cone and insulator” outdoor termination
“Prefabricated composite and capacitor cone, and insulator” outdoor termination.
1.3.3.1 “Prefabricated” Elastomeric Sheds and Stress Cone Outdoor
Termination
A factory premoulded elastomeric moulding, complete with stress cone profile and
sheds, is stretched onto the prepared cable insulation, as shown in Fig. 1.24.
Alternatively the termination can be formed from a separately moulded stress cone
which interlocks with a set of individually moulded sheds. This terminations are
generally not self supporting.
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23
Fig. 1.24 “Prefabricated”
elastomeric sheds and stress
cone outdoor termination
1.3.3.2 “Heat Shrink Sleeve” Outdoor Termination
Heat Shrink “Stress Control Sleeve” Type
This termination, Fig. 1.25, is similar to the heat shrink sleeve joint (1.2.1.4). The
insulation is formed from a heat shrink sleeve, usually with the assistance of a
resistive, or high permittivity method of longitudinal stress control. It is in the form
of either a secondary sleeve, a taped winding or a mastic pad. The sheds are usually
heat shrunk onto the longitudinal sleeve as the final assembly operation on site. This
terminations are generally not self supporting.
Heat Shrink “Capacitor Cone Stress Control” Type
Stress control is provided by a capacitor cone which is formed from layers of
insulating and semiconducting polymeric tapes, usually of the self-amalgamating
type. A heat shrink sleeve and sheds are applied overall, as shown in Fig. 1.26. This
terminations are generally not self supporting.
1.3.3.3 “Elastomeric Sleeve” Outdoor Termination
This type, Fig. 1.27, is similar to the heat shrink sleeve termination shown in
Fig. 1.26, except that the insulation is supplied in the form of a moulded elastomeric
sleeve, which is stretched onto the prepared cable. Premoulded elastomeric sheds are
then stretched onto the sleeve. Sleeves which are pre-loaded with either a resistive,
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Fig. 1.25 Heat shring stress control sleeve outdoor termination
or a high permittivity filler may be applied over the insulation to control the
longitudinal stress distribution. This terminations are generally not self supporting.
1.3.3.4 “Stress Cone and Insulator” Outdoor Termination
A stress cone is fitted onto the prepared cable core, as shown in Fig. 1.28. The stress
cone can be a factory premoulded one or two piece type or alternatively it can be
formed in situ by hand taping or field moulding. The cable core can be wrapped with
either polymeric or paper rolls to a predetermined diameter before the stress cone is
fitted. Alternatively the stress cone can be field moulded using one of the methods
described for the straight joint (item 1.2.1.3). The prepared cable is housed within an
insulator, which is filled with insulating liquid or gas. The insulator can be formed
from either porcelain, thermoset resin or may be of a composite design as shown in
Fig. 1.28, inset, with a rigid core of cylindrical or conical shape onto which
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25
Fig. 1.26 Heat shring
capacitor cone stress control
sleeve outdoor termination
premoulded elastomeric sheds have been fitted or moulded. In Fig. 1.28 an expansion volume is shown above the liquid level. In some cases the termination is
completely filled with liquid and in these terminations external or internal compensation is required for expansion in the form of a pressure tank or a header tank.
1.3.3.5 “Deflector and Insulator” Outdoor Termination
A deflector stress control profile made of metal or semiconducting elastomer is fitted
onto the prepared cable core, as shown in Fig. 1.29. The prepared cable is housed
within an insulator, which is filled with insulating liquid or gas. The insulator can be
formed from either porcelain, thermoset resin or may be a composite design with a
rigid core of cylindrical or conical shape onto which premoulded elastomeric sheds
have been fitted or moulded. Variations of this design exist with and without a high
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Fig. 1.27 “Elastomeric sleeve” outdoor termination
permittivity stress control layer applied adjacent to the cable insulation screen
termination.
1.3.3.6 “Prefabricated Composite and Insulator” Outdoor Termination
An elastomeric moulded stress cone is inserted into a conical thermoset casting,
as shown in Fig. 1.30. Pressure at the stress cone to cable interface is maintained
by metallic springs. In the design shown, the stress cone and conical casting
also segregate the insulating liquid or gas from the cable. The prepared cable
core is housed within an insulator which is filled with either insulating liquid
or gas.
1.3.3.7 “Capacitor Cone and Insulator” Outdoor Termination
Capacitor Cone and Insulator “Cylindrical Capacitor Cone” Type
As shown in Fig. 1.31, pre-shaped cylindrical rolls of polymeric film are wound onto
the cable in situ, with sheets of conducting film interleaved to form a linear
longitudinal voltage distribution. Alternatively the cylindrical capacitor cone can
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27
Fig. 1.28 “Stress cone and insulator” outdoor termination
be assembled onto a tubular insulator in the factory and then loosely fitted over the
prepared core on site.
Capacitor Cone and Insulator “Toroidal Capacitor” Type
This capacitor cone, Fig. 1.32, is formed of discrete toroidal shaped capacitors,
which are stacked vertically on top of one another and are loosely fitted over the
prepared cable core. The prepared cable is housed in an insulator which is filled with
either insulating liquid or gas.
1.3.3.8 “Prefabricated Composite and Capacitor Cone, and Insulator”
Outdoor Termination
As shown in Fig. 1.33, a cylindrical capacitor cone and premoulded elastomeric
stress cone is fitted onto the cable to form a linear longitudinal voltage distribution.
The premoulded elastomeric stress cone is described in 1.3.3.6, Fig. 1.30, and the
cylindrical stress cone is described in 1.3.3.7, Fig. 1.31. The prepared cable is
housed in an insulator which is filled with either insulating liquid or gas.
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Fig. 1.29 “Deflector and insulator” outdoor termination
1.3.4
Types of Indoor Terminations
These are essentially outdoor terminations for which the creepage length and sometimes
the height of the insulator have been reduced for those situations in which the termination is subjected to neither wet atmospheric conditions nor to air pollution. When sheds
are not required, the insulator is of a simple cylindrical or conical shape. The methods of
stress control are the same as those described for the outdoor termination, item 1.3.3.
Indoor terminations closely resemble the types of outdoor terminations shown in
Figs. 1.24, 1.25, 1.26, 1.27, 1.28, 1.29, 1.30, 1.31, 1.32 and 1.33.
Also known as “indoor potheads” or Sealing Ends.
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Compendium of Accessory Types Used for AC HV Extruded Cables
Fig. 1.30 “Prefabricated composite and insulator” outdoor termination
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Fig. 1.31 “Capacitor cone and insulator”, “cylindrical capacitor type” outdoor termination
1.3.4.1 “Prefabricated” Elastomeric Sheds and Stress Cone Indoor
Termination
See Fig. 1.24.
1.3.4.2 “Heat Shrink Sleeve” Indoor Termination
Heat Shrink “Stress Control Sleeve” Type
See Fig. 1.25.
Heat Shrink “Capacitor Cone Stress Control” Type
See Fig. 1.26.
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Compendium of Accessory Types Used for AC HV Extruded Cables
Fig. 1.32 “Capacitor cone
and insulator”, “toroidal
capacitor type” outdoor
termination
1.3.4.3 “Elastomeric Sleeve” Indoor Termination
See Fig. 1.27.
1.3.4.4 “Stress Cone and Insulator” Indoor Termination
See Fig. 1.28.
1.3.4.5 “Deflector and Insulator” Indoor Termination
See Fig. 1.29.
1.3.4.6 “Prefabricated Composite and Insulator” Indoor Termination
See Fig. 1.30.
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Fig. 1.33 “Prefabricated composite and capacitor cone and insulator” outdoor termination
1.3.4.7 “Capacitor Cone and Insulator” Indoor Termination
Capacitor Cone and Insulator “Cylindrical Capacitor Cone” Type
See Fig. 1.31.
Capacitor Cone and Insulator “Toroidal Capacitor” Type
See Fig. 1.32.
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33
1.3.4.8 “Prefabricated Composite and Capacitor Cone, and Insulator”
Indoor Termination
See Fig. 1.33.
1.3.5
Types of Temporary Terminations
These terminations are usually required to be assembled quickly, to be light in weight
and to be small. Their purpose is to enable a cable to be terminated quickly and to be
connected in service for a comparatively short duration. It is usually accepted that the
temporary termination only has to withstand the system ac voltage and not the full
basic insulation level (BIL) of the cable system. The designs and the methods of stress
control are the same as those described for the outdoor termination, item 1.3.3. The
designs are essentially the same as the outdoor terminations shown in Figs. 1.24, 1.25,
1.26, 1.27, 1.28, 1.29, 1.30, 1.31, 1.32 and 1.33. The types 1.3.5.1, 1.3.5.2 and 1.3.5.3
are light in weight and small. The use of the light weight “composite insulator”
Fig. 1.28, inset, can make types 1.3.5.4 to 1.3.5.8 suitable.
Also known as “temporary potheads” or temporary Sealing Ends.
1.3.5.1 “Prefabricated Elastomeric Sheds and Stress Cone” Temporary
Termination
See Fig. 1.24.
1.3.5.2 “Heat Shrink Sleeve” Temporary Termination
Heat shrink “Stress Control Sleeve” Type
See Fig. 1.25.
Heat shrink “Capacitor Cone Stress Control Cone” Type
See Fig. 1.26.
1.3.5.3 “Elastomeric Sleeve” Temporary Termination
See Fig. 1.27.
1.3.5.4 “Stress Cone and Insulator” Temporary Termination
See Fig. 1.28.
1.3.5.5 “Deflector and Insulator” Temporary Termination
See Fig. 1.29.
1.3.5.6 “Prefabricated Composite and Insulator” Temporary
Termination
See Fig. 1.30.
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1.3.5.7 “Capacitor Cone and Insulator” Temporary Termination
Capacitor Cone and Insulator “Cylindrical Capacitor Cone” Type
See Fig. 1.31.
Capacitor Cone and Insulator “Toroidal Capacitor” Type
See Fig. 1.32.
1.3.5.8 “Prefabricated Composite and Capacitor Cone and Insulator”
See Fig. 1.33.
Appendix: Glossary of Component Names
Glossary of Names for Components Used in Accessories for Extruded
Cables
Adaptor Moulding
Pièce moulée d’adaptation
A type of “elastomeric moulding” usually of the “stress cone” type employed in
prefabricated accessories such as the “premoulded straight joint” of the two and
three piece types (1.2.1.2, Figs. 1.8 and 1.9) and some types of stress cones for
terminations. These mouldings are designed a) to fit a range of cable sizes, by
having different internal bore diameters and b) to have a constant external
diameter such that an outer elastomeric cylindricai moulding of constant size
can be fitted. The outer moulding is usually designed to be slid back over the
cable sheath during jointing.
Adhesive Tape
Ruban adhésif
Tape that is supplied pre-coated with an adherent layer. The tape is usually a
polymer with insulating or semi-conducting properties.
Anchor Plate
Plaque d’ancrage
The component which rigidly connects the joint shell of an anchor joint to a
concrete or steel structure for the purpose of segregating unequal mechanical
loading between two cables.
Back-to-Back Straight Joint (1.2.1.5)
Jonction “tête-bêche”
The joint insulation is part formed from either a “dielectric liquid” or “dielectric gas”
under pressure, contained within “trunking”. The design is essentially based upon
either two “metai enclosed GIS terminations” or two “oit immersed transformer
terminations” connected together within the same trunking. Also termed “back-toback” splice.
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35
Types of Back-to-Back Straight Joint
• Back-to-back joint with two insulators
Jonction “tête-bêche” à 2 isolateurs (1.2.5.1, Fig. 1.12)
• Back-to-back joint with one insulator
Jonction “tête-bêche” à 1 isolateur (1.2.5.2, Fig. 1.13)
• Back-to-back joint without insulator
Jonction “tête-bêche” sans isolateur (1.2.5.3, Fig. 1.14).
Barrier Insulator
Isolateur d’arrêt
A shaped insulator, usually formed from porcelain or cast resin, which is used a)
in a transition joint to prevent the impregnant in the paper cable from entering
the polymeric cable, b) in straight joint designs which employ oil of SF6 insulation and c) in some types of straight joint designs to prevent the migration of
moisture from a damaged polymeric cable to a sound cable.
Barrier Plate
Plaque d’arrêt
A metal plate to which bushing insulators are clamped within a three core
transition joint. Alternatively the thermoset resin plate which is cast integrally
with the three bushing insulators. See “bushing”.
Base Plate
Plaque de base
A metal support plate to which the insulator of a cable termination is rigidly
bolted. The base plate is usually connected to earth potential a) directly by a local
connection or b) by connection to the insulation screen, metallic sheath or shield
wires of the cable. See “bonding lead”.
Bifurcating Joint
Jonction de dérivation
See “Y branch joint”.
Blind-Head Insulator
Isolateur borgne
A cylindrical insulator used in a metal enclosed GIS termination which is permanently sealed at its high voltage end in the factory to prevent SF6 gas from entering
the termination in service. One method is to have a solid high voltage electrode
embedded into an insulator cast in thermoset resin. A plug-in connector is required
to transmit current from the conductor to the high voltage electrode. An external
adaptor is usually employed to transmit current to the off-going busbar. See “metal
enclosed GIS termination”, “busbar adaptor” and “plug-in connector”. Also termed
a “closed-top” insulator and a “plug-in” insulator.
Bonding Lead
C^
a ble de raccordement d’écran
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An ancillary cable comprised of an insulated conductor, which is connected to the
cable metallic sheath or screen wires at a) terminations and b) screen interruption
joints. The conductor area is normally sized to carry the specified short circuit
current of the cable system. The insulation is required to meet the same or a higher
voltage performance than the cable oversheath, depending on whether the bonding lead is of the single or concentric conductor type.
In all cable systems the bonding leads connect the lower metalwork of the
cable terminations to an approved earth system usually via a link box, such that
the system short circuit current can be carried along the cable screening wires or
metallic sheaths from one earth system to the other.
In a “cross bonded” single core cable system one bonding lead conductor is
connected to each side of the insulated flange in each screen interruption joint.
Concentric bonding leads are recommended, because the reduced surge impedance helps to protect a) the insulated flange and b) the insulated screen gap from
flash-over. The concentric bonding leads from the three adjacent joints are usually
terminated in a link box, which contains a) links to transpose the cable sheaths or
screen wires and b) sheath voltage limiters (SVLs) which are designed to limit the
magnitude of transient voltages on the cable oversheath and across the insulated
flange.
Busbar
Barre collectrice
The off-going conductor that connects to a) the “conductor stalk” on an outdoor,
indoor or oil immersed transformer termination and b) the “busbar adaptor” on a
GIS termination.
Busbar Adaptor
Pièce de connexion
The off-going current carrying connection on a “metal enclosed GIS termination”
(1.3.1.1–1.3.1.5), which on one face fits to the embedded electrode or to the
conductor stalk, and on the second face fits to the particular design of off-going
busbar.
Bushing
Borne traversée
A type of “barrier insulator” employed in either a three core transition joint, or a
single core transition joint of the non-fed type, to prevent the impregnant in the
paper insulated cable from entering the polymeric cable. It is usually formed from
cast resin into which a solid conductor rod has been embedded. It has a central
flange which is designed to be sealed either to a “barrier plate” or to a “joint shell”
The insulation on each side is normally conical or cylindrical in shape, with
sufficient length to provide the “creepage” distance.
Cable Chamber
Cuve d’extrémité
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Compendium of Accessory Types Used for AC HV Extruded Cables
37
The metallic “trunking” into which a “metal enclosed GIS termination” is bolted.
The trunking at this position is sometimes of different diameter to the trunking
that screens the rest of the SF6 gas insulated busbar.
Capacitor Cone
Cône à répartition capacitive ou cône condensateur
Insulation which contains a number of capacitors in series. It is designed to
give a linear voltage distribution along either a) the prepared cable core, b) the
surface of an insulator, or c) both. Capacitor cones are usually employed in
terminations (eg 1.3.1.4, 1.3.2.4, 1.3.3.2, 1.3.3.7 and 1.3.3.8). The cylindrical
type of capacitor cone (1.3.3.7, Fig. 1.31) is constructed from metallic or
semiconducting foils, which form a series of overlapping cylinders insulated
from each other by rolls of polymeric film. This type of cylindrical capacitor
cone can be wrapped directly onto the cable core or can be preformed in the
factory. Alternatively the capacitor cone can be formed from discrete toroidal
shaped capacitors (1.3.3.7, Fig. 1.32), which are slipped over the prepared
cable core and stacked one on top of the other. Also termed a “condenser
cone”.
Cast Barrier
Corps isolant en résine thermodurcissable
See “resin casting”.
Central Insulator
Corps isolant en résine thermodurcissable
A type of resin casting used in a prefabricated composite type of joint (1.2.1.2,
Fig. 1.6). See “resin casting” and “prefabricated straight joint”.
Closed Top Insulator
Isolateur borgne
See “blind-head insulator”.
Composite Insulator
Isolateur composite
An “insulator” used in cable terminations of the “outdoor” (1.3.3), “indoor”
(1.3.4) and “temporary” (1.3.5) type. The “composite” insulator has a rigid
cylindrical core onto which pre-moulded elastomeric or polymeric “sheds” have
been fitted. The “sheds” are usually formed from silicone rubber. The core is
usually formed from thermoset resin reinforced with glass fibre.
Compression Device
Dispositif de compression
The device employed to compress the elastomeric “stress cone” in prefabricated
designs of joints and terminations of the “composite” type (1.2.1.2, 1.3.1.3,
1.3.3.6 and 1.3.3.8), to achieve an intimate fit with a) the cable core and b) the
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“resin casting”. The device is usually an assembly of components which includes
a thrust cone and a set of metallic springs. See also “stress cone”, “resin casting”
and “central insulator”.
Condenser Cone
Cône condensateur
See “capacitor cone”.
Conductor Rod
Barre conductrice
A metal rod embedded in a thermoset bushing to enable connection to be made
between two cable conductors in a transition joint (1.2.2.2, Fig. 1.16 and 1.2.2.3,
Fig. 1.17). See “bushing”.
Conductor Screen
Ecran sur conducteur
The conducting or semiconducting layer at high voltage, which is applied over
the conductor and upon which the insulation is applied. See “screen”. Also
termed “HV screen”, “HT screen”, “inner screen” and “conductor shield”.
Conductor Stalk
Tige de sortie
A metal connector which terminates the cable conductor to enable a current
carrying connection to be made to a busbar. See “busbar”.
Connector
Connecteur
The generic name for the conducting connection between a) cable conductors, b)
cable screen wires and c) one cable conductor and a conductor stalk at a
termination. The connection can be of the permanent type or of the separable
type. See “ferrule”, “MIG weld”, “thermit weld” and “conductor stalk”.
Connector Screen
Ecran sur connecteur
The conducting or semiconducting layer at high voltage, which is applied over
the conductor connector and upon which the joint insulation is applied. See
“screen”, “connecte” and “ferrule screen”. Also termed “HV screen”, “HT
screen” and “connector shield”.
Corona Shield
Ecran pare-effluves
A shaped conducting component positioned around a conductor or busbar connector in a back-to-back straight joint (1.2.1.5, Figs. 1.12, 1.13 and 1.14) and in a
termination (e.g. 1.3.3.4–1.3.3.8). Its purpose is to control the electrical stress
distribution and thereby prevent the occurrence of corona (partial discharge) in
the surrounding liquid or gaseous insulation.
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Compendium of Accessory Types Used for AC HV Extruded Cables
39
Creepage Distance
Ligne de fuite ou chemin rampant
The shortest distance measured along an insulating interface between conducting
components at high and Iow voltage.
In a joint the creepage distance is that between the end of the “insulation
screen” and the exposed “conductor screen”, measured along the interface
between the cable core and the applied joint insulation.
For a termination the “external creepage” distance is the distance between the
upper and Iower metalwork of the insulator, which includes the upper and Iower
surfaces of the “sheds”.
For an outdoor termination the “protected creepage” is the cumulative surface
distance of the underside of each shed. The “external” creepage and “protected”
creepage lengths are often specified to meet a particular level of atmospheric pollution.
Crosslinked Insulation
Isolation réticulée
Electrical insulation that has been changed from a thermoplastic to a thermoset
material by a chemical reaction which forms links between adjacent long chain
molecules. Crosslinked insulation has improved mechanical performance at high
operating temperatures because it does not melt. The cross-linked insulation can be
formed from a polymer with a semi-crystalline structure such as polyethylene
(PE) or from an elastomer with an amorphous structure such as ethylene propylene
rubber (EPR). Crosslinking can be achieved by a chemical reaction or by radiation.
In the chemical reaction method, an agent termed a curative is contained within the
insulation to promote the crosslinking process, usually with the application of heat.
Also termed “vulcanised” or “cured” insulation. This process also applies to the
crosslinked screens.
Cured Insulation
Isolation réticulée
See “crosslinked insulation”.
Deflector Cone
Déflecteur
A factory formed “stress control profile” of metal or semi-conducting polymer,
positioned adjacent to the termination of the cable insulation screen to control stress.
it is usually employed in combination with either a liquid or gaseous insulation of
high electric strength in accessories such as terminations of the “deflector and
insulator” type (1.3.3.5) and straight joints of the “back to back” type.
Dielectric
Diélectrique
An insulating material with high electric strength.
Dielectric Fluid
Fluide diélectrique
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A “dielectric gas” or “dielectric liquid” with high insulating properties.
Dielectric Gas
Gaz diélectrique
A gas with high insulating properties, such as SF6, N2 or SF6/N2 mixture. These
gases are usually pressurised to achieve the required dielectric strength. N2
requires a significantly higher pressurisation than SF6.
Dielectric Liquid
Liquide diélectrique
A liquid with high insulating properties, eg. silicone liquids, synthetic hydrocarbon liquids and minerai oils.
Earth Screen
Ecran de terre
See “insulation screen”.
Elastomeric Moulding
Corps isolant en élastomère
An insulating component that has been premoulded in the factory from an
insulating polymer, which has elastic properties (low modulus of elasticity) in
the working temperature range of the accessory. The component usually has one
or more integral screens formed from a semiconducting elastomer.
Also termed a “rubber moulding” or “synthetic rubber” moulding.
Embedded Electrode
Electrode encastrée
See “HV electrode” and “HT electrode”.
Extruder
Extrudeuse
A powered machine used to prepare a) the cable insulation in the factory and b) the
joint insulation for some types of field moulded joints (1.2.1.3, Table 1.1). The
machine is comprised of a long rotating “screw” with a helical thread-form of
“flights” of varying pitch, which is contained within a heated “barrel”. The polymer
is fed into one end of the barrel, usually in the form of small pellets. The polymer is
melted and compressed into a viscous liquid termed the “melt”, which is homogenous and void free. The melt is extruded from the end of the barrel under the
pressure generated by the screw into either a) the cable insulation die tool or b) the
joint mould tool).
Ferrule
Douille de raccordement
A cylindrical metal connector between cable conductors or between cable screen
wires.
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Compendium of Accessory Types Used for AC HV Extruded Cables
41
Types of ferrule:
Types de douilles de raccordement
• Compression Ferrule
Douille à sertir
A metal tube into which the conductors to be joined are inserted. The tube is then
compressed by a hydraulic press tool.
• Flush Ferrule
Douille équidiamétrale
The ferrule is nominally made flush with the diameter of the conductor, either by
a) compressing, b) removing a layer of wire, or c) welding.
• Mechanical Bolted Ferrule
Douille mécanique à visser
The current carrying connection is made by compressing the conductor inside the
ferrule by tightening threaded bolts. The bolts are finished flush with the surface
of the ferrule.
• Soldered Ferrule
Douille soudée (à basse température)
A metal ferrule is placed around the two conductors. The assembly is then filled
with hot molten solder (a lead alloy).
• Stop Ferrule
Douille borgne
The ferrule has a central internal barrier to segregate the conductors. Used a) in a
transition joint to prevent the flow of impregnant from a paper cable and b) in a
straight joint to prevent the migration of moisture from a damaged cable to a
sound cable.
• Welded Ferrule
Douille soudée (à haute température)
The two conductors are fused together by the application of molten metal. See
“MIG weld”, “TIG weld” and “thermit weld”.
Ferrule Screen
Ecran sur douille
The conducting or semiconducting layer at high voltage which is applied over the
ferrule and upon which the joint insulation is applied. See “screen” and “ferrule”.
Also termed “connector screen”, “HV screen”, “HT screen” and “ferrule shield”.
Field Moulded Straight Joint (1.2.1.3)
Jonction moulée sur site
The joint insulation is melted, moulded and consolidated to the prepared
insulation of both cables in situ, ie. “in the field”. Also termed “field moulded
splice”.
Types of Field Moulded Straight Joint (1.2.1.3, Table 1.1)
• Tape moulded
Rubanée-formée
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• Crosslinked tape moulded
Rubanée-formée et réticulée (rubanée cuite)
• Extrusion moulded
Moulée par extrusion
• Crosslinked extrusion moulded
Moulée par extrusion et réticulée
• Injection moulded
Moulée par injection
• Crosslinked injection moulded
Moulée par injection et réticulée
• Block moulded
Moulée par blocs
• Crosslinked block moulded
Moulée par blocs et réticulée.
Filling Compound
Matière de remplissage
An insulating material used to fill some types of accessories. At amblent and at
operating temperatures it is substantially solid. During assembly of the accessory
it is heated to elevated temperature to reduce the viscosity and permit it to be
poured. See “waterproof compound”.
Filling Liquid
Liquide de remplissage
An insulating liquid used to f II some types of accessories, for example straight
joints of the “back-to-back type” and terminations which are protected within
hollow insulators. See “insulating liquid” and “dielectric liquid”.
Filling Oil
Huile de remplissage
An insulating liquid used to fill some types of accessories. The term “oil”
specifically relates to a minerai oil.
Flashover Distance
Ligne de contournement
The shortest distance between high voltage and low voltage metalwork in gaseous
or liquid insulation through which an electric discharge (flashover) can occur.
GIS Termination
Extrémité pour PSEM
A termination into Gas Insulated Switchgear. See “metal enclosed GIS
termination”.
Glass Fibre Box
Coquille en fibres de verre.
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Compendium of Accessory Types Used for AC HV Extruded Cables
43
A particular type of “joint box”. The box is placed around the joint shell and is
filled with compound to provide electrical insulation and corrosion protection
(1.2, Fig. 1.3). The box is pre-moulded from a thermoset or thermoplastic resin,
which has been reinforced with glass fibres. See “filling compound” and “waterproof compound”.
Glass Fibre Reinforcement
Renforcement en fibres de verre
A bandage of woven glass fibre tape which is impregnated with a thermoset resin.
It is applied over a plumb to mechanically reinforce it against a) longitudinal
sheath forces and b) internai pressure.
Heat Shrink Sleeve
Manchon thermorétractable
An extruded tube of crosslinked polyolefin is heated in a factory process to above
its crystalline melting point and is expanded to a large diameter. It is then allowed
to cool and freeze at the larger diameter. During assembly the sleeve is positioned
over the accessory and is again heated to above the crystalline melting point, such
that the sleeve contracts to form an intimate fit. The insulation and screens may be
supplied as one integral sleeve or as several individual sleeves. Stress control
sleeves which are pre-loaded with either a resistive or high permittivity filler may
also be applied over the accessory to control the stress distribution. Heat shrink
sleeves can also be used to form a) the joint protection and b) seals at the
conductor, sheath and oversheath.
Heat Shrink Sleeve Straight Joint (1.2.1.4)
Jonction thermorétractable
The joint insulation is formed from one or more “heat shrink sleeves”. Also
termed a “heat shrink sleeve splice”.
HT Electrode (High Tension)
Electrode HT
See “HV electrode”.
HT Screen (High Tension)
Ecran HT
See “HV screen” and “conductor screen”.
HV Electrode (High Voltage)
Electrode HT
A shaped conducting component which is embedded within a moulded insulator
to electrically screen the conductor connection. Also termed electrode and
“embedded” electrode.
HV Screen (High Voltage)
Ecran HT.
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The conducting or semiconducting layer which is applied over all components at
high voltage. See “screen”, “conductor screen” and “ferrule screen”. Also termed
“HT screen” and “HV shield”.
Indoor Termination (1.3.4)
Extrémité intérieure
A cable termination which interfaces with air insulated equipment, but which is
protected from climatic conditions. These are essentially outdoor terminations,
which have had the insulator creepage length and height reduced. Also termed
“indoor pothead”.
Types of Indoor Terminations:
Prefabricated elastomeric sheds and stress cone (1.3.4.1)
A jupes en élastomère et à cône déflecteur préfabriqués
Heat shrink sleeve type (1.3.4.2)
A manchon thermorétractable
-stress control sleeve (1.3.4.2, Fig. 1.25)
avec manchon de contrôle du champ
-capacitor cone stress control (1.3.4.2, Fig. 1.26)
avec cône condensateur
Elastomeric sleeve (1.3.4.3, Fig. 1.27)
A manchon élastomère
Stress cone and insulator (1.3.4.4, Fig. 1.28)
A cône déflecteur et isolateur
Deflector and insulator (1.3.4.5, Fig. 1.29)
A déflecteur et isolateur
Prefabricated composite and insulator (1.3.4.6, Fig. 1.30)
A cône déflecteur composite et isolateur
Capacitor cone and insulator (1.3.4.7)
A cône condensateur et isolateur
-cylindrical capacitor cone (1.3.4.7, Fig. 1.31)
avec condensateurs cylindriques
-toroidal capacitor (1.3.4.7, Fig. 1.32)
avec condensateurs toroïdaux
Prefabricated composite and capacitor cone and insulator (1.3.4.8, Fig. 1.33)
A cône déflecteur composite, cône condensateur et isolateur.
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Compendium of Accessory Types Used for AC HV Extruded Cables
45
Inner Screen
Ecran intérieur
See “conductor screen”.
Insulated Flange
Flasque isolant (1.3.4.8)
The generic name for the cylindrically shaped insulator which electrically separates a) the two halves of a metallic joint shell or b) the lower metalwork of a
termination. The insulated flange can be a) an individuel annular ring of porcelain
or thermoset resin (1.2, Fig. 1.1, 1.3.1.5, Fig. 1.23), b) an integral part of a cast
resin barrier in a joint (1.2.2.2, 1.2.2.3, 1.2.2.4, Figs. 1.16, 1.17, 1.18, 1.19 and
1.1.3) or c) an integral part of a cast resin insulator in a termination (1.3.1.1–
1.3.1.4). The insulated flange together with the insulated screen gap are essential
parts of a specially bonded cable system. See “sectionalising ring” and “screen
interruption”. Also termed “insulated ring” and “resin ring”.
Insulated Gap
Interruption d’écran
See “screen interruption”.
Insulating Liquid
Liquide isolant
A liquid with high electrical strength used principally to fill and insulate some
types of terminations and back-to-back joints. Examples are minerai oil, synthetic
hydrocarbons (such as polyisobutene) and silicones. See aise “dielectric liquid”,
“filling liquid” and “filling oil”.
Insulating Tape
Ruban isolant
Tape with high electrical strength can be used to form the insulation or part
insulation of an accessory. It can be of the “adhesive” or “self-amalgamating”
type or simply of the non-adherent type.
Insulation
Isolation
Material of high electric strength which is applied between the conductor screen
and the insulation screen.
Insulation Screen
Ecran sur isolation
The conducting or semiconducting layer at earth potential applied over the
insulation. Also termed “earth screen”, “LV screen”, “ground screen”, “outer
screen” and “insulation shield”.
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Z. Iwata
Insulator
Isolateur
The generic name for pre-formed solid insulation and particularly of the hollow
insulators used in cable terminations.
In addition to their insulating duty, the “Insulators” employed in cable terminations (1.3.1.1 to 1.3.1.4 and 1.3.3.4 to 1.3.3.8) are designed to a) support the cabie,
b) protect the cable insulation, c) contain oil or gas insulation from leakage, d)
segregate the cable from external atmospheric conditions e) segregate the cable
from the oil or gas insulation used in other manufacturer’s equipment and f)
withstand conductor thermomechanical forces. Insulators employed in cable terminations are usually formed from a thermoset casting or from porcelain, with a
hollow interior and either a cylindrical or a conical exterior shape. The outer surface
of the insulator is often formed in the shape of annuler protrusions termed “sheds”.
Insulator designs of the metal enclosed GIS and transformer termination types
are sometimes employed in transition joints and straight joints of the “back-toback” type (1.2.1.5). See also “porcelain”, “composite insulator”, “pedestal
insulator”, “resin casting”, “shed”, “barrier insulator” and “bushing”.
Joint (1.2)
Jonction
The generic name for the insulated and fully protected connection between two or
more cables. It provides an insulated path for the flow of current between the
conductors. Also termed a “splice”.
Types of Joints
See:
• “Straight joints” (1.2.1)
Jonctions droites
• “Transition joints” (1.2.2)
Jonctions de transition
• “Y branch joints” (1.2.3)
Jonctions en Y ou en T – Jonction de dérivation.
Joint Box
Boı̂te de jonction
The generic name for the waterproof housing which is fitted around the joint as
part of the “joint protection” (1.2, Figs. 1.3 and 1.5). The box is normally formed
from a moulding of thermoplastic polymer or thermoset resin, the latter usually
being reinforced with glass fibre (termed a “glass fibre box”). After being
assembled around the joint, the box is usually filled with a waterproof insulating
compound, such as bitumen, or thermoset resin. See also “joint protection”,
“glass fibre box” and “waterproof compound”.
Joint Protection
Protection de jonction
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Compendium of Accessory Types Used for AC HV Extruded Cables
47
The generic name given to the outer coverings of the joint which, depending upon
the particular application, a) protect the joint metalwork from corrosion, b)
prevent water from entering the joint and c) electrically insulate from earth
potential the insulation screens, shield wires and joint shell. Types of protection
are “joint shell protection”, “joint” be and “glass fibre box”. Protection can also
be formed from tape and heat shrink sleeves.
Joint Shell
Enveloppe de jonction ou enveloppe métallique
The metal tube which contains the joint insulation (1.0, Fig. 1.1), to a) provide
electrical continuity between sheaths, b) contain short circuit current within the
cable system, c) form an impervious water tight barrier and d) contain the filling
of liquid or gas.
Joint Shell Protection
Protection de l’enveloppe de jonction
The covering applied to the joint shell which provides a) anti-corrosion protection
and b) electrical insulation from earth potential for insulated sheath systems.
Lower Metalwork
Pot d’entrée
The metal tube or gland connected to the base of a termination insulator which a)
seals the cable and b) enables electrical connection to be made to the metal sheath
or wire screen. Also termed “bottom” metalwork, “end bell”, “plumbing gland”
and “wiping gland”.
LV Electrode (Low Voltage)
Electrode de terre
The shaped conducting component which is embedded within a moulded
insulator to provide stress control. Also termed “LV Screen” and “earth
electrode”.
Metal Enclosed GIS Termination (1.3.1)
Extrémité pour station blindée - Extrémité pour PSEM
A cable termination which connects to a busbar within metal trunking, insulated
with gas. The gas is usually pressurised SF6. The busbar is usually connected to
switchgear. Also termed “GIS” termination, “metalclad” termination, “SF6”
termination and “metal enclosed GIS pothead”.
Types of Metal Enclosed GIS Terminations
• Stress cone and insulator (1.3.1.1)
A cône déflecteur et isolateur
• Deflector and insulator (1.3.1.2)
A déflecteur et isolateur
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Z. Iwata
• Prefabricated composite “dry” type (1.3.1.3)
A cône déflecteur composite et isolateur, type sec
• Capacitor cone and insulator (1.3.1.4)
A cône condensateur et isolateur
• Directly immersed (1.3.1.5)
Type directement immergé
MIG Weld
Soudure MIG
A weld made by the Metal Inert Gas process in which a consumable wire
electrode, usually aluminium, is fed continuously into an electric arc under a
shield of inert gas, where it is melted and propelled to fuse into the conductor.
Off-Going Connector
Raccordement de sortie
The device that connects the “conductor staik” in a termination to an off-going
busbar. Also termed a “busbar connector”.
Oil Immersed Transformer Termination (1.3.2)
Extrémité pour transformateur
A termination into oil insulated metalclad busbar trunking, this usually being
part of the transformer housing. Also termed “oil immersed transformer
pothead”.
Types of Oil Immersed Transformer Terminations
• Stress cone and insulator (1.3.2.1)
A cône déflecteur et isolateur
• Deflector and insulator (1.3.2.2)
A déflecteur et isolateur
• Prefabricated composite “dry” type (1.3.2.3)
A cône déflecteur composite et isolateur, type sec
• Capacitor cone and insulator (1.3.2.4)
A cône condensateur et isolateur
• Directly immersed (1.3.2.5)
Type directement immergé
Outdoor Termination (1.3.3)
Extrémité extérieure
A cable termination which interfaces with air insulated equipment and which is
subjected to full climatic conditions. See “termination”. Also termed an outdoor
“pothead”.
Types of Outdoor Terminations
• Prefabricated elastomeric sheds and stress cone (1.3.3.1, Fig. 1.24)
A jupes en élastomère et à cône déflecteur préfabriqués
• Heat shrink sleeve type (1.3.3.2)
1
•
•
•
•
•
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Compendium of Accessory Types Used for AC HV Extruded Cables
49
A manchon thermorétractable
-stress control sleeve (1.3.3.2, Fig. 1.25)
avec manchon de contrôle du champ
-capacitor cone stress control (1.3.3.2, Fig. 1.26)
avec cône condensateur
Elastomeric sleeve (1.3.3.3, Fig. 1.27)
A manchon élastomère
Stress cone and insulator (1.3.3.4, Fig. 1.28)
A cône déflecteur et isolateur
Deflector and insulator (1.3.3.5, Fig. 1.29)
A déflecteur et isolateur
Prefabricated composite and insulator (1.3.3.6)
A cône déflecteur composite et isolateur
Capacitor cone and insulator (1.3.3.7)
A cône condensateur et isolateur
-cylindrical capacitor cone (1.3.3.7)
avec condensateurs cylindriques
-toroidal capacitor (1.3.3.7)
avec condensateurs toroïdaux
Prefabricated composite and capacitor cone and insulator (1.3.3.8)
A cône déflecteur composite, cône condensateur et isolateur.
Painted Screen
Ecran graphité
A semiconducting screen normally formed by brushing Iiquid paint onto polymeric insulation. The paint is loaded with a conducting filler, usually dispersed in
a resin binder and rendered liquid by a solvent, which subsequently evaporates.
See “screen”. Also termed “painted shield”.
Pedestal Insulator
Isolateur support
A short insulator of porcelain or thermoset resin which is used to insulate either
a termination baseplate (1.3.3.4–1.3.3.8) or a joint shell (1.2, Fig. 1.4) from
earth potential. Also termed “stand-off” insulator and “post” insulator. See
“insulator”.
Pencil
Cône
The conical shape into which the insulation of the cable core is formed in a joint
(1.2, Fig. 1.1) or termination. Pencils are usually employed in taped joints and
in field moulded joints. They are designed to withstand the electrical stresses at
the interface between the insulation of the cable and joint. Pencils of shorter
Iength are often employed in a cable termination adjacent to the conductor
connector to facilitate the application of either a sealing tape or a heat shrink
sleeve.
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Z. Iwata
Plug-In Connector
Connecteur embrochable
A metal connector which terminates the conductor. It is inserted into a mating
electrode usually embedded in a thermoset casting. Current carrying contact is
made by sprung connectors or by elasticity of the component. See “blind-head
insulator”.
Plug-In Insulator
Isolateur borgne
See “blind head insulator”.
Plumb
Soudure au plomb lissé
A conducting connection and seal which is formed between the metal sheath and
a) the joint shell, or b) the termination lower metalwork, by the hand application
of a hot lead alloy. Also termed a “wipe”.
Porcelain
Porcelaine
Solid insulation formed from vitrified clay, used primarily for outdoor termination
insulators and “pedestal insulators”. The name is sometimes used in the abbreviated foret for “porcelain insulator”. See “insulator”.
Pothead
Extrémité
See “termination”.
Prefabricated Straight Joint (1.2.1.2)
Jonction préfabriquée
Prefabricated straight joints employ insulation that has been preformed and tested in
the factory. The usual methods of manufacture are to mould elastomeric insulation
and to cast thermoset resin insulation. Also termed “prefabricated splice”.
Types of Prefabricated Straight Joint
• Composite (1.2.1.2, Fig. 1.6)
Composite
• Premoulded one-piece (1.2.1.2, Fig. 1.7)
Prémoulée en une pièce
• Premoulded two-piece (1.2.1.2, Fig. 1.8)
Prémoulée en deux pièces
• Premoulded three-piece
Prémoulée en trois pièces (1.2.1.2, Fig. 1.9).
Resin Barrier
Corps isolant en résine thermodurcissable
See “resin casting”.
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Compendium of Accessory Types Used for AC HV Extruded Cables
51
Resin Casting
Corps isolant en résine thermodurcissable
A rigid insulating component manufactured from a thermoset resin (usually
epoxy resin), used to form a) the central insulator in joints of the prefabricated
composite type (1.2.1.2), b) the barriers in some types of transition joints (1.3.2
and 1.3.3) and c) the insulator in metal enclosed terminations (1.3.1.1–1.3.1.4).
Also termed “resin barrier” and “cast barrier”. See “barrier insulator” and “central
barrier”.
Rubber Moulding
Corps isolant en élastomère
See “elastomeric moulding” and “synthetic rubber moulding”.
Screen
Ecran semi-conducteur
A smooth conducting layer in intimate contact with the insulation. It is designed
to a) contain the electric field within the insulation and b) minimise the magnitude
of the electric stress by the elimination of irregularities in the surface, (termed
“stress raisers”). Also termed a “shield”.
Screen Interruption
Interruption d’écran
The “insulated gap” formed in the insulation screen of a joint, which together with
the “insulated flange” in the joint sheil, electrically separates the cable screen on
one side of the joint from that on the other. Screen interruption joints are
necessary for specially bonded cable systems, which together with “bonding
leads” and link boxes permit the metallic sheaths or screening wires to be
transposed for cross bonding. See “bonding leads”. Also termed “insulated
gap”, “sheath interruption” and “sheath segregation”.
Screen Termination
Arrêt d’écran
The name given during jointing to the end position of the cable insulation screen
during jointing, after the screen has been removed from the core and the insulation prepared. See “screen”.
Sealing End
Extrémité
See “termination”.
Sectionalizing Ring
Anneau de sectionnement
A type of “insulated flange”. An insulating ring which electrically separates two
halves of a) a metal joint shell (1.0, Fig. 1.1) or b) the lower metalwork of a
termination (2.1.1, inset and 2.1.5). The ring can be made from a thermoset
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Z. Iwata
moulding, a reinforced thermoset component or porcelain. Also termed a “resin
ring”, when formed from a thermoset moulded or machined component.
Self Amalgamating Tape
Ruban auto-amalgamant
An elastomeric tape which is consolidated to itself by the action of stretching and
wrapping.
Semiconducting Screen
Ecran semi-conducteur
A polymeric or elastomeric resin that has been loaded with an electrically
conducting filler to give it sufficient conductivity to act as a screen, whilst
exhibiting similar thermomechanical properties to the cable and joint insulation.
It has a significantly lower conductivity than a metallic screen. The semiconducting screening material can be extruded, moulded or applied in tape form. See
“screen”. Also termed “semiconducting shield”.
Sheath Closure
Etanchéité de gaine
The generic name for the seal between the metallic sheath of the cable and either
the joint shell or termination lower metalwork. See “plumb”.
Sheath Interruption
Interruption d’écran
See “screen interruption”.
Sheath Segregation
Interruption d’écran
See “screen interruption”.
Shed
Ailette, Jupe
One of the disc shaped protrusions on the outer surface of a termination (1.3.1.1–
1.3.1.5) which increases the effective surface length of the insulator without
increasing its height. These are mainly used on outdoor terminations, which are
exposed to rain, ice, fog, salt, mist and to atmospheric pollution. Small sheds are
sometimes used on indoor, oil immersed transformer and GIS terminations. See
“creepage distance”. Also termed a “weather” shed.
Shield
Écran
See “screen”.
Splice
Jonction
See “joint”.
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Compendium of Accessory Types Used for AC HV Extruded Cables
53
Straight Joint (1.2.1)
Jonction droite
A joint which connects two cables of the same type.
Types of Straight Joint
• Taped Joint (1.2.1.1)
Jonction rubanée
• Prefabricated Joint (1.2.1.2)
Jonction préfabriquée
• Field Moulded Joint (1.2.1.3)
Jonction moulée sur site
• Heat Shrink Sleeve Joint (1.2.1.4)
Jonction thermorétractable
• Back-to-Back Joint (1.2.1.5)
Jonction “tête-bêche”
Stress Cone
Cône déflecteur
A shaped insulating component with a screened “stress control profile”. It is used
for stress control at the end of either the low voltage insulation screen or the high
voltage electrode (1.3.1.1, 1.2.2.4, 1.3, 1.3.1.3, 1.3.1.5, 1.3.3.1, 1.3.3.4, 1.3.3.6
and 1.3.3.8). It is usually formed from a moulded or machined polymer, elastomer
or thermoset resin.
Stress Control Electrode
Electrode de contrôle de champ
The conducting component which controls the electric field in an accessory, it can
be placed:
a) Adjacent to the end of the insulation screen
b) Adjacent to the conductor in a premoulded joint.
Stress Control Profile
Ecran déflecteur
The name for the shape of the conical insulation screen that is positioned
adjacent to the termination of the cable insulation screen (1.2, Fig. 1.1). The
screen shape can be a) preformed in the factory as part of a “stress cone”
moulding or as a “deflector cone” or b) formed during the assembly of the
accessory on site by “field moulding” or by the application of insulating
tape.
Synthetic Rubber Moulding
Corps isolant en élastomère
See “elastomeric moulding”.
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Z. Iwata
Taped Straight Joint (1.2.1.1)
Jonction rubanée
Semiconducting and insulating tapes are wound onto the cable to form the
conductor screen, the insulation, the stress control profile screens, the insulation
screen and the screen interruption insulation. Also termed “taped splice”.
Types of Taped Straight Joint
• Self amalgamating tape
Ruban auto-amalgamant
• Adhesive tape
Ruban adhésif
Temporary Termination (1.3.5)
Extrémités temporaires
A cable termination that is designed to be assembled quickly and to be
connected in service for a comparatively short time. They are typically smaller
and lighter in weight than the permanent types of “outdoor termination” and
“indoor termination”. It is usually accepted that they only have to withstand the
system ac voltage and not the full basic insulation level (BIL). Also termed
“temporary pothead”.
Types of Temporary Terminations
• Prefabricated elastomeric sheds and stress cone (1.3.5.1 to 1.3.5.8)
A jupes en élastomère et à cône déflecteur préfabriqués
• Heat shrink sleeve (1.3.5.2)
A manchon thermorétractable
-stress control sleeve type (Fig. 1.24)
avec manchon de contrôle du champ
-capacitor cone stress control type (Fig. 1.26)
avec cône condensateur
• Elastomeric sleeve (1.3.5.3)
A manchon élastomère
• Stress cone and insulator (1.3.5.4)
A cône déflecteur et isolateur
• Deflector and insulator (1.3.5.5)
A déflecteur et isolateur
• Prefabricated composite and insulator (1.3.5.6)
A cône déflecteur composite et isolateur
• Capacitor cone and insulator (1.3.5.7)
A cône condensateur et isolateur
-cylindrical capacitor cone type (Fig. 1.31)
avec condensateurs cylindriques
-toroidal capacitor type (Fig. 1.32)
avec condensateurs toroïdaux
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Compendium of Accessory Types Used for AC HV Extruded Cables
55
• Prefabricated composite and capacitor cone (1.3.5.8, Fig. 1.33)
and insulator
A cône déflecteur composite, cône condensateur et isolateur.
Termination (1.3)
Extrémité
The generic name for the connection between a cable and other electrical equipment. Also termed “sealing end” and “pothead”.
Types of Terminations
• Metal Enclosed GIS Terminations (1.3.1)
Extrémités pour PSEM
• Oil Immersed Transformer Terminations (1.3.2)
Extrémités pour transformateur
• Outdoor Terminations (1.3.3)
Extrémités extérieures
• Indoor Terminations (1.3.4)
Extrémités intérieures
• Temporary Terminations (1.3.5)
Extrémités temporaires
Thermit Weld
Soudure aluminothermique
A weld formed by igniting a mixture of combustible material and powdered metal
that melts and fuses to connect two cable conductors.
TIG Weld
Soudure TIG
A weld made by the Tungsten Inert Gas process in which an electric arc is struck
between a tungsten electrode and the conductor under a shield of inert gas. A
consumable hand held welding rod, usually aluminium, is fed into the arc where it
is melted and fused to connect the conductors.
Transition Joint (1.2.2)
Jonction de transition A joint which connects two cables of different types, for
example a polymeric extruded cable to a self-contained oil filled cable. Transition
joints are sometimes employed to connect cables of the same type, but with
widely differing conductor sizes. Also termed “transition splice”.
Types of Transition Joints
• Polymeric extruded cable to mass impregnated cable (1.2.2.1)
C^able à isolation synthétique – c^able au papier imprégné
• Polymeric extruded cable to oil or (1.2.2.2) gas filled paper cable three core
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Z. Iwata
C^able à isolation synthétique unipolaire c^able tripolaire à huile ou à gaz
• Polymeric extruded cable to oil (1.2.2.3) or gas filled paper cable single core,
non-fed type
C^able à isolation synthétique unipolaire c^able unipolaire à huile ou à gaz, type
“non-alimenté”
• Polymeric extruded cable to oil or gas (1.2.2.4) filled paper cable single core, fed
type
C^able à isolation synthétique unipolaire - c^able unipolaire à huile ou gaz, type
“alimenté”.
Trunking
Enveloppe d’extrémité
The metallic cylinder that contains a) the SF6 gas in metal enclosed GIS (1.3.1) or
b) the oil in a transformer termination. The trunking also forms a) the insulation
screen and b) the return conductor for short circuit current. The trunking adjacent
to a GIS termination is termed a “cable chamber”. The short length of trunking
used to contain the SF6 gas or oil in a joint, of the “back-to-back insulator” type
(1.2.1.5) is termed the “joint shell”.
Upper Metalwork
Tête d’extrémité
The high voltage metal components at the top end of a cable termination, which
are normally comprised of the top sealing plate, the clamp ring and the corona
shield.
Vulcanized Insulation
Isolation vulcanisée
See “crosslinked insulation”.
Waterproof Compound
Matière d’étanchéité
The generic name for the viscous liquid used to fill a) the joint box and b) the
metallic joint shell of some types of joint (1.2, Fig. 1.3). The compound conforms
and adheres to the joint components (ie joint shell or screened insulation). It
provides electrical insulation and sealing against moisture ingress. Bitumen is one
form of compound, this is normally poured hot and cools to a high viscosity
liquid. Thermosetting resin is another form of compound, which upon curing
forms an adherent solid or elastic mass. See “joint box”, “glass fibre box” and
“joint protection” and “filling compound”.
Waterproof Seal
Etanchéité extérieure
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Compendium of Accessory Types Used for AC HV Extruded Cables
57
The seal between the “joint box” and the cable oversheath. It is usually formed
from a) thermoset resin putty, b) fibre glass reinforced resin, c) heat shrink sleeve,
or d) waterproof tape. The seal is required to contain the compound filling and to
prevent the ingress of water.
Weather Shed
Ailette, jupe
See “shed”.
Wipe
Soudure au plomb lissé
See “plumb”.
“Y Branch Joint” (1.2.3)
Jonction en Y ou T - Jonction de dérivation
A joint that connects three cables of nominally the same type. The joint is usually
configured in the shape of the letter Y. Also termed “bifurcating joint” and “Y
branch splice”.
Zensuke Iwata was born in Tokyo, Japan, on October 5, 1944.
He received the B.S. degree in Electrical Engineering from the
University of Tokyo, Japan, in 1968. In 1968 he joined the
Furukawa Electric Co., Ltd., Japan, where he has been engaged
several years in research and development of high-voltage power
cables and their accessories before taking other positions in the
Furukawa Electric Co. In 2003 he successfully carried out the
long-term field test of the real scale H.T. superconducting cable
system as the Managing Director and CTO of the Furukawa
Electric Co. In 2004 he was appointed as the President of Nuclear
Fuel Industries, Japan, and retired in 2014. Zensuke Iwata convened Cigré WG 21.06 which published Technical Brochures 89
and 177. He received the TC Award in 1995. He chaired the ISTC
of Jicable in 2003.
2
A Guide to the Selection of Accessories
Zensuke Iwata
Contents
2.1
2.2
2.3
2.4
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Compatibility of the Accessory with the Cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.1 Number of Cable Cores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.2 Cable Constructional Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.3 Conductor Area and Diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.4 Operating Temperature of the Cable Conductor and Sheath under Continuous,
Short Term Overload and Short Circuit Current Loading . . . . . . . . . . . . . . . . . . . . . . .
2.2.5 Compatibility of the Accessory with the Type of Cable Insulation
and Semiconducting Screens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.6 Cable Electrical Design Stresses to be Withstood by the Accessory . . . . . . . . . . . .
2.2.7 Mechanical Forces and Movements Generated by the Cable on the Accessory . . .
2.2.8 Short Circuit Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Compatibility of the Accessory Performance with that of the Cable System . . . . . . . . . . .
2.3.1 Circuit Performance Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3.2 Circuit Life Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3.3 Metallic Screen Bonding Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3.4 Earth Fault Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Compatibility of the Accessory with the Cable System Design and Operating
Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4.1 Type of Cable Installation Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4.2 Standard Dimensions for Cable Termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Zensuke Iwata has retired.
The guide in this Chapter 2 has been prepared by WG 21.06 and published in Cigré TB 177. At the
end of the chapter some references are given. They are the original references. Proposed further
readings are given in Chapter 4 and following chapters.
Z. Iwata (*)
Kamakura, Japan
e-mail: z.iwata@kamakuranet.ne.jp
© Springer Nature Switzerland AG 2021
P. Argaut (ed.), Accessories for HV and EHV Extruded Cables, CIGRE Green Books,
https://doi.org/10.1007/978-3-030-39466-0_2
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2.4.3 Type of Accessory Installation Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4.4 Jointing Limitations in Restricted Installation Locations . . . . . . . . . . . . . . . . . . . . . . . .
2.4.5 Mechanical Forces Applied to the Accessory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4.6 Climatic Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4.7 Type of Accessory Outer Protection Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4.8 Situations Requiring Special Accessory Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5
Verification of Accessory Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5.1
Use of the Specific National or International Type Test Specification
for the Accessory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5.2
Use of the Cable Test Specification in the Absence of an Accessory
Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5.3
Type Test Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5.4
Type Tested Accessory in Combination with the Particular Cable . . . . . . . . . . . .
2.5.5
Pre-Qualification Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5.6
Satisfactory Service Record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5.7
Test for Accessories in Specially Bonded Cable Circuits . . . . . . . . . . . . . . . . . . . . . .
2.5.8
Tests for Water Tightness of Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5.9
Additional Tests for Cable Terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5.10 Pressure Vessel Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.6
Quality Assurance Scheme for Accessory Design and Manufacture . . . . . . . . . . . . . . . . . . . .
2.6.1 The Routine Test Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.6.2 Quality Assurance Approval for Manufacture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.6.3 Routine Tests on Prefabricated Moulded Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.6.4 Sample Tests on Individual Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.7
Quality Assurance Scheme for Accessory Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.7.1 Quality Assurance Approval for Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.7.2 Quality Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.7.3 Training of Personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.7.4 Assembly Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.7.5 Special Assembly Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.7.6 Preparation of the Assembly Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.8
Compatibility of the Accessory with Specified after Laying Tests . . . . . . . . . . . . . . . . . . . . . .
2.8.1 Voltage Test on Main Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.8.2 Partial Discharge Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.8.3 Voltage Withstand Test on the Cable over Sheath and Joint Protection . . . . . . . . .
2.8.4 Current Balance Test on the Cable Sheath and Screening Wires . . . . . . . . . . . . . . . .
2.9
Maintenance Requirements of the Accessory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.9.1 Monitoring of Fluid Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.9.2 Voltage Withstand Tests on the over Sheath and Joint Protection . . . . . . . . . . . . . . .
2.9.3 Shelf Life of Accessories for Emergency Spares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.9.4 Availability of Accessory Kits for Emergency Spares . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.10 Economics of Accessory Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.10.1 Cost of the Accessory Complete with all Components . . . . . . . . . . . . . . . . . . . . . . . .
2.10.2 Cost of Guarantee and Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.10.3 Cost of Assembly Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.10.4 Cost of Preparing the Installation Environment for the Accessory . . . . . . . . . . . .
2.10.5 Cost of Safe Working Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.10.6 Cost of Special Jointing Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.10.7 Cost of Training . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.10.8 Comparative Cost of Cable and Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.10.9 Cost of Verification of Accessory Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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2
A Guide to the Selection of Accessories
2.1
61
Introduction
The reliability and performance of a cable circuit is dependent in equal measures on
the designs of the cable and accessory and on the skill and experience of the person
who is assembling the accessory. The cable insulation is extruded in the factory
under controlled process conditions using selected materials of high quality. It is
equally important that the same quality measures are employed for the manufacture
of the accessories in the factory and for their assembly on site onto the specially
prepared cable.
It is essential to select the design of accessory to be exactly compatible with the
particular cable type and the particular service application. Compatibility should be
validated by electrical type approval tests and be supported by either prequalification
tests, or service experience. In particular the performance of the accessory is
dependent on the quality, skill and training of the jointing personnel and on the
use of the specialised tools required for a particular accessory.
The itemised sub-headings below form the basis of the information that is needed
by the manufacturer and installer of the cable and accessories. For many applications
the cable manufacturer also manufactures, supplies and installs the accessories as
part of the complete cable circuit, thus the information is immediately available
inhouse. In the event that the user purchases the accessories separately from the
cable, then the following items form the basis of the questions that should be asked to
the manufacturers of the cable and accessories to ensure that the accessories are
suitable.
2.2
Compatibility of the Accessory with the Cable
2.2.1
Number of Cable Cores
The user should determine whether the cable construction is of single, three core or
triplex construction (i.e. three single core cables twisted together). The design of the
accessory and the method of assembly is dependent upon the number of cable cores;
however it is unusual for three core extruded cables to be employed above 60 kV.
2.2.2
Cable Constructional Details
For satisfactory service performance it is most important that the correct size of
accessory is selected to suit the particular cable. The outer diameter of the cable
insulation, its tolerance and shape are particularly important in the selection of an
accessory employing a pre-moulded component, such as an elastomeric stress cone
or an elastomeric joint moulding. Such components are designed to fit a specific
range of diameters of prepared cable insulation (that is with the insulation screen
removed and the insulation smoothed and shaped). The components must not be
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used outside this range. The minimum diameter is determined by the need to achieve
sufficient pressure to eliminate voids at the interface with the cable insulation. The
maximum diameter is determined by such considerations as a) preventing damage by
over stretching during assembly and b) limiting the maximum pressure at the
interface such that compression set of the cable insulation and moulded insulation
is minimised.
The diameter and tolerance ratio of the conductor and of its compaction (the radio
of the effective cross sectional area of the metal to the total area occupied) are needed
in selecting a connector that will exhibit stable conductivity and high mechanical
strength.
The diameters and tolerances of the cable metallic barrier and over sheath are
needed to ensure that accessory metallic flanges and other components can be passed
back over the cable during assembly.
The following dimensional and constructional details should be obtained by the
user to ensure compatibility of the accessory with the cable:
The detailed cable construction should be obtained from the cable manufacturer,
which includes the following information as a minimum requirement. Diameters,
maximum and minimum tolerances, eccentricity dimensions, construction and material need to be obtained for each of the following cable components:
•
•
•
•
•
•
•
Conductor and special features (e.g. water blocking), if any
Conductor screen
Insulation (ovality and eccentricity dimensions are required)
Insulation screen
Screen wires, if any
Longitudinal water blocking, if any
Metallic barrier, if any, for example whether an extruded sheath, a welded sheath,
or a laminated foil barrier. Also whether of cylindrical or corrugated form
• Over sheath
• Armour, if any
• Special features (e.g. presence of optical fibre or pilot wires).
2.2.3
Conductor Area and Diameter
The user should ensure that the accessory has been designed and tested for the
particular cable conductor size. The electrical performance of an accessory design
can become critical on large conductor cables because of the high cable insulation
screen stress.
The user should ensure that the conductor connections in the complete kit of
components are supplied to suit the particular conductor construction. The conductor
connection must be capable of carrying the same current as the cable conductor and
must be capable of withstanding the cable longitudinal thermomechanical forces,
these being proportional to the cross sectional area.
2
A Guide to the Selection of Accessories
2.2.4
63
Operating Temperature of the Cable Conductor and Sheath
under Continuous, Short Term Overload and Short Circuit
Current Loading
The materials of the accessory must be capable of operating satisfactorily at the
operating temperatures specified for the cable. For example, cables with LDPE
insulation have a typical continuous maximum operating temperature of 70 C and
cables with XLPE insulation have an operating temperature of 90 C, (IEC
840 1988). The short term overload temperatures depend upon the type of cable
and application. The temperature of the conductor under short circuit is typically
taken as 250 C for XLPE and 160 C for paper insulated cable, (IEC 986 1989). The
permitted short circuit temperature of the cable extruded metallic sheath or screen
wires is determined by the type of metallic sheath and thermoplastic over sheath, this
temperature usually being significantly less than that of the cable insulation.
2.2.5
Compatibility of the Accessory with the Type of Cable
Insulation and Semiconducting Screens
2.2.5.1 Physical Compatibility with the Extruded Cable
The insulation of the polymeric cable must be identified by the user. There are
significant differences between the electrical and mechanical characteristics of
extruded insulation. The usual insulants for extruded polymeric cables in the voltage
class of 60 kV and above being XLPE (crosslinked polyethylene), LDPE (low
density polyethylene), HDPE (high density polyethylene) and EPR (etylene propylene rubber).
2.2.5.2 Chemical Compatibility with the Extruded Cable
The type of insulating liquid or lubricant used in joints and terminations should be
identified to ensure that these do not affect the properties of the polymeric insulation
and semiconducting screens employed in the cable and accessories. For example a)
hydrocarbon liquids at elevated temperature can cause swelling of XLPE and EPR
insulation and reduction of the conducting properties of screens and b) silicone
liquids can have an effect on silicone rubber components.
2.2.5.3 Compatibility with the Paper Insulated Cable
In the case of transition joints between polymeric cable and paper insulated cable it is
important to establish whether the cable is of the internally or externally pressurised
type and whether the fluid dielectric is a gas or a liquid; these details will determine the
performance requirements of the barrier plate that segregates the two cables. In the
case of mass impregnated non pressurised cables it is important to determine the type
of impregnating compound and whether it is of the liquid type or of the non draining
type; these details will determine the chemical suitability of the materials employed
within the joint to segregate the impregnating fluid from the insulation of the polymeric cable and joint. Penetration of a hydrocarbon impregnating into the polymeric
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cable can result in swelling and modification of the electrical characteristics of the
semi-conducting screens and insulation of both the cable and accessory components,
thereby reducing their electrical performance. Loss of the impregnating fluid into the
polymeric cable can result in eventual electrical failure of the paper cable.
2.2.6
Cable Electrical Design Stresses to be Withstood by
the Accessory
The user is advised to obtain the magnitude of the cable stresses at the conductor and
insulation screens, or obtain the dimensions of the cable, thereby permitting the stresses
to be calculated. The unit of stress is kV/mm calculated at Uo voltage. There are
significant differences in the magnitude of the electrical design stress employed in
cables, these being dependent upon the type and thickness of insulation, the conductor
size, the system voltage and the lightning impulse voltage. It is essential that the
accessory has been designed and tested to operate at the particular cable design stress.
The stress at the cable insulation screen is of particular significance because this
normally determines the maximum design stress in the accessory. The insulation
screen stress is usually of higher magnitude in those cables designed for high system
voltages and large conductor diameters.
2.2.7
Mechanical Forces and Movements Generated by the Cable
on the Accessory
The magnitude of the forces and movements generated by the cable on the accessory
depends upon the cable materials, the method of cable manufacture and the type of
cable installation design (i.e. rigid or flexible installation).
The following mechanical strains are dependent on the cable construction:
• Insulation retraction (shrink back)
• Insulation radial thermal expansion
• Over sheath retraction (shrink back).
The following forces are dependent upon the cable construction, current loading,
operating temperature, method and type of cable constraint and accessory design:
• Conductor thermomechanical thrust and retraction
• Sheath thermomechanical thrust and retraction.
2.2.8
Short Circuit Forces
Electromagnetic forces are present during a short circuit between the individual
conducting components of the accessory and between the adjacent cables and the
accessory. The following information is applicable:
2
A Guide to the Selection of Accessories
65
• Method of constraint of the accessory and cable
• Dimensions of the individual accessory components
• Method of constraint and the spacing of adjacent cables.
2.3
Compatibility of the Accessory Performance with that
of the Cable System
2.3.1
Circuit Performance Parameters
The current rating and optimum circuit economics are dictated by the cable conductor size, cable material costs and the method of installation. To achieve the optimum
economical solution it is important that the accessory design is not allowed to limit
the performance of the cable. The accessory must therefore match the following
cable performance:
• Rated voltages (Nominal system voltage U and maximum Um)
• Current rating
(Current magnitude)
• Continuous, cyclic and short time overload.
(Current magnitude, time and temperature).
• Short circuit rating, “phase to earth” and “phase to phase”
(Current magnitude, asymmetry, time and temperature).
• Basic impulse level
(Withstand voltages for lightning impulse and switching surge).
(Flash over voltage for the system insulation co-ordination of outdoor terminations, if specified (IEC 71 1993)).
2.3.2
Circuit Life Required
The accessory should match the design life specified for the particular cable circuit.
This is typically requested to be from 20 to 40 years, however some cable circuits are
installed as temporary links, for example in an overhead line circuit. Such accessories may be designed to be suitable for quick assembly with a reduction in performance and service life.
2.3.3
Metallic Screen Bonding Requirements
The following information is required on a) the type of bonding leads, (concentric or
single conductors) and their conductor size and overall dimensions and b) the type of
cable bonding scheme, for example solidly earthed or specially bonded metallic
screens.
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• Magnitude of induced sheath or screen wire voltage under normal and short
circuit current.
• Magnitude of circulating sheath or screen wire current under normal loading.
• Magnitude of short circuit current.
• Magnitude of specified over sheath lightning withstand voltage and dc withstand
voltage, (ELECTRA 128; E.R. C.55/4 1989; ANSI/IEEE 575-1988 1988).
It is important that the accessory design incorporates means of connecting the cable
screen wires, metallic tapes or sheath and joint shell to the insulation screen.
2.3.4
Earth Fault Requirements
Some Utilities require that short circuit currents be returned within the cable system.
The user should ensure that the accessory is also able to contain this current.
2.4
Compatibility of the Accessory with the Cable System
Design and Operating Conditions
The user is advised to ensure that accessory design is a) compatible with the
particular cable installation design, as this determines the mechanical loading
applied, b) capable of being assembled in the site environmental conditions and c)
capable of a satisfactory service performance under adverse climatic conditions.
2.4.1
Type of Cable Installation Design
• Rigidly constrained (cable laid direct in the ground or close cleated)
• Flexible unconstrained (cable horizontally snaked or vertically waved)
• Semi-flexible (cable constrained, but permitted to exhibit a controlled deflection,
for example at a bridge crossing or adjacent to gas immersed switch gear)
• Unfilled duct.
2.4.2
Standard Dimensions for Cable Termination
The user is advised to ensure the following dimensional compliancies:
• Outdoor and indoor termination: Harmonisation with existing equipment of the
overall height of the off-going bus bar connector and of the bottom metalwork
fixing arrangements to the support structure.
• GIS and transformer termination: Harmonisation of the cable termination with
both the design of the metal clad switch gear (internal diameter, overall length,
off-going bus bar connector, bottom metalwork sealing arrangements and
2
A Guide to the Selection of Accessories
67
pressure) and the design of the support structure (fixing arrangements for the
particular cable constraint selected) (IEC 859 1986).
2.4.3
•
•
•
•
•
•
•
Type of Accessory Installation Environment
Laid direct and buried in the ground
Jointing chamber (in air)
Tunnel
Above ground
Bridge
Tower
Shaft.
2.4.4
Jointing Limitations in Restricted Installation Locations
• Space limitations
• Time limitations (for example arising from road or rail traffic influences)
• Tolerance limitations of assembly personnel (for example arising from extremes
of temperature, humidity, vibration, noise and induced voltage).
2.4.5
•
•
•
•
•
•
•
•
•
•
Mechanical Forces Applied to the Accessory
Thermomechanical forces
Earthquake
Vibration
Off-going bus bar at terminations
Wind loading on bus bars at terminations
Ice loading on bus bars at terminations
Short circuit loading on bus bars at terminations
GIS pressure
Angle of installation of terminations
Hydraulic or pneumatic pressure forces at transition joints.
2.4.6
Climatic Conditions
Accessories require to be suitable for the extremes of climatic conditions expected
both in service and during assembly. Some types of accessories are required to be
assembled under controlled environmental conditions.
• Altitude (reduction of electrical strength of air)
• Air pollution (reduction of electrical strength of outdoor insulator surface)
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•
•
•
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Precipitation (reduction in electrical strength of air and outdoor insulator surface)
Salt fog (reduction in electrical strength of outdoor insulator surface)
Moisture condensation (reduction in electrical strength of insulator surface)
Temperature
Atmospheric humidity.
2.4.7
Type of Accessory Outer Protection Required
The accessory protection is required to provide corrosion protection and, for a
specially bonded cable circuit, insulation from ground.
•
•
•
•
Joint box (laid direct in the ground or in air)
Pedestal insulator (in air)
Moulded sheet insulation (in air, to protect personnel against electric shock)
Metallic fences or screens (in air, to protect personnel against electric shock).
2.4.8
Situations Requiring Special Accessory Protection
• Submerged under water
• Termite infestation
• Fire risk.
2.5
Verification of Accessory Performance
It is strongly recommended that the performance of the accessories is proven on test
with the particular cable type, material, size and manufacture.
The following verification items should be checked by the user.
2.5.1
Use of the Specific National or International Type Test
Specification for the Accessory
If an applicable type test specification is available for the accessory, then these tests
should be undertaken or a type test report provided. A list of world wide test
specifications is given in the References.
2.5.2
Use of the Cable Test Specification in the Absence of an
Accessory Specification
If a type test specification for the accessory does not exist, then it is recommended to
use the type test specification for the cable.
2
A Guide to the Selection of Accessories
2.5.3
69
Type Test Report
The type test report should be obtained, this will give details of the accessory
together with the cable size, performance levels and test specification reference.
The type test usually includes elevated high voltage testing and load cycle testing of
a comparatively short duration (e.g. 20 daily load cycles).
2.5.4
Type Tested Accessory in Combination with the Particular
Cable
The cable size recorded in the type test report should be compared to the required
cable for the particular application. The radial design stress of the test cable should
be equal to or higher than that of the required service cable. The conductor area
recorded in the type test report should be equal to or larger than that of the required
cable. If the conductor size of the particular cable has not been tested it is permitted
to accept tests already performed on a larger conductor (for example on the largest
conductor size in the range). Some specifications require the testing of both the
largest and smallest conductor sizes in the range, (IEC 840 1988).
2.5.5
Pre-Qualification Tests
The pre-qualification test is an endurance test of extended duration (for example one
year). If a recognised pre-qualification test specification does not exist then the user
is recommended to ask for confirmation that long term development tests have been
undertaken. For pre-qualification tests on accessories for use at system voltages
above 150 kV see (ELECTRA 151 1993a, b).
2.5.6
Satisfactory Service Record
Although not essential if the cable and accessories have passed recognized type
approval tests and pre-qualification tests it is advisable to check that the accessories
have a satisfactory service experience.
2.5.7
Test for Accessories in Specially Bonded Cable Circuits
Type approval reports should be provided to demonstrate the adequacy of the electrical
insulation of a) the joint protection and b) the screen interruption. These tests are usually
required to be undertaken on the complete accessory together with the cable. The
exception is for discrete components, such as pedestal insulators, which for some
applications may be tested individually. The tests usually require a combination of
lightning impulse, ac and dc voltage withstand tests (ELECTRA 128; E.R. C.66/1 1979).
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2.5.8
Z. Iwata
Tests for Water Tightness of Joints
Type approval reports should be provided for those joints required to operate
partially or fully submerged under water. Typical applications being installation in
water logged ground or in jointing chambers or tunnels which are liable to flood.
These tests are usually undertaken on the completed joint together with the cable and
should require the application of either temperature cycles or current loading cycles
whilst under water immersion.
For installation in the ground, the test specification may also require the addition
of mechanical tests to demonstrate the ability to withstand forces imposed by soil
loading and by heavy vehicles, (E.R. C.66/1 1979).
For joints in specially bonded cable circuits, installed in the ground, it is usual to
provide a type test report which demonstrates performance when subjected to a
combination of mechanical loading, water immersion, temperature cycling and
elevated voltage withstand tests (item 2.5.7) (E.R. C.66/1 1979).
2.5.9
Additional Tests for Cable Terminations
In addition to the basic electrical type approval test report, the user is advised to seek
confirmation of test performance for the following items:
• Outdoor and indoor terminations:
– Electrical performance of the insulator when subjected to atmospheric pollution in both wet and dry conditions (IEC 815 1986).
– Electrical performance of the insulator when subjected to strong sunlight for
prolonged periods. This is applicable to polymeric insulators only and not to
porcelain insulators.
– Mechanical performance of the insulator when subjected to a) cantilever loading
to simulate forces from wind, bus bar loading and short circuit electromagnetic
loading and b) axial loading to simulate the thermo-mechanical thrust and
retraction of the cable conductor.
– Electrical withstand performance of the cable termination, complete with cable,
under rain spray conditions (IEC 840 1988; IEEE 48-1990 1990; KEMA S10-2).
– Measurement on the complete termination of the radio interference level due to
partial discharges (corona) in air (IEEE 48-1990 1990).
– For application in those countries subject to severe earthquakes, the measurement of the vibration characteristics of the termination complete with its
support structure and cable (IEC 1463).
• GIS terminations and transformer terminations:
– Mechanical performance of the terminations when subjected to a) cantilever
loading to simulate the expansion forces of the off-going bus bar and b) axial
loading to simulate the thermomechanical thrust and retraction of the cable
conductor.
2
A Guide to the Selection of Accessories
71
– Vibration performance of the termination to simulate a) the high frequency
vibration generated by the operation of a circuit breaker, b) when applicable,
the low frequency vibration generated by an earthquake and c) the vibration of
a transformer.
2.5.10 Pressure Vessel Regulations
If the accessory contains fluid under pressure or is connected to GIS metal clad
trunking it is advisable to check the requirements of National Regulations, if they
exist, concerning approval of the design, routine test and type test.
2.6
Quality Assurance Scheme for Accessory Design
and Manufacture
Type approval testing is intended to verify that the design has met the specified
performance. To ensure consistent manufacturing quality, the user should verify the
following items.
2.6.1
The Routine Test Schedule
Compliance with a routine test national specification should be stipulated. Most
manufacturers use a more rigorous in-house routine test specification, in which case
this should be approved by the user (for example (KEMA S10-2; ENEL spec. DJ
4585)).
2.6.2
Quality Assurance Approval for Manufacture
The user should ensure that the accessory supplier or manufacturer provides evidence of an approved Quality Assurance system for design, manufacture, routine test
and traceability complying with an internationally recognised standard, e.g. (BS EN
ISO 9001:1994 1994).
2.6.3
Routine Tests on Prefabricated Moulded Insulation
It is strongly recommended that the user specifies that each factory moulded
insulating component be subjected, as a minimum requirement, to a routine test
comprising an ac voltage withstand test and a partial discharge measurement test.
Consideration should also be given to the application of additional routine tests, for
example, dielectric loss angle measurement, X-ray examination and ultrasonic
examination (KEMA S10-2; ENEL spec. DJ 4585).
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2.6.4
Z. Iwata
Sample Tests on Individual Components
In addition to the tests on moulded insulation described above, there should be
electrical and mechanical tests performed on either all or on representative samples
of production. For example (BS EN 50069:1991 1991; EATS 09-10 1976).
2.7
Quality Assurance Scheme for Accessory Installation
Assembly of the accessories onto cable with extruded insulation is the most vulnerable
part of a project involving the manufacture and installation of a new cable circuit.
Accessories and cables are manufactured and tested under controlled factory conditions,
whereas the in-service performance of the accessory is dependent upon the training, skill
and reliability of the personnel, who are often required to work under adverse site
conditions.
For many project applications one company will manufacture the cable and accessories and undertake to complete the installation of the circuit. In other applications the
installer may complete the circuit using cable and accessories supplied by different
manufacturers. In some applications the installer may only assemble the accessories. For
each application the requirements of the QA system are equally rigorous.
2.7.1
Quality Assurance Approval for Installation
The user should ensure that the installer provides evidence of an approved quality
assurance system for installation to an internationally recognised standard (BS EN
ISO 9001:1994 1994).
2.7.2
Quality Plan
The installer is required to produce a Quality Plan for each project, this includes the
project time schedule together with the requirements for suitably qualified personnel,
training, on-site storage of components and accessories, tools, testing equipment,
constructing materials, assembly instructions, preparation of the jointing environment
and records of the assembly work. It is important that the records of assembly are
traceable to the location of each accessory in the cable circuit. If purchasing separately,
the user is advised to ensure that, for the purposes of traceability, the quality systems of
the cable manufacturer, accessory manufacturer and installer are compatible.
2.7.3
Training of Personnel
When selecting the designs of accessories the user should ensure that training courses are
available for the jointing and supervisory personnel. It is strongly advised that personnel
receive training on the particular designs of accessories and cable.
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73
Examples of the elements of a training course for assembly personnel are:
• General training at specific system voltages with the standard range of accessories
required by the user
• Repeat training after a defined period for those personnel who have completed
general training
• Specified training on a new accessory or cable design for those personnel who
have completed general training.
At the end of the training course the proficiency of the assembly personnel is
normally assessed, for example, by a verbal or written examination, by a practical
test and preferably by performing on the assembled accessories an electrical partial
discharge test and voltage withstand test.
Proficiency is recognised at the completion of training by the issue of a certificate,
which should be checked by the user as part of the quality plan for a specific project. In
many instances a kit of general jointing tools and a set of general assembly instructions
is also issued to the personnel following satisfactory completion of training.
2.7.4
Assembly Instructions
The accessory manufacturer is required to supply a complete set of assembly
instructions together with drawings of the particular accessory.
The instructions should also include lists of the specified assembly tools, the
specified consumable materials and the health and safety precautions. Recommendations for the preparation of the assembly environment should also be given.
It is important that the user studies the instructions before work begins to ensure
that the workplace is correctly prepared and that all the tools and consumable
materials are available.
2.7.5
Special Assembly Tools
Most designs of accessories, particularly those operating at higher system voltages,
require special tools which are purchased or hired from the accessory manufacturer. The
user should ensure that full instructions are provided and that the personnel are trained in
their use. These tools may take the form, for example, of a) hydraulic compression
presses or welding equipment for connecting the conductors, b) cutting equipment to
remove the insulation screen and to shape the cable insulation c) assembly machines
which stretch and position pre-moulded elastomeric components, d) taping machines
that apply tape and e) heated mould tools and mobile extruders for field moulded joints.
2.7.6
Preparation of the Assembly Environment
It is strongly recommended that the assembly area for both joints and termination to
be enclosed within a tent or temporary building, with the objective of providing a
74
Z. Iwata
clean and dry environment. The enclosure should be a) well lit to facilitate accurate
preparation of the cable insulation, b) provided with a sound floor and c) lined with
sealed materials to facilitate cleanliness. In extremes of climate it is good practice
to provide control of temperature and humidity to ensure a) consistent performance
of the personnel and b) consistent properties of the polymeric materials.
2.7.6.1 Joint Assembly
• An appropriately sized joint bay or chamber.
• The provision of a temporary and/or permanent support for the completed joint.
2.7.6.2 Termination Assembly
• A permanent support structure.
• A temporary weatherproof structure during assembly.
• Means of lifting the cable and insulator into position.
2.8
Compatibility of the Accessory with Specified after Laying
Tests
When the installation of the cable and accessories has been completed it is standard
practice to perform electrical tests to demonstrate that the assembly of the accessories is of satisfactory quality and that mechanical damage to the cable and accessories
has not occurred during installation.
The following tests can be performed. It is important to ensure that the accessory
design is suitable for the particular test:
2.8.1
Voltage Test on Main Insulation
DC tests have been traditionally applied to transmission circuits, however their use
on cable with extruded polymeric insulation is not recommended. Experience has
shown that the dc voltage test is not always sufficiently sensitive to detect damaged
cable insulation or incorrectly assembled accessories and hence prevent them from
entering service. In particular the electrical stress distribution under dc voltage in an
accessory is usually significantly different from that under ac voltage in normal
service. The application of an ac voltage is now under evaluation as an after laying
test, either by the application of service voltage from the transmission system or by
the application of test voltage from mobile test equipment (ELECTRA 173 1997).
2.8.2
Partial Discharge Detection
Partial discharge detection techniques are at present being developed for some cable
and accessory applications to check for the absence of damage to the cable during
installation and incorrect assembly of the accessories. Methods are not yet available
for this to be done in a simple manner as a routine commissioning test on normal
cable circuits (ELECTRA 173 1997).
2
A Guide to the Selection of Accessories
2.8.3
75
Voltage Withstand Test on the Cable over Sheath and Joint
Protection
It is usual for specially bonded cable systems, including their accessories, to be
subjected to an after laying test comprised of the application of a dc withstand
voltage applied to the metallic sheath or screen wires (ELECTRA 128; E.R. C.55/4
1989; IEC 229 1982).
2.8.4
Current Balance Test on the Cable Sheath and Screening
Wires
This test is performed on cross bonded cable systems at or adjacent to accessory
positions to confirm that a) the bonding connections of the accessory are correct and
b) the cable lengths and spacing are symmetrical, such that the magnitude of residual
circulating current is of an acceptably low magnitude (E.R. C.55/4 1989; IEC
229 1982).
2.9
Maintenance Requirements of the Accessory
The user should ensure that adequate maintenance tests and checks have been
recommended by the cable and accessory suppliers, for example:
2.9.1
Monitoring of Fluid Insulation
Liquid and gas levels: some types of termination, straight joints and transition joints
are filled with insulating liquid or gas and may require to be regularly inspected or
monitored in service to ensure that neither the liquid or gas have escaped.
2.9.2
Voltage Withstand Tests on the over Sheath and Joint
Protection
These tests are similar to the after laying tests, but are usually performed at reduced
voltage levels (ELECTRA 128; E.R. C.55/4 1989).
2.9.3
Shelf Life of Accessories for Emergency Spares
The user should ensure that information is provided on the shelf life of the components in an accessory for long term storage as these may vary according to the type of
material, the way they are packed and the appropriate temperature and humidity
conditions of storage.
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2.9.4
Z. Iwata
Availability of Accessory Kits for Emergency Spares
The user is recommended to obtain either a sufficient stock of spare accessories or to
have an agreement with the manufacturer to supply accessories at short notice. The
design of an accessory for emergency use may be different from that installed.
2.10
Economics of Accessory Selection
A comparison of the relative costs of different designs of accessory kits should not
be undertaken without giving due consideration to the total costs of installation and
assembly. The following are the main items of cost.
2.10.1 Cost of the Accessory Complete with all Components
The accessory design should be checked to ensure that it is a complete kit and will be
supplied with all the components and assembly instructions for the particular application. Some components that may not necessarily be supplied by all accessory manufacturers are for example a) conductor connections and anti-corrosion protection for joints
and b) bus bar take-off connectors and support metalwork for termination.
2.10.2 Cost of Guarantee and Insurance
At the higher system voltages it is more usual for the cable and accessories to be
supplied, installed and guaranteed as a “turn-key” project. Under such circumstances
the guarantee will usually extend to a specified number of years in service. If the user
decides to divide the supply and installation of accessories between companies, it is
recommended that the cost of financial self insurance be considered, because the
responsibility for an accessory failure in service can be difficult to apportion between
the accessory manufacturer, the cable manufacturer and the installer.
2.10.3 Cost of Assembly Time
The jointing time required to assemble accessories can differ dependent on their
design. Similarly the time required to assemble the anti-corrosion protection and the
final mechanical support to the accessory can be the over-riding factors in determining the jointing time.
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A Guide to the Selection of Accessories
77
2.10.4 Cost of Preparing the Installation Environment
for the Accessory
Accessories require the provision of a weatherproof enclosure together with the
environmental conditions necessary for jointing (e.g. good lighting, cleanliness and,
when necessary, air conditioning. The supply of electricity and gas may be required).
Details are given in item 2.7.6.
2.10.5 Cost of Safe Working Conditions
In addition to the cost of constructing the installation environment to comply with
the regulations for safe working practices (items 2.10.4 and 2.7.6), the provision may
be required for temporary and permanent protection to a) the installer’s personnel
from electric shock during assembly and b) the user’s personnel when the accessory
is in service.
2.10.6 Cost of Special Jointing Tools
There may be significant differences in purchase cost and hiring charges of the tools
required for different accessories.
2.10.7 Cost of Training
Qualified jointers who are trained to assemble the particular accessory should always
be employed. The user should decide whether it will be more cost effective to a)
employ qualified and experienced personnel to assemble the accessories, or b)
employ qualified and experienced personnel to install the cable and assemble the
accessories as part of a turn-key contract, or c) incur the on-going costs of training
and regular repeat training for his own personnel.
2.10.8 Comparative Cost of Cable and Accessories
The design of the cable can influence the cost of the accessory design. Thus a
reduction in the cost of the cable construction may result in an increase in the cost
of the accessories. Similarly an increase in the cost of installation by laying longer
lengths of cable may achieve a reduction in overall costs by requiring fewer joints.
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Z. Iwata
2.10.9 Cost of Verification of Accessory Performance
If a type test report is not available for the particular cable and accessory in
combination then the user is advised to allow for the cost of performing a type
approval test. This cost may be born by the supplier, in the case of a turn-key project,
but this is less usually so in the case of separately supplied cable and accessories.
References
ANSI/IEEE 575-1988.: Guide for the application of sheath-bonding methods for single-conductor
cables and the calculation of induced voltages and currents in cable sheaths (1988)
BS EN 50069:1991.: Specification for welded composite enclosures of cast and wrought aluminium
alloys for gas filled high voltage switch gear and control gear (1991)
BS EN ISO 9001:1994.: Quality Systems: Model for Quality Assurance in design, development,
production, installation and servicing (1994)
E.R. C.55/4.: Insulated sheath power cable systems (1989)
E.R. C.66/1.: Type approval testing procedure: protective boxes for use with buried accessories
employed on 33kV–400 kV insulated sheath power cable (and for sheath sectionalising insulation embodied in such accessories) (1979)
EATS 09-10.: Porcelain insulators for 33, 66, 132, 275 and 400 kV pressure assisted cable outdoor
sealing ends (1976)
ELECTRA 128.: Guide to the protection of specially bonded cable systems against sheath over
voltages (Report of WG 21.07)
ELECTRA 151.: Recommendations for electrical tests pre qualification and development on
extruded cables and accessories at voltages > 150 (170) kV and 400 kV (420) kV. (December
1993 pp. 15–19: WG 21.03) (1993a)
ELECTRA 151.: Recommendations for electrical tests, type, sample and routine on extruded cables
and accessories at voltages > 150 (170) kV and 400 kV (420) kV. (December 1993 pp. 21–
29: WG 21.03) (1993b)
ELECTRA 173.: After laying tests on high voltage extruded insulation cable systems (Report of
WG 21-09) (1997)
ENEL spec. DJ 4585.: Prescrizioni per il collaudo di giunti e terminali unipolari cavi isolati con
gomma etilenpropilenica
IEC 1463.: Bushings – Seismic Qualification
IEC 229.: Test on cable over sheaths which have a special protective function and are applied by
extrusion (1982)
IEC 71.: Insulation Coordination. Part 1 (1993): Definitions, principles and rules. Part 2 (1976):
Application guide
IEC 815.: Guide for the selection of insulators in respect of polluted conditions (1986)
IEC 840.: Tests for power cables with extruded insulation for rated voltages above 30 kV (Um ¼
36 kV) up to 150 kV (Um ¼ 170 kV)) (1988)
IEC 859.: Cable connections for gas-insulated metal-enclosed switch gear for rated voltages of
72.5 kV and above (1986)
IEC 986.: Guide to the short-circuit temperature limits of electric cables with a rated voltage from
1.8/3 (3.6)kV to 18/30 (36)kV (1989)
IEEE 48-1990.: Test procedures and requirements for high-voltage AC cable terminations (1990)
KEMA S10-2.: KEMA specification of requirements to be met by accessories for single-phase
power cables with extruded insulation for rated voltages between 50 and 220 kV
Section 3.: Summary of world wide usage of accessories for HV extruded cables (Chapter 4.1)
(Report of WG 21-06)
2
A Guide to the Selection of Accessories
79
Zensuke Iwata was born in Tokyo, Japan, on October 5, 1944.
He received the B.S. degree in Electrical Engineering from the
University of Tokyo, Japan, in 1968. In 1968 he joined the
Furukawa Electric Co., Ltd., Japan, where he has been engaged
several years in research and development of high-voltage power
cables and their accessories before taking other positions in the
Furukawa Electric Co. In 2003 he successfully carried out the
long-term field test of the real scale H.T. superconducting cable
system as the Managing Director and CTO of the Furukawa
Electric Co. In 2004 he was appointed as the President of Nuclear
Fuel Industries, Japan, and retired in 2014. Zensuke Iwata convened Cigré WG 21.06 which published Technical Brochures 89
and 177. He received the TC Award in 1995. He chaired the ISTC
of Jicable in 2003.
3
Interfaces in Accessories for Extruded
HV and EHV Cables
Henk Geene
Contents
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.1 Terms of Reference of JTF 21/15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.2 Interfaces to be Studied . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.3 Materials Involved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Interface Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.1 Smoothness of the Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.2 Contact Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.3 Lubricant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.4 Electrical Field Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.5 Temperature and Temperature Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.6 Quality of Accessory Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Long Term Performance of Interfaces in Cable Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.1 Migration of the Lubricant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.2 Movements in the Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.3 Reduction of the Interface Pressure due to Relaxation of Materials . . . . . . . . . . . . . .
3.3.4 Electrical Ageing of Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4 Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.5 Recommendations and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1
81
82
82
83
85
86
87
87
88
90
90
90
91
91
91
92
92
94
94
Introduction
Interfaces in joints and terminations of extruded HV cables have been identified as
crucial parts. Some of the mechanisms related to ageing are not well understood. For
this reason, a task force has been established to study the behaviour of interfaces in
H. Geene (*)
Prysmian Group, Product Management HV Accessories, The Hague Area, Netherlands
e-mail: henk.geene@prysmiangroup.com
© Springer Nature Switzerland AG 2021
P. Argaut (ed.), Accessories for HV and EHV Extruded Cables, CIGRE Green Books,
https://doi.org/10.1007/978-3-030-39466-0_3
81
82
H. Geene
accessories for HV and EHV extruded cables. The scope was limited to non-bonded
interfaces between solid insulating materials, but included the applied lubricants.
The Joint task force 21/15 (JTF21/15) was installed by Study Committee SC21
(Insulated Cables now SC B1) and SC15 (Materials now SC D1) and called
“Interfaces in accessories for extruded HV and EHV cables” The members of the
task force were cable systems and/or material experts. The report of the work has
been published as Cigré TB 210.
Within Cigré, interfaces was also subject of study for WG15.10. This working
group was concentrating on the material aspects of interfaces and had developed and
selected interface models for laboratory testing.
3.1.1
Terms of Reference of JTF 21/15
The joint task force is reviewed the state of the art regarding the interface behaviour
in accessories for extruded HV and EHV cables.
The targets objectives for JTF 21/15 were:
• To evaluate short term behaviour of interfaces (parameters influencing withstand
strength)
• To evaluate ageing behaviour and relevant parameters
• To make practical recommendations for evaluating, testing and installing interfaces in extruded HV and EHV cable systems.
The task force did not deal with partial discharges and electrical treeing in interfaces,
since these processes are strongly influenced by the type of accessories (materials,
design, etc.).
The focus was on the parameter settings to prevent partial discharges in interfaces
and those phenomena that could lead to partial discharges in service. Partial discharge detection on installed Cable Systems was the subject of Cigré WG 21-16
which published Cigré TB 182 (Cigré WG B1-16 2001).
3.1.2
Interfaces to be Studied
The interfaces to be studied are those in accessories for extruded HV and EHV cables
between solid insulating materials. Although the cable is an essential part of the
accessory, it will not always be explicitly mentioned (Fig. 3.1).
Interfaces in accessories are between:
• Rubber insulating body and cable insulation, in a liquid or gas filled termination
(a) dry-type termination (b), in a composite joint (c) or joint (d),
• Stress-cone and epoxy joint body, in a dry-type termination (b) or composite
joint (c)
• Adapter sleeve and joint body (e)
3
Interfaces in Accessories for Extruded HV and EHV Cables
83
Fig. 3.1 Typical accessory
arrangements for HV extruded
cables (Peschke and
Olshausen 1999)
3.1.3
Materials Involved
Interfaces exist between two solid polymer parts. The materials involved in these
interfaces and various related abbreviations are summarized in Table 3.1. The
international standards dealing with symbols and abbreviations of polymers respectively rubber and latex latices appear not to be harmonized yet.
Polyethylene mainly divides into two big families: LDPE (Low Density Poly
Ethylene, density in the range of 0.910-0.925 g/cm3) and HDPE (High Density Poly
Ethylene, density in the range 0.941–0.965). In addition to these two main families,
it is worth mentioning LLDPE (Linear Low Density Poly Ethylene). In cable
manufacturing PE is used both for insulation and for jacketing; the cross-linking
of PE (peroxide or silane) leads to XLPE (Cross Linked Poly Ethylene) and is widely
used both for MV and HV cables, particularly for allowing high operating temperatures up to 90 C.
The general term EPR is used as an abbreviation for Ethylene Propylene Rubber
(see Table 3.1). EPR divides into two kinds of polyolefin polymers: EPM and
EPDM. EPM represents an Ethylene Propylene copolymer while EPDM denotes a
84
H. Geene
Table 3.1 Summary of symbols and abbreviations of plastics
Abbreviation
in literature
SiR, SIR,
MVQ, VMQa
RTV
RTV-2
LR, LSR
XLR
HTV, HCR
EPR
EPM
EPM, P
EPDM
EPDM, S
EPDM, P
EP
HDPE,
LDPE
XLPE
Material (as used in this
paper)
Silicone rubber
Room Temperature
Vulcanising, 2-component
silicone rubber
Liquid Rubber, Liquid
Silicone Rubber, Extra
Liquid Rubber
High Temperature
Vulcanising, High
Consistency Rubber
Ethylene Propylene Rubber
Ethylene Propylene
Copolymer
(‘EPM, P’ stands for
peroxide vulcanised EPM)
Ethylene Propylene Diene
Terpolymer
(‘EPDM, S’ stands for
sulphur vulcanised; ‘EPDM,
P’ see above)
Epoxy resin
High Density Polyethylene,
Low Density Polyethylene
Cross-linked polyethylene
Grease, silicone oil, paste,
lubricant
Abbreviation
(as used in this
paper)
SiR
DIN ISO
1629 Mar
1992
MVQ,
VMQ
DIN EN ISO
1043 Part
1 Jan 2000
SI
EPR
EPM
EPMb
EPM
E/P
E/P
EPDM
EPDM
–
Epoxy
PE
–
–
XLPE
Lubricant
–
–
EP
PE
PE-LD
PE-HD
PE-X
–
RTV
LR
HTV
Q indicates rubbers with poly-siloxane-groups in the main chain, e.g. MVQ ¼ Methyl-Vinyl-PolySiloxane
b
M indicates rubbers with saturated poly-methylene main chain; R indicates rubbers with unsaturated poly-carbon main chain. Note: this deviates from the wide spread use to indicate rubbers in
general by R
a
terpolymer based on three monomers: Ethylene, Propylene and a non-conjugated
Diene. Both grades EPM and EPDM are suitable for peroxide cross-linking while
only EPDM allows sulphur cross-linking. Mixing of EPR with other components
leads to the final EPR compounds for power cables and accessories applications.
SiR consists of a so-called silicone-oxygen (polysiloxane) polymeric main chain,
which exhibits high thermal and high UV stability. This main polymeric chain
carries methyl-groups as well as other functional groups like vinyl- or hydrogenfunctions. RTV, XLR, LR or HTV (definitions see Table 3.1) rubbers are the most
widely used grades in electrical applications. Whereas RTV-2, XLR and LR are
3
Interfaces in Accessories for Extruded HV and EHV Cables
85
vulcanised by a so-called addition curing reaction of A- and B-component, HTV
rubber normally is peroxide cross-linked. The main differences in RTV-2 versus LR
or HTV are viscosity and processing. SiR can be formulated to obtain very low Shore
hardness and modulus of elasticity (Strassberger and Winter 1997).
Various types of Epoxy and fillers are used for electrical applications. Among
them a typical resin system is solid Bisphenol A type [2,2-Bis-(4-hydroxyphenyl)propane)] epoxy resin. Technical production of oligomeric epoxy resins involves
reaction of Bisphenol A with Epichlorhydrin to give a reactive intermediate. These
reactive epoxy resin intermediates are the basis, which is polymerized (polyaddition)
with so called hardeners. Hardeners could be either solid powdery acid anhydrides or
aliphatic polyamines resp. polyamidoamines. Cycloaliphatic epoxy resins are cured
normally with acid anhydrides. Aminic systems can be hardened at room temperature or below 80 C, acidic systems need temperatures over 80 C for hardening.
Results are the various Epoxies, which are classified as duroplastics.
Lubricants are widely used as slip-on materials to ease the installation of cable
accessories. Silicone greases as well as silicone fluids can be used with either SiR or
EPR accessories. Other materials are greases based on fluorinated polymers or
polyethylene glycol modified greases. Generally spoken, grease is formulated of a
liquid basis polymer and a thickener, mostly silica flour and some additives. In
contrast to grease e.g. silicone fluid is a pure silicone polymer. Regarding installation
and interface, the degree and speed of migration of the paste into the insulating
material are of interest. In the case of a pure fluid the interface may get dry after a
certain period of time, while for greases the thickener may remain in the interface
(Willems et al. 1995).
3.2
Interface Parameters
Interfaces are characterized by the initial or short-term breakdown strength and longterm ageing properties. In Sect 3.3 the ageing phenomena will be discussed while in
this section the focus will be on the initial breakdown strength.
The electrical withstand strength of interfaces is influenced by a combination of
several parameters. In the design of interfaces the following parameters should be
taken into account:
•
•
•
•
•
•
Smoothness of the surfaces
Contact pressure on the interface
Type of lubricant in the interface
Electrical field distribution in the interface
Temperature and temperature changes
Quality of accessory installation.
Most of the parameters mentioned, interact with each other. In the following
paragraphs, the parameters will be discussed separately.
86
3.2.1
H. Geene
Smoothness of the Surfaces
According to literature (Kreuger 1989), the discharge in a cavity in insulating materials
occurs at approximately the same (or higher) voltage as between equally spaced metal
electrodes. This voltage is for a certain gas given by the Paschen curve. According to
this curve, the breakdown stress of a gap is depending on the gap distance, type of gas
and pressure in the gap. At fixed pressure, the Paschen curve indicates higher breakdown
stresses for smaller gaps. In line with the diagram in Fig. 3.2 the smaller the cavities, the
higher the stresses at which partial discharges incept.
Interfaces without microscopic cavities do not exist. Surface scratches in the order
of a few microns are inevitable. In order to avoid partial discharges arising form these
scratches, the size of cavities should be limited to a few microns (depending on the
electrical stress). Therefore an accurate adaptation of the insulating surfaces in the
interface is needed. This can be achieved by smoothening of the insulation surfaces.
The surface smoothness of moulded rubber or epoxy insulators can be achieved
by equivalent surface smoothness of the moulds. Smoothness in the order of a few
micrometers can be achieved without difficulties. The surface smoothness of the
cable insulation, however, is depending on the applied peeling and smoothing
techniques, performed on site in a less well-controlled environment. This part of
the interface depends on the jointer skills. Therefore it is desirable, particularly for
high stress accessory designs, to prescribe the required smoothing technique for the
Fig. 3.2 Breakdown strength of air gaps, derived from the Paschen Curve (Kreuger 1989)
3
Interfaces in Accessories for Extruded HV and EHV Cables
87
preparation of the cable insulation. Although interface pressure is discussed in a
separate paragraph, it is mentioned here, that the pressure in the interface and the
adaptability of the insulating materials, determine the sensitivity to surface
irregularities.
Typical example for calculating the surface smoothness from the Paschen curves
(Kreuger 1989).
Assume a typical radial stress in the cable insulation, adjacent to the interface, of
3.6 kV/mm at Uo (radial stress at the insulation screen of the cable) and assume that
the accessory is required to be free of partial discharges at 2 Uo, then the inception
stress in a possible gap has to be higher than:
Egap ¼ er,PE =er,cav Emin 2
¼ 2:3=1 3:6 2 ¼ 16:7 kV=mm
Reading from Fig. 3.2, the cavity size in such case has to be smaller than about
20 μm.
Sanding with grade 400 leads to a roughness Rz ¼ 10 μm (Rz ¼ RmaxRmin).
Assuming that the mould irregularities are significant smaller (order of 1 μm) the
achieved cable insulation smoothness with paper grade 400 is sufficient.
3.2.2
Contact Pressure
As described in paragraph 3.2.1, the sensitivity of the interface to irregularities
depends on the interface pressure (Fig. 3.3). High interface pressures minimize the
size of micro cavities in the interface. In practice, two different methods to achieve
the required interface pressure have proven to be suitable (Fig. 3.3):
• Application of external mechanical forces, using springs. This method is often
used in the so-called inner cone model of composite joints or dry-type terminations, pushing a rubber part against an epoxy body
• Use of elasticity of the rubber body expanded on the cable insulation. This
method is often used in slip-on joints and stress-cones. Expansion percentages
of 5–50% are common practice. The interface pressure obtained by this method
depends on:
– E-modules of the applied rubbers
– Strain of the rubbers
– Wall thickness of the rubber.
3.2.3
Lubricant
Lubricants are basically used to relieve the friction between rubber parts and the
other insulating materials during installation. Silicone fluids and greases are commonly used for this application.
88
H. Geene
y
→
p
x
z
material strength
XLPE
electrical interface strength
E
SIR
→
Rz=const.
electrical
strength of air
transition
zone
(nearly) only
cavities
(nearly) no
cavities
Interface pressure, surface smoothness
Fig. 3.3 Electrical interface strength vs. interface pressure and surface smoothness (Kunze 2000a)
Lubricants also tend to increase the initial breakdown strength (Fig. 3.4). However it is not recommended to use lubricants for filling cavities. On the long-term,
lubricants probably migrate (at least partly), resulting in a more or less dry interface,
possibly leaving air gaps behind.
The migration rate of the lubricant depends on:
•
•
•
•
Type of lubricant
Type of insulating materials
Contact pressure
Temperature.
Another issue regarding lubricants is the presence of air bubbles trapped in the
interface during installation. In particular greases with a high viscosity are more
likely to enclose air bubbles. The design of the accessory or the applied installation
method should prevent the formation of air bubbles (Fig. 3.4).
3.2.4
Electrical Field Distribution
During operation of the cable system, the interfaces are subjected to electrical
stresses (Fig. 3.5). The following stress characteristics can be distinguished:
• Direction
• Amplitude
• Distribution.
3
Interfaces in Accessories for Extruded HV and EHV Cables
89
Fig. 3.4 Effect of lubricant oil on the breakdown strength of a typical XLPE-SIR interface (Kunze
2000a)
Fig. 3.5 Typical electrical
field distribution in the
interface of a pre-moulded
joint
90%
70%
50%
30%
10%
Enorm
E tan
x
The component along the surface of the insulators is called the parallel, longitudinal
or tangential electrical stress and is generally regarded as the most important one.
Also the amplitude (e.g. for inception of partial discharges) and the distribution
(e.g. for electrical treeing) will affect the interface behaviour.
It is preferred that areas with highest electrical stress coincide with highest
interface pressure. In most of the accessory designs the shape of the stress-cones
and embedded electrodes control the electrical field distribution (Fig. 3.5).
90
H. Geene
3.2.5
Temperature and Temperature Changes
It is known that operating temperatures influence the withstand stresses of insulating
materials. Although this might contribute to the weakening of the interface, thermomechanical effects usually have a much larger influence at the interface, as they
could lead to movements along the interface. Reasons are e.g. differences in thermal
expansion coefficients or external mechanical forces. In this respect temperature
changes i.e temperature cycling and/or temperature gradient (are of more) are of
more importance than temperature itself.
High temperatures in cable and accessories can lead to deformations of the cable
insulation. During the cooling down period of cable and accessories thermal shrinkage of materials will occur. This may result in pressure changes at the interface and
should be properly taken into account during design of accessory design.
3.2.6
Quality of Accessory Installation
The installation of accessories is considered as the most critical step in realizing a
cable system. In particular the interfaces are influenced by the installation, since in
most cases the cable insulation is prepared on site. The insulation surface must be
prepared most carefully. Installation instructions must clearly indicate the cable
preparation, including the smoothing technique and/or the required smoothness.
During installation, also the positioning of components is of utmost importance.
The installation procedure and instructions, including the drawings, must be clear
and unambiguous.
During the installation the following aspects should be taken into account,
•
•
•
•
•
•
Final cable diameter and roundness
Straightness of the cable
Smooth and regular insulation surface
Smooth and regular transition from insulation screen to cable insulation
Correct positioning of accessory parts
Dryness and cleanliness.
It is essential that the jointers shall be well trained, to provide the necessary skills.
See ▶ Chaps. 2, ▶ 5 and ▶ 6 of this book for further information.
3.3
Long Term Performance of Interfaces in Cable Accessories
The ageing of interfaces can be considered as a change in one or more parameters
mentioned above, leading to a decrease of the electrical withstand strength of the
interface. Electrical ageing of interfaces, as a result of intrinsic electrical ageing of
the applied materials, is not likely to occur. The electrical stresses in the interface are
low compared to the withstand stresses used for cables or accessories (Kunze
3
Interfaces in Accessories for Extruded HV and EHV Cables
91
2000a). More likely, mechanical and thermo-mechanical effects change the interface
parameters. Thermo-mechanical effects can cause formation of cavities and in
extreme situations even gaps between the insulating materials. It is obvious that
gaps or large voids cause partial discharging, followed by electrical treeing or
tracking in the interface.
The formation of cavities and gaps in interfaces can be the result of a combination
of effects, such as:
•
•
•
•
•
Migration of the lubricant
Movements in the interface
Reduction of the interface pressure due to relaxation of materials
Electrical ageing of interfaces
Contamination of the interface.
3.3.1
Migration of the Lubricant
It is general practice to use lubricants in accessories to relieve the friction between
cable and accessory parts during installation. Already during the installation most of
the lubricant is pushed out of the interface. The remaining film of lubricant will
disappear in time, due to migration into the insulation materials. Depending on the
type of lubricant and the materials applied, the migration time can vary between
hours and years. Greases composed of fluid and solid filler can dry out (migration
into the insulating materials), leaving filler behind. Sufficient interface pressure in
combination with the smoothness of the surfaces will prevent the formation of
cavities.
3.3.2
Movements in the Interface
Interfaces have been shaped carefully in order to obtain a secure fit between the
insulating surfaces. If the insulating surfaces can move in respect to one another, due
to thermal expansion or external forces, the interface pressure can decline locally
causing a weak spot and in some extreme cases even gaps in the interface. The
insulating surfaces shall be shaped in such a way that if movements can occur, this
will not lead to the formation of gaps.
3.3.3
Reduction of the Interface Pressure due to Relaxation
of Materials
Interface pressure can decrease due to deformation of the cable insulation or due to
relaxation of the rubber.
Deformation of the cable insulation can occur at high temperatures. The accessory design has to prevent unacceptable deformation of the cable insulation.
92
H. Geene
Relaxation of the rubber can occur in those designs where the interface pressure is
achieved by expanding the rubber sleeve onto the cable insulation. To prevent
critical low interfaces pressures, the setting of the rubber should stabilize at a safe
value. Important parameters describing the setting of rubber are the so-called
compression set and tension set.
In the case of interface pressure applied by external means (i.e. springs), their
mechanical design has to secure a sufficient pressure level during the lifetime.
3.3.4
Electrical Ageing of Interfaces
Due to the fact that partial discharge is a symptom of an insulation defect, the
inception and occurrence of partial discharges may accompany the electrical ageing
of interfaces as well.
Because of the different accessory designs on the market, it is impossible to deduce
a single relationship between the magnitude of partial discharges and the remaining
lifetime. However, in individual cases, partial discharge characteristics and its development may give indications for the incipient failure (Smit et al. 1997; Smit 1999).
3.4
Testing
There are several ways interfaces in HV accessories can be tested. Roughly speaking
we can distinguish between laboratory testing and on site testing. Laboratory tests
can be performed on many levels:
• Material test
• Model tests on material samples
• System tests on cable and accessories.
As none of these tests can solely represent the characteristics of the interface
completely, the optimum has to found in a combination of these tests.
Regarding an interface, the breakdown strength of the insulation materials itself is
of minor importance, due to the lower electrical stresses in the interface section.
More important for the interface breakdown strength are the mechanical properties
of the materials, i.e.:
•
•
•
•
Modulus of elasticity
Hardness
Compression set or tension set
Surface roughness.
The right combination of these mechanical properties has to ensure a tight fit
between the insulation surfaces, thus leading to the required electrical interface
performance.
3
Interfaces in Accessories for Extruded HV and EHV Cables
93
Tests on interface models offer the possibility of a statistical result evaluation of
different interfaces at relatively low cost. Cigré WG15.10 has dealt with the subject
of models intensively (Nagao et al). An important conclusion that can be drawn from
their work is that different model types should be used to investigate different aspects
of electrically and/or mechanically stressed interfaces.
A model for real accessory design purposes should be a realistic simulation of the
practical interface situation (Kunze 2000b; Nagao et al) or e.g by using a lower
voltage class accessory of the same design (Smit et al. 1997).
A good interface design has to prevent inception of partial discharges. Therefore
the models studying electrical treeing in interfaces can be of importance for basic
material investigation. For the evaluation of interface design parameters, partial
discharge free arrangements are more suitable. The results of model tests can directly
be used for comparison of different parameter settings. The absolute values can be
transferred to real accessory designs, using special algorithms, but should be done
with great care.
Once a design is completed, prototypes subjected to system tests are indispensable for the qualification of interfaces.
Development tests on systems should represent electrical, thermal and thermomechanical service conditions. For this reason it is recommended to include the
following conditions in the development test program:
•
•
•
•
•
Elevated electrical stresses to accelerate ageing
Mechanical stress due to simulate installation and service conditions
Thermo-mechanical stress during load cycles
Transient voltages as impulse voltage
Partial discharge monitoring (continuously or periodically).
In particular the thermo-mechanical conditions are most complicated to predict. The
thermo-mechanical forces highly depend on the design and the way of installation
e.g.: flexible and rigid installations, load and environmental conditions. During the
development and qualification of HV cable systems, the accessories should be
installed in practical worst-case condition (maximum mechanical forces). Testes
should incorporate heating cycles and voltage simultaneously. During the cycle
period, partial discharge measurements should be made at different conductor
temperatures. After thermo-mechanical ageing it is recommended to perform the
impulse voltage test, in order to detect possible weakening of the interface.
Outdoor terminations sometimes have to operate at low temperatures. This
circumstance can represent a more critical condition for interfaces than elevated
temperatures. Testing of these terminations in cold conditions and varying temperatures should be taken into account during the development.
To verify the performance of the interface and the complete accessory, the
prequalification test as recommended by Cigré (WG 21.03 1993) and standardized
by IEC (62067) is a necessary and reliable method for testing.
The final step in commissioning a cable system is the after laying test. The AC
voltage test is an important one to verify the correct preparation and installation of
94
H. Geene
the accessories on site (Nagao et al). Testing with DC voltage is not recommended.
The electrical field distribution in the interface for DC voltage can differ completely
from AC voltage (IEC60840 1999).
If there is a need for monitoring accessories in service (e.g. higher failure rate than
normal), the most appropriate test method is on-line partial discharge monitoring.
The partial discharge tests are preferably executed under different environmental
and/or load conditions, in order to determine the thermo-mechanical impact on the
interface. The recommended frequency of testing will highly depend on the nature of
the discharge pattern and accessory type. In high stress accessories (e.g. slip-on
joints for EHV) partial discharges in interfaces in the order of a few pico-coulombs
can lead to breakdown within hours, while for some low stress accessories
(e.g. outdoor termination) partial discharges in interfaces can be withstood sometimes for several years.
3.5
Recommendations and Conclusions
Interfaces in HV and EHV cable accessories should be designed in such a way that
under operating conditions always a tight fit between cable and accessory or between
other insulating bodies is secured. Once the insulating surfaces do not adapt carefully, cavities will be formed leading to inception of partial discharges.
A proper interface design does not allow partial discharges. Below the inception
level of partial discharge, no detectable ageing will take place. Once discharges have
been ignited, accelerated ageing will start, most probably leading to electrical treeing
in the interface and finally failure of the accessory.
The reliability of interfaces in HV and EHV extruded cable accessories is strongly
dependent on the mechanical and thermo-mechanical design of the accessories and
the interaction with its environment, i.e. way of installation and service conditions.
During the development of cable systems, these circumstances have to be taken into
account. For this reason the long term or prequalification tests of the entire system
(cable and accessories) is of eminent importance.
The quality of the interface depends on the cable surface preparation. This has to
be ensured by clear procedures, adequate quality management systems (e.g. ISO
9001 (1994)) and skilled jointers.
Although there is no general relation between the partial discharges and the
remaining lifetime, trend analyses by means of online partial discharge monitoring
can give indication if risk of failure is involved for the type of PD patterns observed.
References
Cigré WG 21.03.: Recommendations for electrical tests prequalification and development on
extruded cables and accessories at voltages > 150 (170) and 400 (420) kV, Elektra No
151 (December 1993)
Cigré WG B1-16.: Partial Discharge Detection in Installed HV Cable Systems. Cigré Technical
Report 182 (April 2001)
3
Interfaces in Accessories for Extruded HV and EHV Cables
95
Densley, J., Nadolny, Z.: PD characteristics of model interfaces for extruded cable systems –
influence of contaminants, Cigré WG15-10
Fournier, D., Lamarre, L.: Effect of pressure and length on interfacial breakdown between two
dielectric surfaces. In: IEEE International Symposium on Electrical Insulation, Baltimore, June
7–10, 1992, pp. 270–272
Geene, H.T.F., van der Wijk, G.P., Pultrum, E.: Development and qualification of a new 400kV
XLPE cable system with integrated sensors for diagnostics, Cigré 1998, paper 21-103
Gockenbach, E., Kunze, D.: Makroskopische, innere Grenzflächen in Hochspannungskabelgarnituren, VDE Fachtagung ‘Einfluss von Grenzflächen auf die Lebens-dauer elektrischer
Isolierungen’ (Bad Nauheim, 21–22 Sept 1999)
IEC 62067.: Power cables with extruded insulation and their accessories for rated voltages above
150kV (Um¼170 kV) up to 500kV (Um¼550 kV) – Test methods and requirements
IEC 60840.: Power cables with extruded insulation and their accessories for rated voltages above
30 kV (Um¼36 kV) up to 150 kV (Um¼170 kV)-Tests methods and requirements (1999)
Imai, N., Andoh, K.: Development of pre-fabricated joints for 275 kV XLPE cables, Jicable (1991),
paper A.5.4
ISO 9001.: Quality Systems-Model for quality assurance in design, development, production,
installation and servicing (1994)
Kärner, H., Kodoll, W., Seifert, J., Tanaka, T., Nagao, M.: Interfacial phenomena affecting electrical
insulating properties in composites, Cigré WG15-10
Kreuger, F.H.: Partial Discharge Detection in High-Voltage Equipment. Butterworth & Co, London
(1989)
Kunze, D.: Eine neue Muffengeneration für VPE-isolierte Höchstspannungskabel, Elektrizitätswirtschaft, Jg. 96 (1997), Heft 26
Kunze, D.: Untersuchungen an Grenzflächen zwischen Polymerwerkstoffen unter elektrischer
Hochfeldbeans-pruchung in der Garniturentechnik VPE-isolierter Hochspannungskabel. Dissertation Uni Hannover, Shaker Verlag Aachen (2000a). ISBN 3-8265-7721-3
Kunze, D.: Macroscopic internal interfaces in high voltage cable accessories, Cigré session (2000b),
paper 15-203
Nadolny, Z., Braun, J.M., Densley, R.J.: Effect of mechanical pressure and silicone grease on partial
discharge characteristics for model XLPE transmission cable joint. In: Proceedings of ISH’99
(London, August 1999)
Nagao, M., Ka, S., Murramotto, Y., Tanaka, T.: Model specimens for testing interfacial properties in
EHV extruded cable splices and preliminary results, Cigré WG15-10, 15-10-Nagao-01-98
Nagao, M., Ka, S., Murramotto, Y., Tanaka, T.: Model specimens for testing interfacial properties in
EHV extruded cable splices and preliminary results, Cigré WG15-10, 15-10-Nagao-01-99
Peschke, E., Olshausen, R.V.: Cable Systems for High and Extra-High Voltage. PIRELLI, Publicis
MCD Verlag, Erlangen (1999). ISBN 3-89578-118-5
Report on Internal interfaces of modern electrical insulation systems, Cigré WG 15-10 Meeting
Palais des Congres Paris, France, September 1, 1998
Ross, R.: Dealing with interface problems in polymer cable terminations. IEEE Electr. Insul. Mag.
15(4), 5–9 (1999)
Ross, R.: Investigating and monitoring the reliability of interfaces in polymer cable terminations. In:
Proceedings at IEEJ Kansai Meeting on Insulation Diagnosis
Ross, R., Megens, M.G.M.: Aging of interfaces by discharging. In: Proceedings of ICPADM (2000)
Ross, R., Megens, M.G.M.: An interface testing cell for multi-stress ageing. In: Proceedings ISEIM
98
Smit, J.J.: Life management of electrical infrastructure. In: Cigré SC15-Symposium “Service
Ageing of Materials in HV Equipment”, Sydney (1999), key-note paper
Smit, J.J., Gulski, E., Pultrum, E.: Partial discharge fault analysis of SIR-based cable terminations.
In: Proceedings of International Symposium on High Voltage Engineering, Montreal, vol.
4, p. 513 (1997)
Strassberger, W.: Silicone Elastomers for Transmission and Distribution
Strassberger W., Winter H.-J.: Silikonelastomere in der Mittel- und Hochspannungstechnik. ETG
Fachbericht Nr. 68, pp. 7–14. VDE-Verlag GmbH, Berlin, Offenbach (1997)
96
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Strassberger, W., Winter, H.-J.: Silikonelastomere . . ., ETG-Fachbericht
Tanaka, T.: Polymer interfaces, associated with electric insulation systems. Cigré Colloquium on
Advanced Materials (Boston, 18 Aug 1997)
Willems, H.M.J., Geene, H.T.F., Vermeulen, M.R.: A new generation of HV and EHV extruded
cable systems, Jicable (1995), paper A.1.6
Henk Geene has a Master’s degree in Electrical Engineering
from the Technical University in Eindhoven, the Netherlands.
Shortly after graduation, he joined the Dutch cable manufacturer NKF (nowadays part of the Prysmian Group) where he
started as an engineer to develop High and Extra High Voltage
cable accessories. Currently, he is responsible for product management and sales of the Prysmian high voltage accessories.
He is past Dutch Member of Cigré Study Committee D1,
Convener TF15/21 “interfaces in HV cable accessories,” Convener TF21.10 “thermal ratings of HV cable accessories,” participated as a Member in several Cigré Working Groups, and is
currently Chairman of the IEEE Insulated Conductors Committee (ICC).
He is author of several papers and publications on a wide range
of subjects in the field of high voltage cable accessories and
their interaction with other components in the cable systems.
4
Qualification Procedures for HV and EHV AC
Extruded Underground Cable Systems
Jean Becker
Contents
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.1.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.1.2 Scope and Terms of Reference of WG B1.06 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.1.3 Experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 Long Duration Test on EHV Cable Systems (170 < Um < 550 kV) . . . . . . . . . . . . . . . . . . .
4.2.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2.2 Revision of the Present Prequalification Test Procedure . . . . . . . . . . . . . . . . . . . . . . . . .
4.2.3 Changes in a Prequalified Cable System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2.4 Recommendations to IEC 62067 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3 Long Duration Test on HV Cable Systems (36 < Um 170 kV) . . . . . . . . . . . . . . . . . . . . . .
4.3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3.2 Prequalification Test for HV Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3.3 Exchanges and Modifications in a Prequalified HV Cable System . . . . . . . . . . . . .
4.3.4 Recommendations to IEC 60840 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.5 Annexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.5.1 Terms of Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.5.2 Sensitivity of Partial Discharges in XLPE Cable Insulation to Change
of Electrical Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.5.3 Functional Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.5.4 Tests From Functional Analysis not in IEC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
102
102
103
103
107
107
110
112
121
122
122
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132
133
134
134
135
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187
Jean Becker: deceased.
J. Becker (*)
Charleroi, Belgium
© Springer Nature Switzerland AG 2021
P. Argaut (ed.), Accessories for HV and EHV Extruded Cables, CIGRE Green Books,
https://doi.org/10.1007/978-3-030-39466-0_4
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98
J. Becker
Summary
IEC test requirements have evolved over the years from the component-based approach
in IEC 840 to the system based approach. Accessories are considered together with the
cable, in IEC 62067 Ed.1 and in the most recent edition of IEC 60840 Ed.3.
In its meeting in Madrid of 2001, Study Committee B1 decided to install a Task
Force TF 21.11 to get SC B1 prepared to issue future recommendations for evolutions of IEC 62067 taking into account the expected innovations in cable technology,
the need to reduce the time-to-market and the overall cost to introduce new evolutions as well as service experience collected by the Cable Industry.
TF 21.11 issued in 2002 a proposal of Terms of Reference and Scope of Work for
a new Working Group which was launched as WG B1.06 in Paris Study Committee
meeting in 2002.
In July 2005 WG B1.06 circulated its final draft of report for approval by SC B1.
Comments were received from France, Japan, The Netherlands and Italy.
As time schedule for issuing the new Edition of IEC 62067 Ed.1 was critical, SC
B1 agreed to go in more detailed recommendations and decided in its meeting of
Rosenön (SE), September 2005 to launch a Task Force to finalise the report and write
clear and practical recommendations for appropriate changes in IEC 62067 Ed.1 and
IEC 60 840 Ed.3.
This chapter published as Cigré TB 303 is the result of the Work of WG B1.06
and of the Task Force.
Section 4.1 of this chapter is an Introduction, which recalls and details the Scope
of Work and the Terms of Reference and gives an overview of the service experience
of HV and EHV cable systems so far as well as a survey of experience obtained by
testing EHV cable systems.
At voltages up to and including 150 kV extruded insulation has largely superseded paper-insulated cables for new installations.
Much of the service experience with HV XLPE cable systems is based on cables
with moderate design stresses. A new generation of “slim-design” HV cables is being
developed, with similar technology and design stresses to those seen in EHV XLPE
systems. Hence historical service experience with HV cable systems is not necessarily
a good guide to the likely future service experience of these novel systems.
XLPE has only recently become the insulation of choice for many utilities for
EHV transmission circuits. The introduction of XLPE for longer transmission
circuits has been facilitated by the use of a one-year heat cycle voltage test called
Prequalification (PQ) test, which was recommended by Cigré in 1993 and afterwards
specified in IEC 62067 Ed.1 in 2001.
Following the successful completion of a number of PQ programmes, some large
400 and 500 kV cable circuits have been installed and commissioned.
There is still limited experience with EHV XLPE cable systems. The designs,
manufacturing methods and materials employed in joints and terminations differ
significantly amongst manufacturers. Thus the service experience from any particular
system cannot necessarily be taken as a guide to the likely service experience of other
systems. The long term behaviour of an EHV system has to be demonstrated by a well
specified PQ test.
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
99
Section 4.2 covers long duration tests on EHV cable systems and the different
features, which are examined:
•
•
•
•
•
Design concept
Electrical performance of cable and accessories
Performance of a cable system under prolonged heat cycling
Aspects of installation design and practice
Ability of the Installer to joint in realistic conditions rather than laboratory
conditions.
From the existing service experience in both long duration tests and in operation
as mentioned in Sect. 4.1, it is confirmed that a Prequalification test (PQ test) is still
necessary to demonstrate the long-term reliability. Improvements of this test are
proposed such as measurement of partial discharges as a mean to provide early
warning and offer possibility of repair before failure.
A procedure to be adopted in case of failure of a component during the PQ test is
introduced and a modification to the final impulse test is proposed.
Then changes in an already prequalified cable system are evaluated. A procedure of
extension of qualification is recommended and a table is given to indicate in main
cases of changes the test sequence to adopt, instead of repeating the complete PQ test.
A new test called Extension of Qualification Test (EQ test) is proposed mainly in
case of changes of or in accessories. This test shall be performed in a laboratory on
one or more samples of complete cable of the already prequalified cable system. At
least two accessories of each type that need the extension of qualification shall be
tested. A total of 80 heating cycles shall be carried out of which the last 20 cycles
shall be under a voltage of 2 U0.
As a summary and conclusion from its reflections WG B1.06 makes the following
recommendations to IEC for further consideration in future editions of IEC 62067:
• To maintain a Prequalification (PQ) test for the basic qualification of a new cable
system.
• To allow in case of a failure of an accessory the continuation and completion of
the PQ test for the undisturbed components of the loop.
• To introduce in case of less significant changes/modifications at prequalified
components a simplified long-term test (80 cycles) called “Extension of Prequalification (EQ) test”.
• To perform the lightning impulse test at the end of the PQ test at the complete test
loop or, in case of practical problems with test equipment, in any other test
arrangements, which include the accessories.
• To include sample tests at accessories in IEC 62067 Ed.1 as in IEC 60840 Ed.3.
These tests are intended to check not only the intrinsic quality of the accessory,
but also the quality of the installation, which is critical at the EHV level.
Section 4.3 similarly covers long duration tests on HV cable systems.
Due to experience on EHV cable systems it becomes more common nowadays to
produce cables with reduced insulation thickness at the high voltage level. This leads
100
J. Becker
to higher dielectric stresses nearly as high as in the EHV field not only at main
insulation but also at the interfaces between cables and accessories.
In the meantime, new types of accessories are appearing on the market, of
course with no earlier experience. These accessories should be able to fit to the
older types of cables with thicker insulation and the newer types of cables with
reduced insulation (changes of an existing HV link with a new cable type or repair
of an older link).
Taking into account that service experience collected so far on HV cable systems
working at usual stresses was rather good, the Working Group recommend that cable
systems should be considered rather than cables or accessories alone when higher
stresses are adopted.
After giving detailed examples of calculated stresses (AC and impulse) in different types of accessories, the WG recommends to adopt a prequalification procedure
when electrical stresses are above given limits.
A Prequalification (PQ) test shall be performed only on cable systems where the
calculated nominal electrical stresses at the conductor screen will be higher than
8 kV/mm and/or at the insulation screen higher than 4 kV/mm. This Prequalification
test can be omitted in some special cases listed in Sect. 4.3.
Contrary to the Prequalification test for EHV systems, in this case the test is
simplified because it can be performed in a laboratory and 180 cycles are
required.
The proposed layout of cable system is described as well as the test sequence.
Then changes in a prequalified cable system are addressed. The Extension of
Prequalification test (EQ) is proposed to be the same as for EHV systems.
As a summary and conclusion from its reflections WG B1.06 makes the following
recommendations to IEC for further consideration in future editions of IEC 60840:
• To introduce a Prequalification (PQ) test for those HV cable systems where the
calculated nominal electrical stress at the conductor screen will be higher than
8 kV/mm and/or at the insulation screen higher than 4 kV/mm. This test needs not
to be performed if
– Cable systems with the same constructions and accessories of the same family
have been prequalified for higher rated voltages
– Equivalent long term tests have been already successfully carried out
– Good service experience at cable systems with equal or higher stresses can be
demonstrated
• To allow in case of a failure of an accessory the continuation and the completion
of the PQ test for the undisturbed components of the test loop.
• To introduce in case of less significant changes/modifications at prequalified
components a simplified long-term test (80 cycles) called “Extension of Prequalification (EQ) test”.
• To perform the lightning impulse test at the end of the PQ test at the complete test
loop or, in case of practical problems with test equipment, in any other test
arrangements, which include the accessories.
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Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
101
Section 4.4 lists the conclusions of the Working Group. Main ones are:
• EHV Cable systems: there is not sufficient service experience on EHV cable
systems collected so far to introduce major changes to the existing
initial Prequalification test. This PQ test has to be repeated in case of
extension of the range of approval. Within the range of approval, a new
test called Extension of Qualification test is proposed to control changes in
already prequalified cable systems instead of repeating the complete PQ test.
This new test can be carried out on a laboratory loop and will comprise
80 heating cycles combined with voltage application at 2 U0 for the last
20 cycles.
• HV Cable systems: a Prequalification test is recommended for design stresses
above 8 kV/mm on the conductor or 4 kV/mm over insulation. This test can be
carried out on a laboratory loop and will comprise 180 heating cycles combined
with voltage application at 1.7 U0. This PQ test has to be repeated in case of
extension of the range of approval.
Section 4.5 contains all the Annexes introduced in previous sections
Annex 4.5.1: Terms of Reference
Annex 4.5.2: Sensitivity to PD
In this Annex the sensitivity of partial discharges in XLPE cable insulations to
change of electrical stresses is investigated. The conclusion is that dimensional
changes, especially reduction of insulation wall thickness, can result in considerable
higher stresses at defects such as voids or fissures, thus increasing the risk of
inception of partial discharges.
Annex 4.5.3: Functional analysis
• A “Functional Analysis Method” is recommended as means for a systematic
assessment of the significance of changes/modifications at components of a cable
system and thus for the choice of the appropriate test (e.g. PQ or EQ).
• Based on the application of the “Functional Analysis Method” to the most
important components of actual cable systems, guides to test procedures are
given in case of
– Exchange of a cable and/or accessory in a prequalified cable system
– Modification of a cable in a prequalified cable system
– Modification of an accessory within the same family in a prequalified cable
system
Annex 4.5.4: Tests missing in IEC
As a result of the functional analysis exercise (see Annex 4.5.3), a number of tests
that are not included in IEC 60840 Ed.3and IEC 62067 Ed.1 have been identified.
These tests are generally performed as development tests and are summarized in
Annex 4.5.4 for future consideration by IEC.
Annex 4.5.5: References.
102
J. Becker
4.1
Introduction
4.1.1
General
Extra high voltage (EHV) cable systems are designed and built to transmit bulk
electrical power. For this reason, it is imperative that they attain the highest possible
reliability. At the same time, the transmission capacity of the high voltage (HV) cable
links is continuously increasing. This is why reliability considerations of cable
installations in this category are also becoming very important.
Accessories are an integral part of a cable system. Their performance together
with that of the cable determines the overall reliability of the circuit. Accessories are
installed by hand, and therefore their reliability is determined by a combination of
good design, clear instructions, quality assurance (QA) and the skill of the fitters.
The long-term Prequalification (PQ) test was developed to build confidence in the
operation of XLPE cable at EHV levels. A PQ test demonstrates the quality of the
overall design of the system together with the quality of assembly.
IEC test requirements have evolved over the years from the component based
approach in IEC 840 to the system based approach, where accessories are considered
together with the cable, in IEC 62067 Ed.1 and the most recent edition of IEC 60840
Ed.3.
The IEC has published series of test specifications for HV and EHV cables,
accessories and cable systems:
• In 1988, the first specification was published. IEC 840 (renamed later as IEC
60840) is for cables up to 150 kV (Um ¼ 170 kV) [1]. In this specification, type
tests, routine and sample tests were prescribed for cables only.
• In 1999 IEC revised this specification and IEC 60840 Ed.2 was published, in
which accessories were included in type testing [2].
• In 2004 IEC published a third edition, IEC 60840 Ed.3, in which type tests on cable
system and routine and sample tests on prefabricated accessories were introduced [2].
• In December 1993 Cigré Working Group 21.03 published in Electra recommendations for PQ tests, type tests, sample and routine tests for extruded cables and their
accessories for voltages above 150 kV (Um ¼ 170 kV) up to 400 kV (Um ¼ 420 kV)
[3, 4]. In 1997, the voltage range was extended to 500 kV (Um ¼ 525 kV) [5, 6]. In
these recommendations, type tests, routine and sample test procedures were based on
those from IEC 840. Long term AC stressing together with heat cycles up to the
maximum operating temperature followed by impulse tests were prescribed to
demonstrate the long-term electrical and thermo-mechanical performance of the
system (PQ test). It was considered to be imperative that the test set-up reflected
real installation conditions. Test specifications recommended by WG 21.03 were then
implemented in IEC 62067 Ed.1 [7] published in October 2001.
The PQ tests recommended by Cigré and incorporated into IEC 62067 Ed.1 have
been accepted worldwide. As a result, only those manufacturers whose products
have passed long-term PQ tests have been allowed to participate in subsequent EHV
cable projects.
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
4.1.2
103
Scope and Terms of Reference of WG B1.06
It is inevitable that over a period of time an approved cable system undergoes some
changes, such as modifications to the cable construction, higher stress, new type of
accessories, new manufacturing processes, etc. However, there is little incentive to
the manufacturer to make incremental improvements to the product, since these
might invalidate the previous “approval” and require the long and expensive PQ test
to be repeated. Reducing the amount of testing needed would encourage manufacturers to introduce design improvements or measures to reduce cost. For this reason,
Cigré Study Committee B1 launched Working Group WG B1.06 with the task of
revising the qualification procedures for underground high voltage cable systems.
The WG was asked to examine how it might be possible to qualify a modification
to a cable system without making the full set of tests which are presently
recommended or specified in standards. All tests, PQ and type tests were to be
reviewed, although the PQ test has received greatest attention, as it is the most costly
and the longest.
The full scope and terms of reference of the WG are given in Annex 4.5.1.
4.1.3
Experience
4.1.3.1 Ageing of Extruded Polymeric Insulation
The ageing behaviour of extruded insulation of cables under dielectric and/or
thermal stress has been studied extensively [8–16]. No significant ageing could be
detected, even with the most sophisticated test methods presently available [15].
Locally there may be weak points in the insulation: impurities or voids in the
insulation or protrusions at the interface with the semi-conductive screens. These
defects may initiate ageing or accelerate degradation of the cable insulation. In
modern cable factories great care is taken to avoid these defects: extrusion of
extremely clean insulation materials, extrusion of very smooth semi-conductive
materials, careful handling of insulation and semi-conductive materials, etc. Before
leaving the factory, the finished cable is submitted to a routine electrical withstand
test together with measurement of partial discharges. The effectiveness of these
routine tests on HV cables is good as there are very few cable breakdowns on
installed systems.
Other ageing factors (i.e. factors that may affect the capability of components to
fulfil their roles) are described in the 1992 report from WG 21.09 published in
ELECTRA 140, “Considerations of ageing factors in extruded insulation and accessories” [17]. The main “ageing” factors considered in this report are the locked-in
mechanical stresses and shrinkage of cable insulation or outer sheath, maximum
operating or overload temperatures affecting radial expansion and possible permanent deformation and reducing AC and impulse break down strength, deformation
under temperature and externally applied mechanical stress, etc.
The conclusion of this report is: “the extruded polymeric insulants used in high
voltage cables do not appear to exhibit property changes that can be measured easily
or that can be said to be significant in terms of cable life reduction when
104
J. Becker
contaminants from external sources, e.g. water, oil and sulphur are avoided. For
accessories the same may be stated.”
In order to evaluate, to some extent, the electrical ageing aspects of a cable
system, a type test is prescribed in IEC 60840 Ed.3. In IEC 62067 Ed.1, the PQ
test is supposed to evaluate the long-term electrical, thermal and mechanical behaviour of the cable system in an environment near to the conditions in the field.
4.1.3.2 Experience with HV Extruded Cable Systems up to and Including
150 kV
The evolution of XLPE MV and HV systems commenced in the 1960s. In the 1970s,
the first commercial 90-132-154 kV XLPE systems were installed in Europe and in
Japan.
The results of a survey made by Cigré WG 21.09 on cable, associated accessories
and service stresses and lengths installed in different countries were published in
ELECTRA 139 in 1991 [18].
Cigré WG 21.10 has published in Electra 137 [19] a survey on the service
performance of HV AC cable systems. The failure rate of extruded cable systems
was very low (0.1 failures per 100 circuit km per year on cables and accessories external failures were not included). A new Working Group (WG B1.10) was set up
in 2004 to update the service experience data. Results are published in Cigré TB
579, April 2009.
There are a number of designs of joints and terminations currently in use and an
industry standard has not yet evolved. WG 21.06 has described and illustrated the
different types of accessories in use [20], ▶ Chap. 1, “Compendium of Accessory
Types Used for AC HV Extruded Cables” of this book.
At voltage up to and including 150 kV extruded insulation has largely superseded
paper-insulated cables for new installations.
Much of the “good” experience with HV XLPE cable systems is based on older
cable with moderate design stresses. A new generation of “slim-design” HV cables is
being developed, with similar technology and design stresses to those seen in EHV
XLPE systems. Hence historical service experience with HV cable systems is not
necessarily a good guide to the likely future service experience of these novel systems.
4.1.3.3 Experience with EHV Extruded Cable Systems at Voltages above
150 kV
Whilst cable with extruded insulation is in general use for electricity distribution and
at the lower transmission voltages, XLPE has only recently become the insulation of
choice for many utilities for EHV transmission circuits. The introduction of XLPE
for longer transmission circuits has been facilitated by the use of the PQ test.
4.1.3.3.1 Prequalification Test Experience
As cable makers started to develop EHV XLPE cable systems, they needed testing
programmes both to monitor their own progress and to give customers confidence in
the products being developed. Initially, these testing programmes were agreed on a
local or national basis. For example, France used a 250-cycles test for 6000 hours at
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
105
pffiffiffi
3 U0, while Belgium adopted a 100-cycles test at 2 U0. Japan used a half-year test
at relatively low electrical stress based on the degradation factor of the insulation
system.
Plans to install major 400 kV cable systems led Cigré to set up a working Group
to consider an international test specification. The tests were developed to give
confidence that cable systems passing the tests would have a fault rate in service
lower than 0.2 faults/100 km/year. In 1993 Cigré WG 21.03 published a test program
for cable systems above 150 (170) kV [3, 4] and IEC published a specification based
on these documents IEC 62067 Ed.1 in 2001 [7].
In IEC 62067 Ed.1 the definition of the PQ test is as follows: “a test made before
supplying on a general commercial basis a type of cable system covered by this
standard, in order to demonstrate satisfactory long term performance of the complete
cable system. The PQ test need only be carried out once unless there is a substantial
change in the cable system with respect to material, manufacturing process, design
and design levels”.
It is useful to examine some of the early French experience of prequalification
testing. The French (EDF) specification required a long-term test of duration
6000 hours, p
although
many of the tests were continued beyond this. The specified
ffiffiffi
voltage was 3 U0 for 250 heat cycles (167 cycles at maximum service temperature
and 83 cycles at emergency temperature).
Figure 4.1 summarizes long-term test results on 220 kV cable at the EDF
laboratories. Design stresses for the cables (at U0) were 8.5 kV/mm at the conductor
screen and 4.2 kV/mm at the insulation screen.
12
10
Number of failures
8
5
4
2
0
<100
100300
300400
400500
500- 1200- 1450- 2500- 3000- 4000- 5000- 6000- 7000- 11000- 1200- 14000- 16000- >
1200 1450 2500 3000 4000 5000 6000 7000 11000 12000 14000 16000 30000 30000
Time (hours)
Fig. 4.1 Results of long-term tests on 220 kV cable
106
J. Becker
The defects causing breakdown in less than 10 hours were mounting errors in
accessories (5 in joints and 2 in terminations). Eight of the test lengths that failed
prematurely contained artificial defects in their terminations. These tests were to
simulate a defect found in the field. They showed that this type of PQ test is effective
in distinguishing between defective and well-made accessories.
The tests are all from the early stages of development of 220 kV cable systems
(pre 1980). Only 2 breakdowns occurred on cables themselves (150 h and 36000 h).
All the other breakdowns were in the accessories. This indicates the important role of
accessories in determining the overall reliability of the cable system and the importance of carrying out tests on the cable and accessories as a system.
Some of the tests carried out by connecting the cable between phase and earth of
the 400 kV network highlighted the problems associated with this approach. Four of
breakdowns occurring after about 6000 hours happened during a thunderstorm with
lightning strikes falling on the adjacent overhead line. The defects responsible for the
cable failures could not be determined because the cables had experienced the full
short circuit current of the 400 kV network and suffered significant local damage at
the failure site. The use of a dedicated test transformer provides far better control of
the test voltage (avoiding system disturbances) and limiting the short circuit current
allows better forensic examination of the failure site.
The occurrences of failures over a wide range of times (up to 16000 hours)
suggests that it is not advisable to reduce the duration of the 8760 hours PQ test.
In 2001 Parpal [22] summarized the early experience from a number of PQ tests
[23–30]. Subsequently, most of the major EHV cable makers have successfully
completed PQ tests on 400 or 500 kV XLPE cables often with large conductors
(2000 and 2500 mm2).
4.1.3.3.2 Service Experience
The evolution of EHV systems followed with the first EHV XLPE systems being
installed in the voltage range 220–275 kV in the late 1970s. Widespread commercial
use of XLPE cables up to 230 kV was not seen until the 1980s. The first 275 kV
XLPE systems with joints were installed in Japan in 1989 [21]. These were qualified
using Japanese utility specifications.
In France cables insulated with low-density polyethylene (LDPE) preceded
XLPE and were first installed at 225 kV in 1969. Since then more than 1000 km
of LDPE cable has been installed with field-moulded joints and around 600 km of
high-density polyethylene (HDPE) cables with good service experience (Fig. 4.2).
The first 400 kV LDPE cables were installed in France in 1985 and XLPE in
1999. In total, 40 km of cable and 21 back-to-back joints have been installed.
The world’s first 500 kV XLPE system was commissioned in Japan in 1988 and
two subsequent circuits were commissioned in 1988 and 1991. These were relatively
short circuits without joints.
Following the successful completion of a number of PQ programmes, some large
400 and 500 kV cable circuits have been installed and commissioned. These are
summarized in Table 4.1.
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
107
Fig. 4.2 345 kV Cables
installed in a long Tunnel in
Korea
Although the service experience is limited, all the EHV installed systems subjected to the IEC 62067 Ed.1 PQ procedures have, to date, demonstrated satisfactory
behaviour. A more precise picture about the service experience of these cable
systems became available when WG B1.10 “Update of service experience on
underground and submarine cables” concluded his task in 2009. See Cigré TB
379 [19 bis].
4.2
Long Duration Test on EHV Cable Systems
(170 < Um < 550 kV)
4.2.1
General
The prequalification (PQ) test was introduced to compensate for the lack of service
experience with XLPE insulated cables above 150 kV (Um ¼ 170 kV).
The PQ test checks the performance of the cable/accessory system under realistic
conditions. Features examined include:
• Design concept (for example, some early PQ tests at CESI Laboratory showed
that a number of taped joints designs did not perform well in long-term tests).
• Electrical long-term performance of accessories and cable.
• Performance of the cable system under prolonged heat cycling (e.g. thermalmechanical aspects, shrinkage). The 20 thermal cycles specified in the type test
are not sufficient to test for the effect of cable insulation shrink-back within the
assembled accessories.
• Aspects of installation design and practice. For example, PQ tests have shown
that insufficient attention was paid by some installers to arrangements for
clamping the cable adjacent to the joint.
Country
Denmark
(Copenhagen:
Southern cable
route) [54]
Denmark
(Copenhagen:
Northern cable
route
Germany (Berlin/
BEWAG MitteFriedrichshain)
Germany (Berlin/
BEWAG
FriedrichshainMarzahn)
Japan (Tokyo)(3)
[55]
Type of
joints(1)
CPFJ
PMJ
CPFJ+
PMJ
CPFJ+
PMJ
EMJ
Rated
(ϕ–ϕ)
voltage
(kV)
400
400
400
400
500
264
30
48
42
Number
of joints
72
0/12
0/12 (double
systems)
0/12 (double
systems)
3/3
Number of
outdoor/SF6
terminations
3/3
T
T
T
DB
Type of
installation(2)
DB
39.8
5.5
6.3
12
Route
length
(km)
22
2
2
2
1
Number
of
circuits
1
2000
2000
2500 Cu/2400 (4)
1998
1999
Commissioning
year
1997
1600 Cu/1100
1600 Cu/1100
1600 Cu/800
Conductor crosssection/
Transmission
capacity in Winter
Mm2/(MVA)
1600 Cu/975
Table 4.1 Major XLPE cable systems at 400 kV and above. (Data supplied by Cigré WG B1.07, March 2006-TB 338)
108
J. Becker
CPFJ
+PMJ
PMJ
CPFJ
PMJ
PMJ
PMJ
400
400
380
380
400
400
PMJ
400
66
30
3
96
60
96
12
12/0
6/6
6/0
36/0
0/6
12/0
12/12
DB&T&M
DB&D
DB&D
T
T
D&M
8.4
5.2
2.25
14.5
20
12.8
1.3(5)
CPFJ ¼ Composite prefabricated joint, PMJ ¼ premoulded joint and EMJ ¼ extruded moulded joint
(2) T ¼ tunnel, DB ¼ directly buried, D ¼ ducts, D&M ¼ ducts and manhole
(3) Cable system prequalified following Japanese Specifications [48]
(4) 1200 MVA/circuit with forced cooling in the future. 900 MVA/circuit now
(5) 15 core kms/4 circuits X3 phases ¼ 1.3 km
Denmark (Jutland)
United kingdom
(London)
The Netherlands
(Rotterdam)
Austria
(Wienstrom)
Italy (Milan)
United Arab
Emirates (Abu
Dhabi)
Spain (Madrid)
1200 Cu/1400
2000 Cu/2100
2
1600 CU/1000
1200 Al/1200
2500 Cu/1600
2500 Cu/1720
800 Cu/not available
2
1
2
1
2
4
2006
2005
2005
2004
2005
2004
2000
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
109
110
J. Becker
• The ability of the installer to mount accessories under realistic conditions rather
than in the test laboratory. In some cases, this has highlighted the need for
improvements in jointer training. Although not every aspect of the work is tested,
the PQ process gives a good indication of the overall competence of the supplier
of the cable system.
Although some manufacturers have learnt rapidly from problems in the early PQ
tests, this knowledge has not been widely shared. Accessories (and sometimes
cables) are still experiencing problems during PQ and type testing and sometimes
also in service. The WG has the opinion that the state of the art of XLPE cable
technology is not sufficiently advanced that the competence of every manufacturer
can be assumed without evidence. Until such time that a significant body of service
experience has built up, the WG feels that a PQ test is still necessary.
4.2.2
Revision of the Present Prequalification Test Procedure
The prequalification test procedure detailed in IEC 62067 Ed.1 has been reviewed by
the WG.
The main items addressed in order to look for a possible simplification/optimization were:
• The range of Type and PQ approval in relation with the calculated nominal
electrical stresses
• The duration of the heating cycle voltage test
• The procedure in case of a component failure during the test
• The voltage control at the end of the test.
Regarding a possible widening of the present range of type and PQ approval WG
looked very carefully to the sensitivity to change of electrical stress in relation with
the generation of partial discharges. It is recommended to keep the relevant
sub-clauses in IEC 62067 Ed.1 and in IEC 60840 Ed.3 as they are, see Annex 4.5.2.
4.2.2.1 Duration of the Heating Cycle Voltage Test
There is no clear evidence for recommending that the number of 180 heat cycles,
presently specified, should be reduced. It is well known that, if the heating cycles
were not correct in terms of temperature drop, the thermo-mechanical behaviour of
the cable system would not be checked adequately.
There is, also, no possibility to reduce the overall length of the test to 180 days,
because a daily heat cycle is not possible in many practical conditions.
In fact, for cables installed in air or for buried smaller conductor cables with one
day cycle it will be possible to reach, at the end of the cooling period, a conductor
temperature near to ambient temperature. When testing a large conductor cable
buried in the ground it is not always possible to achieve a correct cooling temperature in 16 hours, due to the long thermal time constant of the cable and/or its
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
111
surrounding. Thus the actual duration of the test could vary from 6 months for a
cable system installed in a tunnel to one year for large conductor cables installed in
the ground.
In order to avoid a significant difference in duration of the prequalification test as
a function of the cable construction and installation conditions, WG B1.06 suggests
for the heating cycle voltage test of the prequalification test the duration of one year.
In addition, the practical experience detailed at Sect. 4.1.3.3 has shown that the
duration of the voltage application is an important factor, because failures in
accessories during PQ testing have occurred throughout the one-year test period
[22, 23, 28, 29, 49, 50, 52]. This is another reason why the one-year heat cycle test
with AC voltage on the system is needed to check the long-term electrical behaviour
of the system under test.
Because of these two reasons, it is recommended to maintain the present one-year
duration (8760 hours).
Where partial discharge (PD) tests have been performed at regular intervals
during the long-term test, it was noted that PD activity could initiate at any moment
during the test. For this reason it is recommended to perform partial discharge
measurements on the test assembly to provide an early warning of possible degradation and to enable the possibility of a repair before failure.
The WG considers that it is not easy to specify a PD test on the whole loop as
compulsory, because it can be difficult to achieve an adequate sensitivity when
carrying out a PD test at an unscreened location. This makes it currently difficult
to define a level of background noise that can be achieved in practice.
4.2.2.2 Procedure in Case of a System Component (Cable and/or
Accessory) Failure during the Test
The present IEC 62067 Ed.1 standard does not allow any failure during the heating
cycle voltage test.
However, taking into account that this test is very onerous, the WG considers that
replacement/repair of an accessory failed during the test should be allowed and the
test continued because the replaced/repaired accessory cannot influence the behavior
of the other ones.
On the contrary it is not allowed to repair a cable failure, unless it is caused by an
accidental external damage or the same cable has already been prequalified.
At the end of the 180 loading cycles/one year test and impulse test only the
successfully tested accessories will be prequalified, while the accessory/ies subjected
to repair or replacement will not be prequalified.
However, it is in the option of the cable/accessory manufacturer to continue the
test on the replaced/repaired accessory/ies until it/they complete the 180 loading
cycles/one year test and impulse test. In this case also these accessories are
prequalified.
In the event that during this test another component, fully prequalified (including
the final impulse test), fails, it is possible to repair it and continue the test until the
second run is completed on the replaced accessory/ies.
112
J. Becker
The failure of the component already prequalified (which in this case acts as a
laboratory test component) does not violate its prequalification and should not be
mentioned in the test report.
4.2.2.3 Final Control Test
A lightning impulse withstand test is an effective way of demonstrating that interfacial
pressure within accessories has not relaxed during the PQ test. Also it enables to check
that no irregularity in the semi-conducting screen of the cable has been generated due
to thermo-mechanical forces at for instance bends. As such, the impulse test on the
complete test loop should form an important part of the PQ test sequence.
At present, IEC 62067 Ed.1 requires a hot lightning impulse test on one or several
pieces of cable cut from the PQ test loop. As an alternative to this, a test on the whole
loop is permissible.
The WG has the opinion that after long-term testing, a hot lightning impulse test
on the whole test loop is desirable as a check on the insulation properties at the
interfaces, in the accessories and in the cable. In fact a check on the insulation
properties of the cable only is not sufficient. The WG recommends that IEC 62067
should require a test on the whole loop.
Only in case suitable impulse test equipment is not available at the test site, the
impulse test can be carried out in any other test arrangement on cable sections, which
include the accessories from the test loop, again as a check on the insulation
properties at the interfaces, in the accessories and in the cable (1).
4.2.3
Changes in a Prequalified Cable System
4.2.3.1 Evaluation of Changes in a Prequalified System
According to IEC 62067 Ed. 1 the PQ test need only be repeated if there is “a
substantial change in the cable system with respect to material, manufacturing
process, design and design levels”. A substantial change is defined as one, which
might adversely affect the performance of the cable system and puts the responsibility on the supplier to make the detailed case that a change is not substantial.
There is however no internationally agreed method by which the supplier and
purchaser can evaluate the evidence and come to a decision as to whether the PQ test
or other tests need to be repeated or not.
In order to cover this matter and to evaluate what changes must be considered as
“substantial”, the WG has adopted the Functional Analysis Method described in
Annex 4.5.3. This method correlates the function performed by a certain item to the
tests required to check that function. As a result a number of changes to the components of a cable system that require the repetition of the long-term test were identified.
1()
Note: If the energy of the impulse generator is not sufficient to test the whole cable length, the test
loop could be cut, without moving the accessories, into appropriate sections, which then are
available to be tested with auxiliary terminations.
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
113
However it was realized that some of these changes do not require the repetition
of a full Prequalification test, but a simplified long-term test called “Extension of
Prequalification (EQ) test” could be adopted (see Sects 4.2.3.2 and 4.2.3.3).
The Working Group considers that allowing a shorter laboratory based long-term test
rather than requiring the cable/accessory maker to repeat the full PQ test, will encourage
incremental improvements in technology, whilst reducing the risk to the customer.
The main situations of changes that can be found in practice are:
• The exchange of components (cable or accessories) already prequalified in
systems from different manufacturers and/or from different plants of the same
manufacturer.
• The modification to cable components in a prequalified system
• The modification to accessory components in a prequalified system.
As far as the accessories are concerned, it is important to observe that accessories
of different manufacturers may significantly differ in design, material and construction. For instance a premoulded joint and a taped joint are substantially different and
require a specific Prequalification test (if not already prequalified). For this reason the
concept of accessory families for each type of accessory, i.e. joints, metal enclosed
terminations and outdoor/indoor terminations has been introduced. The names of the
accessory families are defined in ▶ Chap. 1, “Compendium of Accessory Types Used
for AC HV Extruded Cables” (Cigré TB 89 [20]) and are summarized in Table 4.2.
The three main types of changes that can occur in a prequalified system and the
relevant type of qualification test required in each case are discussed below.
4.2.3.1.1 Exchange of Cable and/or Accessory in a Prequalified Cable System
In Table 4.3 a guide to the selection of test procedures is given for the extension of
the prequalification of a prequalified cable system in case of an exchange of cable
and/or an accessory by another cable and/or accessory (from the same family or from
another family), see Table 4.2.
The selected procedure depends on the calculated electrical stresses at the insulation screen of the other cable and/or accessory with respect to the calculated electrical
stresses at the insulation screen of the originally prequalified cable system and on the
prequalification of the cable system containing that other cable and/or accessory.
4.2.3.1.2 Modification to the Cable in a Prequalified Cable System
In Table 4.4 a guide to the selection of test procedures is presented for the extension
of the prequalification tests or of the type tests in case of a modification to the cable
in a prequalified cable system.
The selected test procedure depends on the type of modification of the relevant
cable component. As far as type tests are concerned, in some cases only the relevant
clauses of IEC 62067 Ed.1 type test procedure covering the function of the specific
item changed are considered. The origin of the type of modification may be a change
in material, manufacturing process, design or design level, as indicated for information in Table 4.4.
114
J. Becker
Table 4.2 Accessory family definitions
Accessory families
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
2
2.1
2.2
2.3
2.4
2.5
3
3.1
3.2
3.3
3.4
3.5
3.6
3.7
Joints
Taped joints
Pre-moulded joints
Composite joints
Field moulded joints
Heat shrink sleeve joints
Back to back joints
Transition joints
Branch joints
Metal enclosed terminations families (SF6 and oil immersed)
Stress cone and insulator type
Deflector and insulator type
Prefabricated composite dry type
Capacitor cone and insulator type
Directly immersed termination type
Indoor and outdoor terminations
Prefabricated elastomeric sheds and stress cone type
Heat shrink sleeve type
Elastomeric sleeve type
Stress cone and insulator type
Deflector and insulator type
Capacitor cone and insulator type
Prefabricated composite and capacitor cone and insulator type
Table 4.3 Test procedures in case of an exchange of a cable and/or accessory in a prequalified
cable system
Cable and/or
accessory
cable
Joint
Metal
enclosed
Termination
Outdoor
Termination
Already qualified on another cable
system within the same or higher
insulation screen stress
12.5 + XX2)
(non electrical TT + EQ1)
XX2)
(EQ)
XX2)
Already qualified on another cable
system with a lower insulation screen
stress or not qualified
12 + 13.2
(electrical and non electrical TT + PQ)
12 + 13.2
(TT + PQ)
12 + 13.2
(EQ)
XX2)
(EQ)
(TT + PQ)
12 + 13.2
(TT + PQ)
The numbers given refer to the respective clauses in IEC 62067 Ed.1
EQ consists of the bending test, 60 heat cycles without voltage and the electrical type tests
2)
(XX) Clause to be added in the standard
1)
Cable Insulation
Cable semi-conductive inner and/or
outer screen
Component
Cable Conductor
Type of modification
Larger cross-section
Copper to Aluminium
Insulated wires (enamelled or oxidized...)
Stranded to solid conductor
Water tightness
Change of origin (supplier or production plant)
Transfer extrusion line (see cable insulation)
Different quality of semicon
Change of base resin
Change in cross linking package (peroxide/
antioxidant)
Nature of polymer (XLPE, LDPE, HDPE, EPR)
Higher conductor stress, no increase of insulation
screen stress
Increase of insulation screen stress
Modification
✓
✓
✓
✓
✓
✓
✓
✓
✓
M
✓
P
✓
✓
✓
✓
✓
✓
✓
✓
✓
✓
D
✓
Table 4.4 Guide to the selection of tests because of modifications to a cable in a prequalified EHV cable system
12
12
12
✓
✓
DL
✓
–
–
–
–
–
–
EQtest
–
–
(xx)
(xx)
–
(continued)
13.2
13.2
–
IEC 62067 Ed.1 Clause
number
PQT-test
test
12
13.21)
12
–
12.5
–
12.5
–
12.5.14
–
123)
2)
2)
123)
–
123)
–
12
–
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Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
115
Different types of metal screen
Different type of materials
Different processes
Change in bonding material and/or process to
metal screen
Type of modification
New extrusion line or transfer of extrusion line
with earlier experience in-house
New extrusion line, or transfer of extrusion line
without earlier experience
Change of laying, material, thickness
Modification
v
✓
✓
✓
✓
✓
✓
✓
✓
✓
✓
P
✓
M
✓
✓
✓
D
DL
12.5.4
12.5.14
(if required)
12.4.4 + 12.4.10
12.54)
12.54)
12.54)
12
–
–
–
–
–
13.2
IEC 62067 Ed.1 Clause
number
PQT-test
test
12
–
(XX) Clause to be added in the standard
Remark: in type test, only the relevant clauses are applicable
M: change in material; P: change in manufacturing process; D: change in design (construction); DL: change in electrical design stress level
1)
If higher calculated dielectric stresses at the insulation screen, clause 13.1
2)
Same as for insulation
3)
If outside Range of Type Approval, clause 12.2
4)
As appropriate to outer sheath materials
Cable Metallic screen
Cable
Outer sheath
Cable Bedding (layer over extruded
semicon screen)
Component
Table 4.4 (continued)
–
–
–
–
–
EQtest
116
J. Becker
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
117
4.2.3.1.3
Modification to an Accessory within the Same Family
in a Prequalified Cable System
In Table 4.5 a guide to the selection of test procedures is presented for the extension
of the Prequalification tests or of the Type tests in case of a modification to an
accessory (joint and/or termination), within the same accessory family (see
Table 4.2) in a prequalified cable system.
Table 4.5 Guide to the selection of tests because of modifications to an accessory within the same
family in a prequalified EHV cable system
IEC 62067
Ed.1 Clause
number
PQT-test
Test
–
–
EQtest
(xx)
–
–
(xx)
–
13.2
–
–
–
(xx)
✓
–
–
(xx)
✓
Annex
D
Annex
D
–
–
–
–
–
–
(xx)1)
–
–
(xx)1)
–
–
(xx)1)
Modification
Component
Joints
Terminations:
- outdoor
- indoor
- metal
enclosed
+ SF6
+ oil-immersed
Type of modification
Higher calculated
electrical stress
design and
construction
Compound of main
insulation body
(same base resin)
Changing nature of
polymer, (EPR,
Silicone....)
Material of semi-con
electrodes
Fixation of cable
ends on either side of
the joint
Screen interruption
Outer screen and
Protection design,
(Filling/water
tightness), Outlet of
bonding leads
Higher electrical
stress design of stress
cone (or smaller
metal clad for GIS or
transformer
terminations)
Change in nature of
Filling medium
(e.g. oil to gas....)
Change in the
formulation of the
stress cone
M
P
✓
✓
✓
✓
D
DL
✓
✓
✓
✓
✓
✓
✓
(continued)
118
J. Becker
Table 4.5 (continued)
Modification
Component
Type of modification
compound but with
the same base
polymer
Change of the base
polymer (EPR,
Silicone, . . .) of the
stress cone
compound
Change of insulator
material for indoor or
outdoor terminations.
Change of insulator
design or
manufacturer of
GIS/Transformer
insulator
M
P
D
✓
2)
✓
2)
✓
✓
2)
✓
2)
✓
DL
IEC 62067
Ed.1 Clause
number
PQT-test
Test
EQtest
–
–
(xx)
12
–
–
12
–
–
(xx) Clause to be added in the standard
M: change in material; P: change in manufacturing process; D: change in design (construction);
DL: change in electrical design stress level
1)
When can be demonstrated that the thermo mechanical aspects have no significant influence on the
performances of the termination a Type Test may be sufficient
2)
In case of elastomeric insulators (“silicone” or “EPR”) climatic and pollution test according to IEC
61109 Annex C should be considered
The selected test procedure depends on the type of modification of the relevant
accessory. The origin of the type of modification may be a change in material,
manufacturing process, design or design level, as indicated for information in
Table 4.5.
4.2.3.2 Basic Principles of the Extension of Prequalification (EQ) Test
The Extension of Prequalification consists of a period of 60 days of thermal
pre-conditioning without applied voltage, carried out in laboratory conditions,
followed by the electrical part of the type test.
The 60 daily heat cycles without voltage plus the 20 heat cycles of the type test
applied to the test loop are intended to allow relaxation of most of the mechanical
stresses trapped in the cable insulation during manufacture.
This relaxation results in retraction of the XLPE insulation wherever the cable
is cut.
The retraction of the cable insulation within an accessory, if not provided with a
specific anti-retraction device, can initiate partial discharge activity, leading to failure
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
35.0
Retraction of
oversheath
30.0
Retraction of
insulation
25.0
Retraction (mm)
119
20.0
15.0
10.0
Evelution of
the retraction
5.0
0.0
0
10
20
30
40
50
60
70
80
-5.0
Number of heat cycles
Fig. 4.3 Retraction test on a 5-meter long 1000 mm2 500 kV cable with XLPE insulation and PE
sheath
of the accessory. In fact the considerations made at paragraph Sect. 4.1.3.1 and the
TB “Interfaces in accessories for extruded HV and EHV cables” [53], indicate that
thermal cycles stressing is the main failure mechanism in accessories, which typically include due to their intrinsic construction a number of interfaces.
As shown by Fig. 4.3 the retraction of the XLPE insulation is practically
completed after about 60–80 heat cycles.
In addition the heat cycles are producing a radial expansion and retraction of the
cable insulation and of the accessory components that can also influence the interfacial pressure in accessories.
In order to be able to perform the EQ test in a laboratory, limiting the engagement
of the HV test equipment, it has been decided to perform these pre-conditioning
cycles without applied voltage. Being the EQ test performed in a laboratory, i.e. with
well-defined thermal conditions, it is possible to carry out the heat cycles in
approximately one day also with very large cross-section cables.
To prove that the heat cycling has not affected the integrity of the test loop a
complete electrical type test (as defined in IEC62067 Ed.1) is used.
As the installation design conditions can significantly affect the thermo-mechanical
behaviour of the accessories, the test arrangement shall take this into account.
For instance a rigid installation can be simulated by suitably cleating the cable at
each side of a joint. In order to comply with this requirement a minimum length of
10 m of free cable between accessories is specified for the EQ test.
To maintain a similar degree of risk for the shorter duration of the EQ test
compared to the duration of Prequalification test, at least two accessories of the
same type, instead of one, shall be included in the test loop submitted to the
extension of prequalification.
120
J. Becker
Fig. 4.4 Extension of
Prequalification test loop for a
joint intended for flexible and
rigid installations
Rigid installation
Flexible installation
>10 m
4.2.3.3 Procedure of the Extension of Prequalification Test
The sequence of tests for the extension of prequalification is summarized below. The
numbers in brackets refer to clause numbers of present tests in IEC 62067 Ed.1.
• Check of the insulation thickness of cable for electrical type test to determine the
test voltage values (12.4.1)
• Bending test without final PD test (12.4.4)
• The test assembly may be installed in a laboratory and shall consist of at least
2 accessories of the same type that is to be prequalified. There shall be at least
10 m of cable between accessories. The minimum length of the test loop shall be
at least 30 m. If a joint submitted to EQ has to be used in both flexible and rigid
installations, one joint shall be installed in a flexible configuration, the other rigid.
Where a joint is designed for use only in rigid installations, then both joints shall
be rigidly fixed. Similarly, for a joint intended only for flexible installations, both
joints shall be installed in a flexible test configuration. An example of the test loop
is shown in Fig. 4.4.
• The loop shall have a U bend with a diameter specified in 12.4.4
– The partial discharge test defined in 12.4.5 shall be carried out here to check
the quality of the assembled accessories.
• The thermal preconditioning test consists of 60 heat cycles with no voltage applied.
The heat cycles shall be as given in 12.4.7, i.e. a minimum of 8 hours of heating
followed by at least 16 hours of natural cooling. The steady state conductor temperature shall be between 5 C and 10 C above the maximum cable operating
temperature for at least two hours. At the end of the cooling period the conductor
temperature shall be within 15 C of ambient temperature, with a maximum of 45 C.
• Continue with the partial discharge test (12.4.5) followed by the full sequence of
electrical type test. No failure shall occur.
Note: In case of modification of the cable, in order to cover all the requirements of the type test it is necessary to perform also the non-electrical test on
the cable as specified in 12.5.
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
4.2.4
121
Recommendations to IEC 62067
As a summary and conclusion from its reflections WG B1.06 makes the following
recommendations to IEC for further consideration in future editions of IEC 62067:
• To maintain unchanged the present one-year Prequalification (PQ) test for the
basic prequalification of a new cable system (as a check on e.g. the long-term
electrical and thermal-mechanical behaviour).
• To allow in case of a failure of an accessory the continuation and completion of the
PQ test for the undisturbed components (cable and other accessories) of the loop.
• To perform partial discharge measurements on the prequalification test assembly
during the PQ test to provide an early warning of possible degradation and to
enable the possibility of repair before failure.
• To perform the lightning impulse test at the end of the PQ test on the complete test
loop or, in case of practical problems with test equipment, on cable samples
including each type of accessory. The intention is to check the insulation properties at the interfaces, in the accessories and in the cable.
• To maintain unchanged the present range of Type and PQ approval, see Annex 4.5.2.
• To introduce a simplified long-term test (80 cycles) called “Extension of Prequalification (EQ) test” (see Sect. 4.2.3.3) in case of exchange of prequalified
components (cable and/or accessories) with other components that are already
prequalified in other cable systems with the same or higher calculated electrical
stress at the insulation screen of the subjected system or in case of modification of
a cable or an accessory within the same family in a prequalified cable system (see
Sect. 4.2.3).
• For engineering purposes a “Functional Analysis Method” (see Annex 4.5.3) is
recommended as a mean for a systematic assessment of the significance of
changes/modifications at components (cables and accessories) of a cable system
and thus for the selection of the appropriate test (PQ or EQ test).
• To introduce guides to the selection of appropriate test procedures, based on the
application of that “Functional Analysis Method”, to the most important components of actual cable systems, in case of
– Exchange of a cable and/or accessory in a prequalified cable system
(Table 4.3)
– Modification of a cable in a prequalified cable system (Table 4.4)
– Modification of an accessory within the same family in a prequalified cable
system (Table 4.5)
• To include sample tests on accessories, which are presently “under consideration”
within IEC 62067 Ed.1, following the wording of IEC 60840 Ed.3. For accessories, where the main insulation cannot be routine tested, the partial discharge and
high voltage test should be introduced, but only on one accessory of each type per
contract. These tests are intended to check not only the intrinsic quality of the
accessory (design and materials), but also the quality of the installation (equipment and jointers skill), factors that are very important at the EHV level.
• To align the definition of type tests (sub-clause 3.2.3 of IEC 62067 Ed.1) to the
definition of the prequalification test to ease the potential use of the Tables 4.3,
122
J. Becker
4.4, and 4.5 as a guide for the selection of test procedures in case of changes on
prequalified cable systems.
• It is worth noting that, as a result of the application of the “Functional Analysis
Method” (see Annex 4.5.3), a number of tests have been identified that are not
included in IEC 62067 Ed.1. These tests are generally performed as development
tests and are summarized in Annex 4.5.4 for future consideration by IEC.
4.3
Long Duration Test on HV Cable Systems
(36 < Um ≤ 170 kV)
4.3.1
General
Traditionally EHV cables are working at a significantly higher stress than HV cables
(see Fig. 4.5).
Due to increased competition and good experience with (very) high AC
stresses (12–15 kV/mm and even more) on EHV cable systems it becomes
more common nowadays to produce cables with reduced insulation thickness
[31–33] at the HV level. This leads to higher dielectric stresses nearly as high as
in the EHV field not only at main insulation, but also at the interfaces between
cables and accessories.
The development of reduced insulation thickness cables at the HV level was
successful due to the experience gained by the major cable makers at the production,
testing, installation and good service of EHV cable systems.
Also new types of accessories are appearing on the market, of course with no
earlier experience [34–40]. These accessories should be able to fit to the older types of
cables with thicker insulation and the newer types of cables with reduced insulation
(changes of an existing HV link with a new cable type or repair of an older link).
The following remarks are of major importance:
Working stress (kV/mm)
100
Impulse stresses
10
AC stresses
1
10
100
Voltage level (kV)
Fig. 4.5 AC and impulse conductor stresses of XLPE cables
1000
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
123
• The new highly stressed cables with reduced insulation thickness are generally
produced by experienced cable makers that are using their know-how from EHV
technology: development and production teams, production equipment and process, material handling and control as well as their well trained teams for
installation in the field.
• Failures, if any, during type or after installation tests, tend to occur at the
interfaces between accessories and cables when new systems are tested [41,
42, 45–47]. To assess the reliability of a new HV cable system whose working
stresses are similar to those of the EHV systems, the experienced cable
makers rely on the PQ and type tests they have performed on EHV cable
systems.
• For highly stressed cable systems, type tests are not necessarily sufficient [52].
In several countries long-term tests have been performed on new HV cable
systems [32, 33, 43, 44, 48].
Working Group members recommend that cable systems should be considered
rather than cables or accessories alone, see also [46].
There exist arguments for and against long-term tests on HV cable systems.
For:
• The electrical service stresses and mainly lightning impulse stresses at the core
(interface with prefabricated accessories) of HV cables are becoming almost as
high as the stresses of EHV cables.
• Practical shrinkage tests on cable lengths of 5 meters or more have shown that
cable insulation and over-sheath is only stabilized after around 60 to 80 heat
cycles (see Fig. 4.3). This is confirmed by experts and by the outcome of PQ tests
[23, 28, 49, 50]
• New accessory designs are coming to the market
• The countries that have performed long-term tests on new cable systems before
installing them in the network have reported very good service experience
• Test laboratories that conduct type tests for many suppliers have published the
results of their experience: the failure rate of MV and HV type tests is growing
[45]. The reasons for this could be the lack of experience of some manufacturers
with higher dielectric stresses in cables, the lack of experience with new type of
accessories or all these combined
• Breakdowns in service are recorded on recently commissioned systems.
Against:
• The good and sometimes long experience of some cable makers with HV cables
and cable systems (cables with “reasonable” stresses)
• In some countries where long-term tests are not performed on new cable systems
before installing them in the network, service experience is good, as know-how
has been gained during many years in the HV field
• The reluctance of some utilities or other end-users to test entire systems if they
wish to buy their HV cables and accessories separately.
124
4.3.2
J. Becker
Prequalification Test for HV Systems
4.3.2.1 Range of Prequalification Test
As accessories typically include due to their intrinsic construction a number of
interfaces, the thermal cycles stressing is their most common failure mechanism
(apart from jointing errors). That’s why the critical dielectric stresses in service for
which long term testing should be recommended for HV cable systems depend very
much on the interface stresses with accessories.
For prefabricated accessories (joints or stress-cones), mainly impulse stresses at the
cable insulation screen are most critical. For instance a 400 kV cable has a ratio BIL/U0
lower than HV cables. That means that HV cables with an AC stress of 4 kV/mm at
insulation surface reach an impulse level of 36 kV/mm, as high as a 400 kV system,
which has an AC interface stress of 5.5 kV/mm, etc. (see Table 4.6).
A practical example: A 1600 mm2 400 kV cable with an insulation thickness of
26 mm has a service stress at the insulation surface of 6.5 kV/mm and an impulse
stress at the insulation surface of 40 kV/mm. A 1600 mm2 150 kV cable with an
insulation thickness of 15 mm has a service stress of 4.7 kV/mm at the insulation
screen, i.e. 30% lower than the 400 kV cable, but an impulse stress of 40.3 kV/mm at
the insulation surface, the same as the 400 kV cable.
Based on the above considerations, a PQ test is recommended for cable systems
with insulation screen stresses above 4 kV/mm.
As shown in Fig. 4.5 HV cables have operated at conductor stresses below 8 kV/mm.
In addition, for joints that are taped or field-molded also the AC and impulse
stresses at the conductor screen are critical.
So, if the conductor stresses are higher than 8 kV/mm, it is recommended to
perform the long-term test on the system.
These conclusions are also supported by the evaluation of the sensitivity of
electric stress to changes in dimensions reported in Annex 4.5.2. In fact these
calculations show that for a reduction of the insulation thickness of 5%, the thickness
of a defect between the cable insulation and the premoulded accessory must be
reduced of about 21%, in order to avoid partial discharges.
If the operating stresses at the insulation screen and at the conductor screen are
below 4 kV/mm and 8 kV/mm respectively, they compare with those found in cable
Table 4.6 AC and BIL stresses at the insulation screen for different voltage levels
Um (kV)
U0 (kV)
BIL (kV)
Ratio BIL/Uo
Routine Test (kV)
AC-stress for a BIL-stress of
36 kV/mm at insulation surface
(kV/mm)
AC-stress for a BIL-stress of
40 kV/mm at insulation surface
(kV/mm)
52
26
250
9.6
65
3.74
72.5
36
325
9.0
90
3.99
123
64
550
8.6
160
4.19
145
76
650
8.5
190
4.21
170
87
750
8.6
218
4.18
420
220
1425
6.5
440
5.56
4.16
4.43
4.65
4.68
4.64
6.17
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
125
systems already installed for a long time. Even if most of these cables and accessories have only been type tested, service experience is generally considered good.
So the prequalification test shall be performed only on cable systems where the
calculated nominal electrical stresses at the conductor screen will be higher than
8 kV/mm and/or at the insulation screen higher than 4 kV/mm. The prequalification
test shall be performed except:
• If cable systems including a cable of similar construction and accessories of the
same family have been prequalified for higher rated voltages or
• If an alternative long term test has been carried out on cable systems with the
same construction and accessories of the same family and the manufacturer can
demonstrate good service experience (2) with cable systems with equal or higher
calculated nominal electrical stresses on the conductor and insulator screens, in
the main insulation part(s) and in boundaries of the accessories.
4.3.2.2 Prequalification Test Procedure
As HV cables are less rigid and have generally smaller conductor cross sections than
EHV cables, the thermo-mechanical aspects are less critical than for EHV cable
systems, so the WG has considered that laboratory conditions, instead of an actual
outdoor installation, could be adopted, in this case, for the PQ test.
Being the test performed in a laboratory, i.e. with well defined thermal conditions,
it is possible to carry out correctly the heat cycles in approximately one day also with
very large conductor cross section cables, so 180 daily cycles instead of one year
duration is permissible. This has the advantage of halving the time to market of these
new HV cable systems, combined with a reduction of the overall cost of the PQ test.
The disadvantage is that the long-term behavior of the electrical insulation of the
cable system is checked in only half a year. For these kinds of cable systems, it was
judged as acceptable.
The proposed layout of cable system is:
• Length of cable: one length with a minimum of 20 m without accessories and at
least 10 m for the other lengths between two accessories. The total length
depending on the number of accessories in the system under test
• Number of accessories: at least one of each type
• Test could be performed in a laboratory and not necessarily in a situation
simulating the real installation conditions. Where thermo-mechanical aspects
have to be considered, special test arrangements could be considered. Figures 4.6
and 4.7 show examples of methods to simulate the thermo-mechanical forces on
joints, when a cable is installed in a duct or rigidly fixed.
• The test is to be performed on the cable system (cables and accessories).
2
() Unfortunately it is difficult to give a specific rule about the evaluation of a good service
experience, but the matter has to be dealt with, case by case, between the supplier and the
purchaser.
126
J. Becker
Fig. 4.6 Possible test layout
for cable installed in a duct
J1
J3
J2
Fig. 4.7 Possible test layout for cable anchored on the ground
The test procedure is:
• Test voltage: 1.7 U0
• Number of heating cycles: 180 cycles, cycle duration not less than 24 hours. The
heating by conductor current shall be applied for at least 8 h. The cable conductor
temperature remote from the accessories shall be maintained within the temperature limits of 0 C to 5 C above the maximum conductor temperature in normal
operation for at least 2 h of each heating period. This shall be followed by at least
16 h of natural cooling to a conductor temperature within 10 C of the test
ambient temperature, with a maximum of 45 C. No breakdown shall occur.
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
127
Note: partial discharge measurements are recommended to provide an early
warning of possible degradation.
• Tests after long term testing: hot lightning impulse test on the complete loop
• Examination of the test loop after completion of these tests.
Note: The replacement/repair of an accessory failed during the heating cycle
voltage test is allowed and the test can be continued, because the replaced/
repaired accessory cannot influence the behavior of the other ones.
On the contrary it is not allowed to repair a cable failure, unless it is caused by an
accidental external damage or the same cable has already been prequalified.
At the end of the 180 loading cycle voltage test and the impulse test, only the
successfully tested accessories will be prequalified, while the accessory/ies subjected
to repair or replacement will not be prequalified.
However, it is in the option of the cable manufacturer to continue the test on the
replaced/repaired accessory/ies until it/they complete the 180 loading cycles voltage
test and the impulse test. In this case also these accessories are prequalified.
In the event that during this continued test another component, fully prequalified
(including the final impulse test), fails, it is possible to repair it and continue the test
until the second run is completed on the replaced accessory/ies.
The failure of the component already prequalified (which in this case acts as a
laboratory test component) should not be mentioned in the test report.
4.3.3
Exchanges and Modifications in a Prequalified HV Cable
System
4.3.3.1 Evaluation of Changes and Modifications in a Prequalified
System
As far as the guide to the selection of test procedures in case of an exchange of a
cable and/or an accessory with another one or of a modification of a cable and/or an
accessory of a prequalified cable system is concerned, the same considerations made
at paragraph Sect. 4.2.3 apply.
Also the extension of prequalification test (EQ) is the same as for EHV systems
(see Sect. 4.2.3.1), where Tables 4.3, 4.4, and 4.5 (for IEC 62067 Ed.1) have to be
replaced by Tables 4.7, 4.8, and 4.9 (for IEC 60840 Ed.3).
4.3.3.2 Procedure of the Extension of Prequalification (EQ) Test for HV
Cable Systems
The basic principles of Sect. 4.2.3 apply.
128
J. Becker
Table 4.7 Test procedures in case of an exchange of a cable and/or accessory in a prequalified HV
cable system
Cable and/or
accessory
cable
Joint
Metal
enclosed
Termination
Outdoor
Termination
Already qualified on another cable
system within the same or higher
insulation screen stress
12.4 + YY2
(non electrical TT + EQ1)
YY2)
(EQ)
YY2)
Already qualified on another cable
system with a lower insulation screen
stress or not qualified
12 + ZZ3
(electrical and non electrical TT + PQ)
12 + ZZ3)
(TT + PQ)
12 + ZZ3)
(EQ)
YY2)
(EQ)
(TT + PQ)
12 + ZZ3)
(TT + PQ)
The numbers indicate the respective clauses in IEC 60840 Ed.3
EQ consists of the bending test, 60 heat cycles without voltage and the electrical type tests
2
(YY) Clause to be added in the standard
3
(ZZ) Clause to be added in the standard
1
Table 4.8 Guide to the selection of tests because of modifications to a cable in a prequalified HV
cable system
Component
Cable
Conductor
Cable
semiconductive
inner
and/or
outer
screen
Modification
Type of
modification
Larger crosssection
Copper to
Aluminium
Insulated wires
(enamelled or
oxidized....)
Stranded to
solid conductor
Water tightness
Change of
origin (supplier
or production
plant)
Transfer
extrusion line
(see cable
insulation)
M
P
✓
✓
✓
✓
✓
D
✓
✓
✓
✓
✓
✓
✓
✓
✓
✓
DL
✓
IEC 60840 Ed.3 Clause
number
PQT-test
test
12
(ZZ)1
EQtest
–
12
–
–
12.4
–
(YY)
12.4
–
(YY)
12.5.14
123
–
–
2
2
(continued)
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
129
Table 4.8 (continued)
Component
Cable
Insulation
Cable
Bedding
(layer over
extruded
semicon
screen)
Cable
Metallic
screen
Modification
Type of
modification
Different
quality of
semicon
Change of base
resin
Change in cross
linking package
(peroxide/
antioxidant
Nature of
polymer
(XLPE, LDPE,
HDPE, EPR)
Higher
conductor
stress, no
increase of
insulation
screen stress
Increase of
insulation
screen stress
New extrusion
line or transfer
of extrusion line
with earlier
experience
in-house
New extrusion
line, or transfer
of extrusion line
without earlier
experience
Change of
laying, material,
thickness
Different types
of metal screen
M
✓
P
D
DL
IEC 60840 Ed.3 Clause
number
PQT-test
test
–
123
EQtest
–
✓
123
–
–
✓
12
–
–
12
(ZZ)
–
✓
12
–
–
✓
12
(ZZ)
–
✓
✓
✓
✓
✓
12
–
✓
✓
12
(ZZ)
✓
✓
✓
12.4.4
12.4.18
(if required)
✓
✓
✓
12.3.3 + 12.3.8
–
–
(continued)
130
J. Becker
Table 4.8 (continued)
Component
Cable
Outer
sheath
Modification
Type of
modification
Different type
of materials
Different
processes
Change in
bonding
material and/or
process to metal
screen
M
✓
✓
P
✓
D
DL
IEC 60840 Ed.3 Clause
number
PQT-test
test
–
12.44
EQtest
–
✓
12.44
–
–
✓
12.44
–
–
Note: (YY) and (ZZ), Clauses to be added in the standard
Remark: only the relevant clauses are applicable for type tests
M: change in material; P: change in manufacturing process; D: change in design (construction);
DL: change in electrical design stress level
1
If higher calculated nominal dielectric stresses at the insulation screen, clause 16.1
2
Same as for insulation
3
If outside Range of Type Approval, clause 12.1
4
As appropriate to outer sheath materials
The sequence of tests for the Extension of Prequalification (EQ) test is summarized below. The numbers in brackets refer to clause numbers of IEC 60840 Ed.3.
• Check on the insulation thickness of cable for electrical type test to determine the
test voltage values (12.3.1)
• Bending test without final PD test (12.3.3)
• The test assembly may be installed in a laboratory and shall consist of at least
2 accessories of the same type that is to be prequalified. There shall be at least 10 m
of cable between accessories. The minimum length of the test loop shall be at least
30 m. If a joint submitted to EQ has to be used in both flexible and rigid installations,
one joint shall be installed in a flexible configuration, the other rigid. Where a joint is
designed for use only in rigid installations, then both joints shall be rigidly fixed.
Similarly, for a joint intended only for flexible installations, both joints shall be installed
in a flexible test configuration. An example of the test loop is shown in Fig. 4.4.
• The loop shall have a U bend with a diameter specified in 12.3.3
– The partial discharge test defined in 12.3.4 shall be carried out here to check
the quality of the assembled accessories.
• The thermal preconditioning test consists of 60 heat cycles with no voltage
applied. The heat cycles shall be as given in 12.3.6, i.e. a minimum of 8 hours
of heating by conductor current followed by at least 16 hours of natural cooling.
The steady state conductor temperature shall be between 5 C and 10 C above
the maximum cable operating temperature for at least two hours. At the end of the
cooling period the conductor temperature shall be within 15 C of ambient
temperature, with a maximum of 45 C.
Change of insulator design or manufacturer of GIS/Transformer insulator
Change of insulator material for indoor or outdoor terminations.
✓
2
v
2
✓
2
✓
2
✓
✓
✓
✓
✓
✓
Outer screen and Protection design, (Filling/water tightness), Outlet of bonding
leads
Higher electrical stress design of stress cone (or smaller metal clad for GIS or
transformer terminations)
Change in nature of Filling medium (e.g. oil to gas....)
Change in the formulation of the stress cone compound but with the same base
polymer
Change of the base polymer (EPR, Silicone, . . .) of the stress cone
✓
✓
✓
✓
✓
D
✓
✓
P
M
Type of modification
Higher calculated electrical stress design and construction
Compound of main insulation body (same base resin)
Changing nature of polymer, (EPR, Silicone....)
Material of semi-con electrodes
Fixation of cable ends on either side of the joint
Screen interruption
✓
DL
✓
12
12
–
–
–
–
–
–
–
(ZZ)
(ZZ)1
(ZZ)1
(ZZ)1
–
EQtest
(ZZ)
(ZZ)
–
(ZZ)
(ZZ)
–
–
–
–
IEC 60840
Clause number
PQT-test
Test
–
–
–
–
–
(YY)
–
–
–
–
Annex
–
D
Annex
–
D
–
–
NOTE: (YY) and (ZZ) Clauses to be added in the standard
M: change in material; P: change in manufacturing process; D: change in design (construction); DL: change in electrical design stress level
1
When can be demonstrated that the thermo mechanical aspects have no significant influence on the performances of the termination a Type Test may be
sufficient
2
In case of elastomeric insulators (“silicone” or “EPR”) climatic and pollution test according to IEC 61109 Annex C should be considered.
Terminations:
- outdoor
- indoor
- metal
enclosed
+ SF6
+
oil-immersed
Component
Joints
Modification
Table 4.9 Guide to the selection of tests because of modifications to an accessory within the same family in a prequalified HV cable system
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
131
132
J. Becker
• Continue with the partial discharge test (12.3.4) followed by the full sequence of
the electrical type test (see 12.3.2 item b to h). No failure shall occur.
Note: In case of modification of the cable, in order to cover all the requirements of the type test it is necessary to perform also the non-electrical test on
the cable as specified in 12.4.
4.3.4
Recommendations to IEC 60840
As a summary and conclusion from its reflections WG B1.06 makes the following
recommendations to IEC for further consideration in future editions of IEC 60840:
• To introduce a prequalification (PQ) test for those HV cable systems where the
calculated nominal electrical stress at the conductor screen will be higher than
8 kV/mm and/or at the insulation screen higher than 4 kV/mm (see Sect. 4.3.2).
This test need not to be performed if
– Cable systems with the same constructions and accessories of the same family
have been prequalified for higher rated voltages
– If equivalent long term tests have been already successfully carried out on
cable systems with the same construction and accessories of the same family
and a good service experience at cable systems with equal or higher stresses
can be demonstrated
• To allow in case of a failure of an accessory during the test the continuation and
the completion of the PQ test for the undisturbed components (cable and other
accessories) of the test loop.
• To perform partial discharge measurements on the prequalication test assembly
during the PQ test to provide an early warning of possible degradation and to
enable the possibility of repair before failure.
• To perform the lightning impulse test at the end of the PQ test on the complete test
loop or, in case of practical problems with test equipment, on cable samples
including each type of accessory. The intention is to check the insulation properties at the interfaces, in the accessories and in the cable.
• To maintain unchanged the present range of Type and PQ approval, see Annex 4.5.2
• To introduce a simplified long-term test (80 cycles) called “Extension of
prequalification (EQ) test” (see Sect. 4.3.3.2) in case of exchange of prequalified components (cable and/or accessories) with other components that
are already prequalified in other cable systems with the same or higher
calculated electrical stress at the insulation screen of the subjected system or
in case of modification of a cable or an accessory within the same family in a
prequalified cable system (see Sect. 4.3.3).
• For engineering purposes a “Functional Analysis Method”, see Annex 4.5.3, is
recommended as means for a systematic assessment of the significance of
changes/modifications at components of a HV cable system and thus for the
choice of the appropriate tests (PQ or EQ) or Type Tests (TT).
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
133
• Based on the application of the “Functional Analysis Method” to the most
important components of actual HV cable systems (see Annex 4.5.3), guides to
the selection of test procedures are given in case of
– Exchange of a cable and/or accessory in a prequalified cable system
(Table 4.7)
– Modification of a cable in a prequalified cable system (Table 4.8)
– Modification of an accessory within the same family in a prequalified cable
system (Table 4.9)
• To align the definition of type tests to the definition of the prequalification test
(see sub-clause 3.2.3 of IEC 62067) to ease the potential use of the tables
(Tables 4.7, 4.8 and 4.9) as a guide for the selection of test procedures in case
of changes on prequalified HV cable systems.
• To include an electrical sample test as a check on the properties of the insulation
of HV cables, see Table 4.17, item 25
• It is worth noting that, as a result of the functional analysis exercise (see
Annex 4.5.3), a number of tests that are not included in IEC 60840 Ed.3 have
been identified. These tests are generally performed as development tests and are
summarized in Annex 4.5.4 for future consideration by IEC.
4.4
Conclusions
In this chapter the testing procedures of HV and EHV extruded cables and related
accessories have been reconsidered extensively. Improvements in both effectiveness
(can it be done better) and efficiency (can it be done faster) have been proposed. In
the final proposals the desirable improvement and its practical feasibility are balanced carefully, resulting in a series of well thought practical propositions to
improve extruded cable testing. The main results are summarized below:
• EHV Cable systems: there is no sufficient service experience on EHV cable
systems collected so far to change the existing initial Prequalification test. This
PQ test has to be repeated in case of extension of the range of approval.
Within the range of approval, a new test called Extension of Qualification
(EQ) test is proposed to control changes in already prequalified cable systems
instead of repeating the complete PQ test. This new test can be carried out on a
laboratory loop and will comprise 80 heating cycles combined with voltage
application at 2 U0 of the electrical type test.
• HV Cable systems: a prequalification test is recommended for design stresses
above 8 kV/mm on the conductor or 4 kV/mm over insulation. This test can be
carried out on a laboratory loop and will comprise 180 heating cycles combined
with voltage application at 1.7 U0. This PQ test has to be repeated in case of
extension of the range of approval. Within the range of approval, a new test called
Extension of Qualification (EQ) test is proposed to control changes in already
prequalified HV cable systems. This new test can be carried out on a laboratory
loop and will comprise 60 heating cycles without voltage and followed by the full
134
•
•
•
•
•
J. Becker
sequence of the electrical type tests, with 20 heat cycles combined with voltage
application at 2 U0.
For both EHV and HV cable systems the PQ test will be completed with an
impulse test on the full loop to check that no degradation in the system, especially
at the interface with accessories, has occurred. (Only in case suitable impulse test
equipment is not available at the test site, the impulse test can be carried out in any
other test arrangement including each type of accessory taken from the loop).
For both PQ and EQ tests, PD tests are recommended to provide an early warning
of possible degradation and to enable the possibility of a repair before failure.
Several tables are provided as guides to determine the appropriate test sequence in
case of changes or modifications.
Functional Analysis is a good tool to help engineers to manage a wide range of
potential changes. Examples are given in Annex 4.5.3.
In Annex 4.5.4 tests from Functional Analysis, not yet published in IEC standards, are summarized. This list of tests will be handed to IEC TC 20 for further
consideration.
4.5
Annexes
4.5.1
Terms of Reference
4.5.1.1 Title
Revision of Qualification Procedures for High Voltage and Extra High Voltage AC
Extruded Underground Cable Systems.
4.5.1.2 Scope
After the official qualification of a cable system, there are possible changes (new cable
construction, higher stress, new extrusion line, new process, new type of accessories. . .)
especially if this cable system is manufactured over several years, and the question
raised is to examine how it is possible to qualify this new system without making the full
set of tests which are presently recommended or specified in standards.
A WG has been launched on this item limited to AC extruded cable systems. All
tests, prequalification and type tests will be reviewed, even if the prequalification test
should be examined first, as it is the most costly and the longest.
4.5.1.3 Terms of reference
For the range of AC extruded underground cable systems for voltages above 30 kV
up to 500 kV, review and complete the qualification procedures for the different HV
voltage ranges with the goal to come quickly and economically to the market with
innovative solutions but without jeopardizing the reliability of the installed system:
• Propose tests where there are lacks e.g. short circuit tests, climatic tests on
terminations. . .
• Evaluate whether in high voltage systems up to 150 kV a long term test has to be
recommended above given dielectric service stresses or where the innovation is
not built on earlier experience
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Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
135
• Define what “earlier experience” means
• In case of major innovation in EHV cable systems, evaluate whether long term
test can be replaced by shorter ones, which should be defined by the WG.
In order to build up a guide of qualification procedures depending on earlier
qualification(s) at the same and/or different voltage levels and on field experience.
4.5.2
Sensitivity of Partial Discharges in XLPE Cable Insulation
to Change of Electrical Stress
Contents
1. Introduction
2. Cable standards and electric stress
3. Sensitivity of electric stress to change of cable dimensions
4. Determination of risk of discharge caused by change of dimensions
5. Effect of change of cable dimensions on discharge free operation
6. Conclusions
4.5.2.1 Introduction
In Cigré WG B1.06, a question was raised whether the range of type approval and of
PQ approval could be widened. This Annex provides details of the analysis made for
this purpose. Dielectric stress level variations specified in relevant sub-clauses of the
current IEC standards were used as a starting point in this work.
As a first step of the process, we can determine the rate of change of electric field
strength inside a radial cable with respect to:
• The change of the insulation inner radius, without changing the insulation thickness
• The change of the insulation thickness, without a change of the inner radius.
The obtained relationships are the so-called sensitivities of field strength to a
dimensional change. They can indicate, for example, what effect a 1% change of the
insulation thickness has on the field strength at the insulation outer surface.
In the next step, the sensitivity values together with Paschen’s curve can be
used to calculate the change of the discharge inception voltage in insulation
defects. The Paschen curve describes the relationship between breakdown voltage and size of defect together with gas pressure within the defect. In this study
we are concerned with discharge free operation of the cable. Therefore, it is more
useful that instead of the discharge inception voltage the maximum defect size is
determined from the above relationship at a given voltage across the defect and at
a given pressure.
Two types of defects are considered in this study: a spherical void located on the
conductor screen interface and a fissure located on the outer insulation surface. The
former can be seen as a worst-case scenario of a manufacturing fault while the latter
can represent a defect at the interface to accessories.
The model calculations presented in this study are first order estimations of the
risk of electrical discharge in voids from a change in electric stress at insulation
136
J. Becker
interfaces caused by dimensional changes of insulation. In the practical situation,
stresses at the interfaces may be different because of the actual geometry. However
the model calculations describe the worst-case situation.
4.5.2.2 Cable Standards and Insulation Stress
Sub-clauses 12.3.1 of IEC 60840 Ed. 3 and 12.4.1 of IEC 62067 Ed. 1 state that the
test voltage values have to be adjusted if insulation thickness of the tested cable
system exceeds 105% of the nominal insulation thickness with the upper limit at
which the adjustment is allowed of 115%.
The range of type approval sub-clause 12.1 of IEC 60840 and sub-clause 12.2 of
IEC 62067 state that the approval is valid for systems in which:
• Calculated nominal conductor stress at the conductor screen does not exceed
110% of the tested system
• Calculated nominal insulation stress at the insulation screen does not exceed the
insulation screen stress of the tested system.
In this context, we are considering whether it is possible to widen the range of
approval without jeopardizing performance of the cable system.
4.5.2.3 Sensitivity of Insulation Stress to Change of Cable Dimensions
Electric field strength at a radial location x in a concentric cable is expressed as
Ex ¼
U0 1
x ln Rr
ð4:1Þ
where
r is the inner radius of the insulation,
R is the outer radius of the insulation
w is the insulation thickness
We are interested in the field strength at two locations within insulation, namely,
on the inner surface and on the outer surface. Using R ¼ r + w, we get
U0 1
r ln rþw
r
ð4:2Þ
U0
1
r þ w ln rþw
r
ð4:3Þ
Er ¼
ER ¼
which is also shown in Fig. 4.8.
Electrical stress sensitivity is defined as the rate of change of field strength with
respect to a given dimension. In this work, we consider the rate of change of field
with respect to insulation inner radius, r, and with respect to insulation thickness, w.
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
137
Fig. 4.8 Electric field strength in a concentric cable
4.5.2.3.1 Sensitivity to Change of Inner Radius
Sensitivity to change of inner radius only is obtained by differentiating Equations
(4.2) and (4.3) with respect to r, which gives
dEr
U
w
kV
1
¼ 2 0rþw
mm
dr
r ln r ðr þ wÞ ln rþw
r
dEr
U0
w
kV
¼
1
rþw
mm
dr
ðr þ wÞ2 ln rþw r ln r
r
1
mm
ð4:4Þ
1
mm
ð4:5Þ
if U0 is in kV and all dimensions are in mm.
4.5.2.3.2 Sensitivity to Change of Insulation Width
Differentiating (4.2) and (4.3) with respect to w gives the following expressions of
sensitivity to change of insulation width only
dE r
U0
kV 1
¼
dw r ðr þ wÞ ln rþw2 mm mm
r
rþw
U 0 ln r þ 1 kV 1
dER
¼
2
dw
ðr þ wÞ ln rþw mm mm
ð4:6Þ
ð4:7Þ
r
4.5.2.3.3 Sensitivity Per Unit
The absolute value of sensitivity, as described by Eqs. (4.4), (4.5), (4.6), and (4.7), is
useful only for a specific cable if its operating voltage and relevant dimensions are
known. To make sensitivity expressions more general, we can represent them in per
unit terms. The per unit base for the field change dEr and dER will be the respective
nominal field intensities Er and ER. The per unit base for the dimension change dr
and dw will be the respective dimensions r and w. These lead to the following results.
138
J. Becker
dE r
dr
dE R
dr
PU
dE r =Er dEr r
w
1
¼
¼
rþw 1
E
r
þ
w
dr
dr=r
log
r
PU
r
dE =E
dE r
r
w
1
¼ R R¼ R
¼
1
dr ER r þ w r log rþw
dr=r
r
¼
dE r =Er dE r w
w
1
¼
¼
rþw
E
r
þ
w
dr
dw=w
log
r
PU
r
dE R =ER dER w
w
1
¼
¼
þ1
¼
r þ w log rþw
dr ER
dw=w
r
dEr
dw
dE R
dw
PU
¼
ð4:8Þ
ð4:9Þ
ð4:10Þ
ð4:11Þ
The obtained expressions can now be used to estimate sensitivity values for a
range of cable designs. The operating voltage will be reflected in the value of the
insulation width, w, while the conductor size will be reflected in the value of the
inner radius r.
4.5.2.3.4 Numerical Example
To provide a more specific numerical example of sensitivity calculations we consider
two cables whose dimensions are tabulated in Table 4.10. These data were applied to
sensitivity Eqs. (4.8), (4.9), (4.10), and (4.11) and the obtained results are shown in
Table 4.11.
Table 4.11 results show that a decrease of insulation thickness by 1% leads to an
increase of the field strength at the insulation screen by approximately 1.2% in both
types of cables. At the same time, an increase of the inner radius by 1% leads to an
increase of field intensity at the insulation screen by approximately 0.2%.
Similar calculation results are shown graphically in Fig. 4.9a, b for a range of
values of r and w. The obtained plots show that variations of the field strength
Table 4.10 Dimensions of
two example cables
Rated voltage Uo/U (kV)
Conductor cross-section
Conductor radius
Insulation inner radius (r)
Insulation thickness (w)
Insulation outer radius (R)
127/220 kV
2000mm2
28.95 mm
30.95 mm
20.80 mm
51.75 mm
220/380 kV
1600mm2
24.4 mm
27.0 mm
26.6 mm
53.6 mm
Table 4.11 Sensitivity to dimensional change in two example cables
Change of r only
Change of w only
Change of r only
Change of w only
Rated voltage
127/220 kV
127/220 kV
220/380 kV
220/380 kV
dEr/Er
0.22 dr/r
0.78 dw/w
0.28 dr/r
0.72 dw/w
dER/ER
+ 0.18 dr/r
1.18 dw/w
+ 0.22 dr/r
1.22 dw/w
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
a
Field sensitivity to change of insulation inner radius
0.4
dEr/dw 220 kV
dER/dw 220 kV
dEr/dw 380 kV
dER/dw 380 kV
0.3
0.2
Field sensitivity (PU)
139
0.1
0
-0.1
-0.2
-0.3
-0.4
20
22
24
26
28
30
32
34
36
38
40
Inner radius (mm)
Field sensitivity to change of insulation width
b
0
dEr/dw 220 kV
dER/dw 220 kV
dEr/dw 380 kV
dER/dw 380 kV
Field sensitivity (PU)
-0.2
-0.4
-0.6
-0,8
-1
-1.2
15
20
25
30
35
Insulation width (mm)
Fig. 4.9 Field strength sensitivity to change of dimension for a range of values of the insulation
inner radius and width
sensitivity to dimensional change are relatively small within a large range of
dimension values. The sensitivity values are also very similar for the two types of
cables considered. This is an important observation, which allows the definition of
sensitivity to be generalized for the entire range of practical cable designs.
140
J. Becker
Now, we will consider how these changes of electric field strength affect the risk
of discharge in the interface regions in the presence of voids.
4.5.2.4 Determination of Risk of Discharge Caused by Change
of Dimensions
4.5.2.4.1 Size of Discharge-free Defects
We consider two types of defects in which discharges can occur
• Spherical void located on the conductor screen interface
• Fissure located on the insulation screen interface.
Spherical defects near the conductor screen usually originate from manufacturing
faults and they can be detected by factory quality control tests. Fissure defects at the
interface with accessories pose a greater risk because they can be introduced during
installation and they are not as easily detected.
Both types of defects are found in most practical cable systems in operation. At a
given field strength a discharge free operation is possible if size of defects is
sufficiently small. A discharge free operation may be still possible even under
increased field strength if the defect size is further reduced. The maximum size of
discharge free defects at operating voltage Uo can be estimated from sensitivity of
defect size to a relative increase of the field strength in the insulation, dEins/Eins, at
the defect location. This is done with the help of Paschen curve shown in Fig. 4.10.
In the context of this analysis, the Paschen curve can represent relationship
between breakdown voltage, Ubd, within a defect of given size at given gas pressure
inside the defect (Bar-mm). Instead of breakdown voltage, the breakdown field
strength can be obtained from the curve, as shown in Fig. 4.11.
Ubreakdown [kV]
1000
100
10
1
0.0
0.001
0.01
0.1
1
Bar mm
Fig. 4.10 Paschen’s curve for air at 20 C
10
100
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
141
Ubd (kV)
Ebd (kV/mm)
40
35
30
25
Ubd (kV) from Paschen
20
Ebd (kV/Barmm)
and (kV/mm, 1B)
15
10
5
0
0.01
0.0
1
Defect dimension (Barmm)
Fig. 4.11 Breakdown voltage and breakdown field strength as a function of defect dimension in
mm from Paschen curve at p ¼ 1 Bar
U
U
εi
εe
Ei
E0=U/d
d
E0=U/d
εe
E
d
Ee
εi
Ei=E013εe/(εi+2εe)
Ei=E0(εe/εi)
Ei=2.26E0
(a)
Ei=1.23E0
(b)
Fig. 4.12 Electric field calculations inside a fissure (a) and spherical defect (b)
The field intensity within the defect can be determined from the field strength in
the insulation at the defect location considering also permittivity difference between
the defect (gas, ε ¼ 1) and surrounding insulation (XLPE, ε ¼ 2.26). In a radial field,
such as in the case of fissure at the interface to an accessory, a simple ratio of
dielectric permittivity of insulation material and of gas inside the defect gives the
field increase factor inside the fissure. This is illustrated in Fig. 4.12a. For a gas filled
sphere the field increase factor is equal to 1.23, as shown in Fig. 4.12b.
Taking into account the field increase factors from Fig. 4.12 and the breakdown
field strength of the defect from Fig. 4.11 we can obtain the relationship between
the size of a breakdown free defect and the field strength in the surrounding
dielectric. It is quite clear that nearly twice stronger field is needed to initiate
142
J. Becker
Fig. 4.13 Maximum field
intensity in the surrounding
dielectric at p ¼ 1 Bar, with no
partial breakdown in the
defect
30.
25.
Ei(kV/mm)
20.
15.
sphere
10.
5.
0.
0.0
0.
1
-mm 1B
discharges in a spherical void in comparison with fissure. The related curves are
depicted in Fig. 4.13.
Using Eqs. (4.2) and (4.3) we can calculate partial discharge inception voltage
from field intensity for a defect located on the conductor screen interface and the
insulation screen interface respectively. Typically, we consider a fissure on the
insulation screen and a spherical void at the conductor screen interface.
1
R
U sphere
¼ pffiffiffi Er r ln
i
r
2
kVrms
ð4:12Þ
1
R
¼ pffiffiffi ER R ln
U fissure
i
r
2
kVrms
ð4:13Þ
A range of values of inception voltage as a function of defect size can be obtained
for the two cables listed in Table 4.10 by substituting to Eqs. (4.12) and (4.13)
appropriate field intensity values from Fig. 4.12 together with respective cable
dimensions. The obtained results together with the cable nominal voltage are
shown in Figs. 4.14 and 4.15.
The comparison of the discharge inception voltage Ui with the nominal voltage
U0 on these plots gives the maximum size of a discharge free defect of approximately 30 μm (at p ¼ 1 Bar) in the 127/220 kV cable and approximately 20 μm
(at p ¼ 1 Bar) in the 220/380 kV cable.
4.5.2.4.2
Size Sensitivity of Discharge Free Defects to Change of Field
Strength
The Paschen curve in the form of field strength vs. defect size, Fig. 4.11, shows that
the higher the field intensity the smaller defect size must be for a discharge free
operation of the cable. We are interested in determining the relative rate of change of
the defect size with respect to the relative change of field intensity in the dielectric at
a given location.
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
Inception voltage (kV-rms) for a 127/220 (245) kV
XLPE cable, 2000 mm2, at conductor screen,
sphere
350.00
300.00
250.00
200.00
150.00
100.00
50.00
0.00
0.01
0.1
1
143
Inception voltage (kV-rms) for a 127/220 (245) kV
XLPE cable, 2000 mm2, at insulation screen
350.00
Inception voltage (kg-rms)
Inception voltage (kg-rms)
4
300.00
250.00
200.00
150.00
100.00
50.00
0.00
0.01
10
0.1
1
10
Bar.mm
Bar.mm
Ui (kV-rms) spleet
U0 (kV-rms)
Ui (kV-rms) bol
U0 (kV-rms)
Fig. 4.14 Partial discharge inception voltage, as a function of the size at p ¼ 1 Bar, in a spherical
void at the conductor screen interface and in a fissure at the insulation screen interface in a
127/220 kV, 2000 mm2 cable
400.00
350.00
300.00
250.00
200.00
150.00
100.00
50.00
0.00
0.01
Inception voltage (kV-rms) for a 220/380 (420) kV
XLPE cable, 1600 mm2, at insulation screen,
Inception voltage (kg-rms)
Inception voltage (kg-rms)
Inception voltage (kV-rms) for a 220/380 (420) kV
XLPE cable, 1600 mm2, at conductor screen,
sphere
0.1
1
10
450.00
400.00
350.00
300.00
250.00
200.00
150.00
100.00
50.00
0.00
0.01
Bar.mm
0.1
1
10
Bar.mm
Ui (kV-rms) bol
U0 (kV-rms)
Ui (kV-rms) spleet
U0 (kV-rms)
Fig. 4.15 Partial discharge inception voltage, as a function of the size at p ¼ 1 Bar, in a spherical
void at the conductor screen interface and in a fissure at the insulation screen interface in a
220/380 kV, 1600 mm2 cable
dðBar mmÞ
dEi
¼f
Bar mm
Ei
ð4:14Þ
These parts of the Paschen curve where Barmm > 0.01 (> 0.01 mm at p ¼ 1 Bar)
can be modelled in sections as an exponential function of the following form
Ebd ¼ bðBar mmÞa
ð4:15Þ
144
J. Becker
Differentiating both sides of (15) with respect to Barmm gives
dE bd =dðBar mmÞ ¼ baðBar mmÞa1 ¼ a Ebd =ðBar mmÞ
ð4:16Þ
At the same time
Ebd ¼ εi Ei
ð4:17Þ
dE bd ¼ εi dEi
Substituting (4.17) to (4.16) and rearranging gives the desired form of sensitivity
dðBar mmÞ 1 dE i
¼
Bar mm
a Ei
ð4:18Þ
in which a is the exponent coefficient of the exponential function modelling the
Paschen curve.
Equation (4.18) allows us to obtain sensitivity values from estimating the value of
exponent a from the Paschen curve. Taking the logarithm of both sides of (4.15)
gives
log Ebd ¼ a log ðBar mmÞ þ log ðbÞ
ð4:19Þ
Now, the values of a and b can be found from the curve Ebd ¼ f(Barmm) in
Fig. 4.11. The obtained results are shown in Tables 4.12 and 4.13.
Values of 1/a shown in Table 4.13 indicate that within the pd. area of 0.03–
0.1 mm at p ¼ 1 Bar a 1% increase of the electric field strength will require a 2%
reduction of the defect size for a discharge free operation of the cable. Within the
pd. area of 0.1–0.3 mm at p ¼ 1 Bar the corresponding reduction of the defect size is
Table 4.12 Data points from Paschen’s curve in Fig. 4.10
Barmm
0.01
0.03
0.1
0.3
1
3
log (Bar-mm)
2
1.5228
1
0.5229
0
0.477
Table 4.13 Estimated
parameters
Barmm
0.01–0.03
0.03–0.1
0.1–0.3
0.3–1
1–3
Ubd (kV)
0.35
0.55
1.00
2.10
5.00
11.0
a
0.59
0.50
0.26
0.30
0.28
Ebd (kV/mm)
35
18.3
10
6.67
5
3.67
Log (b)
0.34
0.50
0.74
0.70
0.70
log Ebd
1.544
1.262
1.000
0.824
0.699
0.565
1/a
1.7
2.0
3.8
3.3
3.5
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
145
3.8%. For the range of 0.1–3 mm, the reduction of the defect size is stated to be 3.5%
in case of a 1% increase of the electric field strength.
4.5.2.5 Effect of Change of Cable Dimensions on Discharge Free
Operation
A change of insulation dimensions will result with a change of electric field intensity.
This was considered in Sect. 4.5.2.3 and defined as field strength sensitivity to
change of inner radius and to change of width of insulation. We will combine
these findings with results of Sect. 4.5.2.4 to determine conditions of discharge
free operation if dimensions of cable insulation change. There are two main cases
that need to be considered
• Decreased insulation thickness (“slim” design)
• Increased conductor size.
At the same time, we concentrate on the case of possible discharges occurring in a
fissure located at the insulation screen interface as more important from the practical
point of view.
4.5.2.5.1 Cable Systems with “Slim” Design
By recalling results from Table 4.11 in Sect. 4.5.2.3 we know that a 1% reduction of
insulation width will result with a 1.2% increase of the field strength at the insulation
screen interface. At the same time, the defect size sensitivity to change of field for a
discharge free operation is stated to 3.5, see Table 4.13. Therefore, the combined
effect will be 1.2% 3.5 ¼ 4.2% of reduction of permissible size of defects for a
discharge free operation. From this, it is straightforward to see that a 5% decrease of
insulation width leads to a necessary reduction of the size of contributing defects by
21%.
4.5.2.5.2 Cable Systems with Increased Conductor Size
Results presented in Table 4.11 show that a 1% increase of the conductor radius
contributes to a 0.2% increase of the field strength on the insulation screen interface.
This gives the total effect of 0.2% 3.5 ¼ 0.7% decrease of permissible size of
contributing defects. An increase of the conductor cross-section from 1600 mm2 to
2000 mm2 results with an approximate increase of the insulation inner radius by
12%. This corresponds to a necessary decrease of permissible size of contributing
defects by approximately 8.4%.
4.5.2.6 Conclusions
The effect of change of insulation dimensions on the size of discharge free defects in
high voltage cables was analyzed in this Annex. The following results were obtained
for the two types of design considered.
146
J. Becker
4.5.2.6.1 “Slim” Design
For each 1% reduction of the insulation width the reduction of fissure radial
dimension by approximately 4.2% is necessary for a discharge free operation.
Considering reduction of insulation width of 5%, as specified in the current range
of type approval, will require a reduction of the fissure size by 21%.
4.5.2.6.2 Increased Conductor Size
An increase of the conductor cross-section size from 1600 mm2 to 2000 mm2
without changing the insulation width will result with a necessary decrease of
permissible size of contributing defects located on the insulation screen interface
by approximately 8.4%.
4.5.2.6.3 Conclusion
The above results show that widening the current range of type approval described
by IEC 60840 and IEC 62067 will lead to an unacceptable increase of risk of partial
discharge in operating cable systems. Therefore, it can be concluded from this study
that the range of type approval in relevant IEC standards ought not to be changed.
4.5.3
Functional Analysis
Use of Functional Analysis in case of Changes in Cable and Accessory Components
of HV and EHV Systems.
4.5.3.1 Introduction
International Standards provide plant manufacturers with a consistent set of tests that
allows them to demonstrate that their equipment meets certain minimum criteria. For
the purchaser, testing to International Standards provides a degree of assurance that
the plant or equipment can be operated safely and reliably. Although testing to
International Standards is often time consuming and expensive, once a manufacturer
and purchaser have agreed that the test requirements have been met, the product is
“approved” and further purchases of the same product are relatively simple. One
advantage of testing to International Standards is that many purchasers worldwide
will accept the test evidence, without the tests having to be repeated.
A significant disadvantage of International Standards is that once a product is
“approved” there is little incentive to the manufacturer to make incremental
improvements to the product, since these would invalidate the “approval” and
require the type approval tests to be repeated.
This Annex sets out a process whereby the significance of any change can be
evaluated and the need for further testing agreed.
4.5.3.2 Functional Analysis Method
In principle, it should be possible to classify any change to a cable as a change that
might change the performance characteristics (“major” change), requiring a repeat of
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
147
type testing, or as a “substantial change” requiring a repeat of prequalification
testing, or a “minor” change requiring little or no repeating of testing.
The tests in international cable standards have evolved either to simulate the
service conditions experienced by the cable (system) (often in an accelerated manner) or to test for the presence of specific defects and deficiencies. The tests have
evolved to ensure that a cable (system) is able to survive the various functions that it
has to perform during its lifetime and their resulting stresses (electrical, mechanical
and chemical). For example, a cable has to be bent during production, transportation
and installation, so the IEC Standards include a bending test. The Working Group
has extended this principle to examine how a change to the cable design or
manufacture might affect its performance and hence what further testing might be
required.
The methodology adopted by the WG was first to perform a functional analysis to
consider the functions performed by each part of a cable’s and accessories construction and how each function is tested presently in IEC 60840 Ed.3 and IEC 62067
Ed.1.
The WG then considered a number of possible changes a manufacturer might
make to the cable system. The functional analysis was then used to determine what
further testing might be required.
The result of this exercise is summarized in Table 4.14 as far as the constituents of
the cable itself are concerned and in Tables 4.15 and 4.16 for the components of
joints and terminations respectively. It must be mentioned that this analysis is based
on the present knowledge and could be updated and used as guidance for future
work.
For each constituent part, the table identifies;
• The functions performed by that component
• The feature which identifies if the function is being fulfilled or the threat posed if
it is not
• Comments that give further details of the threat or alternative test procedures. The
tests in IEC 60840 Ed.3 or IEC 62067 Ed.1 which check that the function is being
performed satisfactorily
• Some tests described in the Functional Analysis are missing in IEC60840 Ed.3
and 62067 Ed.1 (e.g. short-circuit, side-wall pressure, etc.). The full list of
missing tests is given in Annex 4.5.4.
The main changes to cables and accessories in a prequalified cable system, which
require the repetition of the type test (or part of it) or of the prequalification tests or of
the extension of qualification, are summarized in Tables 4.4 and 4.5 in part 4.2 of this
chapter.
The cable supplier and purchaser may use the functional analysis to discuss if any
change to a constituent part might lead to a change in the performance characteristics
or reliability of the cable system. This is particularly useful where the change is
outside the scope of Tables 4.4 and 4.5 of part 4.2.
Cable’s
component
A
Conductor
-a. Prevent longitudinal water
penetration
-a. No corrosion when using Al
conductor
3
Water blocking
4
Chemical
properties
-b. No degradation due to layers over
conductor (tape or semi-con)
-a. Bending before type tests (S:
§12.3.3/§12.4.4)
-a. Satisfy the minimum bending radius
without harmful mechanical
deformation
-b. Support pulling during installation
2
Mechanical
properties
-a. Water penetration test (T:
§12.4.18/§12.5.14)
-a. Examination
after type test (IEC60840/ IEC
62067) or long
term PQ test (IEC 62067)
- b. Compatibility
test (T: §12.4.4/§124)
-b. No test
-b. Calculation of thermal short
circuit temperaturre
Specification/Threat
C
-a. No overheating with nominal current
-b. Limit temperature with thermal short
circuit current
Function or
Property
B
1
Electrical
conductivity
Test to check the functionality
(Relevant paragraphs of IEC 60840
Ed.3/62067 Ed. 1 in brackets –IEC
62067 Ed. 1 in Italics)
D
-a. Resistance measurement
(S: §10.5/§ 10.5)
b. Limitation of pulling force to be
given by the manufacturer
a. Test if water blocking properties
required
a. If Al conductor avoid: water ingress
+chemical species (e.g. contaminations,
solvents)
Comments
E
a. Measurement to check design
Verification of AC resistance of large
conductors with insulated wires or other
special properties: See WG B1-03 –
Large cross-sections and composite
screen designs: For large cross-sections,
AC resistance test should be performed
as type test (see TB TB 272 of Cigré
WG B1-03 from 2005)
b. If temperature rise is considered
dangerous, a short circuit test is
proposed as a development test. Check
that there is no degradation of tapes and
extruded semi-con after short circuit
test
Table 4.14 Functional Analysis of a High Voltage Cable and cable components (Abbreviations: Routine: R, Sample test: S, Type test: T, Development: D,
Prequalification: PQ)
148
J. Becker
Tape over
conductor
(optional)
-a. Resistance sufficiently low to avoid
PD and to avoid voltage over semicon
during fast transients
-a. Good mechanical properties
-a. No degradation of conductor or
semi-con
-b. Stability of electrical resistivity after
heat cycles
-a. Avoid penetration of semi-con into
conductor
2
Mechanical
properties
3
Chemical
properties
4
Interface with
other components
-a. Low interface resistivity with
connectors
-b. Thermal-mechanical expansion/
deformation (Influence of shape of
wires on interface of extruded semi-con
with insulation)
-c. Avoid water penetration
1
Electrical
resistance
5
Interface with
other components
or accessories
b. PQ not in IEC 60840 Ed.3
-b. Thermal cycles: 20 (T:
§12.3.6/§12.4.7) or 180 (PQ: §13.2.3
on cable system)
-c. Water penetration test (T:
§12.4.18/§12.5)
(continued)
c. Water penetration may lead to
chemical degradation of the insulation
mainly if the conductor metal is
aluminum
-a. PD measurement (R,T; §9.2/§9.2- a. Covered by type tests
§12.3.4/§12.4.5)
+Lightning impulse test (T; 12.3.7/
§12.4.9) + examination (T: §12.3.8/
§12.4.10)
-a. Bending test (T: §12.3.3/§12.4.4)
Examination after completion of the
type test
(T: §12.3.8/§12.4.10)
-a. Compatibility test on whole cable
(T:§12.4.4/§12.5.4)
-b. Resistance measurement after
b. Can be confirmed by test §12.3.9/
heat cycles
§12.4.11 on semicon indirectly and its
data should be shown by manufacturer
if required
-a. Visual examination after
manufacturing in hot oil + impulse
test (S; 12.3.7/§12.4.9)
a. Taken into account in accessories part
-a. See accessories
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
149
Cable’s
component
A
Inner extruded
semiconducting
screen
-a. Resistivity measurement before
and after ageing
(T: §12.3.9/§12.4.11)
-b. Resistivity measurement before
and after ageing
(T: §12.3.9/§12.4.11)
-a. Stability of electrical properties with
ageing
3
Chemical
properties
-b. Stability of electrical resistivity after
heat cycles
-a. Bending + 20 thermal cycles (T:
§12.3/§12.4)
-b. Bending (T: §12.3.3/§12.4.4) + 20
thermal cycles (T§12.3.6/§12.4.7)
-c. Heat cycles (T§12.3.6/§ 12.4.7) and
shrinkage test (T §12.4.13)
-a. Resistance to mechanical bending
during manufacturing and installation
-b. Stability of form with thermal
constrains
-c. Shrinkage of semicon
Specification/Threat
C
-a. Smoothening of electrical field at the
insulation interface (avoid protrusions,
voids, contaminants).
-b. Avoid PD at inner surface of
insulation
-c. Resistivity sufficiently low, to avoid
PD, in the whole range of service
temperatures and to avoid voltage over
semicon during fast transients
Test to check the functionality
(Relevant paragraphs of IEC 60840
Ed.3/62067 Ed. 1 in brackets –IEC
62067 Ed. 1 in Italics)
D
-a. AC (R, T, PQ §9.3/§9.3, §12.3.6/
§12.4.7, §13.2.3 and impulse test (T,
PQ: §12.3.7/§12.4.9, §13.2.4
-b. PD tests (R, T: §9.2/§9.2§12.3.4/§12.4.5)
-c. Resistivity measurement
(T: §12.3.9/§12.4)
2
Thermalmechanical
properties
Function or
Property
B
1
Electrical
properties
Table 4.14 (continued)
b. 20 cycles are considered sufficient by
the WG to evaluate this functionality
c. For type tests, the shrinkage test acts
as a check on the properties of the
material. For the long term test, the
shrinkage test is not necessary when
these long term tests are performed
successfully on the cable system
Comments
E
a. Some standards and customer’s
specifications prescribe to check on a
sample that there are no protrusions,
voids or contaminants larger than their
permissible level. It is a good tool to
check the quality of interfacesprotrusions and contamination.
However electrical routine tests are
considered necessary to have a view of
the quality on the full length of the cable
and are still mandatory.
150
J. Becker
4
Interface with
conductor and
insulation
-c. Compatibility test on whole cable
(T:§12.4.4/§12.5.4)
+Resistivity measurement of semicon
before and after compatibility test (T:
§12.3.9/§12.4.11)
-a. Compatibility
test on whole cable (T:§12.4.4/
§12.5.4)
-b. Type test (T: §12.3/§12.4) or long
term test (PQ: §13.2)
-c. Bending + heat cycling (min
80 cycles -D) + PD: ((T: §12.3/§12.4
-d. Examination of surface in hot oil
-c. Compatibility with layers or
conductor below and with insulation
-a. Compatibility with conductor or
layers below and with insulation
(See above and underneath)
-b. No degradation of insulation by
migration of low molecular species
-c. Good bonding of extruded semiconducting screen with insulation
-d. No deformation of semicon surface
due to penetration of semicon between
the conductor’s wires
(continued)
b. No PQ long term test in IEC 60840
Ed.3
c. Good bonding of extruded
semiconducting screen with insulation
is generally not a problem but should be
checked at least once with a new
material.
Tests could be performed on model
cables. 20 cycles are not considered
enough to check whether the bonding
with insulation remains correct. When
180 PQ cycles are performed, this
property is indirectly checked
d. Quality control
c. PIXE (Particle induced X-ray
Emission) measurements have shown
that there is no ionic migration from the
semi-con into the insulation during heat
cycling tests or in service. However,
there is some diffusion of the
antioxidant and low molecular weight
species during the curing process and
afterwards Some customers ask to
check the moisture content in the
semicon (<1000 ppm content)
Influence on the dielectric behavior of
the insulation system?
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
151
Cable’s
component
A
Insulation
Function or
Property
B
1
Dielectric
properties
Table 4.14 (continued)
-b. No harmful voids in the bulk or in
the interface with semiconducting
screens
-c. Stability of dielectric properties with
thermal and electrical ageing
Specification/Threat
C
-a. Withstand to AC stresses and
lightning/switching impulses
-c. Thermal cycles: 20 (T: §12.3.6/
§12.4.7) or 180 (PQ: §13.2.3)
-b. PD routine test (§9.2/§9.2)
Test to check the functionality
(Relevant paragraphs of IEC 60840
Ed.3/62067 Ed. 1 in brackets –IEC
62067 Ed. 1 in Italics)
D
-a. AC: routine test on each length
and type test and regular impulse
tests: on samples and with type test
AC (R, T, PQ) §9.3/§9.3, §12.3.6/
§12.4.7, §13.2.3 and
Lightning (S, T, PQ) §12.3.7/§12.4.9,
§13.2.4 Switching (T, PQ) §12.4.8 on
EHV system
c. PQ not in IEC 60840 Ed.3. Thermal
cycles check mainly the possible
deformation of the insulation. No
thermal or electrical ageing was ever
demonstrated under normal service
conditions. Some physical-chemical
parameters presented changes after
pre-qualification tests but they were not
Comments
E
a. Following a study made in Japan,
switching impulse breakdown values
on cables are higher than for lightning
impulse.
For EHV cable systems switching
impulse is still relevant
Some customers prescribe to check on a
sample that there are no protrusions,
voids or contaminants larger than their
permissible level. WG has considered
that protrusions and contamination
examination on a small sample is less
relevant than an electrical routine test
on the whole length of cable (Same as
before. See page 2)
b. No PD shall be allowed, as they may
be harmful. Good sensitivity
152
J. Becker
3
Chemical
properties
2
Thermalmechanical
properties
-a. Compatibility with inner and outer
semi-con
-c. Stability of form under the pressure
of accessories and under the pressure of
the thermal- mechanical expansion of
the conductor
-a. Compatibility test- (T: ageing test
on complete cable §12.4.4/§12.5.4)
-a. Bending test followed by PD and
dielectric tests + examination after
tests (T: §12.3/§12.4)
-b. Hot set test (S: §10.9/§10.9, T:
§12.4.10/§12.5.10)
Ageing and mechanical test on
material (T:§12.4.2/§12.5.2)
-c. Heating cycles with bending in test
set up (T: §12.3.6/§12.4.7)
Long term test with cable system
installed in conditions near reality
(PQ: 180 cycles §13.2.3)
-a. Resistance to mechanical bending
during manufacturing and installation
-b. Stability of mechanical and
dielectric properties with temperature
and thermal ageing
-d. Capacitance (S: §10.10/§10.10)
-e. Tanδ measurement (T: §12.3.5/
§12.)
-d. Low dielectric constant
-e. Low dielectric losses,
(continued)
c. In IEC 60840 Ed.3 no long-term PQ
test is performed on cable systems. (This
problem is considered in Sect. 4.3) The
experience in the field shows whether the
behavior of the cable system is correct. It
would be wise to make a long term cycles
test also on new cable systems below
220 kV at a relatively high value of
electrical stress except if a similar system
has been tested for higher voltage
e. Preliminary test can be performed on
insulating material before extruding it
on cable
correlated to any degradation of the
dielectric properties of the insulation.
Microscopic defects may, however, lead
to local degradation. This possible
degradation can be expressed by a
power law
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
153
Outer extruded
semiconducting
screen
Cable’s
component
A
1
Electrical
properties
2
Thermalmechanical
properties
4
Interface with
inner and outer
semicon and
accessories
Function or
Property
B
Table 4.14 (continued)
See inner semicon
Same as inner semicon
-d. Smoothness of surfaces and purity
of insulation
Same as inner semicon
-c. Shrinkage of insulation
-a. Compatibility test. Ageing test on
complete cable (T:§12.4.4/§12.5.4)
-b. 20 cycles (T: §12.3.6/§12.4.7) or
b. In IEC 60840 Ed.3 no long-term test
180 cycles (PQ:§13.2.3)
PQ is performed on cable systems.
Long term tests would be useful as a
development test D for new designs on
cables or accessories under specific
conditions. (This problem is considered
in Sect. 4.3)
-c. Shrinkage test (T: §12.4.13/—) or c. No need for a shrinkage test if longlong term cycling test in presence of term tests with cycles are performed.
accessories D or (PQ: §13.2.3)
For type tests it acts as a test on the
material properties
-d. Test in hot oil as a production test
useful
See inner semicon
Comments
E
b. In IEC 60840 Ed.3 no long-term PQ
test is performed. Presence of water
prohibited avoiding electrochemical
(water) treeing. This can be avoided by
a metal sheath over the cable core
-a. Compatibility with inner and outer
semi-con: see above
-b. Compatibility with accessories
interfaces
Specification/Threat
C
-b. Resistance to oxidation and thermal
degradation (see above)
Test to check the functionality
(Relevant paragraphs of IEC 60840
Ed.3/62067 Ed. 1 in brackets –IEC
62067 Ed. 1 in Italics)
D
-b. 20 cycles (T) §12.3.6/§12.4.7 or
180 cycles (PQ §13.2.3)
154
J. Becker
Layer over
Semicon
(optional)
3
Chemical
properties
4
Interface with
insulation and
outer layer or
(and) metal screen
and accesses
1
Electrical
properties
2
Thermalmechanical
properties
3
Chemical
properties
a. See inner semicon
-a. PD measurement (R: §9.2/§9.2,
and T:§12.3.4/§ 12.4.5)
-a. Bending test before type test (T:
§12.3.3/§12.4.4)
Examination after completion of the
type tests (T:§12.3.8/§12.4.10)
-b. 20 cycles (T: §12.3.6/§12.4.7) + PD
test (§ 12.3.4/§ 12.4.5) + examination
(§12.3.8/§12.4.10)
-c. Water penetration test (T:
§12.4.18/§12.5.14)
-a. Low resistivity to avoid PD at
interface with screen
-a. Resistance to mechanical bending
during manufacturing and installatn
-c. Water-blocking tapes possibly avoid
the longitudinal water penetration
(if required)
-a. Compatibility with semi-con and
screen
-b. Stability of electrical resistivity after
heat cycles
-a. Compatibility test. Ageing on
complete cable (T: §12.4.4/§12.5.4)
-b. 20 cycles (T: § 12.3.6/
§12.4.7) + measurement of resistivity
after ageing
b. See inner semicon
-b. Stability of electrical resistivity after
heat cycles
a. Same as inner semicon, but
compatibility with outer layer or (and)
metal screen
- b. Prevent deformation of the semicon
and the insulation...
a. See inner semicon
-a. Same as inner semi-con, but
compatibility with outer layers or (and)
metal screen
(continued)
a. Some customers ask to check the
moisture content in the semicon
(<1000 ppm content) as for the inner
semicon. Influence on the dielectric
behaviour of the insulation system?
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
155
1
Electrical
properties
Metal Screen/
Sheath
2
Mechanical
properties
Function or
Property
B
4
Interface
with semi-con
and metal screen
Cable’s
component
A
Table 4.14 (continued)
-e. Good contact between metal screen/
sheath and semicon layer below
-a. Supports mechanical bending
-c. Electrical connection when more
than one metallic screen is applied
-d. Current sharing in two metal layer
constructions
-b. Collects capacitive current and
induced currents
-b. Avoid deformation of insulation (see
above)
-a. Satisfy the short-circuit conditions
Specification/Threat
C
-a. Compatibility test (see above)
- e. PD test + cycles + PD (T: §12.3./
§12.4.)
-a. Bending test before type test (T:
§12.3.3/§12.4.4)
-Examination after completion of the
type tests
(T: §12.3.8/§12.4.10)
Test to check the functionality
(Relevant paragraphs of IEC 60840
Ed.3/62067 Ed. 1 in brackets –IEC
62067 Ed. 1 in Italics)
D
-a. Ageing on complete cable (T) but
no measurement on tape (see above)
-b. 20 cycles (T: §12.3.6/§12.4.7+
examination §12.3.8/§12.4.10)
-a. Calculation of
cross section needed (following IEC
60949 and 61443)
-b. Resistance measurement
as for conductor (S, T: §10.5/§ 10.5,)
and dimensions of the screen (§10.7/
§10.7)
-b. Calculation of losses (depending
on installation conditions - see IEC
60287)
-c. T: Heat cycling and temperature
measurements
-d. Current sharing following
conductivities.
d. Missing in IEC! Cigré WGB1-03 has
made a report TB 272 on this subject in
2005
Comments
E
156
J. Becker
3
Chemical
properties
-a. No corrosion of the metal
-f. Fatigue in case of composite metal
foil screen when installed in non buried
conditions
-g. Side wall pressure in case of
composite metal foil screen
-e. Fatigue in case of lead or lead alloy:
possible growth of crystals and
Assuring
-d. Radial water tightness in case of
composite metal foil screen
-b. Limited deformation of insulation
and outer semicon in case of short
circuit temperature rise
-c. Supports radial pressure during
heating
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
(continued)
b. No official thermal short-circuit test
in IEC specifications concerning HV
cables
-c. Thermo-mechanical test with heat c. To be defined: sidewall pressure test
cycles
as recommended Cigré in ELECTRA
141 and IEC 61901 TR
Only to be performed if needed for a
special application
-d. Technical Report of IEC (IEC
61901 TR) recommending a long
term test in water (see also Cigré
recommendations from ELECTRA
141): D
-e. Check in relevant standards
e. Other tests like slow elongation (O.
dealing with lead alloys that the
lmm/h) or “cone” test could be
chosen alloy is well adapted to the
proposed to check the quality of the
application in the field:
lead extrusion?
EN 12548, EN 50307 or equivalent.
Micrographic tests could be useful to
evaluate the grain size of the
extruded lead (Quality control
during extrusion of lead sheath)
-f. A fatigue test (: repeated bending) f. To be defined: number of bendings,
could be recommended as a
diameter of bending...
development test D
-g. Technical Report of IEC(IEC
61901 TR) recommending a side wall
pressure test (see also Cigré
recommendations from ELECTRA
141): D
-a. Corrosion test following
ELECTRA 141 or IEC Technical
Report (IEC 61901 TR) when using
Aluminium foil or IEC 60229, Clause
4.2 for Aluminium metallic layer
-b. Thermal short-circuit test on
screen (D)
4
157
Over sheath
Cable’s
component
A
Specification/Threat
C
-b. Compatibility with layers or semicon
-a. Satisfy temperature measurement
-b. Satisfy short-circuit conditions
-c. Satisfy mechanical conditions
-b. Insulate for AC and impulse
voltages in case of cross bonding or
single point bonding
1
-a. Electrical insulation of screen from
Electrical properties earth if required
-d. Radial water tightness in case of
metal foil or sheath
-c. (Especially in case of lead or lead
alloy sheath: fatigue problem possible)
5
-a. Compatibility (see above)
Interface with
semi-con or layer
and over-sheath
-b. Correct connection with accessories
and with accessories screens
4
Temperature
Monitoring (if any)
Function or
Property
B
Table 4.14 (continued)
-d. Corrosion test following
ELECTRA or IEC Technical Report
(IEC 61901)
-a. AC/DC test on sheath (R: §9.4/
§9.4) or a spark test during
manufacturing
-b. Test combined with test on outer
protection of joints
-a.b.c. Short circuit test with the
installed sensors (mainly if sensors
are optical fibers) would be useful as
a development test D
-a. Compatibility test: -Ageing of
complete cable (T: §12.4.4/§12.5.4
with visual examination)
-b. Heat cycles: 20 cycles (T:
§12.3.6/§12.4.7) or 180 cycles (PQ:
§13.2.3)
And thermal short-circuit test
(development test D)
-c. To make the right choice of lead:
see EN 12548 and EN 50307
Test to check the functionality
(Relevant paragraphs of IEC 60840
Ed.3/62067 Ed. 1 in brackets –IEC
62067 Ed. 1 in Italics)
D
-b. Compatibility test
c. Fatigue of lead may lead to cracks but
may be they do not yet appear during
long-term PQ tests
b. Long term PQ test not in IEC 60840
Ed.3
a. See electric contact properties after
compatibility test
Check that the sensor is not destroyed
by the short circuit temperature and the
electromagnetic forces
Comments
E
158
J. Becker
-c. Resistance to abrasion during
installation
-d. Good mechanical qualities before
and after ageing e.g. no cracking of the
outer sheath
-e. Resistance to fire if required
-a. Supports mechanical bending during
installation
-b. Resistance to mechanical impact
during and after installation
-c. Resistance to the chemicals in
ground
-d. Resistance to termites and rodents
where needed (special additives or
design)
3
-a. Compatibility with screen
Chemical properties
-b. Resistance to UV
2
Thermalmechanical
properties
-d. Correct behavior in case of shortcircuit on outer screen
-c. No degradation of this property
-b. Mechanical impact: see
ELECTRA 141 for metal foils or IEC
Technical Report (IEC 61901 TR)
and in addition to §12.4.19
-c. Tests according to IEC 60229,
Clause 4.1
-d. See the different tests on the
different types of materials in IEC
(§12.4., §12.5.)
-e. Tests under fire following the
relevant tests in IEC (§12.4.17,
§12.5.13)
-a. Compatibility test: -Ageing on
complete cable (T: §12.4.4/ §12.5.4)
-b. Carbon black content in PE
oversheaths: (T: §12.4.12/§12.5.12)
-UV stabilizer in other materials:
accelerated weathering test
-c. Choice of material depending on
the application
-d. Special tests depending on type of
termites and rodents: D
-c. 20 cycles (T: §12.3.6/§12.4.7) + AC
and impulse test on sheath
-d. Short circuit test on screen in
network conditions as a development
test D
-a. Bending test (T: §12.3.3/§12.4.4)
(continued)
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
159
1
Different electrical
and mechanical
needs
Complete
cable
-a. No degradation because of
interactions between all components
and of components themselves
-b. No ingress of water to avoid
insulation degradation and dielectric
problems with accessories
Specification/Threat
C
-a. See above
-b. Shrinkage of over-sheath may give
problems with accessories
-a. Examination after completion of
the type tests
(T: §12.3.8/§12.4.10)
-b. Short circuit test as D depending
on the network conditions (to be
decided with the network engineers)
-b. Water penetration test (T:
§12.4.18/§12.5.14)
-b. Long term cycling in presence of
accessories: PQ or D (T: §12.4.14/-)
Test to check the functionality
(Relevant paragraphs of IEC 60840
Ed.3/62067 Ed. 1 in brackets –IEC
62067 Ed. 1 in Italics)
D
Comments
E
–
b. Included in long-term
pre-qualification test of IEC 62067 (§
13.2.3) but not in IEC 60840 Ed.3.
Shrinkage, if any, is not necessarily
finished after 20 cycles.
Remarks:
- Long-term tests could be performed where necessary as development tests when not prescribed in specifications. See the recommendation from the WG in this report.
(See Table 4.17)
- The functions are determined by the construction. The construction, the materials applied and the production process applied determine the functional properties. The
standards take this into account with the Range of Type Approval.
- A short circuit between conductor and metal screen/shield may influence most of the functions described by thermal effects and mechanical effects (thermal expansion
and shrinkage of materials). Adherence of layers/screens is also tested with this test. Should this lead to an extension of the test series with a type test or a development test?
After discussion it was concluded that a short circuit test should be recommended as a development test.
- In the IEC 62067 and the IEC 60502-2, there is an electrical Sample test as a check on the properties of the insulation. In the IEC 60840 there is no electrical sample test
on the insulation. It would be wise to perform a lightning impulse test as soon as the stress level near the inner semi-conducting screen reaches values as in IEC 62067. This
may be the case when reducing the insulation thickness so that the inner AC service stress is becoming as high as 8 kV/mm.
- The current standards IEC 60840 Ed.3 and IEC 62067 Ed.1 cover the most important functions. No tests should be deleted. May be tanδ could be performed on
materials instead of being performed on cable insulation (but be careful, as it seems that tanδ can be influenced by the diffusion of some products into the insulation)
Function or
Property
B
4
Interface with
screen, accessories
or external
aggression
Cable’s
component
A
Table 4.14 (continued)
160
J. Becker
Joints components
A
Metallic connection
and its eventual
covering
-a. Supports the compression and
extension efforts during cycles from
cable conductor
(Does not allow wrinkling of
conductor during heating cycles)
-a. Dissipates correctly the heat
generated in the connection and avoids
overheating in the center of the joint
-a. Compatibility of the possible used
additives with the semi-con of the joint
(Grease, mastic, water sealant)
3
Thermal
function
4
Interface
with joint
semi-con
-b. Supports short circuit current
and temperature
Specification/Threat
C
-a. Transports nominal current
without overheating
2
Mechanical
properties
Function or
Property
B
1
Electrical
continuity/
electrical
resistivity
-a. Heat cycles, but without voltage,
of connections (D: §12.3.6/
§12.4.7) + Measurement of
temperature of connector versus
conductor + examination §12.3.8/
§12.4.10)
-a. Long- term test (D or PQ: §
13.2.3 + examination)
-b. Short circuit test following the
network needs: D
(Such a test is part of IEC 6121)
-a. Heat cycles of cable loop with
joint installed: 20 cycles (T: §12.3.6/
§12.4.7+ examination §12.3.8/
§12.4.10)
Or long term test (PQ: §133)
Test to check the functionality
(Relevant paragraphs of IEC 60840
Ed.3/62067 Ed.1 in brackets-IEC
62067 Ed. 1 in Italics)
D
-a. Heat cycles on connections Use
IEC 61238-1 when appropriate (5
not welded): D
Table 4.15 Functional analysis of High Voltage cable joint and joint components (Same as in Table 4.14)
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
(continued)
a. Such a PQ test is not prescribed in
IEC 60840 ed3
Test is also possible on materials: semicon plates in air oven exposed to the
additives
a. Are 20 cycles enough to see the
effects of longitudinal efforts? In IEC
60840 ed3 long term PQ tests are
missing to check the long term
behavior of joints
See tensile strength of welded
connectors
a. If a reliable program to calculate the
temperature profile in a joint is
available, it may replace the test on
cable system
Comments
E
a. No prescription in IEC 60840 ed3 or
62067 ed1
IEC61238-1 is presently only
prescribed for 30 kV connections and
below but could be useful for HV
connections Short circuit temperature
shall not be at 250 C but derived from
short circuit currents selected from the
data of IEC 61443
b. No short circuit test prescribed in
IEC 60840 ed3 or 62067 ed1
4
161
Insulation (field
grading)
Joints components
A
Possible additives
(grease, mastic,
water sealant...)
1
Dielectric
function
Function or
Property
B
1
Electrical
function
2
Thermal
properties
3
Chemical
properties
4
Interface with
joint semi-con
Table 4.15 (continued)
-b. Reasonably low tanδ, to avoid too
high dielectric losses during voltage
application
-c. Maintenance of the dielectric
qualities of the system during the
lifetime
-a. Continuation of the insulation of
the cable: Withstand to AC stresses
and lightning/switching impulses
-a. Supports the temperature of the
connection during service without
degradation
-a. Gives some protection against
electrical degradation of the contact
of the connection
-a. Compatibility of the possible used
additives with the semi-con of the
joint
Specification/Threat
C
-a. No negative influence on the
conductivity of the contact
-c. Long term tests + impulse test on
assembly + (PQ:
§13.2.3 + §13.2.4) + PD test after
after long term test
-a. Heat cycles of connections: see
above. Examination of the additive
after cycling
-a. Heat cycles of connections: see
above. Examination of the additive
after cycling
-a. Long- term test (D or PQ:§
13.2.3 + examination) Or test on semiconducting materials in air oven
exposed to the additives
-a. Partial discharge test (R, S,: § 9.2
and 11.2.a) and (T:§ 12.3.4/§12.4.5)
and voltage test (R, S: § 9.3 and 11.2.
b), heating cycle test (T: § 12.3.6/
§12.4.7)
Lightning impulse test during type
tests (T:§ 12.3.7/§ 12.4.9) or long
term test (PQ: §13.2.4)
-b. Tanδ test (T: §12.3.5/§12.4.6)
Test to check the functionality
(Relevant paragraphs of IEC 60840
Ed.3/62067 Ed.1 in brackets-IEC
62067 Ed. 1 in Italics)
D
-a. Heat cycles on connections (see
above)
c. PQ Test missing in IEC 60840 ed3.
Impulse test may be sufficient to detect
lack of adherence.
PD monitoring during type testing or
long term testing would be a good tool
to check the evolution of the adherence.
Comments
E
162
J. Becker
3
Interface
properties
2
Thermalmechanical
properties
-a. Maintenance of good contact with
cable insulation (see above) or interface
with other joint components
-b. Compatibility with cable insulation,
lubricants and joint’s semi-con
-c. Shrinkage of cable materials
-d. No slipping on cable with pressure
from one side (prefabricated:
composite or pre-molded joint)
-b. Heat cycles (T: §12.3.6/§72.4.7)
Long term tests (PQ: §13.2.3 for EHV)
-c. Long term shrinkage test as D on
5 m long cable: see French
specification for high voltage and extra
high voltage cables NFC 32 352 or C
33 253
-b. Short circuit test following the
needs of the network would be useful
as a development test D
-c. Development test D: check of
temperature drop in the insulation
during heat cycling
-d. Long term test on system installed
in a test arrangement representative of
installation design (PQ:
§13.2.3 + §13.2.:
-a. Long term tests + impulse +PD
(PQ: §13.2.3+ §13.2.4)
-b. Maintenance of mechanical quality
in case of short circuit
-c. Good heat dissipation
-a. Long term tests + impulse (PQ:
§13.2.3 + §13.2.4)
-a. Maintenance of good contact with
cable insulation (good elasticity and
compatible shrinkage of the different
layers) with time at ambient and with
cycles
(continued)
b. Long term PQ test missing in IEC
60840 ed3
c. The shrinkage test made following
the French specifications shows that the
insulation and sheath materials shrink
back during a quite long time:
80 cycles or even more are often
needed to stabilize the shrink back
a. Long term PQ test missing in IEC
60840 ed3
d. Long term PQ test missing in IEC
60840 ed3
a. A long-term PQ test is not
prescribed in IEC 60840 ed3. A
development test: “pressure versus
time of contact of joint insulation to
cable insulation”, would be an
alternative for pre-molded type
insulation
No such test in IEC 62067 ed1 nor in
IEC 60840 ed3
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
163
Interface matters
including cleaning
material,
lubricants..
Joints components
A
2
Chemical
properties
3
Thermalmechanical
properties
4
Interface
properties
4
Chemical
properties
1
Electrical
properties
Function or
Property
B
Table 4.15 (continued)
-a. Compatibility of lubricants with
cable and joint’s insulation, and cable
and joint’s semi-con
-a. No slipping on cable with pressure
from one side (prefabricated or
pre-molded joint)
-a. The materials used to clean or to
lubricate the surfaces of the cable or the
joint insulation shall not degrade the
dielectric properties of the system. The
lubricant is also filling up the microholes between the two insulating
surfaces
-a. No harmful ageing of material
-a. No harmful ageing of material
Specification/Threat
C
-d. Compatibility of interface additives
(lubricants..) with cable insulation/
semicon material and joint insulation/
semicon material
a. Long term PQ tests missing in IEC
60840 ed3
-a. Long term tests + impulse + PD
(PQ: §13.2.3 + §13.2.4)
-a. Development test D to check the
good behavior of materials in contact
with additives: check of mechanical
properties of cable materials and joint
materials after ageing in air oven
a. Long term test followed by PD tests
will give an indication whether the
contact between the the surfaces remain
correct
Long term PQ tests missing in IEC
60840 ed3
a. Long term PQ tests missing in IEC
60840 ed3
Comments
E
d. Manufacturers responsibility
-a. Long term tests + impulse + PD
(PQ: §13.2.3 + §13.2.4
Test to check the functionality
(Relevant paragraphs of IEC 60840
Ed.3/62067 Ed.1 in brackets-IEC
62067 Ed. 1 in Italics)
D
-d. Development test D to check the
good behavior of materials in contact
with additives: check of mechanical
properties of cable materials and joint
materials after ageing in airen
-a. Long term tests + impulse + PD
(PQ: §13.2.3 + §13.2.4)
164
J. Becker
Metal screening,
connection to cable
screen
3
Chemical
properties
4
Screen
disconnection
(for crossbonding)
2
Mechanical
properties
1
Electrical
function
-a. Thermal cycles (T: §12.3.6/§12.4.7)
-a. AC and impulse tests on outer
protection of joints (T Annex
H/Annex D)
-a. Withstands dielectric transients
Thermal short circuit test following
the needs of the network would be
useful as a development test D (see
IEC 61443)
-b. Development test D:Thermal
cycling with current circulating in the
screen and temperature measurement in
the screen area + examinon
-a. 20 Thermal cycles (T: §12.3.6/§
12.4.7).
Thermal short circuit test following the
needs of the network would be useful
as a development test D
-b. 20 Thermal cycles (T: §12.3.6/
§12.4.7). + Examination
-c. Be sure that the correct lead alloy
for the metal sheath of cable has been
chosen following EN 50307 and EN 18
-a. Thermal cycles with current
circulating in the screen:D
-a. Compatibility with cable and joint
materials
-b. No harmful deformation of cable or
joint insulation
-c. No cracking near the connection in
case of lead or lead alloy sheath of
cable
-a. No hot spot at connection
-b. Current sharing between double
screens if present
-a. Transfers currents circulating in
cable screen, transfers short circuit
current.
(continued)
c. Cracking may need more than
180 cycles to appear (180 cycles: long
term test following IEC 62067 ed1).
Severity depends largely on the
installation environment and
conditions.
a. No short circuit test in IEC 62067
ed1 nor in IEC 60840 ed3
a. Currents in the screen may be
important and the ability of the screen
connection not to overheat during
cycling should be checked (not in
cycling tests in IEC)
No such short circuit test in IEC 62067
ed1 nor IEC 60840 ed3
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
165
Outer
protection
(Eventual) Filling
Joints components
A
2
ThermalMechanical
function
-a. Eventually rigidifies the joint
4
ThermalMechanical
properties
1
Electrical
function
-b. No degradation of dielectric
function with ageing and during
short circuit
-a. Mechanical protection of joint
-a. Isolation of joint from earth
-a. Avoid water ingress to the
insulation
-a. Compatibility with surrounding
material
-a. Avoid high thermal resistance
Specification/Threat
C
-a. Avoid water ingress to the
insulation
3
Water
tightness
1
Filling of
housing
2
Chemical
properties
Function or
Property
B
5
Water
tightness
Table 4.15 (continued)
-a. Test on outer protection (T: Annex
H/Annex D)
-b. Long term test (PQ:§
13.2.3 + §13.2.4) Short circuit test on
metal screen
-a. Development test to check the good
behavior of materials in contact with
additives: check of mechanical
properties of cable materials and joint
materials after ageing in air oven
-a. Water tightness test
Long term heat cycles with joint
immersed or in ground followed by a
sheath voltage test
Test to check the functionality
(Relevant paragraphs of IEC 60840
Ed.3/62067 Ed.1 in brackets-IEC
62067 Ed. 1 in Italics)
D
-a. Water tightness test
Long term heat cycles with joint
immersed or in ground followed by a
sheath voltage test
a. Design aspect of system
b. Long term PQ tests missing in IEC
60840 ed3
a. Design aspect
a. Design aspect
Comments
E
166
J. Becker
1
Overall
properties
-a. Long term test (PQ: §13.2.3 for
EHV) + voltage withstand test on outer
protection after long term test
-a. Compatibility with inside
material, resistance against soil
aggression (if cable installed in
ground) or other surroundings
- a. Possible shrinkage of cable oversheath and/ or shrinkage of joint
outer protection to be taken into
consideration when designing the
outer protection
-a. No degradation because of
interactions between all components
and of components themselves
-b. No water penetration before and
after heat cycling into the cable
system
-b. Test in water on outer protection (T:
Annex H/Annex D) or better: Long
term test (PQ: §13.2.3 for
EHV) + insulation resistance test on
outer protection after long term test
-a. Examination after completion of the
type tests (T: §12.3.8/§12.4.10)
-a. Check the shrinkage of the cable
sheath and joint protection after heat
cycling of 20 cycles (T: §12.3.6/§
12.4.7) or 180 cycles (PQ: §13.2.3)
-a. Test in water on outer protection (T:
Annex H/Annex D)
-a. Avoid water ingress into the cable
b. Long term PQ tests missing in IEC
60840 ed3
a. May be 20 cycles are not enough to
see the long term behavior of the
shrinkage effect Long term PQ tests
missing in IEC 60840 ed3
a. Long term PQ tests missing in IEC
60840 ed3
Remarks
- Long-term tests could be performed where necessary as development tests when not prescribed in specifications.
- See the recommendation from the WG in this report (See Table 4.17)
- A short circuit between conductor and metal screen/shield of the cable system may influence most of the functions described by thermal effects and mechanical effects
(thermal expansion and shrinkage of materials). Adherence of layers/screens is also tested with this test. Should this lead to an extension of the test series with a type test or a
development test? After discussion it was concluded that a short circuit test should be recommended as a development test
- In IEC 60840/Ed.3, sample tests on accessories are included. (In the IEC 62067 yet under consideration). They should be included also in the IEC 62067
- General remark: what about checking of skill of the jointers and effectiveness of mounting instructions? People responsible for installation of the accessories shall
consider this in their quality assurance and quality control process. See ▶ Chap. 5, “Cable Accessory Workmanship on Extruded High Voltage Cables”.
Note: to compare the clauses of the IEC specifications IEC 60840 Ed. 3 and IEC 62067 Ed. 1 table with the equivalent clause of IEC Specifications published in
2011 in 2011, see the list of correspondence in pages 71 to 73
Complete joint
5
Interface with
cable oversheath
3
Water
tightness
4
Chemical
properties
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
167
Electrical field grading
(stress cones, capacitive
or non linear grading
Component of
termination
A
Metallic connection of
conductor to network
3
Chemical
properties
4
Interface with
network
1
Dielectric
function
2
Mechanical
properties
Function or
Property
B
1
Electrical
continuity/
electrical
resistivity
-b. Maintenance of these qualities
with ageing
-a. Connection fits with terminal lugs
of network interface –(Sliding
contacts, bimetallic interfaces...)
-a. Field grading of dielectric stresses
in order to pass AC and lightning/
switching impulses
-a. Resistance to corrosion
-b. Supports short-circuit current and
temperature
-a. Supports compression/ extension
efforts during cycling of cable
conductor
-b. Supports the thermal short circuit
efforts
Specification/Threat
C
-a. Transfers nominal current without
overheating
-a. Partial discharge (R §9.2) and
voltage test (R §9.3) Lightning
impulse (T §12.3.7/§12.4.9)
Switching impulse on EHV
material (T)§12.4.8) Long term test
(PQ §13.2.3) followed by lightning
impulse (PQ: 13.2.4) and PD
-b. See above
-b. Short circuit test (D) following
the network ds
-a. 20 cycles (T) §12.3.6/§ 12.4.7 or
long term test (PQ § 13.2.3 for
EHV)
-b. Short circuit test following the
needs of the network would be
useful as a development teD
a. Humidity and pollution test as a
development test D
Test to check the functionality
(Relevant paragraphs of IEC 60840
Ed.3/62067 Ed. 1 in brackets IEC
62067 Ed. 1 in Italics)
D
-a. Heat cycles on connections Use
IEC 61238-1 when appropriate (5
not welded): D
Table 4.16 Functional analysis of High Voltage terminations and components of terminations (Same as in Table 4.14)
a. PD after long term test shows that
adherence between stress relieve
components is still good Long term
PQ tests missing in IEC 60840 Ed.3
-Matter for engineering of network
Comments
E
a. No prescription in IEC 60840 Ed.3
or 62067 Ed. 1 Short circuit test
values could be selected from the
data of IEC 60859
b. No short circuit test prescribed in
IEC 60840 Ed.3 or 62067 Ed. 1
a. System aspect
Long term PQ tests missing in
IEC 60840 Ed.3
b. No such test in HV IEC
specifications
168
J. Becker
Interface matters
including cleaning
material, lubricants...
-a. The materials used to clean or to
lubricate the surfaces of the
insulation of the cable or the
termination shall not degrade the
dielectric properties of the system.
The lubricant is also filling up the
micro-holes between the two
insulating surfaces
-a. Good compatibility with cable
insulation system and lubricants
(between cable insulation and stress
relieve component) if any
-b. Resistance to filling medium
(oil...)
4
Interface
quality
1
Electrical
properties
-a. Resistance to thermal ageing
3
Chemical
properties
2
Thermalmechanical
properties
-c. Reasonably low tanδ, to avoid too
high dielectric losses during voltage
application
-a. Maintenance of good contact with
cable insulation (good elasticity and
compatible shrinkage of the different
layers) with time at ambient and with
cycles
-b. Dissipation of thermal losses
-c. No harmful cable deformation
-b. Development test D on
materials in contact with filling
medium: check of mechanical,
chemical and dielectric properties
of cable materials and termination
materials after ageing in airen
-a. Long term tests + impulse + PD
(PQ: §13.2.3 + §13.2.4
-a. Long term test: (PQ: §13.2.3)
and PD after long term
test + examination
-a. Development test: pressure of
contact versus time and long term
AC test with cycles, Long term test:
(PQ: §13.2.3) and PD) after long
term test
-b.
-c. Long term test: (PQ: §13.2.3)
and PD after long term
test + examinon
-a. Long term test: (D: §13.2.3)
anD
-c. Tanδ test on loop with
terminations (T: §12.3.5/§12.)
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
(continued)
a. Long term test followed by PD
tests will give an indication whether
the contact between the surfaces
remains correct Long term PQ tests
missing in IEC 60840 Ed.3
a. Long term test needed if no earlier
experience with a similar product
Long term PQ tests missing in IEC
60840 Ed.3
a. Long term test needed if no earlier
experience with a similar product
Long term PQ tests missing in IEC
60840 Ed.3
b. Manufacturers responsibility
b. Calculation. Not measurable
c. Long term PQ tests missing in IEC
60840 Ed.3
a. PD after long term test shows that
adherence between stress relieve
components is still good. Long term
PQ tests missing in IEC 60840 Ed.3
4
169
1
Dielectric
functions
Insulator/Envelope
(Porcelain, synthetic
insulator, epoxy...)
2
Thermalmechanical
properties
Function or
Property
B
2
Chemical
properties
3
Thermalmechanical
properties
4
Interface
properties
Component of
termination
A
Table 4.16 (continued)
-c. Good long term resistance to
higher temperatures
-a. Resistance to mechanical forces
from the HV connection
-b. Resistance to seismic activity
-b. Resistance to leakage currents and
evacuation of these currents
-a. Correct creep distance and length
in air or gas
-a. Compatibility of lubricants with
cable, insulation, semiconductor and
termination components
-a. No slipping or restraining on cable
due to pressure
Specification/Threat
C
-a. No harmful ageing of material
-b. Calculations according to IEC
61463
-c. Long term test: (PQ:
§13.2.3) + examination
(PQ:§13.2.5)
-a. Development test D to check the
good behavior of materials in
contact with additives: check of
mechanical properties of cable
materials and terminations
materials after ageing in air oven
-a. Lightning impulse (T: §12.3.7/
§12.4.9) Switching impulse (T: §
12.4.8) for voltages above 300 kV
-b. For outdoor terminations, Salt
fog test. Climatic test following
IEC 61442: development tes
-a. Cantilever test: D
Test to check the functionality
(Relevant paragraphs of IEC 60840
Ed.3/62067 Ed. 1 in brackets IEC
62067 Ed. 1 in Italics)
D
-a. Long term tests + impulse + PD
(PQ: §13.2.3 + §13.2.4)
c. Long term PQ tests missing in IEC
60840 Ed.3, but useful even for this
range of voltages
a. Not prescribed by IEC HV specs;
Internal test
b. Length of creep distance adapted
to the degree of pollution
a. Switching impulse for voltages of
300 kV and above
Comments
E
a. Long term PQ tests missing in IEC
60840 Ed.3
170
J. Becker
Filling medium (if any)
2
Thermal
properties
3
Chemical
properties
and interface
3
Interface
quality with
filling medium
and
surrounding
4
Chemical
properties
1
Electric
properties
-a. Good compatibility with cable
material in contact (insulation,
eventually semi-con) and stress
controlling material
-c. Maintenance of dielectric
properties with ageing
-a. No harmful degradation of the
material with ageing
-b. Low dielectric losses
-a. Long term test (PQ:
§13.2.3) + examination (PQ:
§13.2.5)
-a. Long term test (PQ
§13.2.3) + examination (PQ:
§13.2.5)
Development test to check the good
behavior of materials in contact
with additives: check of
mechanical properties of cable
materials and joint materials after
ageing in airen
-a. Development test on filling
material: breakdown tests
-b. Long term test (PQ:
§13.2.3) + examination (PQ: §13.2
-a. Development test: Climatic tests
following IEC 61109
-a. Resistance to UV, climate, water
and pollution
-a. Good dielectric breakdown values
-a. Development test D: Climatic
tests following IEC 61109
-b. Long term test (PQ
§13.2.3) + examination (PQ:
§13.2.5)
-d. Short circuit test with internal
electrical fault: D
Internal overpressure test:
-a. Resistance to climatic and
polluting surrounding
-b. Compatibility with filling medium
-e. Good heat dissipation
-d. Resistance to internal arcing in
case of breakdown in the termination
(no harmful projections)
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
(continued)
a. Long term PQ tests missing in IEC
60840 Ed.3 Responsibility of the
manufacturer
a. Long term PQ tests missing in IEC
60840 Ed.3
b. Long term PQ tests missing in IEC
60840 Ed.3
a. Manufacturers responsibility
b. Long term PQ tests missing in IEC
60840 Ed.3
d. No test in IEC HV specs for cable
terminations or similar equipment
such as bushings and instrument
transformers
e. Engineering problem; depends
very much on surrounding and
protection means
4
171
Component of
termination
A
Screen/Earth connection
Table 4.16 (continued)
2
Thermalmechanical
properties
Function or
Property
B
1
Electrical
functions
-c. Impulse and DC/AC test
between earth and screen as a type
test
T
–
-a. Thermal short circuit test of the
earth connection following the
needs of the network would be
useful as a development test
D With visual examination
-b. Be sure that the correct lead
alloy for the metal sheath of cable
has been chosen following EN
50307 and EN 12548
-c. In case of disconnection from
earth, electrical withstand between
earth and screen
-d. Suppression of screen currents
with single end earthing or special
bonding
-a. No degradation of connection and
surrounding with thermal short
circuit
-b. No cracking near the connection
in case of lead or lead alloy sheath of
cable
-b. Short circuit test following the
needs of the network would be
useful as a development test D
Thermal cycles with current in the
screen (D)
-b. Evacuates short circuit current
and circulating currents with both
ends earthed
Specification/Threat
C
-a. Fixation of earth potential
Test to check the functionality
(Relevant paragraphs of IEC 60840
Ed.3/62067 Ed. 1 in brackets IEC
62067 Ed. 1 in Italics)
D
b. Cracking does not necessarily
appear already after long term
cycling tests
d. Engineering problem: -Single end
earthing High frequency waves at
GIS ends to be solved by coaxial
connections to earth
Comments
E
a. Engineering problem, to be
considered when installing the
system. Bimetallic connections to be
considered with special care
b. No short circuit test in IEC 60840
Ed.3 nor in IEC 62067 Ed. 1
Currents in the screen may be
important and the ability of the
screen connection not to overheat
during cycling should be checked
(not in cycling tests in IEC)
172
J. Becker
-b. Correct sealing and no fluid
leakage
-a. No degradation because of
interactions between all components
and of components themselves
-a. Withstand AC/DC/Impulse in
specially bonded systems
-a. Supports the weight of
termination and cantilever forces on
termination
-a. No corrosion of the base plate
-a. No corrosion of contact points
-a. Resistance to climatic and
polluting surrounding
-b. Compatibility with filling medium
-a. Examination of deterioration
after completion of the type tests
(T) §12.3.8/§12.4.10 and short
circuit test
-a. AC/DC and impulse test on
screen connection versus base plate
-a. Examination when making
climatic tests
-a. Development test D: Climatic
tests following IEC 61109
-b. Long term test (PQ
§13.2.3) + examination (PQ:
§13.2.5)
a. Leakage may come up with time in
service and, may be, will not be
detected during long-term
development tests. It needs regular
inspection or special protection if no
inspection is possible
a. Design aspect
a. Design aspect
a. Design: choice of metals and
protection
a. Design aspect
b. Long term PQ tests missing in IEC
60840 Ed.3
Remarks
- Long-term tests could be performed where necessary as development tests when not prescribed in specifications.
- See the recommendation from the WG in this report. See Table 4.17
- A short circuit between conductor and metal screen/shield of the cable system may influence most of the functions described by thermal effects and mechanical effects
(thermal expansion and shrinkage of materials). Adherence of layers/screens is also tested with this test. Should this lead to an extension of the test series with a type test or a
development test? After discussion it was concluded that a short circuit test should be recommended as a development test
- General remark (same as for joints):
- What about checking of skill of the jointers and effectiveness of mounting instructions? People responsible for installation of the accessories shall consider this in their
quality assurance and quality control process. See ▶ Chap. 5, “Cable Accessory Workmanship on Extruded High Voltage Cables”.
Note: to compare the clauses of the IEC specifications IEC 60840 Ed.3 and IEC 62067 Ed.1 table with the equivalent clause of IEC Specifications published in
2011 in 2011, see the list of correspondence in pages 71 to 73
Complete
termination
Base plate
3
Interface
quality with
filling medium
and
surrounding
4
Chemical
1
Mechanical
properties
2
Chemical
properties
3
Base plate
insulators
1
Overall
properties
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
173
174
J. Becker
The process for determining if further testing is required is described in the
attached Flowchart.
When a supplier proposes a change to an approved cable system, the functional
analysis tables may be used to determine the functions performed by the component
of the cable or the accessory that may be changed. The development test evidence is
then considered by the supplier and purchaser to see if the change has increased the
risk that this cable or accessory will not perform as well as before.
If the development tests prove that there is no or only a “minor” increase in risk,
then no further testing is required.
If there is a “major” increase in risk, because of a change in a component of cable
or accessory that might change the performance characteristics, then further shortterm (type) testing is required but the PQ tests need not to be repeated. The
functional analysis table shows which IEC tests are appropriate for each component
of cable or accessory that will be changed. In some circumstances a threat may be
identified, which is unlikely to be revealed in a normal type test. There are other
situations in which other even more efficient tests can be used (for example in the
accelerated thermal ageing of accessories). In these circumstances it is appropriate
for the supplier and purchaser to agree a further program of development tests rather
than repeating the type tests.
If the proposed change introduces a “significant” increase in risk, then both the
Type tests and PQ tests should be repeated.
The analysis described above can be extended to cover any components and
materials not specifically listed in the functional analysis tables. It must be remembered that a small change in a component of cable and/or accessory does not
necessarily mean a small increase in risk. Changing a small component, such as a
lubricant or the material used for a wiping cloth can dramatically increase the risk for
a cable system failure.
Using a combination of functional analysis and risk assessment should allow the
supplier and purchaser to agree on the optimum program of tests to minimize the cost
of testing whilst managing the risk of potential future cable system failure.
4.5.3.3 Functional Analysis Tables
The functional analyses is divided in the following tables
• Table 4.14 Cable components
• Table 4.15 Joint components
• Table 4.16 Termination components
The tables are structured as follows:
• Column A describes the components from the inner part to the outer part.
• Column B describes per component the functions or properties of the components
such as electrical properties, mechanical properties, etc.
• Column C describes per function or property the specification that has to be taken
into account in the design of the component or the possible threat during operation.
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
175
• Column D describes per function the test to check the functionality. Where
possible, reference is made to the relevant paragraphs of IEC 60840 Ed. 3 and
IEC 62067 Ed.1.
• Where tests do not exist in these standards, reference is made to other IEC
standards or test recommendations. Distinction has been made between Routine
test (R), Type test (T), Sample tests (S), Development tests (D), and Prequalification tests (PQ).
• Column E gives, when necessary, further comments or clarifications
List the components that have been changed
List the functions performed by these components
Review development tests to establish if
the risk to the cable system has changed
NO
Haw the risk increased?
YES
No further testing required
YES
Is the increase in
risk small?
NO
test and type test
Is the threat
adequately covered
by the type test?
NO
YES
Repeat the type test
Carry out enchanced type
testing or further
development testing to
show there is no
Perform EQ test
Fig. 4.16 Flowchart showing how functional analysis can be used to determine the extent of
testing required following a change to a component of the cable system
Item
1
Test not in IEC 60840 or/and IEC
62067
Short circuit tests on cable and
accessories
g) Check that here is no degradation
of dielectric function with ageing and
during short circuit on outer
protections (oversheath, outer
protection of joints or terminations
h) No degradation of the conductivity
of connections after short circuit tests
Function and threat/specification
a) Cable conductor’s conductivity:
Limit temperature with thermal
short circuit current
b) Electrical properties of the outer
metal screen: - Satisfy the shortcircuit conditions
c) Short circuit on outer metal screen.
Limited deformation of insulation
and outer semi conductive layers in
case of short circuit temperature rise
d) Correct behavior of over-sheath in
case of short-circuit on outer screen:
influence of temperature or
mechanical effort
e) Short circuit test on screen to check
thermal monitoring sensors if any
f) Short circuit on metal connections
(joints and terminations): hot spot?
d. Check that the sensor is not
destroyed by the short circuit
temperature and the electromagnetic
forces
e. Short circuit test following the
network needs
f. Short circuit test following the
network needs (Such a test is part of
IEC 6123)
c. Short circuit test on screen in
network conditions as a development
test
Comment
a. If temperature rise is considered
dangerous, a short circuit test is
proposed as a development test
Table 4.17 Tests from functional analysis not in IEC 60840 or/and IEC 62067 but recommended by WG B1-06
Recommendations
a. – f. Development test
176
J. Becker
Sheath voltage test combined with
long term prequalification test on
cable
Long term heat cycling test (not in
IEC 60840) on cable or system (With
or without voltage application)
2
3
a) Check the shrinkage of the cable
sheath versus the accessories
protection and the absence of water
ingress below the outer protection
(can be done without voltage
application)
b) Check that there is no degradation
on outer protections
a) Cable conductor chemical
properties: No corrosion when using
Al conductor
b) Cable conductor’s interface with
insulation and accessories:
-Thermal- mechanical expansion/
deformation-Avoid water penetration
c) Semi-con interface with
insulation: -No
degradation of insulation by
migration of low molecular species
d) Insulation: Stability of dielectric
properties with thermal and electrical
ageing
d. Thermal cycles check mainly the
possible deformation of the
insulation. No thermal or electrical
ageing was ever demonstrated
under normal service conditions.
Some physical-chemical
parameters presented changes
after pre-qualification tests but
they were not correlated to any
degradation of the dielectric
properties of the insulation.
Microscopic defects may, however,
lead to local degradation. This
degradation can be expressed by a
power law
a. If Al conductor avoid: +water
ingress +chemical species
(e.g. contaminations, Solvents)
b. Water penetration may lead to
chemical degradation of the
insulation mainly if the conductor
metal is aluminum
a. When making pre-qualification
long term test this test is indirectly
done if after long term test a sheath
voltage test is performed
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
(continued)
d. We propose a PQ test
and an EQ test for the high
stress designs
c. Part of development test
b. We propose a PQ test
and an EQ test for the high
stress designs
Development test
4
177
Item
Test not in IEC 60840 or/and IEC
62067
Table 4.17 (continued)
g) Interface of insulation with inner
and outer semicon and accessories: Compatibility with accessories
interfaces and filling media (joints,
terminations)
h) Correct connection of screens with
accessories screens
(Especially in case of lead or lead
alloy sheath: fatigue problem
possible)
i) Mechanical properties of
connections of joints or terminations:
-Supports the compression and
extension efforts during cycles
Function and threat/specification
e) Thermal-mechanical properties of
insulation: -Stability of form under
the pressure of accessories and
under the pressure of the thermalmechanical expansion of the
conductor
f) Chemical properties of insulation
and filling media of accessories:
-Resistance to oxidation and thermal
degradation of insulation
Long term tests would be useful as
a development test for new designs
on cables or accessories in all cases
f. We propose a PQ test
and an EQ test for the high
stress designs
f. Long term test with cable system
installed in conditions near reality
(PQ: 180 cycles §13.2.3): the
behavior of the cable system is
correct. It would be wise to make a
long term cycles test also on new
cable systems below 220 kV at a
relatively high value of electrical
stress except if a similar system has
been tested for higher voltage
Presence of water prohibited
avoiding electrochemical (water)
treeing. This can be avoided by a
metal sheath over the cable core
i. Part of development
tests
h. We propose a PQ test
and an EQ test for the high
stress dess
g. We propose a PQ test
and an EQ test for the high
stress designs
Recommendations
e. We propose a PQ test
and an EQ test for the high
stress designs
Comment
178
J. Becker
Cantilever test on termination
Dielectric test on screen
disconnections (terminations)
Dielectric test on base plate
insulators of terminations
Measurement of stability of the
resistance of semi- conductive tapes
on cable
Examination of XLPE cable
insulation in hot oil
Examination of protrusions and
contaminants on cable
5
6
9
10
8
7
Climatic and salt fog tests on outdoor
terminations (mainly on synthetic
and composite terminations)
4
a) Interface of tape over conductor
with semicon:-Avoid penetration of
semi-con into conductor
a) Smoothness of interface between
semicon and insulation and
cleanness of insulation
from cable conductor (Does not
allow wrinkling of conductor
during heating cycles) lead
behavior at connection
(no cracking,)
j) No slipping of joint on cable with
pressure from one side
(prefabricated: composite or
pre-molded joint
a) Resistance to leakage currents and
evacuation of leakage currents (IEC
61109?), Resistance to UV on
synthetic insulators
a) Resistance to mechanical forces
from the HV connection
a) Withstand the dielectric constraints
(Ac and impulse)
a) Withstand the dielectric constraints
(Ac and impulse)
a) Chemical properties of semiconductive tapes-Stability of
electrical resistivity after heat cycles
a. Some customers or standards
prescribe to check on a sample that
there are no protrusions, voids or
contaminants. WG has considered
that protrusions and contamination
a. Can be confirmed by test §12.3.9/
§12.4.11 on semicon indirectly and
its data shall be shown by
manufacturer if required
j. Long term test on system installed
in a test arrangement representative
of installation den
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
(continued)
Possibly as quality control
Quality control
Quality control
Part of development test
Part of development test
Part of development test
Part of development test
j. We propose a PQ test
and an EQ test for the high
stress designs
4
179
Moisture content in inner and outer
extruded semi-conductive layer on
cable
Grain size measurement on lead
sheath on cable
Evaluate Fatigue in case of lead or
lead alloy on cable:
Evaluate Fatigue in case of
composite metal screen on cable
Side wall pressure test on cable
12
13
14
15
Test not in IEC 60840 or/and IEC
62067
11
Item
Table 4.17 (continued)
a) Fatigue in case of composite metal
foil screen when installed in non
buried conditions Test to be defined
a) Side wall pressure in case of
composite metal foil screen
a) Evaluate the extrusion quality of
the lead to have an idea of its fatigue
behavior
a) Speed of crystal growth due to heat
cycling and vibration
Function and threat/specification
a. To be defined: sidewall pressure
test as recommended Cigré in
ELECTRA 141 (also future IEC
61901TR)
Only to be performed if needed for a
special application
a. Possible growth of crystals and
fissuring
-Check in relevant standards dealing
with lead alloys that the chosen alloy
is well adapted to the application in
the field:
EN 12548, EN 50307 or equivalent
examination on a small sample is less
relevant than an electrical routine test
on the entire length of cable
Some customers ask to check the
moisture content in the semi-con
(<1000 ppm content) Influence on
the dielectric behavior of the
insulation system?
a. To make the right choice of lead:
see EN 12548 and EN 50307
Comment
Development test where
applicable
Development test where
applicable
Development test where
applicable
Quality control
Possibly as quality control
Recommendations
180
J. Becker
Long term thermal cycling test in
water on cable
Mechanical impact on oversheath
Accelerated weathering test
Test on outer protection to check the
resistance to rodents and termites on
cable
Heat cycles on connections (joints
and terminations)
16
17
18
19
20
b) Evaluate how currents are
distributed when a double screen is
applied
c) Evaluate heat dissipation in the
joint
a) Electrical continuity/electrical
resistivity: -Transports nominal
current without overheating
a) Check mechanical behavior of
oversheath and metal screen
(mainly if metal foil bonded to
over-sheath)
a) Test of UV behavior of over-sheath
material
a) Mechanical behavior of over
sheath
a) Radial water tightness in case of
metal foil or sheath
c. Can be replaced by calculation if
effective method is available
a. Special tests depending on type of
termites and rodents
N.B. There is no international
standard dealing with criteria of these
kind of resistance.
a. Use IEC 61238-1 when
appropriate: D
IEC61238-1 is presently only
prescribed for 30 kV connections
and below but could be useful for
HV connections
a. Radial water tightness in case of
composite metal foil screen
A technical specification in IEC
recommending a long term test in
water (see also Cigré
recommendations from ELECTRA
141) (also IEC 61901TR)
a. Mechanical impact: see ELECTRA
141 (also IEC 61901TR) for metal
foils
(continued)
Development test
Development test where
applicable
Development test
Development test
Development test where
applicable
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
181
Evaluate heat dissipation in
accessories either by calculation or
temperature measurement
Sample tests on accessories in IEC
62067 are currently “under
consideration”
Electrical sample test as a check on
the properties of the insulation
23
24
25
PD test on accessories after long term
test
Test not in IEC 60840 or/and IEC
62067
Compatibility test of additives and
filling material with cable and
accessories material
22
Item
21
Table 4.17 (continued)
In IEC 62067 and IEC 60502-2, but
not in IEC 60840
Function and threat/specification
a) Check whether the additives do not
harm the quality of insulations or
semi-con materials of cable and
accessories
a) Evaluate whether the cycles have,
or not, created a ionizing defect at the
interface between the cable insulation
and the accessories insulation
a) Check of temperature drop in
the insulation during heat cycling
Evaluate heat dissipation in the
joint
They are yet in the IEC 60840 ed.3.
Thy should also be included in the
IEC 62067
Perform a lightning impulse test as
soon as the stress level near the inner
semicon screen reaches values as in
IEC 62067, meaning higher than
8 kV/mm
a. Can be replaced by calculation if
effective method is available
Comment
Sample test in IEC 60840
on cable sample
Sample test
Development test
Development test
Recommendations
Development test
182
J. Becker
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
183
4.5.3.3.1 Remark
A number of tests are identified in the functional analysis tables that are neither
in IEC 62067 Ed.1 nor in IEC 60840 Ed.3. These tests are considered by the WG as
Prequalification tests, Extension of Prequalification tests, Type tests, Sample tests
and development or quality control tests. These tests are enumerated in Annex 4.5.4.
4.5.4
Tests From Functional Analysis not in IEC
A number of tests are identified in the functional analysis tables, see Annex 4.5.3,
that are neither in IEC 62067 nor in IEC 60840.
Most of these tests are recommended by the WG as development or quality
control tests.
One test, the Long Term Heating Cycling Test, is currently not in IEC 60840
Ed.3. For high stress designs it is proposed to include such a test as a Prequalification
(PQ) test and as an Extension to Prequalification Test.
Another test (item 24) is considered to be a Sample test, namely the Sample Tests
on accessories in the IEC 62067. They are yet under consideration and should follow
the regime of the IEC 60840 Ed.3.
Electrical sample test on cable insulation for IEC 60840 (item 25) is
recommended, see also Table 4.14. It is included in the IEC 62067 and the IEC
60502-2 (Fig. 4.16).
All these tests are enumerated in Table 4.17.
List of Clause Numbers of IEC 62067 and IEC 60840 Tests
In the functional analyses tables the clause numbers are those of IEC 62067 Ed.1
from 2001 and IEC 60840 Ed.3 from 2004.
In the editions of 2011 the clause numbers of IEC 60480 Ed.4 and IEC 62067
Ed.2 have been changed. In the introduction IEC made the following comment:
“The clause numbering of IEC 60840 and IEC 62067 (which has been revised at the
same time) has been coordinated to achieve as much commonality as possible to
assist users who use both standards.”
Those who want to use the functional analyses tables might only have the last
versions of the IEC specifications and would not easily find the clauses mentioned in
the tables. So a comparison has been prepared to find easily the equivalent clauses in
the new versions of the relevant specifications.
Here a list of clause numbering of tests in IEC 60840 Ed.3 (2004) and Ed.4 (2011)
and in IEC 62067 Ed.1 (2001) and Ed.2 (2011).
184
J. Becker
Clause Number
IEC
IEC
60840
62067
Ed.3
Ed.1
2004
2001
9
9
9.1
9.2
9.3
9.4
10
10.1
10.2
10.3
10.4
10.5
9.1
9.2
9.3
9.4
10
10.1
10.2
10.3
10.4
10.5
10.6
10.6
10.6.1
10.6.2
10.6.3
10.7
10.7.1
10.7.2
10.8
10.9
10.6.1
10.6.2
10.6.3
10.7
10.7.1
10.7.2
10.8
10.9
10.10
10.11
–
10.10
10.11
10.12
–
–
11.1
11.2
12
12
12.1.
12.2
12.3
Under
consideration
–
–
12
12.1
12.2
12.3
12.4
Clause
Routine tests on cables and on the main
insulation of prefabricated accessories
General
Partial discharge test
Voltage test
Electrical test on oversheath of the cable
Sample tests on cables
General
Frequency of tests
Repetition of tests
Conductor examination
Measurement of electrical resistance of
conductor and metal screen
Measurement of thickness of cable
insulation and oversheath
General
Requirements for the insulation
Requirements for the cable oversheath
Measurement of thickness of metal sheath
Lead or lead alloy sheath
Plain or corrugated aluminium sheath
Measurement of diameters
Hot set test for XLPE, EPR (and HEPR)
insulations
Measurement of capacitance
Measurement of density of HDPE insulation
Lightning impulse voltage test
Water penetration test
Tests on components of cables with a
longitudinally applied metal tape or foil,
bonded to the oversheath
Sample tests on accessories
Tests on components
Tests on complete accessory
Type tests on cable systems
General
Range of type approval
Summary of type tests
Electrical type tests on complete cable
systems
Clause number
IEC
IEC
60840
62067
Ed.4
Ed.2
2011
2011
9
9
9.1
9.2
9.3
9.4
10
10.1
10.2
10.3
10.4
10.5
9.1
9.2
9.3
9.4
10
10.1
10.2
10.3
10.4
10.5
10.6
10.6
10.6.1
10.6.2
10.6.3
10.7
10.7.1
10.7.2
10.8
10.9
10.6.1
10.6.2
10.6.3
10.7
10.7.1
10.7.2
10.8
10.9
10.10
10.11
10.12
10.13
10.14
10.10
10.11
10.12
10.13
10.14
11
11
11.1
11.2
12
12.1
12.2
12.3
12.4
11.1
11.2
12
12.1
12.2
12.3
12.4
(continued)
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
Clause Number
IEC
IEC
60840
62067
Ed.3
Ed.1
2004
2001
12.3.1
12.4.1
12.3.2
–
12.3.3
12.3.4.
12.3.5
12.3.6
12.3.7
12.4.2
12.4.3
12.4.4
12.4.5
12.4.6
12.4.7
–
–
–
12.3.8
12.3.9
12.4
12.4.8
12.4.9
12.4.10
12.4.11
12.5
12.4.1
12.4.2
12.5.1
12.5.2
12.3.3
12.5.3
12.4.4
12.5.4
12.4.5
12.5.5
12.4.6
12.5.6
12.4.7
12.5.7
12.4.8
12.5.8
12.4.9
12.5.9
12.4.10
12.5.10
12.4.11
12.4.12
12.5.11
12.5.12
12.4.17
12.5.13
Clause
Test voltage values (check of insulation
thickness)
Tests and sequence of tests
Special provisions
Bending test
Partial discharge tests
Tan δ measurement
Heating cycle voltage test
Lightning impulse voltage test followed by a
power frequency voltage test
Switching impulse voltage test
Lightning impulse voltage test
Examination
Resistivity of semi-conducting screens
Non-electrical type tests on cable
components and on complete cable
Check of cable construction
Tests for determining the mechanical
properties of insulation before and after
ageing
Tests for determining the mechanical
properties of oversheaths before and after
ageing
Ageing tests on pieces of complete cable to
check compatibility of materials
Loss of mass test on PVC oversheaths of
type ST2
Pressure test at high temperature on
oversheaths
Test on PVC oversheaths (ST1, ST2) at low
temperature
Heat shock test for PVC oversheaths (ST1
and ST2)
Ozone resistance test for EPR and HEPR
insulations
Hot set test for EPR,(HEPR) and XLPE
insulations
Measurement of density of HDPE insulation
Measurement of carbon black content of
black PE oversheaths (ST3 and ST7)
Test under fire conditions
185
Clause number
IEC
IEC
60840
62067
Ed.4
Ed.2
2011
2011
12.4.1
12.4.1
12.4.2
–
12.4.3
12.4.4
12.4.5
12.4.6
12.4.7
12.4.2
–
12.4.3
12.4.4
12.4.5
12.4.6
12.4.8
12.4.9
12.5
12.4.7.1
12.4.7.2
12.4.8
12.4.9
12.5
12.5.1
12.5.2
12.5.1
12.5.2
12.5.3
12.5.3
12.5.4
12.5.4
12.5.5
12.5.5
12.5.6
12.5.6
12.5.7
12.5.7
12.5.8
12.5.8
12.5.9
12.5.9
12.5.10
12.5.10
12.5.11
12.5.12
12.5.11
12.5.12
12.5.13
12.5.13
(continued)
186
J. Becker
Clause Number
IEC
IEC
60840
62067
Ed.3
Ed.1
2004
2001
12.4.18 12.5.14
12.4.19 –
12.4.13
–
12.4.14
–
12.4.15
–
12.4.16
–
NA
13
13.1
13.2
13.2
13.2.1
13.2.2
13.2.3
13.2.4
13.2.5
–
–
–
13
13
13.1
13.2
13.3
14
14
–
–
14.3.2
14.3.1
NA
NA
Clause
Water penetration test
Tests on components of cables with a
longitudinally applied metal tape or foil,
bonded to the oversheath
Shrinkage test for PE, HDPE and XLPE
insulations
Shrinkage test for PE oversheaths (ST3 and
ST7)
Determination of hardness of HEPR
insulation
Determination of the elastic modulus of
HEPR insulation
Prequalification test of the cable system
General and range of prequalification test
approval
Prequalification test on complete system
Summary of prequalification tests
(Check of insulation thickness) Test voltage
values
Test arrangement
Heating cycle voltage test
Lightning impulse voltage test
Examination
Tests for the extension of the
prequalification of a cable system
Summary of the extension of
prequalification test
Electrical part of the extension of
prequalification tests on complete cable
system
Type tests on cables
General
Range of type approval
Summary of type tests
Electrical type tests on completed cables
Type tests on accessories
General
Range of type approval
Summary of type tests
Electrical type tests on accessories
Test voltage values
Clause number
IEC
IEC
60840
62067
Ed.4
Ed.2
2011
2011
12.5.14 12.5.14
12.5.15 12.5.15
12.5.16
–
12.5.17
–
12.5.18
–
12.5.19
NA
13
13.1
13
13.1
13.2
13.2.1
13.2.2
13.2
13.2.1
13.2.2
13.2.3
13.2.4
13.2.5
13.2.6
13.3
13.2.3
13.2.4
13.2.5
13.2.6
13.3
13.3.1
13.3.1
13.3.2
13.3.2
14
14.1
14.2
14.3
14.4
15
15.1
15.2
15.3
15.4
15.4.1
NA
NA
(continued)
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
Clause Number
IEC
IEC
60840
62067
Ed.3
Ed.1
2004
2001
14.3.2
15
14
15
14
15.1
14.1
15.2
14.2
4.6
Clause
Tests and sequence of tests
Electrical tests after installation
General
DC voltage test of the oversheath
AC voltage test of the insulation
187
Clause number
IEC
IEC
60840
62067
Ed.4
Ed.2
2011
2011
15.4.2
16
16
16.1
16.1
16.2
16.2
16.3
16.3
References
[1] IEC 60840 Ed.1 1998, “Tests for Power Cables with Extruded Insulation of
Rated Voltages above 30 kV (Um ¼ 36 kV) up to 150 kV (Um ¼ 170 kV)”
[2] IEC 60840 Ed.2, February 1999 and Ed.3, April 2004, “Power Cables with
extruded insulation and their accessories for rated voltages above 30 kV (Um ¼
36 kV) up to 150 kV (Um ¼ 170 kV) - Test methods and requirements”
[3] ELECTRA 151, December 1993, Cigré Working Group 21.03 “Recommendations for electrical tests type, sample and routine, on extruded cables and accessories at voltages >150 (170) kV and 400 (420) kV”
[4] ELECTRA 151, December 1993, Cigré Working Group 21.03 “Recommendations for electrical tests prequalification and development on extruded cables and
accessories at voltages >150 (170) kV and 400 (420) kV”
[5] Cigré SC21 Website paper Doc 97.08, 1997, Working Group 21.03 “Recommendations for electrical tests (type, special and routine) on extruded cables and
accessories at voltages >150 (170) kV and 500 (525) kV”
[6] Cigré SC21 Website paper Doc 97.07, 1997, Working Group 21.03 “Recommendations for electrical tests prequalification and development on extruded
cables and accessories at voltages >150(170) kV and 500 (525) kV”
[7] IEC 62067 Ed.1, October 2001,” Power Cables with extruded insulation and their
accessories for rated voltages above 150 kV (Um ¼ 170 kV) up to 500 kV (Um ¼
550 kV) – Test methods and requirements”
[8] “Evolution of ac breakdown strength of XLPE HV cable after long term test, and
correlation with physical properties” 4th International Conference on Conduction
and Breakdown in Solid Dielectrics, Sestri Levante, Italia (1992). J. Bezille,
H. Janah, J. Becker and H. Schädlich
[9] “Evolution of ac and impulse breakdown strength of HV cable after long
term test. Correlation with physical properties” C.E.I.D.P., Arlington, Texas,
USA 94, Annual Report, pp. 582–87 (1994). J. Bezille, H. Janah, J. Chan
and M. D. Hartley, See also Jicable 95, Versailles, France, paper A.8.3
(pp. 212–14)
188
J. Becker
[10] “Les limites des études de vieillissement sur le polyéthylène”, Jicable 95, Versailles, France, paper B.9.1 (pp. 476–80) F. Duchateau et al.
[11] “Optimisation des procédures physico-chimiques d’analyses destinées à l’étude
du vieillissement du polyéthylène, isolant pour c^ables d’énergie” Jicable 95, Versailles, France, paper B.9.2 (pp. 481–87) F. Duchateau et Co-auteur
[12] “Investigation of XLPE insulations after high stress ageing”, Jicable 95, Versailles, France, paper B.9.4 (pp. 494–99) H. Schädlich and J. Klass
[13] “AC field ageing of power cables”, Jicable 99, Versailles, France, paper B 3.3
(p405) J. L. Parpal, P. Mirebeau, D. Coelho, H. Janah, F. Gahungu, J. Cardinaels
et D. Meurer
[14] “Assessment under high dielectric field of the long term behaviour of power
polyethylene insulant”, Jicable 99, Versailles, France, paper B 4.2 (pp 424–429)
R. Clavreul, M. H. Luton, J. Berdala, H. Janah and P. Laurenson
[15] “Evaluation of modelling of thermo-electric ageing of XLPE insulated power
cables: the ARTEMIS outcome”, Jicable 03, Versailles, France, paper B.7.5
(pp 525–530) C. Laurent and A. Campus
[16] “Electrical Degradation and Breakdown in Polymers”, IEE Materials and
Devices Series 9, Peter Peregrinus Ltd, 1992, ISBN 0-86341-196-7 Dissado L.
A and Fothergill J.C
[17] ELECTRA 140, February 1992, Working Group 21.09 “Considerations of
ageing factors in extruded insulation cables and accessories”
[18] ELECTRA 139, 1991, Working Group 21-09 “Working Gradient of HV and
EHV Cables with Extruded Insulation and its Effects”
[19] ELECTRA 137, 1991, Working Group 21-10 “Survey of the service performance on HV AC cable systems”
[19 bis] Cigre TB 379, April 2009, Working Group B1,10 “Update at Service
Experience of HV Underground and Submarine Cable Systems”
[20] Cigré TB 89, 1994, Working Group 21.06, “Accessories for HV extruded
cables, types of accessories and terminology”
[21] “Development and Installation of Long-Distance 275-kV XLPE Cable Lines in
Japan”, Cigré paper 21-102, Paris 1990. K. Kaminaga, T. Asakura, Y. Ohashi,
Y. Mukaiyama
[22] “Prequalification testing of EHV XLPE cable system”; Understanding and
Managing Underground Transmission and Distribution Cables, CEA Workshop,
June 10–13, 2001. Jean-Luc Parpal.
[23] “New 400kV XLPE Long Distance Cable Systems, Their First Application of
the Power supply of Berlin” Cigré paper 21-109, Paris 1998 Henningsen C. H.,
Muller K. B., Polster K. and Schroth R. G
[24] “Development of High Stress HV and EHV XLPE Cable Systems”, Cigré paper 21–
108, Paris 1998 Attwood J. A., Gregory B., Dickenson M., Hampton R.H. and Svoma R
[25] “Development of a 420 kV XLPE Cable System for the Metropolitan Power
Project in Copenhagen”, Cigré paper 21-201, Paris 1996 P. Andersen,
M. Dam-Andersen, L. Lorensen, O. Kjaer Nielsen, S.H. Poulsen, B.S.Hansen,
T. Tanabe, S. Suzuki
[26] “State of the Art in EHV XLPE Cable Systems”, Jicable 99, Versailles, France,
paper A 2.2 (pp 44–49) A. Bolza, D. Kunze, S. Norman, S. Pöhler
4
Qualification Procedures for HV and EHV AC Extruded Underground Cable. . .
189
[27] “Long term test of 500kV XLPE cables and accessories” Cigré, Paper 21-202,
Paris 1996 Kaminaga K., et al.
[28] “Prequalification Testing of 345kV Extruded Insulation Cable System” Cigré
paper 21-101, Paris 1998 Parpal J.L. et al.
[29] “Prequalification testing of 290/500(525) kV extruded cable system at IREQ”,
Jicable99, Versailles, France, paper A.2.3 (pp 50–55) Parpal J. L. et al.
[30] “Development and Qualification of a new 400 kV Cable System with Integrated
Sensors for Diagnostics”, Cigré paper 21-103, Paris 1998 G.P. Van der Wijk,
E. Pultrum, H.T.F. Geene
[31] “Qualification of a highly electrically and mechanically stressed AC cable
system”; Jicable 03, Versailles, France, paper A.2.1 (pp 38–44) Erisson et al.
[32] “Design of a new 150 kV cable system for the Belgian electrical network”,
Jicable 99, Versailles, France, paper A.1.5 (pp 25–30) Couneson/Argaut et al.
[33] “150 kV underground links in Belgium: A new technical stage for XLPE
insulated cables”; Cigré paper 21–101, Paris 2000 Couneson/Becker et al.
[34] “Development of factory expanded cold shrinkable joint for HV XLPE
cables”; Jicable 03, Versailles, France, paper A.5.1 (pp 148–153)
Kobayashi et al.
[35] “Development of cold shrinkable joints for 110-230 kV XLPE cables”; Jicable
03, Versailles, France, paper A.5.3 (pp 164–169) Nakamura et al.
[36] “Super compact rubber block joint with high dielectric constant layer”; Jicable
03, Versailles, France, paper A.6.1 (pp 175–180). Ninobe et al.
[37] “Micro varistor based field grading elements for HV terminations”; Jicable
03, Versailles, France, paper A.6.3. (pp 186–190) Gramespaker et al.
[38] “Anti explosion protection for HV porcelain & composite terminations”; Jicable
03, Versailles, France, paper A.6.2 (pp 86–190) Gahungu et al.
[39] “New dry outdoor termination for HV extruded cables”; Jicable 03, Versailles,
France, paper A.6.4 (pp 191–196) Dejean et al.
[40] “Plug-in type connection technique using HV-connex on encapsulated components in high voltage equipment up to Um ¼ 245 kV”; Jicable 03, Versailles,
France, paper A.6.5 (pp 197–198) Deister et al.
[41] “Type testing of cables and accessories”; Jicable 99, Versailles, France, paper
C.10.1 (pp 880–883) Berlijn et al
[42] “Type testing of cables and their accessories, some statistics”; CIRED May
2003 Pultrum et al.
[43] French specification for HV cables: NF C 32 352 “Insulated or protected cables
for power systems. Single core cables with polymeric insulation of rated voltages
above 30 kV (Um ¼ 36 kV) up to 150 kV (Um ¼ 170 kV)”
[44] French specification for EHV cables: C 33 253 “Insulated cables for power
systems. Single core cables with polymeric insulation of rated voltages above
150 kV (Um ¼ 170 kV) up to 500 kV (Um ¼ 525 kV)”
[45] “Testing of extruded cables: experiences in type testing, PQ testing and test after
installation. What do we learn from it?”; Cigré paper B1-104, Paris 2004
E. Pultrum, S.A.M. Verhoeven
[46] Contribution to the discussion of the Cigré SC B1 session, Paris 2004
E. Dorison
190
J. Becker
[47] ELECTRA 205, December 2002, TF21-05 “Experiences with AC Tests after
installation on the main insulation of polymeric (E) HV cable systems”
[48] JEC-3408-1997, Standard of The Japanese Electrotechnical Committee, “High
Voltage Tests on Cross-Linked Polyethylene Insulated Cables and their Accessories for Rated Voltage From 11kV up to 275kV”; The institute of Electrical
Engineers of Japan
[49] “Prequalification testing of EHV XLPE cable systems”; CEA Workshop, June
10–13, 2001 J.L Parpal.
[50] “Prequalification testing of 290/500 kV Extruded cable system at IREQ”;
Jicable 99, Versailles, France, paper A 2.3 (pp 50–55) J.L Parpal at al.
[51] “EHV XLPE cable systems up to 400 kV – more than 10 years filed experience”; Cigré paper B1-102, Paris 2004 W. G. Weissenberg, U. Rengel, R. Scherer
[52] “Prequalification test of 400 kV XLPE cable system “; Jicable 95, Versailles,
France, paper A.1.3 (pp 11–15) Helling K., Henningsen C.G., Polster K., Bosotti
O., Mosca W., Tellarini
[53] Cigré TB 210, 2002, Joint Task Force 21/15 “Interfaces in accessories for
extruded HV and EHV cables”
[54] “Development of a 420kV XLPE Cable System for the Metropolitan Power
Project in Copenhagen”; Cigré paper 21-201, Paris 1996
[55] “Construction of the world’s first long-distance 500kV XLPE cable line”; Cigré
paper 21-106, Paris 2000
Jean Becker was born on 30 August 1938. He got a diploma as
Electrical engineer AIM AILG in Electronics and Electrotechnique from the University of LIEGE in Belgium as: “Master
of Science in Engineering.” From 1964 to 2003 he has been in the
Electrical Cable Business. Involved in the development and testing of all kinds of cables (low, medium, and high voltage, communication cables, special cables), in the manufacturing of low,
MV, HV, and EHV cables, in the development and testing of HV
and EHV accessories in the design of HV and EHV links, and the
installation of HV and EHV cables. He was the Competence
Center Manager of the Extra High Voltage Cables for the Nexans
Group during the last 10 years of his career in this business career.
Since 1978, he was a Member of IEC TC20-WG16, dealing with
the international specifications of low, medium high, and extra
high voltage cables, accessories, and cable systems. Since 1985 he
was in Cigré as an expert in HV and EHV cable systems. He has
been the Convener of two Cigré Working Groups and contributed
to several other Cigré WGs as an expert. Since his retirement in
2003, he was a consultant. As such he continued to work with
Cigré and has been involved as an expert in breakdown problems
of HV and EHV cable systems.
Jean was serving as Secretary of the ISTC of Jicable 2015 when he
suddenly passed away in April 2015, leaving the Cable Community in great sorrow.
5
Cable Accessory Workmanship on Extruded
High Voltage Cables
Kieron Leeburn
Contents
5.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.3 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.3.1 Inclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.3.2 Exclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.4 Related Literature and Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.4.1 Related Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.4.2 Additional Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5 General Risks and Skills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.6 Technical Risks and Required Specific Skills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.6.1 Conductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.6.2 Insulation Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.6.3 Metallic Sheath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.6.4 Oversheath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.6.5 Installation of Joint Electric Field Control Components . . . . . . . . . . . . . . . . . . . . . . . . .
5.6.6 Installation of Termination Electric Field Control Components . . . . . . . . . . . . . . . . .
5.6.7 Outer Protection of Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.6.8 Filling of Terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.6.9 Handling of Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.7 Skills Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.7.1 Aspects to be Tested . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.7.2 Methods of Qualification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.7.3 Certification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.7.4 Duration of Certification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.7.5 Upskilling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.7.6 New Accessory Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
192
192
194
194
194
194
194
195
195
197
197
202
209
217
217
227
230
233
233
237
238
238
239
239
240
240
Published as Cigré TB 476 in October 2011
K. Leeburn (*)
CBI Electric African Cables, Chief Engineer Process and Product in HV, Vereeniging, South Africa
e-mail: Kieron.leeburn@cbi-electric.com
© Springer Nature Switzerland AG 2021
P. Argaut (ed.), Accessories for HV and EHV Extruded Cables, CIGRE Green Books,
https://doi.org/10.1007/978-3-030-39466-0_5
191
192
K. Leeburn
5.8 Set Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.8.1 Organisation of Jointing Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.8.2 Positioning of Joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.8.3 Environmental Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.8.4 Cable End Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.8.5 Verification of Each Step . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.8.6 Measuring of Diameters, Ovality, Concentricity, Position . . . . . . . . . . . . . . . . . . . . . . .
5.8.7 Safety and Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.8.8 Environmental Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.8.9 Quality Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Appendix A: Model Certificate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Appendix B: QA Document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.1
240
240
241
241
241
241
242
242
242
242
243
249
256
Summary
This Chapter 5 (Published as Cigré TB 476) covers workmanship associated with the
jointing and terminating of AC land cables incorporating extruded dielectrics for the
voltage range above 30 kV (Um ¼ 36 kV) up to 500 kV (Um ¼ 550 kV). Cigré TB
476 is a complement of Cigré TB 177 (See ▶ Chaps. 1, “Compendium of Accessory
Types Used for AC HV Extruded Cables” and ▶ 2, “A Guide to the Selection of
Accessories”), the recommendations of which are not questioned in this chapter. A short
section covers general risks and skills, but the bulk of the chapter focuses on the specific
Technical Risks and the associated skills needed to mitigate these risks. This is done for
each installation phase. This Chapter is not an Instruction Manual, but rather gives
guidance to the reader on which aspects needs to be carefully considered in evaluating
the execution of the work at hand. The supplier’s Instruction Manual is considered the
primary source of technical information. A section on skills assessment helps the
qualification of jointers. Finally, attached appendices give samples of a certificate and
QA documentation.
This chapter is intended for a broad range of readers. It is risk mitigation focussed
so the reader can develop his personal use for the document.
5.2
Introduction
High Voltage cable accessories are manufactured using high quality materials and very
sophisticated production equipment. Recent technical and technological developments
in the field in their design, manufacturing and testing have made it possible to have pre
moulded joints and stress cones for terminations up to 500 kV as well as cold shrink
joints for up to 400 kV. One conclusion of Cigré TB 379 – Update of service
experience of Underground and Submarine cables – is that internal failure rates of
accessories, particularly on XLPE cable are higher than other components and are of
great concern. Focus on quality control during jointing operations must be maintained.
Many utilities have adopted the “system approach” by purchasing the cables as
well as the major accessories from same supplier. Some of these utilities would also
5
Cable Accessory Workmanship on Extruded High Voltage Cables
193
request that the link should be installed by the supplier or by a contractor under the
supplier’s supervision in a “turn Key” fashion. The main advantage of this approach
is that the entire responsibility for the materials and workmanship is clearly the
supplier’s.
Some customers have adopted the component approach by purchasing the cables
and the accessories from different suppliers and to entrust the installation to a third
party.
In all cases, it is imperative that, the installation be carried out by qualified
jointers who follow the jointing instructions provided by the supplier.
International standards such as IEC and IEEE provide the necessary guidelines
concerning the interface between cables and accessories. However, it is highly
recommended that the responsible engineer should satisfactorily verify the compatibility of the different components of the link.
It is of vital importance to manage the interface between the cables and the
accessories in order to reduce the potential technical risk.
One of the trends that have been developing in the international cable technology
is the reduction of the cable insulation thickness and the corresponding increase of
electrical stresses. This tendency is based on a better knowledge and an improved
quality of the insulating material and the extrusion process. The cables and accessories are made under well-defined factory conditions. Their quality and reliability
are assured by adherence to well defined specifications. The accessories, however,
are mounted on site, and notwithstanding that this job is done by skilled and trained
jointers, it is often performed in more delicate and undefined conditions than in the
factory.
It is noted that most of the new HV links will be built using XLPE insulated
cables. With the imminent retirement of experienced jointers, a major shortage in this
field has been identified. There are few well structured training programmes and
accreditation processes in place in order to meet demand. Jointer skills are vital in
ensuring the reliability of the new links.
This chapter captures the state of the art of Jointing. It is considered the Best
Practice by the members of the SC B1 Study Committee as of 2009. It is acknowledged that other practices which are not explicitly covered in this brochure are not
necessarily bad practices. Great care should be exercised and the approach agreed
where a departure from this chapter is envisaged. Where alternative techniques are
detailed, no preference is intended nor implied unless specifically mentioned.
Diagrams are provided to illustrate the concept described and should not be
interpreted literally.
Working under induced voltages or currents is not considered in this Chapter. As
mentioned in Sect. 5.8.7, in this case precautions have to be taken to eliminate or
minimize the risk further work is in progress by WG B1.44.
Note: For the range above 36 kV, the risks associated with jointing are
considered significant due to the risk of a Medium 7Voltage (MV) jointing
(continued)
194
K. Leeburn
philosophy being applied to High Voltage (HV) cables. Cigré TB 303
(▶ Chap. 4, “Qualification Procedures for HV and EHV AC Extruded
Underground Cable Systems” of this book) indicates the qualification procedures for HV and EHV AC extruded underground cable systems.
5.3
Scope
5.3.1
Inclusions
The Scope is limited to all accessories of:
•
•
•
•
•
Extruded dielectric cables;
AC cables;
Land cables;
HV Cables covered by IEC 60840;
EHV Cables covered by IEC 62067;
Note: Asymmetric joints (eg different conductor material; conductor size;
insulation thickness; . . .etc. . .) are not specifically covered as the permutations are too numerous. Where these are encountered, each of the components should be evaluated in terms of the Technical Risks and the required
General and Specific Skills needed.
5.3.2
Exclusions
The scope specifically excludes:
•
•
•
•
•
•
•
•
•
After installation tests;
Cable pulling and Laying;
Direct Current Cables;
Fault finding;
Fluid Filled Cables;
Maintenance;
Submarine Cables;
Superconducting Cables;
Transition joints between Fluid Filled and Polymeric cables.
5.4
Related Literature and Terminology
5.4.1
Related Literature
• IEC 60050 Chapter 461: electric cables.
5
•
•
•
•
•
Cable Accessory Workmanship on Extruded High Voltage Cables
195
The defined vocabulary can be assumed valid throughout this brochure except
where specific note to the contrary is made.
Cigré TB 177 –Accessories for HV cables with extruded insulation.
This brochure is still a valid guide to the selection of accessories (▶ Chaps. 1,
“Compendium of Accessory Types Used for AC HV Extruded Cables” and ▶ 2,
“A Guide to the Selection of Accessories”). Annex in ▶ Chap. 1, “Compendium
of Accessory Types Used for AC HV Extruded Cables” concerns the terminology
(update of TB 89). It is adopted in its entirety except where specific note to the
contrary is made.
Cigré TB 194 – Construction, Laying and installation techniques for
extruded and self contained fluid filled cable systems.
Cigré TB 210 JTF 21/15 – Interfaces in high voltage accessories (▶ Chap. 3,
“Interfaces in Accessories for Extruded HV and EHV Cables”).
AEIC CG4-97 Guide for installation of extruded dielectric insulated power
cable system rated 69 kV through 138 kV (2nd ed.)
TB 379 Update of service experience of HV Underground and Submarine
Cable Systems (2004–2008)
5.4.2
Additional Terminology
• Jointing – A process referring generically to all types of assembly/mounting of
both joints and terminations. The term splicing is used in North America.
• Jointer – A person skilled in the art of Jointing. The term splicer is used in North
America.
• Due Care – This refers to familiarity with the specific activity, tool or material
being handled. It is intended to stress the importance of understanding and
precisely executing the work to be carried out.
• Technical Risk – An aspect, which, if not mitigated, could lead to the premature
failure of the cable and/or accessory.
• Good practices – Recommendation, based on practical experience, which can
mitigate Technical Risks.
• Work phases – Installation steps during cable workmanship of cable accessories.
• General skills – Skills normally acquired by jointers through training/exposure to
common HV cable accessories.
• Specific skills – Skills not commonly acquired. Requires specific training.
In this brochure tables conclude the general and specific skills and technical risks
related to a work phase.
5.5
General Risks and Skills
The quality and performance of any new link or replaced joints and terminations are
highly dependent on the skills and competence of the jointers who need to ensure the
proper installation of these accessories under less than ideal field conditions (Table 5.1).
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Table 5.1 General risks and required skills
Work Phase
Preparing the
jointing area
Risks
Accidents leading to cable or
accessories damage
Electric shocks
Traffic accidents
Collapse of joint bay or trench
Cable preparation
Cable straightening
Underside cable is blind
Over heating of insulation
Mechanically damaging the cable
Incomplete removal of graphite or
semi-conductive coating
Cutting cable too short
Cable outer sheath
cleaning
Cutting the cable
Preparing cable
insulation
Plumbing
Installing
terminations
All phases
Access to site with
installation under
voltage
Rough insulation surface leading
to bad interface between cable and
accessory
Local fire
Burns and loss of life or materials
Falling, injury
Personal injuries
Personal injuries
General skills
Sense of organisation and selection
of proper tools and equipment
Knowledge of electricity (voltage
induction, absence of voltage,
phasing etc.)
Proper grounding connections
Familiarity with safety and security
measures
Proper bracing
Due care
Use of electric heaters
Use of hydraulic equipment
Due care
Proper measurements
Use of an electric saw
Proper use of sanders
Meticulous sanding
Mastering the use of an open flame
(torch)
Mastering the use of fire
extinguisher
Working on scaffolding and at
heights
First aid help and reanimation
Training to have the authorisation
to work on site with installation
under voltage
Systematic and compulsory training is required by all High Voltage jointers.
However, other basic and general skills are also important. These include:
•
•
•
•
•
•
•
•
Sense of observation and organisation;
Environmental and safety awareness;
Problem solving, sometimes called “common sense”;
Ability to read and interpret drawings and instructions in the relevant language;
Good knowledge of materials and their physical and mechanical properties;
Good familiarity and handling of different electric and hydraulic tools;
Good understanding of electricity;
Precision in taking physical measurements.
Other essential basic attributes include:
• Patience;
• Dexterity;
• Discipline;
5
Cable Accessory Workmanship on Extruded High Voltage Cables
•
•
•
•
Sense of engagement;
Responsibility;
Physical fitness;
Mental fitness.
5.6
197
Technical Risks and Required Specific Skills
The primary source of technical information is the instruction manual supplied by
the accessory manufacturer. The required skills listed here are generally ordered
from the conductor outwards. It should be emphasised that this is not the order of
assembly of the accessory (some components need to be “pre-parked” before the
conductor is joined as these components cannot be added later).
It is essential that the jointer be well trained in the necessary skills.
Each element below first describes the procedure and then the associated known
risks as well as the essential skill set needed.
In addition it is emphasised that adherence to the instruction manual is essential.
5.6.1
Conductors
5.6.1.1 Conductor Preparation
The preparation phase includes:
• Cutting conductors according to the relevant instruction manual;
• Removing insulation using an approved tool;
• Protecting the cable from damage and metallic particles, while cutting the
conductor;
• Cleaning the insulation surface with an approved solvent, if it has been
contaminated;
• Removing tapes and powders;
• Cleaning conductor wires of fillers or coating compounds before jointing.
5.6.1.2 Compression
Deep indentation, hexagonal and other techniques of crimping are considered here.
These techniques include:
• Cleaning any enamel coating e.g. by applying heat or abrasion if applicable,
otherwise MIG/TIG welding must be adopted (Figs. 5.1 and 5.2);
• Deforming the ferrule and conductor by deep indentation or compression. It is
suitable for both copper and aluminium conductors;
• Using an hydraulic press;
• Carefully choosing the correct dies or punch and ensuring their compatibility with
the press jaws;
• Checking the number, position and sequence of compression as it may vary
depending on the conductor size and the compression tool capability. Aluminium
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K. Leeburn
Fig. 5.1 Cable end prepared
for top connector application
Fig. 5.2 Copper ferrule
suitable for compression
conductors usually require longer ferrules and more compression positions than
copper conductors;
• Removing, any sharp edges or marks from the ferrule, after compression, unless it
is screened by a metallic shield (Figs. 5.3, 5.4, and 5.5).
Good practice includes:
• Performing a trial compression on a spare sample of the actual conductor using a
spare ferrule and the actual tools and dies available.
5.6.1.3 MIG/TIG Welding
This technique includes:
• Using arc welding in gas with a feed wire of copper or aluminium;
• Ensuring that the wire is appropriate to the welding machine/method;
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Cable Accessory Workmanship on Extruded High Voltage Cables
199
Fig. 5.3 Examples of presses for compression
Fig. 5.4 Hexagonal
compression
• Cutting the conductor ends diagonally to form a V shape when placed in the
welding jig;
• Avoiding overheating of insulation during welding. Heat sinks or forced coolers
are generally applied on both sides of the exposed conductor and temperature
monitored with thermocouples;
• Removing enamel where enamelled copper wires are MIG/TIG welded, prior to
welding;
• Removing any sharp edges or marks from the connector, after welding.
Good practice includes:
• Performing trial MIG/TIG Welds on a spare sample of the actual conductor using
the actual jigs and welding equipment.
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K. Leeburn
Fig. 5.5 Deep indentation
5.6.1.4 Thermit Weld
Sometimes called exothermic welding or Cadweld. It uses chemical reagents in a
reusable crucible, placed above a mould specifically designed for the conductors
being welded.
This technique includes:
• Placing the correct quantity of reactants in a crucible;
• Taking care to avoid porosity and cavities in the welding mass due to any
presence of moisture or filler in the conductor;
• Carefully setting the gap between the conductors;
• Setting the crucible and mould assembly;
• Firing the reactants so they drop into the mould, melting the ends of the conductors together (Fig. 5.6);
• Dressing the weld. During this process, the presence of any porosity should be
noticeable.
Note: A safety and health risk is the high explosive reaction and formation
of gases that prevent this technique being used in confined areas.
Good practice includes:
• Preheating the mould to remove moisture;
• Performing a trial thermit weld on a spare sample of the actual conductor
(or connector) and the actual weld metals and moulds available (Fig. 5.7).
5.6.1.5 Mechanical Connection
This technique uses bolts to apply pressure to the underlying conductor. It can be
used on both copper and aluminium conductors. Either bolts are tightened until they
shear ensuring the correct connection force or they are tightened by a torque wrench
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Cable Accessory Workmanship on Extruded High Voltage Cables
201
Fig. 5.6 MIG welding
Fig. 5.7 Thermit Weld
to a specified torque. One connector may cover multiple conductor sizes. These
connectors do not require special tools.
This technique includes:
• Tightening the bolts in sequence as prescribed by the instruction manual;
• Removing any sharp edges or marks from the connector after breaking the head of
bolts by torque;
• Filling any holes if applicable (Figs. 5.8 and 5.9).
Good practice includes:
• Restraining the connector while applying tightening torque for small conductor
sizes (Table 5.2).
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K. Leeburn
Fig. 5.8 Mechanical connectors with shear bolts
Fig. 5.9 Mechanical
connectors tightened with
torque wrench
Table 5.2 Technical risks and specific skills for conductor connection techniques
Work phase
Conductor
preparation
Compression and
indentation
MIG/TIG
welding
Thermit weld
Mechanical
connection
Finishing of
connectors
5.6.2
Technical Risks
Contamination of
insulation
Wrong dies or punch
Wrong press
Overheating of the
cable
Moisture
Porosity
Overheating of the
cable insulation
Incorrect gap
Bolt too deep
Specific Skills
Cleaning of conductor and filler removal
Sharp edges
Depressions
Due care
Due care
Cleaning of conductor and filler removal Specific
MIG/TIG WeldingTechniques
Cleaning of conductor and filler removal Thermit
Welding
Due care
Insulation Preparation
The preparation of the cable insulation is considered to be the most critical step in the
installation of accessories on extruded cables.
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203
5.6.2.1 Straightening
In general, accessories require straightness of the cable during preparation. This can
be achieved by either cold straightening or hot straightening techniques. Cable has
the tendency to bend again as a result of the elastic memory of the insulation.
5.6.2.1.1 Cold Straightening
This technique includes:
• Straightening cable by bending if it has a solid Aluminium conductor. After
mechanical straightening, the cable will remain in its corrected position;
• Straightening of cables with stranded conductors by bending the cable beyond its
straight position and letting it return to a straight neutral position.
5.6.2.1.2 Hot Straightening
This technique includes:
• Heating the insulation to the specified temperature for the specified duration;
• Cooling it down while the cable is fixed in a straight position. The temperature
and duration can vary depending on conductor size as well as, insulation material
and thickness (Table 5.3).
5.6.2.2 Stripping of Insulation Screen
During this step, it is essential to follow the instruction manual requirements
especially with regard to:
• prepared core diameter;
• required roundness of the cable insulation.
Methods used for removing the screen are peeling, scraping and hot stripping or a
combination of these.
5.6.2.2.1 Peeling
This common technique includes:
• Carefully setting the tool to minimise the loss of insulation;
Table 5.3 Technical risks and specific skills for cable straightening techniques
Work phase
Cold
straightening
Hot
straightening
Technical risks
Excessive bending
Specific skills
Due care
Overheating due to inadequate temperature control Hot
core is more prone to mechanical damage
Operation of
heating equipment
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• Moving the peeling tool which contains a specially shaped knife in a circular
direction to remove the screen. It is inevitable that during peeling some core
insulation will be removed too (Figs. 5.10 and 5.11).
Good practice includes:
• Performing a peeling trial on an off-cut of the actual cable to be jointed to check
the setting of the tool.
5.6.2.2.2 Scraping
In most cases this technique uses glass and includes:
• Moving a fragmented, sharp piece of glass at a shallow angle over the insulation
screen, thereby removing the semiconducting layer until the cable insulation
becomes visible;
Fig. 5.10 Hot straightening of cable while fixed in straight position
Fig. 5.11 Examples of peeling tools
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Cable Accessory Workmanship on Extruded High Voltage Cables
205
• Repeating around the circumference ensuring even removal while avoiding flat
spots, cuts and dents. The scraping method results in a minimum loss of cable
insulation, but requires great skill.
Scraping can be combined with peeling in order to reduce the installation time
(Fig. 5.12).
5.6.2.2.3 Hot Stripping
This can only be performed on cables with strippable screens. This technique
includes:
• Heating the insulation screen with a torch or hot air gun;
• Cutting the screen longitudinally;
• Stripping the pieces like a banana. Hot stripping is a common method for cables
with EPR insulation.
The amount of heat applied should be carefully controlled (Table 5.4).
5.6.2.3 Preparing the End of the Insulation Screen
It is essential that the transition from the insulation screen to the cable insulation
surface is:
• Correctly tapered without depression particularly in the insulation;
• Smoothly prepared without any step;
Fig. 5.12 Scraping by glass
Table 5.4 Technical risks and specific skills for removing the insulation screen techniques
Work
phase
Peeling
Scraping
Hot
stripping
Technical risks
Uneven travel of the peeling tool Blunt tool Removing
too much insulation if the cable is not completely round
Flat spots on the insulation surface Cuts/dents in the
insulation surface
Burning of cable surface
Specific skills
Appropriate to insulation
type
Glassing
Handling the torch on
semiconducting layer
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K. Leeburn
• Within the specified dimensional tolerances.
Irregularities in this area can lead to a mismatch between field control body and
the cable insulation causing field enhancement and reduction of the interface
pressure.
The end of the insulation screen can be chamfered by means of peeling or
scraping. Peeling tools used for this purpose contain a specially angled knife. The
chamfer can also be achieved by carefully scraping with glass.
Sometimes semi-conducting paint is used to achieve a fine tapered transition.
Good practice includes:
• Checking the peeling tool settings by performing a trial on a spare piece of cable.
5.6.2.4 Smoothening the Insulation Surface
The quality of the interface between the cable insulation and field control body
significantly affects the reliability of the joint (▶ Chap. 3, “Interfaces in Accessories
for Extruded HV and EHV Cables”: ref. Cigré TB 210, Cigré JTF 21/15 Interfaces in
high voltage accessories).
Installation instructions should clearly indicate the cable preparation details,
including (Fig. 5.13):
• The smoothing technique
• The required degree of smoothness
• Dimensional tolerances.
The methods of smoothing the insulation surface include polishing, melting and a
combination of polishing and melting.
5.6.2.4.1 Polishing
This common technique involves circumferential sanding of the insulation to
remove grooves remaining from the peeling or scraping process. Generally emery
cloth is used with grain sizes ranging from 150 to 400 grit. For EHV accessories, a
grain size finer than 400 grit may be needed to achieve sufficient smoothness.
Fig. 5.13 Chamfering of the
end of the insulation screen
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207
5.6.2.4.2 Melting
This phase achieves a smooth insulation surface by melting and deforming the cable
insulation surface (Figs. 5.14; Table 5.5).
Melting techniques include:
• Applying a heat shrinkable tube made from fluorine or silicone rubber over the
cable insulation and shrinks it to fit on the insulation surface. The temperature of
the insulation surface is then controlled to above the melting point of the cable
insulation. The smoothness of the inner surface of the tube is transferred to the
insulation surface during the application of heat;
• Applying heat directly to the surface of the insulation. This is usually done with a
hot air gun rather than a flame which could scorch the surface of the insulation
(Table 5.6).
Flat spots in the cable surface should be avoided, as these could result in areas of
low interfacial pressure.
5.6.2.5 Cleaning of Insulation
The cable insulation surface has to be thoroughly cleaned in order to remove any
residue left during the insulation preparation.
Fig. 5.14 Polishing of the insulation
Table 5.5 Technical risks and specific skills for preparing the end of the insulation screen
Work
phase
Peeling
Scraping
Painting
Technical risks
Uneven travel of the peeling tool Blunt tool
Removing too much insulation if the cable is not completely
round
Cuts/dents in the insulation surface
Thick edge (untapered)
Specific skills
Handling peeling
tools
Glassing
Due care
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Table 5.6 Technical risks and specific skills for smoothening the insulation surface
Work phase
Polishing
(sanding)
Melting
Technical risks
Surface roughness Incorrect diameter Excessive ovality
Eccentric core preparation Flat spots on the insulation surface
Overheating, burning and deformation of cable surface
Damage during removal of heat shrink tube
Specific skills
Due care
Heating
technique Due
care
Table 5.7 Technical risks and specific skills for cleaning the cable insulation surface
Work phase
Cleaning with
solvent
Technical risk
Wrong solvent Too long exposure Dissolving of semiconducting
paint Cross contamination
Specific
skills
Due care
This is best achieved by using a lint free cloth or tissue wetted with an appropriate
cleaning fluid. Only solvents supplied with the jointing kit, or specifically defined
(full chemical name), should be used due to the risk of incompatibility.
Where semi-conducting paint has been used, be aware that the solvent can
remove the paint.
Water based cleaning fluids are strongly discouraged as they might leave moisture
or residues like soap on the surface.
Good practice includes
• Cleaning from the conductor end towards the semiconducting screen cut and
disposing of the cloth thereby preventing contamination (Table 5.7).
5.6.2.6 Shrinkage
Some insulation has stretch memory introduced into its molecular structure during
the extrusion process. When heated (during load) the insulation may revert to its
relaxed state. This shrinkage can cause a mismatch of the field control components.
Three known methods of mitigating this risk are:
• Locking the insulation e.g. by applying a clamp over the joint connector which
grips into specially peeled grooves in the insulation;
• Pre-shrinking the insulation to ensure all potential shrinkage in the joint has
already taken place;
• Tolerating the anticipated shrinkage in the design of the joint.
5.6.2.7 Lubrication
Lubricants are used to relieve the friction between different surfaces (cable and
accessories) during installation. Lubricants can fill possible gaps and increase the
initial breakdown strength. It is recommended that jointers do not take advantage of
5
Cable Accessory Workmanship on Extruded High Voltage Cables
209
Table 5.8 Technical and specific skills for limitation of the cable insulation shrinkage
Work phase
Insulation groove
Pre-shrinking
Technical risk
Wrong dimensions
Overheat the insulation
Specific skills
Due care
Handling of equipment
Table 5.9 Technical risks and specific skills for lubrication phase
Work phase
Lubrication
Technical risk
Polluting of lubricated surface
Technical skill
Due care
this feature, as lubricants will eventually be absorbed by the insulating materials,
resulting in reduced breakdown strength.
Lubricants used are commonly based on silicone oil or silicone grease.
The lubricant should be supplied in the jointing kit, or specified by the accessory
manufacturer to ensure compatibility with cable and accessory components
(Tables 5.8 and 5.9).
Care should be taken to avoid contamination by pollutants sticking to the
lubricant.
5.6.3
Metallic Sheath
The metallic sheath on cables is usually applied as a moisture barrier and mechanical
protection and/or to conduct sheath currents (inductive and capacitive) and fault
currents.
The connection between metallic sheath and accessory casing (joint shell or
wiping bell of the termination) should maintain these characteristics.
5.6.3.1 Welded Aluminium Sheath (WAS)
5.6.3.1.1 Preparation of Cable Sheath
This preparation phase includes:
• Cutting the welded aluminium sheath and the outer sheath perpendicular to the
cable axis;
• Taking great care to avoid damaging the underlying cable core;
• Using specifically designed tools for these operations;
• Making longitudinal cuts to remove the sheath and facilitate the mechanical and
electrical connections to other metallic components and allowing more room for
subsequent steps.
5.6.3.1.2 Metallic Sheath Continuity
Two methods can be used to maintain the earth screen continuity:
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Fig. 5.15 Connection on top
of the aluminium sheath
Welded aluminium sheath
Outer
sheath
Accessory casing
Plumbing
CABLE CORE
Connection on Outside of the Aluminium Sheath
This connection phase includes (Fig. 5.15):
• Peeling of the non-metallic outer sheath. This is usually done by applying heat to
the outer sheath;
• Cleaning of the aluminium surface to eliminate, amongst other things, the factory
applied glue and the aluminium oxide;
• Tinning of the accessory casing which is generally in copper or aluminium;
Connecting the WAS to the accessory casing by using the plumbing technique.
Connection under the Aluminium Sheat
This connection phase includes:
•
•
•
•
Making longitudinal cuts of the aluminium sheath and the outer sheath;
Opening out the aluminium sheath bonded to the outer sheath;
Inserting a connecting piece under the aluminium sheath;
Ensure an electrical and mechanical contact between the connecting piece and the
aluminium;
• Tinning the accessory casing which is generally in copper or aluminium;
Joining the connecting piece to the accessory casing by using the plumbing
technique or by mechanical assembly.
Additional Copper Wire Insulation Screen
Where a copper wire screen is applied in combination with the WAS, the connection
can include the following:
• Plumbing the wires into the tin wipe;
• Connecting the copper wires with the accessory casing using mechanical means
(eg lug);
• Connecting the copper wire screen of both cable ends (for joints) using mechanical means (eg ferrule);
5
Cable Accessory Workmanship on Extruded High Voltage Cables
211
• Connecting the copper wires directly with the bonding cables. (This can only be
applied if the copper wire screen is rated to handle the sheath currents).
Reinforcement
Glass fibre reinforced epoxy resin may be required over the tin wipes to improve
their mechanical strength (Fig. 5.16; Table 5.10).
5.6.3.2 Corrugated Sheaths: Aluminium (CAS); Copper (CCS); Stainless
Steel (CSS)
The techniques described apply to all three types unless specifically indicated
otherwise. The corrugation can be helical or discrete ring shape.
5.6.3.2.1 Preparation of Cable Sheath
The preparation phase includes:
•
•
•
•
Removing of the outer sheath perpendicularly to the cable axis;
Cleaning of bitumen and other coatings;
Removing of the oxide layer (CAS) by brushing vigorously;
Applying tin coating to a section of the corrugated sheath using the appropriate
flux;
• Removing of the corrugated sheath at the tinned section and rounding the
remaining edge.
Note: On CSS, longitudinal cutting is not recommended due to the hardness
of the stainless steel. One method of preparation is to drill a hole on a crest of
the corrugation and insert a special cutter in the hole. The sheath is cut
along the helical crest. After completion of one revolution, the trough is cut
by special scissors.
Accessory casing
Welded aluminium sheath
Plumbing or
mechanical assembly
Tightening device
Liaising piece
CABLE CORE
Fig. 5.16 Connection under the aluminium sheath
Outer
sheath
212
K. Leeburn
Table 5.10 Technical risks and specific skills for WAS connection
Work phase
Preparation of
cable sheath
Metallic screen
continuity
Connection on top
of WAS
Metallic screen
continuity
Connection under
WAS
Plumbing
Copper wire screen
Reinforcement
Technical Risks
• Cutting into the underlying
layers
• Overheating underlying layers
• Weak metallic screen continuity
due to an incomplete cleaning or
preparation of the aluminium
sheath or/and the metallic
connection before plumbing
• Faulty earth screen continuity
due to an improper mechanical
connection
• Damage to underlying layers
• Overheating the cable core
• Melting of the aluminium sheath
• Enclosing voids in the tin wipe,
which could lead to a weak
connection
• Poor plumbing connection of
the wire screen
• Poor mechanical connection due
to wrong dies or press
• Uncured resin
• Faulty glass-fibre tape
application
Specific Skills
• Handling of specific tools for this
work
• Removing the glued outer sheath
• Removing glue
• Tinning and Plumbing Techniques
• Controlling the heat of the torch
• Due care
• Plumbing Techniques
• Controlling the heat of the torch
• Plumbing technique
• Crimping techniques
• Resin mixing and glass-fibre
application techniques
Good practice includes:
• Cutting the metallic sheath on the crest of the corrugations.
5.6.3.2.2 Metallic Screen Continuity
Two common methods used to make electrical connection onto corrugated sheaths
are Plumbing and Soldering (Fig. 5.17).
Plumbing
This technique includes:
•
•
•
•
Applying a special tin alloy under heat to the surface of CAS;
Applying plumbing grease as a soldering flux, while heat is applied with a torch;
Deforming, compacting and smoothening the tin alloy by means of wiping;
Building up the valleys to provide a flat surface (platform) for making earthing
connections easier;
• Joining the connecting piece using similar plumbing techniques. These connection pieces can be solid or flexible.
5
Cable Accessory Workmanship on Extruded High Voltage Cables
Outer
sheath
Apply tin
coating
213
Cut on crest and
round remaining
Fig. 5.17 Preparation of cable sheath
Good practice includes:
• Leaving as much metallic sheath on the cable as possible to act as a heat sink
during the plumbing process as well as protecting the underlying layers from
splatter during the wiping process;
• Moving the torch circumferentially to ensure even heat distribution;
• Applying generous amount of tallow will keep the area of the wipe cool.
Note: Making a good, solid and smooth tin wipe, requires specific skills from
the jointers. Jointers that have been used to work with fluid filled accessories
should have the required specific skills.
Soldering
Where the connecting piece is braided tinned copper, this technique includes:
•
•
•
•
Tinning the surface of the sheath using the appropriate flux;
Fastening the braid to the tinned sheath using tinned copper binding wire;
Soldering the braid and binding wire to the tinned aluminium (copper) sheath;
Repeating the above on the joint or termination casing as appropriate.
5.6.3.2.3 Additional Copper Wire Insulation Screen
Where a copper wire screen is applied (specifically for CSS), the connection can
include the following:
• Plumbing the wires into the tin wipe;
• Connecting the copper wires with the accessory casing using mechanical means
(eg lug);
• Connecting the copper wire screen of both cable ends (for joints) using mechanical means (eg ferrule);
• Connecting the copper wires directly with the bonding cables. (This can only be
applied if the copper wire screen is rated to handle the sheath currents).
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K. Leeburn
Good practice includes:
• Leaving as much metallic sheath on the cable as possible to act as a heat sink
during the plumbing process as well as protecting the underlying layers from
splatter during the wiping process;
• Moving the torch circumferentially to ensure even heat distribution;
• Applying generous amount of tallow will keep the area of the wipe cool;
• Cutting the metallic sheath on the crest of the corrugations.
5.6.3.2.4 Reinforcement
Glass fibre reinforced epoxy resin may be required over the tin wipes to improve
their mechanical strength.
5.6.3.3 Lead Sheath
5.6.3.3.1 Preparation of Cable Sheath
This preparation phase includes:
• Cutting the lead sheath taking great care to avoid damaging the underlying cable
core. A safe method is to make one shallow (partial) circumferential cut and two
shallow longitudinal cuts toward the end. A tool specifically designed for this
operation should be used;
• Tearing the lead strip between the longitudinal cuts;
• Tearing the sheath along the circumferential cut (Table 5.11).
5.6.3.3.2 Metallic Screen Continuity
Plumbing is the most common method for connecting the lead sheath with the
accessory casing.
5.6.3.3.3 Additional Copper Wire Insulation Screen
Where a copper wire screen is applied in combination with the lead, the connection
can include the following:
• Plumbing the wires in the tin wipe;
• Connecting the copper wires with the accessory casing using mechanical means
(e.g. lug);
• Connecting the copper wire screen of both cable ends (for joints) using mechanical means (e.g. ferrule);
• Connecting the copper wires directly with the bonding cables. (This can only be
applied if the copper wire screen is rated to handle the sheath currents).
5.6.3.3.4 Reinforcement
Glass fibre reinforced epoxy resin may be required over the tin wipes to improve
their mechanical strength.
5
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Table 5.11 Technical risks and specific skills for Corrugated Sheath connections
Work phase
General
Technical Risks
Connecting cable screens where not intended
Cable
Preparation
Overheating the cable core during oversheath
removal
Cutting into underlying layers
Tinning
Use of wrong metal
Lack of brushing into valleys
Uneven circumferential heat (dry joint)
Excessive heat damaging underlying layers
Accidental oxidization of surface by touching or
other material contamination
Use of wrong gas
Use of wrong metal
Excessive heat damaging underlying layers Wipe
exceeds tinned area
Use of wrong gas
Poor plumbing connection of the wire screen.
Poor mechanical connection due to wrong dies or
press
Weak metallic screen continuity due to a bad
cleaning or preparation of the aluminium sheath
or/and the metallic connection before plumbing
Cutting into underlying layers
Platform Wipe
(CAS)
Copper wire
screen (CSS)
Connection
Cutting of
metallic sheath
Braided tinned
copper soldering
Reinforcement
Wrong flux
Overheating underlying layers
Insufficient braided copper pieces
Uncured resin
Faulty glass-fibre tape application
Specific skills
Know risks and
function of screen
connections
Controlling the heat of
the torch
Handling of specific
tools for this work
Tinning Techniques
Controlling the heat of
the torch
Due care
Plumbing Techniques
Plumbing techniques
Crimping techniques
Tinning and Plumbing
Techniques
Handling of specific
tools for this work
Soldering Techniques
Due care
Resin mixing and
glass-fibre application
techniques
5.6.3.4 Laminated Sheaths: Aluminium Polyethylene Laminate (APL);
Copper Polyethylene Laminate (CPL)
5.6.3.4.1 Preparation of Cable Sheath
This preparation phase includes:
• Carefully applying heat;
• Scraping until a clean surface is achieved.
5.6.3.4.2 Metallic Screen Continuity
This connection phase can include:
• Connecting the APL/CPL layer directly to the accessories with a roll spring, or
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K. Leeburn
• Folding the aluminium (APL) or copper (CPL) back over the spring and applying
an additional external connection. Sometimes an additional copper fabric tape is
used under the contact spring on either side. Folding back requires multiple
longitudinal cuts before bending outwards to ensure there is a clean aluminium
surface facing outwards. Where a semiconducting coating is bonded to the inside
of the APL this will need to be removed as well to ensure a good contact.
CPL also allows for:
• Plumbing, which makes it possible to establish a metal enclosed, moisture proof
connection between the cable sheath and the accessory casing. Great care has to
be taken when applying the heat for plumbing (Table 5.12; Fig. 5.18);
• Soldering with a soldering iron which is usually preferred. However this can be
achieved only if an additional tinned copper foil is used to cross the gap between
the cable sheath and the accessory casing.
5.6.3.4.3 Additional Copper Wire Insulation Screen
If a copper wire screen is applied in combination with APL/CPL, it is essential to
establish an electrical contact between the copper wire screen of the cable and the
laminated aluminium/copper sheath.
This can be achieved by:
• Bending the copper wires back and clamping using a roll spring, or
• Collecting the wires together and crimping in a lug or ferrule.
Table 5.12 Technical risks and specific skills for lead sheath connection
Work phase
Cable
Preparation
Technical Risks
Overheating the cable core during
oversheath removal
Cutting of lead
sheath
Plumbing
Cutting into the cable core
Copper wire
screen
Reinforcement
Overheating the cable core
Melting of the lead sheath
Enclosing voids in the tin wipe, which
could lead to a weak connection
Poor plumbing connection of the wire
screen.
Poor mechanical connection due to wrong
dies or press
Uncured resin
Faulty glass-fibre tape application
Specific skills
Controlling the heat of the
torch
Handling of specific tools for
this work
Handling of specific tools for
this work
Plumbing Techniques
Controlling the heat of the
torch
Plumbing techniques
Crimping techniques
Resin mixing and glass-fibre
application techniques
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Fig. 5.18 Arranging metallic sheath continuity with a contact spring
5.6.4
Oversheath
Prior to work, jointer should be aware about the cable design e.g. extruded semiconductive layer or graphite applied on the PVC or Polyethylene oversheath.
5.6.4.1 Case of Graphite Coating
This phase includes:
• Cleaning the graphite for a specified distance from its end;
• Removing all traces of graphite using a clean cloth moistened with a suitable
solvent;
• Abrading the previously washed area using aluminium oxide tape or coarse glass
paper to ensures that the embossed lettering is completely removed. It is essential
that the serving is abraded and any graphite that may be embedded in the extruded
sheath is removed;
• Performing an appropriate resistance measurement to confirm effective removal
of any conductive layers (Table 5.13).
5.6.4.2 Case of Extruded and Bonded Semi-Conducting Layer
Removal by shaving with a spoke shave or glass slides.
• Cleaning the semi-conducting layer for a specified distance from its end;
• Performing an appropriate resistance measurement to confirm effective removal
of any conducting layer.
5.6.4.3 Low Smoke, Zero Halogen, Enhanced Flame Performance
Sheaths
In the case of “special sheath materials”, advice should be sought from the cable
manufacturer.
5.6.5
Installation of Joint Electric Field Control Components
Check that the body is in good condition and that all surfaces (inside and outside) are
completely clean and free from defects. On joints, the accessory body is temporarily
parked on one cable core before connecting the conductor. Special tools are
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K. Leeburn
Table 5.13 Technical risks and specific skills for laminated sheath connections
Work phase
Cutting the cable sheath
Removing the PE cable sheath
by heating
Opening the Aluminium/
Copper foil
Plumbing/soldering
Technical risks
Damaging the cable core
(cutting)
Overheating the cable core
Poor contact due to bad
cleaning
Damage to thin Aluminium/
Copper layer
Damaging the cable core
(cutting)
Excessive heat damaging
underlying layers
Specific skills
Handling of specific tools
for this work
Controlling the heat of the
torch
Handling of specific tools
for this work
Plumbing and soldering
techniques
Table 5.14 Technical risks and specific skills for oversheath preparation
Work phase
Cleaning or removing of the
conductive or semiconducting
layer
Removing of the embossed
lettering
Technical Risks
Local overheating and fire risk due to
incomplete cleaning which can lead to surface
currents
Graphite concentration
Specific
Skills
Due
care
Due
care
generally required to guide the movement of the accessory body into the final
position and subsequently to align it correctly. The tools may include:
•
•
•
•
•
•
Movable supports;
Chain hoists;
Special clamps;
Special seals;
Dry nitrogen;
Lubricating grease which reduces the friction between cable core and the accessory body. Only use the lubrication specified in the instruction manual
(Tables 5.14 and 5.15).
5.6.5.1 Slip on Prefabricated Joint
The slip on technique represents the most common way of installing field control
components. These field control components are usually made from silicon rubber,
(e.g. RTV, LSR and HTV) or EPDM and have an integrated conductive deflector.
This deflector takes over the field control at the end of the semi-conductive insulation
screen of the prepared cable core. The joint body should be checked to ensure that it
is in good condition and that all surfaces (inside and outside) are completely clean
prior to installation.
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Table 5.15 Common Technical risks and specific skills for joint field control components
Work
phase
Core
preparation
Joint
parking
Technical risk
Dimension/tolerance
Specific skill
Due care
Cutting or damaging the joint body
Damage to conductive varnishes Selection of
wrong tools
Use of wrong tools
Use of wrong grease
Handling of sensitive
components
Fig. 5.19 Lubrication of the
joint
The installation phase includes:
• Lubricating the inner surface of the joint body and the cable core with grease or
other liquids specified by the manufacturer;
• Slipping the joint body on the cable core into a parking position in order to
prepare the conductor connection. It is advisable to temporarily cover the conductor during the positioning phase (Figs. 5.19, 5.20, 5.21, and 5.22);
• Checking for smoothness and cleanliness before the joint body is slipped on to the
prepared cable core;
• Slipping the joint body into the final position after making the conductor
connection;
• Using chain hoists or other auxiliary tools to help move the joint body.
• Good practice includes:
• Special movable supports are used in order to guide the movement of the
accessory body;
• Chain hoists with suitably auxiliary slip-on rings might be used in order to pull
the accessory body;
• The use of reference marks on the cable core to ensure correct positioning of the
joint body;
• Check the correct position of the accessory body which should be in accordance
with the instruction manuals. During positioning the accessory body, any slight
bulging of the body caused by the pulling process may in some cases be smoothed
out by slightly turning the body on the cable;
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K. Leeburn
Fig. 5.20 Lubrication of the
cable
Fig. 5.21 Joint body slipping
on the cable core
Fig. 5.22 Final position of
the joint body
• Temporary cover on cable conductor to ensure that the joint body is not damaged
during parking;
• Ensuring that instructions are followed where a specific installation tool is to be
used for locating the accessory body.
5.6.5.2 Expansion Joints
Cold-shrink pre-moulded bodies are expanded either in the factory or on site.
In the case of factory expanded joints, no expansion is required on site. All that
has to be checked is that the joint has not exceeded its expiry date.
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221
Site expanded joints have to be expanded onto a carrier tube in the field, just
before fitting them on the cable. Particular skills and tools are required for making a
field expanded joint or termination. The tools vary with each manufacturer and the
jointer must be trained in their use.
The jointer should ensure that the expanded body is positioned correctly as
specified by the manufacturer (Table 5.16).
Field expansion steps:
• Environmental aspects include:
– Checking to ensure that accessory components and expansion tools are in good
conditions, perfectly clean and free of defects;
– Carrying out expansion in a protected (dust-free environment in order to avoid
having impurities trapped between the carrier tube and the pre-moulded body);
– Ensuring that ambient temperature and humidity are in accordance with
manufacturer instructions (Fig. 5.23).
• Lubrication:
– Applying the specified quantity and type of lubricating oil/grease on the carrier
tube and/or inside the body before starting the field expansion operation;
– Applying lubrication, if specified, to the surface of cable insulation where the
body will be positioned.
For both factory and field expanded joints:
Table 5.16 Technical risks and specific skills for the “slip-on” prefabricated joint installation
Work
phase
Accessory
pulling
Preparation
Parking
Slipping
on
Technical risk
Any damage or cutting into the
body
Wrong joint body
Mis-alignment of the cable
Contamination of components prior
to slide on
Incorrect application of lubrication
Wrong preparation dimensions
Damage while positioning in
parking position due to sharp edges
of the conductor
Incorrect positioning of joint body
Damage by use of chain hoists
Damage of joint body and/or cable
core due to use of wrong tools
Damage due to improper fixation of
the accessory body
Damage to semi-conductive paint
Specific skills
Due care
Due care
Cleaning with specified solvents and the
correct use of grease
Due care
Due care
Awareness of the behaviour of accessory
bodies with different sizes during
movement on the cable core
Application of formulas or graphs for
calculating the premoulded body position
respect to reference marks made on the
cable
Handling of specific tools
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K. Leeburn
Fig. 5.23 Joint body
expansion onto a smooth
carrier tube
• Positioning on the cable.
The expanded body must be initially parked over the cable during the conductor
jointing operations. The body can remain expanded only for the time specified by
the manufacturer according to the material characteristics and the expansion rate.
Then it will be moved and positioned to the final position and the carrier tube
removed.
• Shrinking on the cable.
According to the different design of carrier tubes (i.e. helical tube or smooth onethe tube can be removed by hand or by a specific tool) (Figs. 5.24, 5.25, 5.26, and
5.27; Table 5.17).
5.6.5.3 Field Taped Joints
These cable accessories are formed by applying an insulating tape on suitably
prepared cable ends in the field (installation site). Fusing is only effective if the
tapes are stretched by the correct amount. The taping can be done manually or with
the help of a machine. Taping by the machine achieves a higher quality and/or
performance of the joint.
Field taped joints include:
•
•
•
•
•
•
Self-fusing (or self-amalgamating) rubber tape, which is usually made of EPR;
Semi-conductive self-fusing rubber tape;
Lead tape or copper braid;
PVC tape;
Waterproofing rubber tape;
High permittivity field grading tape (if required), etc...
Some tapes are impregnated with silicon oil to fill overlap gaps.
The taped profile and geometry forms the electrical stress control of the joint.
The taping phase includes:
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Fig. 5.24 Example of lubrication and fitting of a smooth carrier tube for a stress cone and a
joint body
Fig. 5.25 Removal of helical carrier tube from the joint body
Fig. 5.26 Removal of
smooth carrier tube from joint
Fig. 5.27 Cutting of tube
from cable core
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K. Leeburn
Table 5.17 Technical risks and specific skills for field expansion of premoulded body
Work
phase
General
Expansion
of the body
Carrier
tube
removal
Technical risks
The risks listed under Table 6.5.1
apply here
Presence of defects on the carrier
tube (e.g. sharp edges or cracks)
Presence of defects on the
expansion tooling (e.g. damaged
nose)
Breaking of the carrier tube during
removal Damage to the cable
insulation
Specific skills
The skills listed under Table 6.5.1 apply here
Due care
Ability to correctly remove the carrier tube.
Knowledge about handling the special tools
required for the removal of the smooth
carrier tube Handling of special tools and
equipment
Table 5.18 Technical risks and specific skills for field taped joints
Work
phase
Preparation
Taping
Technical risk
Contamination Mis-alignment of
the cable
Wrong tension during taping
Wrong stress control profile
(diameter and length)
Wrong settings of taping machine
Specific skills
Due care
High skill in hand taping
Knowledge of setting and operating taping
machines Reading technical drawings and
measuring
• Applying the tapes at the right pace, stretch, tension (Table 5.18);
• Ensuring that the correct profile is achieved and that air gaps and voids are
managed. Frequent measurement is required;
• Ensuring that the transition point between the taped insulation and the cable core
semiconducting layer is correctly applied;
• When a tapping machine is used, setting the parameters as per operating and
jointing instruction manuals. These settings include tension, pitch and return
limits;
• Continuing the semiconducting layer over the joint with a semiconducting tape;
• Depending on the instruction, lead tape may be applied over the semi-conducting
tape to ensure continuity (Fig. 5.28).
5.6.5.4 Field Moulded Joints (Extruded or Taped)
Tape Moulded and Extrusion Moulded joints are highly specialised. These proprietary joints are usually installed by the manufacturer and are thus not covered here.
5.6.5.5 Heatshrink Sleeve Joint
Heatshrink insulation is commonly used in Medium Voltage cable joints and has
recently been available for some High Voltage applications.
Heatshrink preparation phase includes:
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225
y
B
Stress control
profile
Rj
dy (x, y)
A
dx
Ri
Cable insulation
r
x
Conductor
Fig. 5.28 Taped profile and geometry
Table 5.19 Technical risks and specific skills for heatshrink joint
Work
phase
Shrinking
Technical risk
Wrong order of tube insertion Change in positioning during
shrinking Uneven shrinking Folds in tube
Specific skills
Shrinking of thick
wall tubes
• Careful positioning of the insulation in the heat shrinkable tube;
• Taking into account dimensional changes of the tube with the application of heat;
• Uniformly applying the heat and controlling the temperature in order to ensure
thetubes are shrunk uniformly.
5.6.5.6 Prefabricated Composite Type Joint
This joint consists of an epoxy insulation unit in which an electrode for shielding the
electric field of the connector is embedded and the premoulded stress cones are made
of rubber. Pressure is applied at the interfaces by a compression device which is
usually comprised of metallic springs.
These joints can also be used to connect cables having different conductor cross
sections and/or different insulation thicknesses (Table 5.19).
Assembly phase includes:
• Ensuring the straightness of the cable is within the prescribed limits given in the
instruction manual;
• Parking the joint shells, epoxy and rubber insulators;
• Lubricating the appropriate surfaces with the specified lubricant;
• Connecting the conductors with compression type connector.;
• Fixing the Epoxy insulation unit and Connector completely by fitting the HV
electrode embedded in the Epoxy insulation unit to connector;
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K. Leeburn
Cable
Epoxy insulation unit
Compression device
Connector
Premoulded insulator
Joint shell
HV electrode
Fig. 5.29 Prefabricated composite joint
Table 5.20 Technical risks and specific skills for prefabricated composite joint
Work phase
Insert parts
Setting the epoxy unit and Slide of
premoulded stress cone
Assemble the spring unit
Technical risk
Wrong order of inserting parts
Setting in wrong place
Wrong centering of the cable to
epoxy insulation unit
Damage to cable insulation
Lack of the designed pressure
Specific skills
Due care
Handling of specific
tools for this work
Due care
Due care
• Fitting and compressing with the springs the premoulded stress cones against the
epoxy insulation unit (Fig. 5.29; Table 5.20)
• Wiping the joint shells to the cable sheaths if applicable.
5.6.5.7 Plug-in Joint
Plug-in type joints are based on a premolded joint body, with integrated metal ring
for locking the cable ends in the joint.
The cable end preparation, i.e. installing the plugs, peeling and smoothening of
the cable insulation, require equivalent skills and tools as other premolded or
prefabricated joints. This applies also to the installation of the joint covering.
These joints can also be used to connect cables having different conductor cross
sections and/or different insulation thicknesses.
Specific tools and skills are needed to plug in the prepared cable ends. The tool
can be based on hand driven chain hoists or a hydraulically driven plug-in frame
(Fig. 5.30).
5.6.5.8 Pre-moulded Three Piece Joint
This joint consists of three pre-moulded parts. Two cable adapters containing the
stress control profiles and the main joint sleeve.
Assembly phase includes:
• Ensuring the straightness of the cable is within the prescribed limits;
• Parking the joint main sleeve and other outer components;
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227
Fig. 5.30 Cable plug-in tool
Table 5.21 Technical risks and specific skills for plug-in type joints
Work phase
Inspection of
cable end
Inserting cable
ends
Locking of the
plugs
•
•
•
•
Technical risk
Damaged plugs
Mis-alignment of the cable in case of hand driven
chain hoists
Not locking
Specific skills
Check plug and cable
ends
Due care
Pull back check of
cable
Lubricating the appropriate surfaces with the specified lubricant
Pushing on the cable adapters;
Connecting the conductors including installation of corona shield;
Pushing over the joint main sleeve (Table 5.21; Fig. 5.31).
5.6.6
Installation of Termination Electric Field Control Components
In order to successfully install terminations, the jointer must possess certain skills
and abilities. These depend on the following aspects: the technology of the terminations, the voltage levels and the manufacturer of the cable and accessories. The
procedures and skills as detailed in Sect. 0 above apply.
Installation of HV cable terminations present an additional set of challenges. As
most terminations are installed in a vertical position at a few meters from the ground,
special preparation of the work area is needed. Usually, a scaffolding system is built
around each cable (or the three cables) to facilitate access to cable and reduce strain
on the jointers. Some environmental protection against dust, wind, rain and snow is
also advisable.
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Joint main sleeve
K. Leeburn
Corona shield
HV electrode
Cable adapter
Stress profile
Screen connection
Conductor
connection
Shrinkable sleeves with
moisture barrier
Fig. 5.31 Three piece joint
Table 5.22 Technical risks and specific skills for pre-moulded three piece joint
Work phase
Parking
Core preparation
Pushing on of elastomeric parts
Technical risk
Wrong placing
Wrong measures
Bad surface
Wrong position
Specific skills
Due care
Handling of specific tools for this work
Due care
See also Table 5.16
Particular situations such as installation on poles, high voltage pylons and in
underground power generating station transformer vaults may require special work
area arrangement to ensure safety and ease of access.
5.6.6.1 Slip-on Prefabricated Field Control Components
The risks and skills as detailed in Sect. 0 above apply (Table 5.22).
5.6.6.2 Plug-in Terminations
Plug-in type terminations consist of a field control component usually made from
silicon rubber (e.g RTV, LSR and HTV) or EPDM, and an insulator made from
epoxy resin. This insulator represents the interface to switchgears, transformers or
bushings.
Two designs are commonly available:
• Inner Epoxy Cone – based on a rubber stress cone pushed into the epoxy
insulator, achieving the required interface pressure by means of metal springs;
• Outer Epoxy Cone – based on a rubber mould, pushed onto a conical bushing of
the epoxy insulator, achieving the interface pressure by stretching the rubber
mould.
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229
Table 5.23 Technical risks and specific skills for cone plug-in terminations
Work phase
Installing the epoxy insulator
Inserting cable ends (with or without
stress cone)
Locking of the plugs (if applicable)
Technical risk
Damaging the insulator
Unequal tightening of the bolts
Mis-alignment of the cable
Damaging the cable and or
stress cone
Not locking
Specific skills
Due care Check
torques
Due care
Check locking
Fig. 5.32 Plug-in
terminations based on inner
cone and outer cone model
The cable related part is based on slip-on or plug-in technology.
In this chapter only the plug-in technology is considered.
Installation skills and risks for field control components and insulators can be
taken from Sect. 5.6.5.1.
In addition, the handling of the insulator has to be considered representing an
additional interface to be cleaned and prepared according to given instructions
specified by the manufacturer (Table 5.23; Fig. 5.32).
5.6.6.3 Taped Terminations
This kind of cable accessory is formed by taping (paper) a field control element
(taped cone) in the field (installation site). This technique includes:
• Applying impregnated papers (conductive and insulating) specified by the manufacturer, according to the given measurements and instructions. Alternating
layers of conductive and non-conductive tapes establish a field control element
230
•
•
•
•
K. Leeburn
to be embedded finally in an insulator with a fluid insulation (insulating oil
e.g. silicone oil or polyisobutylene). The papers (width, length and thickness),
number of layers and profile of the taped cone are specified by the manufacturer;
Checking the profile several times during taping. At each time, the jointer should
estimate the final diameter and length of slope based on the diameter of remaining
tape. Usually the profile angle is smaller at the start of the slope and increases
further up;
Applying vacuum treatment to ensure that voids included in the paper wrapped
cone will disappear;
Heating and degassing the filling compound using special equipment in order to
remove any water and gas content. During this procedure the termination has to
be evacuated according to the given instructions. This procedure can last several
hours. During this time all values have to be controlled and monitored;
Avoiding contamination of the vessels and other equipment with water. The
environmental conditions (temperature, humidity, dust) should be
considered here.
5.6.6.4 Heatshrink Sleeve Insulated Terminations
The risks and skills, as detailed in Sect. 0, Heat-shrink sleeve joint apply here.
5.6.6.5 Prefabricated Composite Dry Terminations
The risks and skills, as detailed in Sect. 5.6.5.6, Prefabricated composite type joint
apply here.
5.6.7
Outer Protection of Joints
5.6.7.1 Polymeric Outer Protection by Taping and/or Heatshrink Tubes
Heat shrink tubes allow the installation of a watertight joint without the application
of a compound filled outer protection. The heat shrink tubes are often equipped with
an internal hot-melt glue layer (Fig. 5.33).
The application of tubes includes:
• Parking heat shrink tubes on one or both cable ends, prior to joint installation;
• Moving heat shrink tubes into place after inner joint components have been
applied;
• Shrinking the tubes in position;
• Avoiding excessive heat as it will lead to melting or even burning of the material;
• Ensuring sufficient heat is applied to enable the shrinking process and melting of
the glue;
• Installing an under lying tape layer if the heat shrink is not adequate to withstand
the sheath voltage requirements. A self fusing polymeric tape is often used for this
purpose (Tables 5.24 and 5.25).
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231
Fig. 5.33 Dry type
termination
Table 5.24 Technical risks and specific skills for taped terminations
Work phase
Taped
Accessories
(terminations)
Vacuum
treatment
Technical risk
Wrong order of material Wrong
positioning and diameter of the
specified layers as specified by the
manufacturer
Wrong positioning of conductive
layers Lack of cleanliness and dryness
of all components during taping
Inclusion of particles or voids during
taping must be avoided
Improper degassing
Specific skills
High skill in taping.
Operation of taping equipment
Dealing with measuring tools such as
vernier-callipers Read technical
drawings well
Handling of the equipment and basic
knowledge about the behavior of
fluids and vacuum treatment
Table 5.25 Technical risks and specific skills for polymeric outer protection (taping and/or
heatshrink tubes)
Work phase
Shrinking
Technical risks
Burning the polymeric material in case of too much heat
Insufficient melting of the hot-melt glue in case of too little heat
Folds in the tubes
Gaps between overlapping layers, resulting in leaks
Wrong amount of tension during taping
Specific skills
Heat control
Taping
Alternatively, a fully taped outer sheath is possible. A special tape is needed to
establish a water tight barrier, an insulating sheath and mechanical protection at the
same time.
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5.6.7.2 Outer Protection Assembly
Outer protection housings (including metal protectors, coffin boxes, etc) represent a
cover for joints to be filled with compounds. They can be made from e.g. PVC, PE,
GRP (glass reinforced polyester) or ABS (acrylonitrile butadiene styrene). They may
consist of a tube (to be positioned in the correct parking position) or two half pipes
(installed after positioning of joint body). The function of the outer protection
housing is to act as a container for the filling compounds referred to in 0 below.
This assembly phase includes:
• Parking of the outer protection if applicable;
• Positioning the components according to the instruction manual;
• Sealing all interfaces and openings to the environment by means of recommended
methods and materials like silicone, putty or self amalgamating silicone tapes;
• Filling as soon as possible to ensure no build up of moisture in the outer protector
due to humidity.
In the case where a joint is to be fixed to a support structure this should be done
before the outer protector is filled with compound.
5.6.7.3 Filling Compounds for Joint Protections (Joint Boxes)
The function of the filling compound is to establish a corrosion protection of the joint
body (joint shell) and cable, to improve the thermal conductivity, to avoid the
penetration of water into the joint (waterproof compound) and to ensure that the
screen interruption design is maintained. Products used for the filling include:
•
•
•
•
Cold pouring RTV (Room Temperature Vulcanization);
Mixed (Two component resin);
Heated (bitumen);
Insulating fluid or gas.
The filling phase includes:
• Preparing the work taking account of the environmental conditions such as
temperature, humidity, dust and dirt;
• Heating of the compound (if applicable);
• Mixing of the filling compound. Taking care to ensure the correct amounts of
additives are added, the mixing creates a chemical reaction and can be easily
influenced. Too little catalyst/hardener can result in undercuring. Too high temperature can cause precuring in the mixing pot (Table 5.26);
• Filling by using a pump or pouring the compound.
Good practice includes (when applicable):
• Taking a sample from each batch or joint in order to ensure that it has cured
properly;
• Considering the physical position of the joint in order to avoid air pockets;
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Cable Accessory Workmanship on Extruded High Voltage Cables
233
Table 5.26 Technical risks and specific skills for outer protection assembly
Work phase
Outer protection
assembly
Technical risks
Poor sealing of interfaces leading to loss of compound, poor
filling, etc. and leading to water penetration
Over tightening of bolts leading to cracking of outer protection
Incorrect horizontal positioning of outer protector leading to
poor filling
Specific
skills
Due care
• Not moving the joint before the compound is vulcanized or stable;
• Preventing contamination to ground and waterways.
5.6.8
Filling of Terminations
There are types of terminations that are to be filled with insulating compound,
typically they are metal enclosed GIS terminations and outdoor terminations. They
can be filled with insulating liquid or gas. For taped terminations the process is
covered in Sect. 5.6.6.3. In the case where the termination is to be filled with
compound the manufacturers filling instruction is to be followed; filling compound
may include such items as polybutene, silicon oil or other dielectric fluid, gas or
mixed two component resins.
The different filling compounds involves different steps, the main steps in
preparation phase includes:
• Preparing the work taking account of the environmental conditions such as
temperature, humidity, dust and dirt;
• Heating of filling compound to the correct temperature in order to facilitate filling
(if applicable);
• Evacuating the chamber (if specified);
• Mixing of components (if applicable);
• Filling by using a pump (compound or gas) or pouring the compound.
Good practice includes (when applicable):
• Taking a sample from each batch or termination in order to ensure that it has cured
properly (when applicable);
• Considering the physical position of the termination and be aware about the risk
of including air bubbles inside the chamber;
• Preventing contamination to ground and waterways.
5.6.9
Handling of Accessories
5.6.9.1 Supporting of Accessory
The support structure design for cable and accessories should be part of the civil
engineering. This should be done prior to cable installation and should not be
improvised on site.
234
K. Leeburn
Jointers need to ensure that the supporting structure is installed according to
prepared drawings and/or instructions (Table 5.27; Fig. 5.34).
This assembly phase includes:
• Applying the right amount of torque to the closing screws. Too much torque can
result in deformation of the polymeric jacket, while too little torque will reduce
the friction between cable (and/or joint) with the support structure and give
inadequate support and constraint.
Flame treating the extruded polythene sheath and applying a resin impregnated tape
system, in order to mechanically reinforce the cable/accessory interface where thermomechanical forces and movement might be experienced (Tables 5.28 and 5.29).
Table 5.27 Technical risks and specific skills for filling compounds
Work phase
Preparation
Technical risks
Contamination
Heating filling
compound
Filling of
compounds
(joints)
Overheating of compound
Underheating of compound
Insufficient hardeners or accelerators
Premature curing due to heat
Enclosed air pockets
Check of outer
protection
condition
Wrong order of materials
May be impossible to visually check
the vulcanization status afterwards
Fig. 5.34 Wet type
termination
Specific skills
Due care in cleanliness of equipment
and components
General skills and knowledge in
handling the equipment
The use of special equipment
(e.g. mixer) under clean conditions
Able to check and verify the correct
position Able to check the status of
the vulcanization.
General skills and knowledge in
handling the equipment
5
Cable Accessory Workmanship on Extruded High Voltage Cables
235
Table 5.28 Technical risks and specific skills for filling of terminations
Work phase
Preparation
Technical risk
Contamination
Heating filling
compound
Evacuating
chamber
Mixing of
components
Filling
Overheating of oil
Underheating of oil
Not evacuated enough
Incorrect curing of compounds with A
and B mixing components
Water or humidity presence during filling
Underfilling or overfilling
Air bubbles if the compound is filled or
mixed improperly
Specific skills
Due care in cleanliness of
equipment and components
Handling the equipment
Handling of equipment
Mixing and handling compounds
and tools
Handling the specific tool or
method required
Table 5.29 Technical risks and specific skills for installation of supporting of accessory
Work phase
Closing the clamps
on the cable (and
joint)
Erecting steelwork
Mechanical
reinforcement of
accessories
Technical risks
Applying the wrong torque on the closing
screws
Steelwork modification or the adjustment
on site may weaken the support or cause
steelwork corrosion at a later date
Burning of the PE oversheath Wrong resin
and/or deficient application
Specific skills
General skills and
knowledge in handling
with equipment
General skills
Heating techniques
5.6.9.2 Lifting of Accessories
It is sometimes necessary to lift accessories. It is necessary to lift all or part of the
terminations when fitting to the structure.
The lifting phase includes:
• Setting up the lifting equipment
• Adopting appropriate safety techniques and adherence to sling load ratings
• Securing the lifting device to the accessory taking care not to damage any
components. Supplier guidance should be adopted
• Lifting the accessory ensuring that the cable is not restrained as this may dislodge
some internal components (Fig. 5.35; Table 5.30).
5.6.9.3 Special Bonding Configurations and Link Box Installation
The jointer must have the skill to install the bonding leads (single and concentric),
the link boxes, SVLs, etc. associated with the particular bonding scheme adopted for
the cable circuit. Particular attention is drawn to the removal of the conducting layer,
if supplied, on the bonding leads in order to ensure integrity of the bonding design.
5.6.9.4 Sensor Connections
Many types of sensors can be installed on the cable accessories. These include:
236
K. Leeburn
Fig. 5.35 Example of lifting
of cable terminations by fixing
the lifting device in a) the
cable respectively b) the upper
metalwork of the termination
Table 5.30 Technical risks and specific skills for lifting/moving accessory
Work
phase
Lifting/
moving
•
•
•
•
•
Technical risks
Cable damage and displacing the
internal parts due to bending or twisting
of the cable Broken insulator Cracked
Porcelain Scratched polymeric sheds
Specific skills
General skills and knowledge in handling
with equipment Operator to be trained in
relevant aspect of lifting/moving for
accessory Rigging skills
Temperature;
Distributed temperate sensing;
Pressure (leak);
Partial discharge;
G as density, etc.
The kind of sensors used depends on the accessories and the requirements of the
manufacturer or the user. It should not be assumed that the HV cable jointer
automatically has the required sensor connection skills. The specific sensor supplier
should provide input on the suitable skill set needed.
Special care should be taken where insulated sheath systems are employed as the
sensors must not compromise the earth isolation.
5
Cable Accessory Workmanship on Extruded High Voltage Cables
237
Table 5.31 Technical risks and specific skills for special bonding configurations
Work phase
Connecting bonding lead
Filling link box with
compound e.g. bitumen
Technical risks
Sheath bonding connection error
Disturbed seal on bonding lead may
lead to water ingress
Similar risks as in 0
Specific skills
Knowledge of
bonding design
Due care
General skills and
as 0
Table 5.32 Technical risks and specific skills for sensor connections
Work phase
Connecting
sensors
Technical risks
Sheath bonding connection error Disturbed seal on bonding lead
may lead to water ingress
Specific
skills
Due Care
Note, these activities can be done by a third party (Tables 5.31 and 5.32).
5.6.9.5 Fibre Optics
In some specific installations, cables may be installed with optical fibres, mainly
used for temperature sensing.
Fibre optic cables can be:
• Integrated in the cable;
• Attached to the cable sheath from outside;
• Blown/pulled into a separate tube.
Usually the fibre optics have to be connected in splice boxes. Additional and very
different skills are necessary in order to make fibre optic connections. The general
handling of fibre optics has to be done very carefully.
For fibre optics integrated in the cable, the splice box is usually attached to the
cable close to the joint. It is common practice to integrate the splice box into the
coffin box or protection housing of the joint.
In order to connect the fibre optics to the splice box, one side of the cable must be cut
with an over length, taking the position of the splice box beyond the joint into account
(Table 5.33).
When sheath interruption joints are installed (eg cross bonding), it is common to use
two splice boxes (one on each side of the joint) with an additional intermediate fibre optic
splice box made from non conductive material without any outer metallic protection.
5.7
Skills Assessment
Since education and training differs for each country, it is not appropriate to dictate
the method of assessment and certification. It is recommended that the certifying
authority, normally the accessory manufacturer, keeps an up to date record of the
jointing competencies tested and certified. The methodology of assessment should
also be stated. Where no formally structured assessment and certification is
238
K. Leeburn
Table 5.33 Technical risks and specific skills for installation of fibre optics
Work phase
Handling the optical fibre
Technical risks
Breaking the optical fibre
Removing the stainless
steel fibre protection tube
Damaging the cable core with the
steel tube
Short circuiting of the sheath
interruption of the joint with the steel
tube
Specific skills
Fibre splicing Knowledge
in handling optical fibre
Due care
available, the methodology described in Sects. 5.7.1, 5.7.2, 5.7.3, 5.7.4, 5.7.5, and
5.7.6 should be used.
5.7.1
Aspects to be Tested
Modern high voltage accessories often seem fairly simple in design e.g. pre-molded
joints. This may lead to the incorrect assumption that a jointer with a skill-set suitable for
assembling low voltage accessories can be easily up skilled to high voltage accessories.
However, very careful assembly is needed for high voltage accessories, as these
accessories will operate at very high voltage stresses and, as a result, the margin for
error in assembly is very low. Further, the impact of a system outage is very high.
It is essential that the jointer has the skill-set appropriate to the accessory being
assembled or, if a team is assembling the accessory, then the team should have the
full skill-set between them. Of course in the latter case each jointer should be limited
to working only in his area of competency.
In order to determine the jointer’s skill-set he should be tested for relevant
competencies, as outlined in Sect. 5.6 above.
There may be three levels of competence:
• Apprentice (not allowed to do jointing on their own);
• Jointer (allowed to do jointing on their own);
• Supervisor (highly experienced and could train others).
5.7.2
Methods of Qualification
It is advisable that qualification involve three elements:
• Theoretical understanding of WHY a particular aspect is important;
• Observation that a jointer has understood and executed the instructions correctly;
• Electrical and mechanical testing of the final accessory assembly.
5.7.2.1 Theoretical
This test should demonstrate the jointer’s basic understanding of the theoretical
aspects of the assembly processes e.g. importance of smooth surfaces, cleanliness,
avoiding nicks, etc.
5
Cable Accessory Workmanship on Extruded High Voltage Cables
239
5.7.2.2 Training on the Job and Observation
In this case the jointer has to demonstrate his skill-set under the supervision of a
jointing supervisor, experienced in the type of accessory being assembled and in the
skill-set required.
Quality assurance checklists provide a useful tool for on the job training
verification.
The full assembly of the accessory should be developed into a check list, starting
at materials checking, jointing tent conditions, tools checking, etc. – a typical
overview check list is contained in “5.Appendix A” The jointer must complete the
checklist, as he/she assembles the accessory and the jointing supervisor certifies it is
done correctly.
It is recommended that each jointer keeps a logbook of all the accessories
assembled (type and voltage class).
5.7.2.3 Testing: Electrical & Mechanical
Extensive testing is not always possible, because of practical reasons or is not
financially feasible. Higher voltage systems generally have higher stresses. They
also have higher consequence of failures. As the stress increases, the risk of failure
also increases. It is thus prudent to conduct as many of the following tests as is
financially or technically practical. Following the tests the accessory should be
disassembled to see if there are any problems and, if noted, the jointer should be
further trained in this area until his competency is established.
The tests proposed must considered the particular skills that jointers will use.
Some tests which can be done are HV tests, PD tests or impulse tests at specified
IEC levels.
5.7.3
Certification
A Jointing Supervisor or an Installation Engineer, who has suitable experience and
authority, should certify the jointer, following their completion of Sect. 5.7.2 above.
The Certificate should indicate:
• Voltage class applicable;
• Accessory cover;
• List of skill-sets covered.
Mechanism used for Certification (Sects. 5.7.2.1, 5.7.2.2, and 5.7.2.3) – if Sect.
5.7.2.3, give test details.
5.7.4
Duration of Certification
While it is preferable that a jointer keeps his skills up to date by having a continuous
programme of work, it is recognised that this rarely happens. Very often there can be
240
K. Leeburn
long breaks between periods of jointing activity and there may be a possibility that
there would be a reduction in skills. It is for this reason that the concept of a duration
attached to certification is introduced. If the jointer is regularly using his skill-set
then there is no need for re-certification. In the event that there is a significant gap in
the jointer’s work programme, then the jointer may need to be re-certified. The
re-certification should take place in accordance with the relevant parts of Sects. 5.7.2
and 5.7.3 above. The log book described in Sect. 5.7.2.2 above will help in the
evaluation of the need for re-certification.
5.7.5
Upskilling
A case may arise where a jointer has a fairly good skill-set, but needs to gain some
more skills for a new accessory to be installed that is not too different from
accessories he has previously installed. In this case it may be sufficient for the
jointer to be tested and certified for the additional skills required. We would advise
to err on the side of caution.
5.7.6
New Accessory Type
If the jointer is required to install an accessory, with which he is not familiar, then he
should be fully trained in all of the necessary skills outlined in Sect. 5.6 above, tested
as per Sect. 5.7.2 and certified as per Sect. 5.7.3, as appropriate, before he commences installation.
5.8
Set Up
While, not part of the accessory, set up is complimentary to the accessory, and is thus
covered here. It is recommended the steps outlined below are followed:
5.8.1
Organisation of Jointing Location
Joints are installed in different locations such as, joint bays, manholes, vaults,
tunnels, etc.
The installation crew should ensure that:
• The jointing kits are verified for contents and expiry dates where appropriate;
• The layout of the jointing space is compatible with the required dimensions to
carry out the jointing activities;
• There is adequate space available for tools and equipment as well as the joint
components;
• There is adequate electric power supply, lighting, ventilation and other necessary
services;
• Safety of the personnel is assured through careful planning.
5
Cable Accessory Workmanship on Extruded High Voltage Cables
5.8.2
241
Positioning of Joint
The jointer should ensure that:
• The joint is positioned and supported in accordance with designs;
• The design instruction is followed to ensure the joint does not overheat during
operation due to incorrect depth or backfill;
• The joint should be positioned in the joint bay in such a manner that in the event
of a failure that replacement is possible without serious disruption.
Allowance should also be made for those designs that incorporate rigid joint
designs.
5.8.3
Environmental Conditions
The jointer should ensure that the conditions are suitable with for jointing with
respect to:
•
•
•
•
•
Temperature;
Humidity;
Dust;
Pollution;
Salt.
Depending on the jointing instruction, the joint bay environmental control may
vary from a simple single skinned jointing tent with no temperature or humidity
control to a double skinned tent or jointing container with careful temperature and
humidity control.
In addition the possibility of the jointer perspiring too much must be considered.
5.8.4
Cable End Inspection
At the commencement of jointing, great care should be exercised to inspect the cable
pulling head and tail. They should be very carefully removed and inspected for
moisture penetration, as should the remaining cable – this can be done visually, but it
is best done by immersing a small sample of conductor in hot oil; if there is moisture
present then the oil will crackle. Cable should not be jointed if there is moisture in the
conductor. This should be the subject of discussions between the Installation Company and the Client.
5.8.5
Verification of Each Step
This should be covered in the Instruction Manual Quality Assurance checklists.
242
5.8.6
K. Leeburn
Measuring of Diameters, Ovality, Concentricity, Position
This should be covered in the Instruction Manual Quality Assurance checklists.
5.8.7
Safety and Health
In any jointing operation it is vital that considerable attention is paid to the safety and
health of the jointing operatives and their assistants. Amongst the items that should
be considered and precautions taken to eliminate or minimise the risk are:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Tripping;
Sunburn/sunstroke;
Falling from ladder or into joint bay or other;
Ground Subsidence;
Electrocution/Earthing;
Induced voltages from parallel circuits;
Water, drowning;
Gas;
Traffic;
Attack by animals;
Attack by people;
Lifting/handling;
Noise;
Handling hazardous substances;
EMF exposure;
Explosion/Fire;
Failure of parallel power circuits;
Equipment failure;
Inadequately trained staff and supervision;
Compliance with local safety laws and Regulations.
All of the above should be the subject of a detailed documented risk assessment.
5.8.8
Environmental Aspects
In completing installation operations it is necessary to comply with all relevant local
environmental laws and regulations. In any case, the environmental impact shall be
kept as low, as is reasonably possible.
5.8.9
Quality Insurance
The quality insurance is treated in TB 177 (see ▶ Chap. 2, “A Guide to the Selection
of Accessories”).
Lubrication
Shrinkage
Cleaning of insulation
Basic
Has theoretical knowledge-
CERTIFICATE
-capable to make joint
Operational
5-10 years experience
Supervisory
Cable Accessory Workmanship on Extruded High Voltage Cables
Smoothing the insulation surface
Preparing the end of the semi conducting insulation screen
Stripping of semi conductive insulation screen
Straightening
Insulation Preparation
Mechanical Connection
Thermit Weld
Deep indentation
MIG/TIG Welding
Round and Hexagonal Compression
Conductor preparation
Construction and Procedure description
Conductors
Organisation of jointing location
Check that end bell, etc are passed down the cable, before jointing commences,
so that they are available in the right position for use later in the jointing
installation
Check cable serving, sheath, semi-conducting layer and insulation removed in
truction drawing
Check cable placed in position with correct bending radius
Safety and Health
Cable End Inspection
Environmental Conditions
Positioning of Joint
Organisation of jointing location
Set Up
List below to be reorganised so that it complements
with respect to the sequence in which each operation carried out
Jointing Instruction number/date/revision no:
Accessory; Type. voltage class/
Appendix A: Model Certificate
5
243
ents
Field expansion
Taped Accessories (Joints)
Field moulding Extrusion or taped
Heatshrink tube insulation.
Coldshrink tube insulation.
Prefabricated composite type joint
Prefabricated composite type termination
Polymeric outer protection by taping and/or heatshrink tubes
Oversheath
Preparation of oversheaths
Extruded PVC
Extruded Polyethylene
Low Smoke, Zero Halogen, Enhanced Flame Performance Sheaths
Mechanical Reinforcement of Accessories
Metallic sheath
Welded Aluminium Sheath
Construction and procedure description
Preparation of cable sheath
Metallic screen continuity
Copper wire screen
Corrugated Seamless Aluminium (CSA), Copper (CCS), Stainless Steel
(CSS)
Plumbing
Tig Welding
Lead Sheath {highlight risks and care for cutting}
Aluminium Polyethylene Laminate (APL)
Copper Polyethylene Laminate (CPL)
Corrugated Cu
Stainless steel
Basic
Has theoretical knowl-
CERTIFICATE
Supervisory
with 5-10 years experience
Operational
jointer -capable to
make joint
244
K. Leeburn
d spring loading, if
Expiry Date
Certifying Authority
Signed By
Environmental Aspects
Safety
Fibre optics
Special features
Sensor connections
on system
Common parts about accessory installation (joints and terminations)
Supporting of accessory
Lifting of accessories
tion
Taped Accessories (Terminations)
Heatshrink tube insulation
Fitting OD porcelain/cast resin insulator and top metal
erminations
necessary, to ensure pressure is maintained
Installation of plug-in types
Outer Protection of Joints
Filling compounds (joints)
Basic
Has theoretical knowl-
CERTIFICATE
Supervisory
with 5-10 years experience
Operational
-capable to make
joint
5
Cable Accessory Workmanship on Extruded High Voltage Cables
245
YYYYY
re q u i re d
re q u i re d
re q u i re d
re q u i re d
R e q u i re d
R e q u i re d
R e q u i re d
R e q u i re d
R e q u i re d
R e q u i re d
Environmental Conditions
Cable End Inspection
Safety and Health
Check cable placed in position with correct bending radius
Check cable serving, sheath, semi-conducting layer and insulation removed in
t r u c t i o n d r aw i n g
re q u i re d
re q u i re d
re q u i re d
re q u i re d
R e q u i re d
R e q u i re d
R e q u i re d
Organisation of jointing location
Construction and Procedure description
Conductor preparation
Round and Hexagonal Compression
required
required
required
required
required
required
required
required
required
Preparing the end of the semi conducting insulation screen
Smoothing the insulation surface
Cleaning of insulation
Shrinkage
Lubrication
required
required
required
required
required
Stripping of semi conductive insulation screen
re q u i re d
re q u i re d
re q u i re d
re q u i re d
re q u i re d
re q u i re d
re q u i re d
re q u i re d
re q u i re d
re q u i re d
re q u i re d
re q u i re d
5-10 years experience
Super visor y
Straightening
Insulation Preparation
Mechanical Connection
Thermit Weld
Deep indentation
MIG Welding
Conductors
re q u i re d
R e q u i re d
R e q u i re d
Check that end bell, etc are passed down the cable, before jointing commences,
so that they are available in the right position for use later in the jointing installation
re q u i re d
re q u i re d
re q u i re d
R e q u i re d
-capable to make joint
O p e rat i o n a l
Organisation of jointing location
Has theoretical knowledge-
Basic
Positioning of Joint
Set Up
List below to be reorganised so that it complements
with respect to the sequence in which each operation carried out
Jointing Instruction number/date/revision no:
D sealing end (with internal
stress cone) with cu condr, lead sheath and PE serving with PD test facility
CERTIFICATE FILLED IN SAMPLE
246
K. Leeburn
nts
Filling compounds (joints)
Outer Protection of Joints
Polymeric outer protection by taping and/or heatshrink tubes
Prefabricated composite type termination
Prefabricated composite type joint
Coldshrink tube insulation.
Heatshrink tube insulation.
Field moulding Extrusion or taped
Taped Accessories (Joints)
Field expansion
Mechanical Reinforcement of Accessories
Low Smoke, Zero Halogen, Enhanced Flame Performance Sheaths
Extruded Polyethylene
Extruded PVC
Preparation of oversheaths
Oversheath
Stainless steel
Corrugated Cu
Copper Polyethylene Laminate (CPL)
Aluminium Polyethylene Laminate (APL)
Lead Sheath {highlight risks and care for cutting}
Tig Welding
Plumbing
Corrugated Seamless Aluminium (CSA)
Copper wire screen
required
required
re q u i re d
required
required
required
required
re q u i re d
required
required
required
Metallic screen continuity
required
required
5-10 years experience
Super visor y
required
-capable to make joint
O p e rat i o n a l
Preparation of cable sheath
R e q u i re d
Has theoretical knowledge-
Basic
Construction and procedure description
Welded Aluminium Sheath
Metallic sheath
CERTIFICATE FILLED IN SAMPLE
5
Cable Accessory Workmanship on Extruded High Voltage Cables
247
d spring loading, if necessary,
R e q u i re d
Environmental Aspects
Expiry Date
Certifying Authority
Signed By
R e q u i re d
on system
Safety
Fibre optics
Sensor connections
Special features
re q u i re d
re q u i re d
required
required to know about
PD
required
required
tion
required
required
-capable to make joint
O p e rat i o n a l
Supporting of accessory
Has theoretical knowledge-
Basic
required
Lifting of accessories
Common parts about accessory installation (joints and terminations)
erminations
Fitting OD porcelain/cast resin insulator and top metal
Heatshrink tube insulation
Taped Accessories (Terminations)
CERTIFICATE FILLED IN SAMPLE
Installation of plug types
to ensure pressure is maintained
re q u i re d
re q u i re d
required
required to know about PD
required
required
required
required
5-10 years experience
Super visor y
required
248
K. Leeburn
d and managed
Preparing the end of the semi conducting insulation screen
Stripping of semi conductive insulation screen
sets required
from list
QA Requirement
value/description
Value
QA
checked
by jointer
and ok
Signed
by
Date
Any
comments
Cable Accessory Workmanship on Extruded High Voltage Cables
Straightening
Insulation Preparation
Mechanical Connection
Thermit Weld
Deep indentation
MIG Welding
Round and Hexagonal Compression
Conductor preparation
Construction and Procedure description
Conductors
Check that end bell, etc are passed down the cable, before jointing
commences, so that they are available in the right position for use later
in the jointing installation
Check cable serving, sheath, semi-conducting layer and insulation
ointing
instruction drawing
Check cable placed in position with correct bending radius
Check fully detailed jointing instruction supplied covering all items
listed above and below
Cable End Inspection for no damage /water
Environmental Conditions
Positioning of Joint
Checking that all jointing tools and other required equipment are on
site
Checking that all jointing materials and consumables are on site
Organisation of jointing location
Set Up
Joint/Accessory Drawing number:
Jointing Instruction number/date/revision no:
Accessory Type/voltage class/number:
QA DOCUMENT
Appendix B: QA Document
5
249
preparation
Prefabricated composite type joint
Coldshrink tube insulation.
Heatshrink tube insulation.
Field moulding Extrusion or taped
High Voltage Heat-resistant tape
High Voltage tape
Taped Accessories (Joints)
Field expansion
Mechanical Reinforcement of Accessories
nts
Low Smoke, Zero Halogen, Enhanced Flame Performance Sheaths
Extruded Polyethylene
Extruded PVC
Preparation of oversheaths
Oversheath
Stainless steel
Corrugated Cu
Copper Polyethylene Laminate (CPL)
Aluminium Polyethylene Laminate (APL)
Lead Sheath
Tig Welding
Plumbing
Corrugated Seamless Aluminium (CSA)
Copper wire screen
Metallic screen continuity
Preparation of cable sheath
Construction and procedure description
Welded Aluminium Sheath
Metallic sheath
Lubrication
Shrinkage
Cleaning of insulation
Smoothing the insulation surface
QA DOCUMENT
sets required
from list
QA Requirement
value/description
Value
QA
checked
by jointer
and ok
Signed
by
Date
Any
comments
250
K. Leeburn
d spring loading,
on system
tion
sets required
from list
QA Requirement
value/description
Value
QA
checked
by jointer
and ok
Signed
by
Date
Any
comments
Cable Accessory Workmanship on Extruded High Voltage Cables
Signature of Supervisory Jointer
Signature of Jointer
Environmental Aspects
Safety
Fibre optics
Sensor connections
Special features
Lifting of accessories
Supporting of accessory
Common parts about accessory installation (joints and terminations)
rminations
Fitting OD porcelain/cast resin insulator and top metal
Heatshrink tube insulation
Taped Accessories (Terminations)
Installation of plug-in types
if necessary, to ensure pressure is maintained
Filling compounds (joints)
Polymeric outer protection by taping and/or heatshrink tubes
Prefabricated composite type termination
assemble the spring unit
setting the epoxy unit and slide of premoulded insulator
sleeve compression
insert parts
QA DOCUMENT
5
251
required
required
Check cable placed in position with correct bending radius
Check cable serving, sheath, semi-conducting layer and insulain jointing instruction drawing
required
required
Round and Hexagonal Compression
Thermit Weld
Deep indentation
MIG Welding
required
Construction and Procedure description
Conductor preparation
Conductors
required
Check that end bell, etc are passed down the cable, before
jointing commences, so that they are available in the right position for use later in the jointing installation
required
required
Check fully detailed jointing instruction supplied covering all
items listed above and below
managed
Cable End Inspection for no damage /water
required
per J.I
per J.I
per J.I
description
values
value
description
list
description
dwg
required
Environmental Conditions
d and
list
required
Checking that all jointing tools and other required equipment
are on site
Positioning of Joint
description
list
required
required
dimensional value to be
achieved
to be achieved and dimensions checked
to be achieved
to be achieved
to be achieved
to be achieved
to be achieved
to be achieved
to be achieved
to be achieved
to be achieved
to be achieved
to be achieved
QA Requirement Value
value/
description
Checking that all jointing materials and consumables are on
site
required from list
Organisation of jointing location
Set Up
Joint/Accessory Drawing number
:
YYYYYY
Jointing Instruction number/date/revision no
:
XXXXXX
OD sealing
end (with internal stress cone) with cu cond, lead sheath and PE
serving with PD test facility
QA DOCUMENT FILLED IN SAMPLE
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
Signed
by
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
QA c h e c k e d
by jointer
and ok
xxxxx
xxxxx
xxxxx
xxxx
xxxx
xxxx
xxxx
xxxx
xxxx
xxxx
xxxx
xxxx
xxxx
Date
Any
comments
252
K. Leeburn
required
required
required
Lubrication
Construction and procedure description
Preparation of cable sheath
required
required
required
per JI
per JI
per JI
per JI
per JI
per JI
per JI
per JI
per JI
per JI
per JI
per JI
per JI
description of process and
value to be achieved
description of process and
value to be achieved
description of process and
value to be achieved
description
description of process and
value to be achieved
description
description
description
description of process and
value to be achieved
description of process and
value to be achieved
description of process and
value to be achieved
description of process and
value to be achieved
description of process and
value to be achieved
QA Requirement Value
value/
description
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
Signed
by
yes
yes
yes
QA c h e c k e d
by jointer
and ok
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
Date
Any
comments
Cable Accessory Workmanship on Extruded High Voltage Cables
Low Smoke, Zero Halogen, Enhanced Flame Performance
Sheaths
Extruded Polyethylene
Extruded PVC
Preparation of oversheaths
Oversheath
Stainless steel
Corrugated Cu
Copper Polyethylene Laminate (CPL)
Aluminium Polyethylene Laminate (APL)
Lead Sheath
Tig Welding
Plumbing
Corrugated Seamless Aluminium (CSA)
Copper wire screen
Metallic screen continuity
Welded Aluminium Sheath
required
reqiuired
Shrinkage
Metallic sheath
required
required
required
Preparing the end of the semi conducting insulation screen
Smoothing the insulation surface
required
Cleaning of insulation
required
Stripping of semi conductive insulation screen
required from list
Straightening
Insulation Preparation
Mechanical Connection
QA DOCUMENT FILLED IN SAMPLE
5
253
ents
per JI
per JI
required
required
required
tion
per JI
required
per JI
per JI
per JI
per JI
description
description
description
description
description of process and
value to be achieved
description of process and
value to be achieved
description of process and
values to be achieved
QA Requirement Value
value/
description
Lifting of accessories
required
required
required
required from list
Supporting of accessory
Common parts about accessory installation (joints and
terminations)
rminations
Fitting OD porcelain/cast resin insulator and top metal
Heatshrink tube insulation
Taped Accessories (Terminations)
Installation of plug types
nd spring
loading, if necessary, to ensure pressure is maintained
Filling compounds (joints)
Polymeric outer protection by taping and/or heatshrink tubes
Prefabricated composite type termination
assemble the spring unit
setting the epoxy unit and slide of premoulded insulator
sleeve compression
insert parts
preparation
Prefabricated composite type joint
Coldshrink tube insulation.
Heatshrink tube insulation.
Field moulding Extrusion or taped
High Voltage Heat-resistant tape
High Voltage tape
Taped Accessories (Joints)
Field expansion
Mechanical Reinforcement of Accessories
QA DOCUMENT FILLED IN SAMPLE
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
Signed
by
yes
yes
QA c h e c k e d
by jointer
and ok
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
Date
Any
comments
254
K. Leeburn
Signature of Supervisoy Jointer
Signature of Jointer
re q u i re d
re q u i re d
required
Safety
on system
required for PD
detection
required from list
Environmental Aspects
Fibre optics
Sensor connections
Special features
QA DOCUMENT FILLED IN SAMPLE
g e n e ra l
g e n e ra l
per JI
per JI
g e n e ra l
g e n e ra l
description of process and
value to be achieved
description
QA Requirement Value
value/
description
ye s
ye s
ye s
yes
yes
ye s
yes
Signed
by
yes
QA c h e c k e d
by jointer
and ok
xxxxx
xxxxx
xxxxx
xxxxx
Date
Any
comments
5
Cable Accessory Workmanship on Extruded High Voltage Cables
255
256
K. Leeburn
References
International Electrotechnical Commission IEC 60050 Chapter 461: electric cables
Cigré TB 89 – Accessories for HV Extruded Cables (Chapter 1)
Cigré TB 177 – Accessories for HV cables with extruded insulation (Chapters 1 and 2)
Cigré TB 194 – Construction, Laying and installation techniques for extruded and self contained
fluid filled cable systems
Cigré TB 210 JTF 21/15 – Interfaces in high voltage accessories (Chapter 3)
Association of Edison Illuminating Companies AEIC CG4-97 Guide for installation of extruded
dielectric insulated power cable system rated 69 kV through 138 kV (2nd ed.)
Cigré TB 272 – Large Cross Sections and Composite Screen Design
Cigré TB 379 – Update of service experience of HV Underground and Submarine Cable Systems
Cigré TB 446 – Advanced Design of Metal Laminated Coverings: Recommendations for Tests.
Guide for Use Operational Feed-Back
Kieron Leeburn has a B.Sc. Electrical Engineering from the
University of the Witwatersrand in South Africa. He is employed
by CBI-Electric: African cables as their Chief Engineer covering
product and process design and innovation. He has participated in
a number of working groups in study committee B1 (insulated
cables), and convened B1–22 one on Accessory Workmanship. He
has represented Africa on CAG B1 (customer advisory group on
insulated cables) since its inception. He received the Cigré Technical Committee Award in 2011 for outstanding contribution to the
work of SCB1. He is a Member of IEC TC 20 WG16 (high voltage
cables). He is a Member of the South African Institute of Electrical
Engineers.
6
Guidelines for Maintaining the Integrity
of Extruded Cable Accessories
Eugene Bergin
Contents
6.1 Review of Recent Experience with Failures of Outdoor and Filled Terminations
and Non-buried Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.1.1 Review of Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.1.2 Review the Consequences of Termination Failures for Cables within Substations
and Outside . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.1.3 Survey by B1–29 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2 The Role of Improved Materials, Design, Assembly and Quality Control in Mitigating
the Effects of Termination and Non-buried Joint Failures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2.1 Survey Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2.2 Design and Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2.3 Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2.4 Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.3 The Role of Testing and Condition Monitoring in Minimising the Incidence or Severity
of Termination and Non-buried Joint Failures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.3.1 Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.3.2 Condition Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.4 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.4.1 Existing Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.4.2 New Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Appendix 1: Terms of Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Appendix 2: Bibliography/References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IEC Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CIGRE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Jicable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
261
261
267
267
272
272
277
287
287
288
288
294
296
297
297
298
299
299
299
300
301
Eugene Bergin: deceased.
Published as Cigré TB 560 in December 2013
E. Bergin (*)
Dublin, Ireland
© Springer Nature Switzerland AG 2021
P. Argaut (ed.), Accessories for HV and EHV Extruded Cables, CIGRE Green Books,
https://doi.org/10.1007/978-3-030-39466-0_6
257
258
E. Bergin
Appendix 3: Reminder Chapter 5/TB 476 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Appendix 4: Short Circuit Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low Energy External Fault (Through-fault i.e. Breakdown Outside the Accessory) . . . . .
High Energy Internal Fault (Internal Fault i.e. Breakdown Inside the Accessory) . . . . . . . .
Simulation of the Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Appendix 5: Condition Monitoring Techniques for Terminations and Non-buried Joints . . . .
302
305
305
307
307
308
Executive Summary
This work was motivated by the occurrence of disruptive failures of cable terminations
and the consequential risks. The original scope of the Working Group (WG) was limited
to land XLPE cable systems 110 kV and above. Although priority was given to outdoor
and oil-immersed terminations, joints that are not directly buried were also included.
The Terms of Reference are attached as 6.Appendix 1. Following discussions
within the Working Group on the terms of reference, it was agreed that:
• Bonding and earthing, including SVL failures, were, in the main, not to be included.
• Any relevant learning points from PE cable accessories were to be included,
although polyethylene (PE) cables are no longer installed.
• There should be no time restriction on assets covered by the survey, as the relative
newness of XLPE cable technology would naturally limit the scope.
• The scope was extended to cover voltage ranges from 60 kV and above, as
relevant failures at these voltage levels have also occurred and designs are similar
to those being used at higher voltages.
• Priority was given to outdoor, oil-immersed and GIS terminations, but joints that
are not directly buried were also to be considered.
Those items that needed to be considered and complied with to minimise the
failure rate for terminations and non-buried joints are listed below, following
detailed analysis by WG B1–29.
Development, Prequalification and Type Tests
The nature and scope of tests to be carried out when developing (new) cables and/or
accessories have not been formally standardised and it has been left up to the
individual producers/manufacturers to use their knowledge and philosophy to design
such tests. However, in the early 1990’s the Cigré Task Force 21.03 published
comprehensive recommendations for development tests on extra high-voltage cables
with extruded dielectric, including the associated accessories.
It was recommended that development tests for accessories focus on the following aspects:
• Analysis of chemical, electrical and mechanical behaviour of materials
• Long-term voltage test under thermal load cycles
• Impulse and/or AC step voltage tests, where appropriate, with maximum conductor temperature.
• Short circuit/disruptive discharge tests.
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
259
Type tests in IEC62067 and IEC 60840 focus mainly on the withstand levels of
cables and accessories with respect to a.c. or impulse stresses. They do not supply
much information on the long-term behaviour of components, as the longest voltage
test in these standards is limited to 20 days or 20 cycles of heating and cooling. The
issue of long term tests (typically 1 year) is dealt with in Prequalification Tests in IEC
60840 and is to be carried out if the electrical stresses at the design voltage Uo
exceed 8.0 kV/mm at the conductor screen and 4.0 kV/mm at the insulation screen.
Fluid leakage is a significant cause of termination breakdown and this concern has to
be addressed e.g. through final examination, as in IEC 62067 and 60840 standards,
which states:
“Examination of the cable system with cable and accessories with unaided vision shall
reveal no signs of deterioration (e.g. electrical degradation, moisture ingress, leakage,
corrosion or harmful shrinkage) which could affect the system in service operation.”
Factory Quality Control (QC)
It is essential that full quality control is exercised in the manufacture and supply of
terminations and joints. This applies to all the sub-components of each accessory
e.g. stress cones, jointing material, compounds, etc. A full set of suitable tests
e.g. dimensional checks, electrical tests, as appropriate, should be established and
implemented. The different components of an accessory should be packaged in such
a way as to avoid damage and moisture ingress during transport. Delicate components, such as stress cones, should be shipped in sealed plastic containers. A detailed
list of these components should be included in each box together with a complete set
of assembly instructions. Recommended handling, storage conditions and expiry
dates for any components should also be provided.
On Site Quality Control
It is essential that full quality control is exercised on site with respect to the jointing
area set-up, including the control of dust, humidity and temperature and the use of
the correct jointing tools in good condition. In addition it is essential that suitable
jointing instructions and drawings are supplied and that checks are carried out to
ensure that the proper jointing material is supplied to site, in good condition and
not past it’s expiry date. Finally a proper check-off list (inspection/test plan) should
be used to make sure the jointing is done properly and in accordance with
instructions.
Jointer Certification
As the quality of cable preparation and accessory installation plays a significant part
in the reliability of XLPE accessories, it is critical that cable jointers have sufficient
knowledge and training to carry out the task. It is therefore important that jointers are
continually assessed to ensure competence and to maintain a high standard of
workmanship. These training records and an up-to-date CV of previous works can
be requested for review. Jointers should have valid up-to-date certification, as
contained in Cigré TB 476, for the accessory they intend to assemble.
260
E. Bergin
Tools
The minimum required tools are:
• Those found in a standard tool box, such as knives, screwdrivers, wrenches,
spanners, etc.
• Specific tools for conductor jointing, insulation and semi-conducting screen
preparation, installing pre-molded stress cones, metallic sheath, screen and
armour connecting, inner and oversheath finishing.
Specific tools and consumables shall be specified by the cable and accessory
supplier/s.
Jointing Instructions and Drawings
Jointing instructions and drawings should be part of the quality assurance system.
This is particularly crucial where accessories and cables are supplied by different
providers. It is essential that the correct and suitable jointing instructions and
drawings are used and that they are delivered with the accessory.
Site Testing
It is strongly recommended that an AC voltage test should be carried out on the
insulation of the cable system in accordance with IEC Standards.
Maintenance and Condition Monitoring
In order to reduce the likelihood of failure of a termination or a non-buried joint, an
inspection and test regime is recommended to monitor the condition of accessories.
Many techniques are available to assess the condition of XLPE cable accessories.
However, these techniques vary significantly with regards to practicality, availability
of test equipment and the level of expertise required. The condition monitoring
techniques employed should generally be assessed on a case by case basis and
assessed against the requirements and cost of monitoring compared to the consequence of a failure. A list of the currently available techniques is contained in 6.
Appendix 5.
In the event of oil or compound leakage or other incipient failure mechanism, a
risk assessment should be carried out and corrective action taken if necessary.
Risk Assessment
The continued use of any accessory should be based on:
•
•
•
•
•
•
•
Public and employee safety
The criticality of the circuit
The history of the circuit and its accessories
The potential repair time
The potential cost of an outage to complete the repair
The potential cost of an outage, if a failure occurs
Potential damage from the failure
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
•
•
•
•
•
•
Potential cost of the damage
Effect on reputation, licence compliance and potential for prosecution
Effectiveness of any monitoring system adopted
Availability of monitoring tools and trained personnel
The cost of monitoring
Potential for damage of the accessory due to external factors.
261
In case of a failure in service the first step is to verify if the cable systems (cable
and accessories) has been subjected to the tests (development, prequalification, type,
sample, routine), as requested by the relevant IEC standards or Cigré recommendations. Following that one should investigate manufacture, delivery, installation and
operation to determine the source of the fault.
In the case of new cable systems, utilities should try to adopt designs that either
do not experience disruptive discharge and/or have been tested to ensure the impact
is kept to a minimum.
6.1
Review of Recent Experience with Failures of Outdoor
and Filled Terminations and Non-buried Joints
The Working Group carried out a review of published literature on the subject and
also carried out a survey of the experience of the Working Group members’ and
Study Committee B1 members’.
6.1.1
Review of Literature
The first step taken was to review existing literature and determine what was relevant
to the study of accessory failures. It was agreed reviews should be short and take the
following format:
• Cause of defect
• Consequence of the defect
• Corrective steps taken.
6.1.1.1 Cigré, Jicable and Other Technical Literature
Nothing of particular relevance was found in the published Cigré literature.
A recent paper for Jicable 2011 (A.5.4) described a failure in an XLPE cable
termination installed in a 400 kV GIS substation and the remedial actions taken.
Another Jicable 2011 paper (A.3.7) summarised the experiences of three European
TSO’s. It showed that only a small part of the total cable circuit outage time is due to
the actual repair time. More time was spent on other aspects, such as approvals to
enter the premises, arranging the proper permissions to start repair works, cleaning
the area and getting the necessary parts to site. The relevant literature is listed in 6.
Appendix 2.
262
E. Bergin
6.1.1.2 Statistics
Cigré TB 379 “Update of Service Experience of HV Underground and Submarine
Cable Systems” supplied the statistics in Table 6.1 below regarding XLPE terminations. There is no information in Cigré TB 379 for non-buried joints. The table below
gives an overview of the number of terminations installed on XLPE cables (including PE and EPR) in the period 2001–2005. Later statistics are not available in a Cigré
TB, but the WG addressed this in Sect. 6.1.3 below by gathering up-to-date
experience from those 14 countries that responded to the WG survey enquiry.
The table below (Table 6.2) indicates the failure rates over the same time period
(2000 to 2005):
In Table 6.1, for the period 2001–2005, we can see that for the HV cable systems
(60 to 219 kV) the use of outdoor composite insulators is already a commonly used
technology. For EHV (above 219 kV) this technology is only starting. The same
findings are made with regard to the use of dry type GIS terminations.
From Table 6.2 we can see that the failure rate on terminations for EHV cable systems
(above 219 kV) is around 5 times higher than that for the HV cable systems (60–219 kV).
Table 6.3 gives indicates the failure rate per type of termination and is grouped for
the voltage levels 60–219 and 220–600 kV. For a relatively high number of failures
on terminations, the type of the terminations was not specified. As a result, the reader
must be careful when comparing the different types of terminations.
The information as shown in Tables 6.1, 6.2 and 6.3 is based upon replies
received by WG B1–10 to their questionnaire. For further information regarding
these statistics we refer to Cigré TB 379.
6.1.1.3 Workmanship
Cigré TB 476 “Cable Accessory Workmanship on Extruded High Voltage Cables”
was published in October 2011 and is published in this Book as ▶ Chap. 5, “Cable
Accessory Workmanship on Extruded High Voltage Cables”. This Sect. 6.1.1.3 is
substantially reproduced from that Cigré TB and ▶ Chap. 5, “Cable Accessory
Workmanship on Extruded High Voltage Cables”.
Cigré TB 476 covers workmanship associated with the jointing and terminating
of AC land cables, incorporating extruded dielectrics for the voltage range above
30 kV (Um ¼ 36 kV) and up to 500 kV (Um ¼ 550 kV). This brochure is a
complement of Cigré TB 177 (see ▶ Chaps. 1, “Compendium of Accessory Types
Used for AC HV Extruded Cables” and ▶ 2, “A Guide to the Selection of Accessories” of this book). A short chapter covers general risks and skills, but the bulk of
the document focusses on the specific technical risks and the associated skills needed
to mitigate these risks. This is done for each phase of the installation. This Cigré TB
is not an Instruction Manual, but rather gives guidance to the reader on which aspects
need to be carefully considered in evaluating the execution of the work at hand. High
voltage cable accessories are manufactured using high quality materials and very
sophisticated production equipment. Recent technical and technological developments in the field of their design, manufacturing and testing have made it possible to
have pre-molded joints and stress cones for terminations up to 500 kV, as well as
cold shrink joints up to 400 kV.
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
263
Table 6.1 Terminations installed on XLPE cables (including PE and EPR) in the period 2001–
2005
AC ACCESSORIES
VOLTAGE
RANGE
kV
YEAR OF
INSTALLATION
60 to 109
110 to 219
220 to 314
315 to 500
>500
2001
2002
2003
2004
2005
2001
2002
2003
2004
2005
2001
2002
2003
2004
2005
2001
2002
2003
2004
2005
2001
2002
2003
2004
2005
EXTRUDED CABLES (EPR, PE or XLPE)
O u td o o r
Termination
Outdoor
Termination
- Porcelain
- composite
insulator
27
15
21
24
21
131
128
163
190
285
0
0
6
9
3
0
0
0
0
12
0
0
0
0
0
531
753
513
483
600
267
282
546
226
187
135
63
102
66
60
12
0
0
0
28
0
0
0
0
0
Outdoor
Termination
- Dry Porcelain
12
27
15
24
51
159
216
51
63
162
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Outdoor
Termination
- Dry Composite
Insulator
75
69
96
186
138
32
35
83
32
41
0
0
0
0
12
0
0
0
36
0
0
0
0
0
0
GIS or
Transformer
Termination
GIS or
Transformer
Termination
- Dry
0
6
5
2
3
116
77
130
98
106
54
30
0
3
3
0
0
0
0
12
0
0
0
0
0
311
296
225
190
225
394
565
447
366
389
135
12
42
27
42
0
0
12
0
0
0
0
0
0
0
Table 6.2 Failure rates of terminations over the period 2000 to 2005
Failure rates based on all replies
Termination
Xlpe cables (AC)
60–
220–
219 kV
500 kV
0,006
0,032
ALL
VOLTAGES
0,007
Termination
60–
219 kV
0,005
220–
500 kV
0,018
ALL
VOLTAGES
0,006
Termination
60–
219 kV
0,011
220–
500 kV
0,050
ALL
VOLTAGES
0,013
A. Failure Rate – Internal Origin Failures
Failure rate [fail./yr.
100 comp.]
B. Failure Rate – External Origin Failures
Failure rate [fail./yr.
100 comp.]
C. Failure Rate – All Failures
Failure rate [fail./yr.
100 comp.]
Voltage
range kV
60 to 219
Cable type
Extruded
(XLPE, PE or
EPR)
Accessory type
Outdoor Termination - Fluid
filled - Porcelain
Outdoor Termination - Fluid
filled - Composite insulator
Outdoor Termination - Dry Porcelain
Outdoor Termination - Dry Composite insulator
Outdoor Termination -Type not
specified
Outdoor Termination -Total
GIS or Transformer Termination
- Fluid filled
GIS or Transformer Termination
- Dry
2
2
1
17
37
0
19
1954
1353
0
52152
4222
20771
Total
numbers of
faults
15
2619
Total number of
accessories in 2005
46226
Table 6.3 Failure rates by type of termination over the period 2000 to 2005
0,019
0,015
0,000
0,020
0,024
0,019
Total
failure
rate
0,007
0,015
0,007
0,000
0,000
0,024
0,019
0,002
0,006
0,000
0,020
0,000
0,000
Failure rates
Cause of failure
Internal External
0,003
0,003
0,002
0,002
0,000
0,000
0,000
0,000
Unknown
0,001
264
E. Bergin
220 to
500
Extruded
(XLPE, PE or
EPR)
Outdoor Termination - Fluid
filled - Porcelain
Outdoor Termination - Fluid
filled - Composite insulator
Outdoor Termination - Dry Porcelain
Outdoor Termination - Dry Composite insulator
Outdoor Termination -Type not
specified
Outdoor Termination -Total
GIS or Transformer Termination
- Fluid filled
GIS or Transformer Termination
- Dry
5
0
0
0
18
23
2
2
1493
61
0
53
0
1607
2447
637
0,071
0,330
0,016
0,000
0,000
0,000
0,075
0,071
0,215
0,016
0,000
0,000
0,000
0,030
0,000
0,086
0,000
0,000
0,000
0,000
0,045
0,000
0,029
0,000
0,000
0,000
0,000
0,000
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
265
266
E. Bergin
One of the conclusions of Cigré TB 476 is that internal failure rates of accessories, particularly on XLPE cable, are higher than other components and are of great
concern due the larger impact of a failure. Therefore the focus on quality control
during jointing operations must be maintained.
Many utilities have adopted the “system approach” by purchasing the cables as
well as the major accessories from the same supplier. Some utilities also request
that the link should be installed by the supplier or by a contractor under the
supplier’s supervision in a “turnkey” fashion. The main advantage of this approach
is that the entire responsibility for the materials and workmanship is clearly the
supplier’s. Some customers have adopted the component approach by purchasing
cables and accessories from different suppliers and entrusting the installation to a
third party. In all cases, it is imperative that the installation be carried out by
qualified jointers, who follow the jointing instructions provided by the accessory
supplier.
International standards such as IEC and IEEE provide the necessary guidelines
concerning the interface between cables and accessories. However, it is strongly
recommended that the responsible engineer should verify the compatibility of the
different components of the link. It is of vital importance to manage the interface
between the cables and the accessories in order to reduce the potential technical risk,
e.g. cables and pre-molded accessories having non-compatible diameters or other
non-compatible dimensions or characteristics.
One of the international trends in cable technology has been the reduction of
the cable insulation thickness and the corresponding increase in electrical stress.
This tendency is based on better knowledge, increased quality of the insulating
material and improvements in the extrusion process. Cables and accessory
components are made under well-defined factory conditions and their quality
and reliability are assured by adherence to well defined specifications. However,
the accessories are assembled on site and, notwithstanding that this job is carried
out by skilled and trained jointers, it is often performed in more delicate and less
controlled conditions than in the factory. This means that correct assembly is
even more important, because, with the increased stress level due to the reduced
insulation thickness, bad workmanship will, sooner or later, lead to a breakdown
of the accessory.
It is noted that the majority of the new HV cable links being considered will use
XLPE insulated cables.
Cigré TB 476 captured the state of the art of jointing and is considered the best
practice internationally. It is acknowledged that other practices, which are not
explicitly covered in this brochure, are not necessarily bad practices. Great care
should be exercised and the approach agreed when departing from practices
recommended in Cigré TB 476.
While Cigré TB 476 does not directly refer to failures or the consequences of
failures, it is a comprehensive document on the assembly of cable accessories. If
used properly it can provide vital advice on the avoidance of failures due to bad
workmanship.
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
6.1.2
267
Review the Consequences of Termination Failures for Cables
within Substations and Outside
6.1.2.1 Cigré, Jicable and other Technical Literature
In the case of Cigré the only consequences are the repair times that are covered in
Sect. 6.1.2.2 below.
6.1.2.2 Statistics
From Cigré TB 379, average repair times in days for XLPE systems are set out in the
Table 6.4 below. This average repair time was calculated for all the reported failures
on extruded cables for the corresponding voltage levels. No separate values were
calculated for specific types of accessory.
The definition of repair time as used in the questionnaire by B1–10 is the
following:
Repair time is the cumulative period of time required to mobilize resources, locate
and repair the failure. The repair time associated with a failure is of fundamental
importance since the summation of repair times is required to obtain a measure of
non-availability, which from a reliability viewpoint is of greater significance than
fault rate.
6.1.2.3 Workmanship
Cigré TB 476 does not specifically refer to the consequences of failures, except to
indicate the potential damage in the area, the very serious transmission system
consequences with potential safety implications, loss of load, loss of customers,
poor public relations and potential loss of revenue and additional costs.
6.1.3
Survey by B1–29
The Working Group compiled a survey to be completed by all members of the WG
and SC B1 members, whose country were not represented on the Working Group.
The survey was split into the voltage ranges recommended by Cigré below
(Fig. 6.1):
•
•
•
•
50–109 kV
110–219 kV
220–314 kV
315–500 kV.
Table 6.4 Average repair
time for cables in days
60 to 219 kV
220 to 500 kV
15 days
25 days
268
E. Bergin
Fig. 6.1 Failure due to poor
workmanship (surface scratch
due to bad workmanship)
Replies were received from 14 countries. Terminations and non-buried joints
were dealt with separately. The survey results may be summarised as follows:
6.1.3.1 Survey on Terminations
• A total of 61 failures were reported
• Most of the installations were inside substations with only 6 being in a public area
• The voltage range was from 51 to 400 kV, with the main installations being in the
50–150 kV range
• The installation year varied from 1972 to 2010
• The year of failure varied from 1988 to 2010 Most installations had commissioning tests and, in most cases, voltage tests were carried out as part of
commissioning
• Most installations were outdoor (37)
• The outdoor housings were generally filled with silicon oil or polybutene and the
GIS (Gas Insulated Substation) housings were mainly unfilled
• Most AIS (Air Insulated Substations) installations had composite or polymeric
outer housings – 18 had porcelain housings. However it should be noted that
failures in porcelain housings are likely to be more serious in view of the shards
that are created during the fault
• The terminations were mainly installed by a manufacturer, with only 15 being
installed by a utility or contractor
• The conductor sizes varied from 100 to 2500 sq. mm and were both copper and
aluminium
• The metallic shield varied from lead to aluminium foil to copper wires
• In nearly all cases the cable and termination were from the same manufacturer
• In most cases prequalification test had not been completed
• Nearly all termination designs had undergone type tests
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
269
• In only a few cases were maintenance test carried out – varying from a serving
test, DC test and thermovision tests
• The pollution design ranged varied from normal to serious
• The causes of failure were listed as:
– Termination Design
• Moisture ingress due to inadequate sealing.
• Pre-molded component breakdown.
• Breakdown of insulating material.
– Manufacture
• Poor adherence of pre-molded components within stress cone
• Rough surface of metallic parts leading to Partial Discharge
• In one case manufacture was identified, but a reason was not given.
• Poor fluid quality leading to internal discharges.
– Workmanship
• Damage to primary insulation during jointing.
• Poor fluid treatment prior to filling.
• Poor XLPE surface preparation.
• Poor preparation of the outer semi-conducting layer.
• Copper particles between cable and stress cone.
• XLPE shavings left in position between cable and stress cone.
• Incorrect application of stress cone.
• Cable not sufficiently straightened prior to jointing.
– Overload
• No cases reported in the returned survey results.
– Overvoltage
• Four cases due to switching/lightning surge.
– Animals
• No cases reported in the returned survey results.
– Weather Effects
• No cases reported in the returned survey results.
– Cable Insulation Inadequacies
• Two cases, no details supplied.
– Bonding Problems
• Thermal runaway due to a metal sheath being solidly bonded during
installation. This was not in accordance with the specified bonding design,
which was based on single point bonding.
• Poor earth connection due to mechanical movement causing flash-over.
– Fluid/Gas Problems
• Partial discharge caused by solidifying silicon oil.
• Multiple failures due to leaks of insulating oil.
– External Damage /Sabotage
• No cases reported in the returned survey results.
– Others
• Failure of pressure relief system, leading to loss of insulating fluid.
• Consequences of Failure – fire, outage time, collateral damage, reputation
270
E. Bergin
Fig. 6.2 50 kV porcelain
outdoor cable termination,
leaking high viscous
insulating oil at bottom flange
– Most cases resulted in a disruptive failure and some collateral damage that
required a lengthy repair outage (Fig. 6.2).
• Actions Taken
– New Design
• Method for earthing of sheath improved
• Change in specifications for pre-molded parts
– New Tests
• No new tests were specified in the returned surveys.
– New Installation Specification
• Improved termination fluid filling and treatment processes
• Changes made to compounds used during jointing and methods for handling compounds
• Suitable hold and witness points introduced during jointing
• New XLPE shaping techniques implemented
• Improvements made to Jointing Instructions
– Risk Management
• On-Line PD tests introduced.
• Exclusion zones set up around termination, including screening walls.
– Repair/Corrective Action
• Changed whole joint/ termination.
• Changed stress cone only. All faults required some form of repair or
corrective action to be taken.
– Preventative Action
• In many cases sealing ends that were leaking insulating fluid were replaced
or repaired before an electrical failure occurred.
6.1.3.2 Survey on Non-buried Joints
• 27 failures were reported: 12 of the failures in premolded joints and 11 in taped
joints. The remaining four failures being EMJ (extruded molded) or transition
joints.
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
271
• The location of the joints was generally not stated.
• The voltage range was 50 to 314 kV, but the taped joints were in the lower voltage
range.
• Core sizes varied from 400 to 2000 mm2 with both copper and aluminium
conductors.
• Most joint casings were unfilled.
• The installations were mainly carried out by the manufacturer.
• It was not clear if the joints and cables were from the same manufacturer
• In general the joints were type tested.
• Most joints were commissioned with DC voltage tests (both insulation and serving).
• There was no maintenance testing before failure.
• Many joints failed within 1–2 years of commissioning.
• The causes of failure were attributed as follows:
– Joint Design
• Incorrect stress cone internal diameter.
• Incorrectly shaped embedded electrode.
• Poor tape design.
– Manufacture
• Defective manufacture of stress cone that contained voids.
• Poor quality stress cone material.
• Water penetration via a crack, due to a manufacturing defect within the
metallic casing.
– Installation
• Damaged insulation during jointing.
• Poor shaping of XLPE.
• Voids created, due to poor shaping of insulating tapes.
• Incorrect positioning of stress cones.
• Cable inadequately plugged into joint body.
• Metallic particle contamination.
• Loss of earthing connection to screen wires, due to poor soldering.
• Racking or tray system that permitted joint movement.
– Overload
• No cases of failure were attributed to overload.
– Overvoltage
• One reported case was attributed to a possible lightning strike.
– Animals
• There were no failures attributed to animals.
– Weather Effects
• In only two cases failures were attributed to weather effects, namely water
penetration. The water penetration in joints may be a design/material/workmanship issue
– Unknown
• One case was listed as unknown.
• Consequences of Failure
– No consequences were provided in the survey replies.
• Actions Taken
272
E. Bergin
– New Design
• In most cases where joint design was identified as the cause of failure, the
joint was redesigned.
– New Tests
• Post-installation PD testing of joints was introduced in many cases.
– New Installation Specification
• Hold and witness points were introduced including photographic records.
• New guidance on joint protection and waterproofing was introduced.
• Clean room conditions introduced to joint bays.
• Improvements were made to jointing instructions.
– Risk Management
• Joints identified as potential failure candidates were replaced with either
joints of a different design from the same manufacturer or joints from a
different manufacturer.
• Inspection, partial discharge testing and X-Raying of all joints installed
from the same manufacturer were carried out.
– Repair/Corrective Action
• In most cases the affected joints were removed, which required the insertion of
a new piece of cable and 2 joints and the joint bay was extended to fit the new
joints
– Other
• A new reinforced racking design was introduced
6.2
The Role of Improved Materials, Design, Assembly
and Quality Control in Mitigating the Effects
of Termination and Non-buried Joint Failures
This section examines how matters may be improved with respect to materials,
design, assembly and quality control in preventing termination and non-buried joint
failures and mitigating their effects. As part of this process, the results of the survey
are reviewed to identify the causes of faults and steps identified that could be taken to
ensure these faults did not occur. It should be noted that some of the measures
identified in the Survey Results Sect. 6.2.1 below may be repeated to some extent in
the Sections 6.2.2, 6.2.3, and 6.2.4 dealing with Materials, Design, etc. This was
done to ensure the Cigré TB is as complete as possible.
6.2.1
Survey Results
It is of considerable importance that the results of the survey in Sect. 6.1.3 are taken
into account and that, where causes were identified, these are acknowledged and
steps are taken to avoid these causes in the future. The causes and recommended
mitigations are listed below:
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
273
6.2.1.1 Terminations
6.2.1.1.1
Design
Cause
Unsuitable top O ring seal used leading
to moisture ingress
Powder separation of chemical mixture.
Earthing conductors slipping off metal
sheath in termination by sliding over PE
sheath.
Circulating current flowing through
insulator screen causing overheating
and damage.
Pre-molded insulation degradation at
extremely low temperatures
Damage due to thermal cycling.
Interface design.
Degradation of components in
stress cone.
GIS copper corona shield with thin
layer having whiskers, leading to PD
and breakdown.
Stress cone interface contaminants
Mitigation
Use appropriate O ring and fit properly
Ensure correct compounds are used and
installed correctly
Ensure correct installation. Use checklist
for installation.
Ensure the correct bonding design is
installed
Ensure design suitable for operating
temperatures high and low
Design and test for heat conditions.
(Snaking cable before terminating to
minimise conductor expansion into the
termination)
Change components or design
Use appropriate materials and enhance
the interface design Consider extended
Prequalification Tests.
Design corona shield materials for use in
GIS cable termination box. Inspect all
components prior to fitting.
Jointer trained on fitting accessory, as
recommended in 6.Appendix 3 Ensure
clean conditions when jointing
6.2.1.1.2 Manufacture
One case was identified but no details were supplied – no additional mitigation
proposed.
6.2.1.1.3
Workmanship
Cause
Jointer damaged insulation
Poor XLPE surface shaping – copper
contaminants between cable and stress conecontaminants invasion of oil
Shavings of copper contamination during
the insertion of pre-molded insulation
Mitigation
Follow 6.Appendix 3 Consider use
of inspection test plans (ITP’s)
Follow 6.Appendix 3 Consider use
of inspection test plans (ITP’s)
Follow 6.Appendix 3 Consider use
of inspection test plans (ITP’s)
274
E. Bergin
Poor surface of outer semi conducting layerdefective position of compression device
Void generation between epoxy and stress
cone
Plastic wrap is used for protection during
construction.
Void generation at cable/ stress cone
interface by overbending of cable and
shaving cable insulation too much.
Generation of crack in epoxy insulator by
stressing it more than it was designed.
Overbending of cable.
Void generation at cable/ stress cone
interface by conductor centering error, when
conductor sleeves were compressed Wrong
insert position
6.2.1.1.4
Mitigation
Ensure appropriate design and installation of
lightning protection, when required.
Weather Effects
Cause
Lightning
Water entry
Connection broken, due to
mechanical overload
Jointing with high relative
humidity
6.2.1.1.6
Follow 6.Appendix 3 Consider use
of inspection test plans (ITP’s)
Overvoltage
Cause
One case due to switching/
lightning surge
6.2.1.1.5
Follow 6.Appendix 3 Consider use
of inspection test plans (ITP’s)
Follow 6.Appendix 3 Consider use
of inspection test plans (ITP’s)
Follow 6.Appendix 3 Consider use
of inspection test plans (ITP’s)
Mitigation
Ensure lightning protection used, when needed
Follow 6.Appendix 3 and use proper O ring and fit
it properly (it could be a design/material problem)
Ensure that not overbend
Use of an enclosed air conditioned work
environment Follow 6.Appendix 3
Bonding Problems
Cause
Metal sheath incorrectly bonded on a
single core cable, resulting in a sheath
circulating current that overheated and
damaged the termination
Bad connections; poor design of wiping
gland leading to mechanical movement,
sparking and failure
Mitigation
Ensure bonding design is followed
Carry out checks during
commissioning
Ensure design suitable for operating
temperatures high and low and
installed properly.
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
6.2.1.1.7
Fluid/Gas Problems
Cause
Partial discharge
in fluid
Leaking fluid or
gas
6.2.1.1.8
275
Mitigation
Ensure correct fluid is used and that fluid is properly treated
and tested and that it is at the right level.
Check where fluid or gas is leaking from, repair if necessary,
and top up.
Replace termination or component causing the leak.
Others
Cause
Unknown – breakdown just
above stress cone
Contaminants noticed at the
cable stress cone interface
Moving cables after installation
Mitigation
Ensure design is suitable for high and low
operating temperatures
Remove
Follow 6.Appendix 3
Ensure cables do not exceed their
thermomechanical design limits, are properly
clamped and are not physically disturbed
6.2.1.2 Non-buried Joints
6.2.1.2.1
Design
Cause
Stress cone with incorrect
inner diameter
Shape of embedded
electrode not right
Poor tape design
6.2.1.2.2
Mitigation
Ensure joint is suitable for use on specified cable after
cable is prepared
Ensure design is compatible
Ensure adequate Prequalification and Type Tests are
carried out
Ensure material used has the right properties and
installation instructions. Consider Prequalification
Testing
Manufacture
Cause
Defective manufacture of stress cone
(voids)
Poor material quality
Mitigation
Ensure manufacturer’s QC system is
adequate Consider Prequalification
testing
Ensure manufacturer’s QC system for
materials is adequate Consider
Prequalification testing
276
E. Bergin
Water penetration from a crack, because
of manufacture problem with metallic
sheath
6.2.1.2.3
Workmanship
Cause
Jointer mistakes causing damage to
insulation and poor insulation shield
shaping.
Water penetration, metallic
contaminants, wrong inset position.
Poor adhesion of stress cone
Metallic contaminants in the
insulation tape.
Void generation with poor tape shaping.
Contaminants.
External damage by jointing tool, when
connection box was assembled.
Fibrous contaminant in extruded
insulation. Clamping of screen wires
caused damage of outer semi-conducting
layer
Loose flakes of applied semiconducting
coatings in joint assembly.
6.2.1.2.4
Ensure manufacturer’s QC system is
adequate
Mitigation
Follow 6.Appendix 3 Consider use of
inspection test plans (ITP’s)
Follow 6.Appendix 3 Consider use of
inspection test plans (ITP’s)
Follow 6.Appendix 3 Consider use of
inspection test plans (ITP’s)
Follow 6.Appendix 3 Consider use of
inspection test plans (ITP’s)
Follow 6.Appendix 3 Ensure proper
procedures followed, adequate drying
time and care in positioning of the
joint body.
Overvoltage
Cause
In only one case was joint damage attributed to
possible lightning strike
6.2.1.2.5
Mitigation
Ensure appropriate lightning
protection is used.
Weather Effects
Cause
In only two cases was failure
attributed to weather effects, namely
water penetration.
Mitigation
Follow 6.Appendix 3 Consider use of
inspection test plans (ITP’s). Adequately
designed casing (coffin) filled with
waterproof compound.
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
6.2.2
277
Design and Materials
In considering the design of terminations and joints it is necessary to consider the
materials to be used, the pressures in different parts of the accessory assembly, the
different electrical characteristics, etc.
6.2.2.1 Air Insulated Terminations
Air Insulated Terminations are generally used outdoor to terminate cables in air
insulated substations. They may have porcelain or composite insulators and may be
filled or unfilled. The design adopted may depend on the local environment with
respect to the required basic impulse level voltage (BIL), maintenance requirements,
pollution (industrial and ocean), reliability and altitude. Surface creepage distances
may need to be increased in areas of high pollution, excessive sea spray or at high
altitudes.
6.2.2.1.1 Porcelain Insulators
Glazed electrical grade porcelain is the most common and widely installed insulator.
It has high reliability in terms of electrical and mechanical performance. It requires
periodic maintenance (cleaning) to remove pollution deposits from the insulator
surface (sheds). It has high resistance to surface tracking. Porcelain production is a
mature technology and can be provided for MV to EHV cable terminations and for
both AC and DC application.
However, porcelain can be susceptible to external mechanical damage and to
electrical failure (internal or external). It can shatter on termination failure with
pieces of glazed porcelain and other debris projected over the surrounding area by
the force of the failure. The potential for injury or damage to adjacent equipment in
the surrounding area is high.
6.2.2.1.2 Composite or Polymeric Insulators
There are many types of composite insulators available on the market. The most
common design consists of a fibreglass tube covered by elastomeric sheds (silicone).
This solution is much lighter than a porcelain insulator and is normally much easier
to handle during installation. However, the bond between silicon rubber and the
epoxy glass fibre pipe must be certified as this can be a weak point (Fig. 6.3).
Composite insulators are available up to EHV applications, even though at this
stage there is no long term operational experience at EHV levels.
Composite insulators have many advantages. In particular they have proven to be
reliable even under exceptional events such as earthquakes, system faults and
vandalism. They also provide good insulation performance due to their silicone
housing and the intrinsic hydrophobic characteristic of this material. Well designed
composite insulators have limited ageing. They give satisfactory performance in
heavily polluted areas, where no cleaning or special maintenance is necessary and
this can provide important economic savings.
278
E. Bergin
Fig. 6.3 Composite insulator
filled with synthetic oil
Their technical and economic advantages are of particular significance in the
EHV and UHV range of accessories. This is because of their design flexibility (single
pieces of 10 m or more may be manufactured), relative low weight (10–30% of a
corresponding porcelain insulator), ease of handling for manufacturing and installation and their ability to withstand stresses, such as seismic events and high levels of
pollution.
From the point of view of end-users, a very important feature of composite insulators
is safety. They reduce the potential for manual handling injury during delivery and
installation. Since they are not brittle, the risk following an internal fault, with the
associated projection of material, is greatly reduced compared with porcelain.
The satisfactory long term performance of composite insulators is directly related
to electrical and mechanical design, good selection of the material, good manufacturing processes and quality control.
Environmental constraints of the installation site such as the required BIL,
temperature, barometric pressure (for high altitude), presence of aggressive gases,
pollution, and humidity should be taken into account in the design. Qualification
procedures can help to qualify the technology and the materials and assure the
performance during the required life time of the insulator and these are dealt with
in detail in Cigré TB 455 “Aspects for the Application of Composite Insulators to
High Voltage (72 kV) Apparatus”.
A range of biological growths have been reported on composite insulators leading
to a reduction of the hydrophobicity. However, the overall performance of the composite insulator design generally remains satisfactory. Bird attacks have also been
reported, but this appears to be a problem related to insulators in some countries and
usually only happens when de-energised or before the insulators are put into service.
Another consideration is whether vapour could permeate directly through the
sheds and walls of the housing (polymeric materials are generally slightly permeable
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
279
for vapour) or through the bonding area between flanges and fibre-reinforced plastic
(FRP) tube. Investigations and service experience indicate that the amount of
moisture ingress due to these mechanisms is below the quantities which can pass
through a good sealing system. Quantities can easily be controlled by internal
desiccants as is usual practice for much of the HV apparatus in the electric power
system. In the case of terminations/ sealing ends this is often accomplished by using
filling compounds. Nevertheless research continues in an attempt to better understand these mechanisms and to derive minimum design requirements on composite
hollow core insulators used for HV apparatus applications.
Most damage in composite insulators can be attribute to errors during transport,
un-packing, re-packing, manipulation and storage of the insulators. These aspects
are dealt in detail in Cigré TB 455 “Aspects for the application of Composite
Insulators to High Voltage (72 kV) Apparatus”, Chap. 9, “Handling and Maintenance”. In this chapter, procedures and rules are given for: unpacking, repacking,
storage, handling and cleaning.
A composite termination has the advantages of a simple structure. Its anti-pollution
capacity depends mainly on the number of sheds and their size and orientation. The
terminal must be installed upright, it cannot be installed inclined or curved.
Porcelain and composite terminations are compared in the Table 6.5 below.
It can be seen that each outer housing material has its advantages and disadvantages. The selection of the appropriate termination body depends on the particular
installation conditions.
The satisfactory performance of composite terminations is dependent on the inner
electrodes and the electric field distribution within and along the termination. This, in
turn, depends on the top electrodes, the insulator material, the inner electrodes,
non-linear coatings, cable make-up; etc. All of these components must be designed,
manufactured and installed to control the operating electrical stresses.
6.2.2.1.3 Latest Developments
The latest developments on the market provide two alternative solutions:• Self Supporting Terminations
– A termination filled with silicon based leak-proof gel that replaces the traditional liquid fluids. This solution has been tested up to EHV, but service
experience is available only up to 132 kV. The filling procedure has to be
strictly controlled to ensure proper filling (Table 6.5; Figs. 6.4 and 6.5).
– A fully dry termination, where no liquid or filling is used
• Supported or Flexible Type A Prefabricated Outdoor Termination
• This type of termination has elastomeric sheds and an external stress cone. The
stress cone and the sheds form one single factory-tested premolded component
and they are widely used in the voltage class up to 150 kV. With this termination type a completely “dry” design is obtained. Note this termination is not
self supporting and must be connected to an overhead conductor or to another
component e.g. a surge arrester, able to support the termination.
• Disruptive–proof Outdoor Terminations i.e. terminations that are designed to
limit the consequence of an internal power arc, etc.
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Table 6.5 Comparison of Porcelain and Composite Insulators
Element
Environmental
Chemical
Mechanical
Rating
Performance
Other
Properties
Porcelain Insulators
Can shatter
Periodic cleaning required
Poor pollution performance
It’s earthquake performance is not so
good
Impermeable to animal attack even
when unenergised
Not hydrophobic
Compatibility with SF6 by-products
and oil
Can shatter under fault conditions
Composite Insulators
Safe/Inert
Limited cleaning required
High performance in polluted areas
Good earthquake performance
Possible attack by animals during
storage and while unenergised
Hydrophobic
Compatibility of filling material to
be checked
Will not shatter but may split Low
weight
High weight Vulnerable to
Less susceptible to vandalism
vandalism No moisture ingress
Possible moisture ingress through
through the insulator from outside.1
the insulator from outside.1
1
Note for both types of insulators there may still be some moisture ingress
through the top and bottom metal components or gaskets
No practical temperature limit
Temperature limits of 55 to
(temperature limits exceed those of
+110 C
other components)
Lot of experience, but relatively long Limited service experience
manufacturing time
Because of its weight it’s not so easy
Because of its weight its relatively
to handle and install. Heavy manual
easy to handle and install
handling or mechanical assistance
required
Can be damaged (cracked or chipped) Not so likely to be damaged
by handling and installation. Small
damage can be repaired in-situ.
One must also bear in mind the effect of insulation retraction on the termination.
Retraction is a result of the mechanical stress formed in the insulation during the
manufacturing process. When the cable is cut, in order to install the accessory, the
insulation may retract on the accessory and lead to a failure. This must be taken into
account in the accessory design (Fig. 6.6).
6.2.2.2 GIS and Oil Immersed Terminations
EHV and HV cables may also be directly terminated in SF6 insulated switchgear
(GIS) and transformers to eliminate air-insulated interfaces. This solution has the
significant advantage of markedly reducing substation area requirements and costs
in urban, suburban and industrial plant locations. It also eliminates insulation
contamination from pollutant deposits and reduces exposure to lightning and
vandalism.
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Fig. 6.4 Example of a
170 kV composite cable
termination
Fig. 6.5 Example of a Self
Supporting Fluidless Cable
Termination
GIS and oil immersed terminations have similar construction, except for the use
of a larger top corona shield on the termination in order to reduce the top-end stress.
The electrical stress control for GIS and oil immersed terminations follows the
same approach usually employed for outdoor terminations i.e. it uses a premolded
stress relief cone, which is fitted over the cable insulation. The cable is then
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Fig. 6.6 Example of a Dry
Type Supported Termination
accommodated inside a cast epoxy resin bushing which separates the cable from the
pressurised SF6 or the oil in the termination end box.
The space inside the epoxy bushing can be filled with insulating fluid or SF6 gas.
In order to eliminate any risk of leakage of this fluid or gas from inside the epoxy
bushing, a new generation of dry type SF6 and oil immersed terminations have been
developed. In these dry terminations there is no insulating fluid or gas between the
epoxy insulator and the stress cone, because the latter is in intimate contact with the
inner surface of the bushing; the pressure of the stress-cone at the cable core interface
as well as at the inner epoxy insulator surface can be obtained by means of
compression devices such as springs or by special design of the polymeric part.
It should be noted that currently there is a Joint Working Group B1/B3.33
examining the “Feasibility of a common, dry type interface for GIS and Power
cables of 52 kV and above” (2009–2012) and a Cigré TB is to be issued shortly by
this WG by the end of 2013, ▶ Chaps. 7, “Feasibility of a Common, Dry Type Plugin Interface for GIS and Power Cables above 52 kV” and ▶ 11, “Standard Design of
a Common, Dry Type Plug-in Interface for GIS and Power Cables up to 145 kV”.
6.2.2.3 Insulation Medium
Terminations are generally filled with a dielectric fluid, usually a synthetic (polybutene or silicone based) insulating liquid, at or slightly above atmospheric pressure.
The type and quantity of the fluid depends on the specific design of the termination.
Poor quality of the liquid or contamination, due to external factors (humidity, water
ingress, metallic or other polluting particles, etc), can reduce the electrical performance of the fluid and result in termination failure. One of the most common issues
with the use of fluid is the risk of leakage through the sealing point areas, typically
the weld/plumbing between the cable metallic screen and the bottom part of the
termination or the mechanical seal onto the stress cone. A well-made seal depends
mostly on the skill of the jointers.
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There are also designs that use SF6 gas as the insulation medium, but this solution
has to bear in mind the environmental concerns of using SF6 gas.
6.2.2.4 Connectors
The connector electrically and mechanically joins the conductors of two cables or the
cable and the top connector of a termination. Thus the connector must exhibit good
electrical conductivity to avoid temperatures higher than that of the conductor in any
operating condition and also present sufficiently high mechanical pull-out (tensile)
strength to withstand thermo mechanical stresses during operation. It should be noted
that WG B1.46 is currently working on Conductor Connectors (Mechanical and
Electrical Testing). The final report of WG B1.46 is reproduced in ▶ Chap. 10, “Test
Regimes for HV And EHV Cable Connectors” of this Book. The following types of
connectors are used for extruded cable connections:6.2.2.4.1 Compression Connector
This connector includes a tube of the same material as the cable conductor into
which the conductors to be joined are inserted. The tube is then compressed by a
hydraulic press. The compression connector is the most commonly used type,
because it is easy to install and does not require heat (Fig. 6.7).
The cross section of the connector is at least equal to the cross section of the
conductors to be joined. When the connector is exposed to an electric field, as in
taped joints, it is necessary to provide suitable chamfers at both ends to minimize the
effects of longitudinal electrical stresses.
A special bimetallic connector is used when it is necessary to join a copper
conductor to an aluminium conductor. These connectors are half copper and half
aluminium. The two connector halves are joined in the factory by friction welding.
Some companies use a copper alloy connector for both copper and aluminium
conductors.
6.2.2.4.2 Cad Welding
Another way is to make a connection of copper and aluminium conductors by
Cad-welding on site, though Cad welding is not used that often for aluminium.
This is an exothermic welding process in which metal and metal oxide powders are
placed in a special crucible mold around the parts to be welded. This mixture is
Fig. 6.7 Compression
connector
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ignited resulting in a short high temperature reaction, causing the flow of molten
metals to form a localised solid connection.
6.2.2.4.3 Soldered or Brazed Connector
Soldered connectors are used with small conductor cross sections (below 630mm2)
and with cables having a short circuit current temperature below 160 C, because the
solder can become soft during the cable system operation. Brazed connectors do not
present this problem, but are more difficult to make.
6.2.2.4.4 MIG or TIG Welded Connection
The two conductors are fused together by the application of molten metal. A Metal
Inert Gas (MIG) or Tungsten Inert Gas (TIG) welding process is applied in this case.
Due to the high temperature developed during the process, air or water cooling
clamps are required on both sides of the weld, in order not to damage the cable
insulation The welding process is used for large aluminium conductors and for
insulated wire copper conductors; in the latter the burning of the wire insulation, if
necessary, ensures a good contact between strands. This technology requires an
operator with a very high skill level and is time consuming (Figs. 6.8 and 6.9).
This weld provides a connection with an electrical conductivity, which is equivalent to that of the conductor itself. The connection is not subject to instability due to
decrease of contact pressure as a result of load cycling. However the tensile strength
of the welded connector is significantly (50 to 60%) lower than the ultimate tensile
strength of the conductor, due to the annealing of the conductor near the weld. If
necessary, for submarine cables, the tensile strength can be improved by round
compressing the conductor and the weld (hardening process) (Fig. 6.10).
6.2.2.4.5 Plug-in Connector
Two metal connectors, that terminate the conductor, are jointed through elastic or
multi contact spring loaded contacts that are able to carry the current. Locking pins
Fig. 6.8 Examples of Cad Welding
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Fig. 6.9 Example of a
MIG Weld
Fig. 6.10 Welding of an
aluminium conductor
can be used to anchor the two parts together. Plug-in connectors can easily join
conductors of different materials and cross section.
One of the advantages of a plug-in connection is the shorter length of the joint.
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Fig. 6.11 Plug-in connector
(male contact) on prepared
cable end
6.2.2.4.6 Mechanical Bolted Connector (Shear Bolts)
With these connectors compression of the conductors inside a ferrule is made by
tightening threaded bolts. The bolts shear off at a predetermined torque and are then
finished flush with the surface of the connector. These connectors are extensively
used in MV accessories, and may also be used in HV joints or terminations, subject
to checking their short circuit current and current loading capacity. The compatibility
of these connectors with the termination or joint design must be checked. These
connectors have a diameter larger than the compressed connectors and care must be
taken to ensure there are no bits of bolt protruding above the connector surface.
Before using shear connectors consideration must be given to tensile strength during
load cycling and pull out (Fig. 6.11).
6.2.2.4.7 Mechanical Bolted Connector
With these connectors compression of the conductors inside a ferrule is made by
tightening threaded bolts. These connectors are extensively used in MV accessories,
and may also be used in HV joints or terminations, subject to checking their short
circuit current and current loading capacity. The compatibility of these connectors
with the termination or joint design must be checked. These connectors have a
diameter larger than the compressed connectors and care must be taken to ensure
there are no bits of bolt protruding above the connector surface.
6.2.2.5 Non-buried Joints
Non-buried joints locations may be in tunnels, on bridges, in underground chambers
or similar enclosures.
Non-buried joints for XLPE cables usually have premolded joint bodies with
additional covering for protection against moisture and mechanical damage. The
additional covering could be heat shrink tubes or metal housings with additional
insulating housings/coffins (Fig. 6.12).
Transition joints for XLPE to oil filled cable are often installed as non-buried
joints in underground chambers. They use metal-tubes combined with epoxy insulators as a barrier between the different insulating materials – XLPE and fluid
impregnated paper. In the case of transition joints full quality control must take
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287
Fig. 6.12 Example of a
bolted connector
into account electrical and mechanical stresses for both sides of the joint and any
interface locations.
Water can seep into a non buried joint, if any earth or bonding wire connections to
the joint are not sealed properly.
6.2.3
Assembly
Cigré TB 476 is a comprehensive document on assembly and quality control of
XLPE accessories and the contents pages are attached as 6.Appendix 3. It gives
guidance on aspects of cable accessory workmanship that need to be carefully
considered in evaluating the execution of the work, including the specific technical
risks and the associated skills needed to mitigate them (Fig. 6.13).
Where a termination is to be filled with compound, the manufacturers filling
instruction should be followed. Filling compounds may be such items as polybutene,
silicon oil or other dielectric fluid or gas.
6.2.4
Quality Control
Joints and terminations are delivered to site as kits, which in turn are made up of
many components It is vital to have quality control on all components. The main
insulation is either the premolded joint body or premolded stress-cone, and the
testing requirements for these are as defined in IEC60840 and IEC62067. The
manufacturer shall demonstrate or guarantee that the components forming the
accessory are the same as those tested to IEC standards.
Each component has a specific function, whether it is secondary insulation, oil,
gas or air tightness, mechanical protection, conductor or sheath connection, etc. It is
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Fig. 6.13 Example of
non-buried joints: 145 kV
single core cable joints
installed in a cable jointing
chamber/manhole
essential that the manufacturer has in place quality control plans that define the tests
to be carried out and their frequency and these should be related to the function of the
component. The inspection or testing may include visual, dimensional, mechanical,
dielectric, pressure, whether as an incoming control from sub-suppliers or as final
control as semi-finished products (insulators for example). Components must be
inspected according to drawings and specifications with given tolerances, and there
must be no deviations outside the given tolerances.
Final checking must be done on delivery to site to ensure the right quantity and
quality of materials has been delivered.
Of course the QC aspects with respect to jointing, as set out in Cigré TB 476, must
also be followed. This applies in particular to the certification/ approval for the
jointers and the site conditions.
6.3
The Role of Testing and Condition Monitoring
in Minimising the Incidence or Severity of Termination
and Non-buried Joint Failures
6.3.1
Testing
6.3.1.1 General
In order to prove that a cable system meets the expectations of the customer the role
of testing at all stages of design, supply and in-service is clearly important for both
the supplier and end-user. In addition, once a cable system is in service, it may be
beneficial to carry out in-service testing to assess the condition of the system and its
components. This section will examine the types of testing and condition monitoring
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289
that may be carried out, when assessing a cable system. This is not intended to be
exhaustive, but to provide guidance on the areas that should be considered. The level
of testing required for a cable system should be decided on by the customer, based on
risk and performance requirements.
International standards for underground cable systems generally provide design
rules and testing procedures to assess a cable system and to ensure it meets the
requirements for reliable operation during its design life. These generally focus on
prevention of failure, rather than actions that can be taken to mitigate the consequences of a fault. Some National Standards or individual utility specifications have
introduced fault simulation testing and specify requirements for the performance of
the system under these conditions e.g. an internal arc test is carried out by some
utilities to evaluate the consequence of an internal fault – there is a requirement for
this within IEC 62271 requirements for switchgear testing.
It should be noted that a cable system incorporates the cable, terminations, joints,
internal terminations and joint components, filling media, connectors, screen connections, bonding etc., and great care must be exercised in testing to ensure that all of
the components are properly represented and identified in testing regimes.
6.3.1.2 Development Testing
Development testing is carried out by the cable accessory supplier during the design
of a new accessory. The results of these tests may indicate to the manufacturer and,
where required, the customer, any changes and improvements that can be made to a
cable accessory. An example of development tests are the environmental tests
including salt/ fog, rain and pollution tests, carried out on composite insulators,
which are not covered by cable international standards. These tests are carried out by
manufacturers to demonstrate the long term performance of their products and are
carried out to in-house test specifications. IEC61462 ed. 1.0 covers the test procedures for Composite Insulators for AC Overhead Line with Nominal Voltage
greater than 1000 volts.
Results of development testing are generally not specified by customers, but may
help to inform a decision on the suitability of a cable termination or joint for use for a
particular application or in a particular location, for example the suitability of
terminations for use in areas of high pollution.
Development tests are performed by the manufacturer during the development of
a new accessory and are intended to ensure the accessories long term performance
and to assess safety margins. The tests include:
•
•
•
•
•
Analysis of electrical, mechanical and material compatibility
Electrical tests up to breakdown and mechanical and thermal tests on prototypes
Wet and pollution test on outdoor terminations
Electrical and thermal tests of connectors
Mechanical tests on premolded components (on the insulators and connectors)
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• Fire and disruptive failure performance, including Internal Power Arc test on
terminations in accordance with 6.Appendix 4.
6.3.1.2.1 Insulators
IEC 61462 “Composite hollow insulators –pressurised and unpressurised insulators
for use in electrical equipment with rated voltage greater than 1000 V” specifies both
design and type test requirements for self supporting composite insulators. The tests
in this IEC standard are designed to provide information on material selection,
manufacturing processes, material thickness and adhesion and end fitting material
selection an attachment.
To complete the project of developing a new accessory, construction drawings
shall be prepared of all components and a full size prototype shall be manufactured
and subjected to tests. If the prototype includes specific components such as premolded parts, composite and epoxy resin insulators, it is necessary to develop the
technology to produce these components.
The tests should show the limit in the performance of the accessory and guarantee
a proper safety margin with respect to test values stated in the relevant IEC standard.
Tests carried out must ensure that the entire family of accessories is able to
withstand the stresses, which they may be subjected to in their operational life
(Fig. 6.14).
The termination may be exposed to a saline solution of a different concentration
depending on the level of pollution it will experience. In this condition it is then
subjected to an AC voltage test. For composite insulators with a polymeric coating,
which are subject to aging of the surface, the pollution test is performed after an
aging of 1000 hours in saline fog or an electrical cycle-environmental of 5000 hours
(see IEC 62 217).
Fig. 6.14 Salt-fog test on insulator
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6.3.1.2.2 Connectors
Development testing may also be done for connectors. Thermal cycles are performed
on connectors and contacts used in the accessories following the standards of IEC
61238–1, currently restricted to medium voltage. During the test, measurements of
temperature and electric resistance as a function of time are taken. Short circuit
current tests are also performed on the connectors, Testing of connectors is the topic
of TB 758 which is reproduced in ▶ Chap. 10 “Test Regimes for HV and EHV Cable
Connectors” of this book.
6.3.1.2.3 Filling Fluids
Before using any type of oil or fluid within a specific housing material, equipment
manufacturers should have verified its full compatibility with materials and assembly
processes, including health and safety. This is especially of interest where new types of
fluids or other fillers are considered. Some manufacturers have developed their own
qualification procedures, specifying test conditions in terms of temperature, duration,
safety and final acceptance criteria. This forms part of the development tests.
6.3.1.3 Prequalification Test
Prequalification testing, as in IEC 62067 & 60840, is only specified for cable
systems above 150 kV or where the conductor screen stress is designed to be greater
than 8 kV/mm or the insulation screen stress is designed to be greater than 4 kV/mm,
Prequalification tests are long term tests that are carried to assess the performance
of a cable system and attempt to replicate in-service duty. The test arrangement
should be representative of installed conditions, e.g. fixed and flexible sections and
contain both joints and terminations to give a true replication of the cable system.
These tests are intended to verify the thermo-mechanical and electrical behaviour of
the cable and accessories. In some local standards it is also a requirement to monitor
and record the pressure of any insulating mediums used in order to assess the
robustness of any sealing arrangements.
After testing, all accessories are to be examined to check for any changes or
deterioration that might affect the performance (Fig. 6.15).
Fig. 6.15 Tests on connectors
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6.3.1.4 Type Test
Type tests are carried out on the complete cable system and are required for all
voltages and design stresses. These tests provide a minimum requirement to show
specific cables and accessories are fit for a specific purpose. Type tests, as
specified in IEC 60840 & IEC 62067, focus mainly on the cable system shortterm voltage withstand performance. They include AC, over-voltage and lightning transients combined with material aging effects. Following completion of
these tests, the cable system must be shown to be partial discharge free or to have
a level of discharge below a certain requirement. If any partial discharge is
present, even below the level specified, it may be prudent to identify the cause
of this discharge. Once tests are completed it is important to disassemble all
accessories and closely inspect them for any signs of electrical activity or
physical changes, which may not have caused an electrical discharge, but may
cause mechanical or operational problems. The interpretation shall be based on
the previous experience with development, prequalification and other type tests
(Fig. 6.16).
Fig. 6.16 Type Test loop of
400 kV system
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6.3.1.5 Short Circuit Tests
The WG identified that short-circuit behaviour was not addressed by any IEC
standard relating to HV cable systems. Several utilities have independently taken
the step of specifying an additional type test to check the behaviour of terminations
(especially those containing insulating fluid) when they are subjected to short
circuits. Two cases need to be considered
• A low energy external fault. In this case the fault current passes though the
conductor. The fault is external to the accessory.
• A high energy internal fault. In this case the fault is the result of component failure
or arcing inside the accessory.
Consideration, depending on the design and installation, should be given to
whether it is necessary to do one or both of the above tests to cover the worst case
condition.
These tests are detailed in 6.Appendix 4.
6.3.1.6 Sample Tests
Sample test requirements are outlined in IEC 60840 and 62067. These tests are to be
carried out on a specified number of components and complete accessories during a
production run. For accessories, where the main insulation cannot be routine tested,
IEC 60840 states that a partial discharge and an AC voltage test shall be carried out
on a fully assembled accessory. For individual components the characteristics of
each component shall be verified in accordance with the specifications of the
accessories’ manufacturer, either through test reports from the supplier of a given
component or through internal tests. Also the components shall be inspected against
their drawings and there shall be no deviation outside the declared tolerances.
6.3.1.7 Routine Tests
Routine tests are carried out on some accessory components to be supplied. These
tests should form part of a robust quality control regime and provide confidence in
accessories’ quality. As part of these tests, the main insulation of prefabricated
accessory designs is required to undergo AC voltage and partial discharge tests.
Finally each component should be visually inspected for defects.
Insulators filled with oil, gas, or other material should also undergo a pressure test
before delivery.
6.3.1.8 Tests on Filling Materials
Filling materials, like polybutene or synthetic oil, are selected based on the material
parameters and characteristics and they are approved during the development,
prequalification and type tests. –specification IEC 60836 covers silicon oil.
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It is recommended that a “finger print” of the filling material be determined after
delivery, as this “finger print” might be useful during condition assessment programs
or failure analysis.
Well established material “finger print” techniques are
•
•
•
•
AC electrical strength
Dielectric dissipation factor
Fourier transform infrared spectroscopy (FTIR)
Thermal gravimetric analysis (TGA).
6.3.1.9 Commissioning Tests
Commissioning tests are carried out on the assembled cables, joints terminations,
bonding and earthing once the installation is completed. They are the final tests
performed on the cable system prior to energising and provide the final check that the
system has been correctly designed and installed. The requirements for commissioning
tests will vary depending on the type of circuit installed and the consequences of failure.
There are very few tests that can be carried out that will prove the long term life of
cable, joints and terminations. However, it is recommended that an AC insulation
test is carried out with partial discharge monitoring, if possible, of all joints and
terminations. Ideally this is carried out using a resonant test voltage generator. This
allows the cable system to be energised off-line and at low energy and so there is a
minimised risk of a disruptive accessory failure during the test. The tests may give an
early warning of potential failure points, before a later breakdown of the complete
cable system in service leads to bigger problems. The commissioning tests should be
performed according to the relevant IEC standard.
It is possible to carry out an AC test by energising the termination with system
voltage (soak test) and using on-line partial discharge monitoring. This is not ideal,
as noise from the system can mask discharge activity occurring within the accessory.
In addition, if a breakdown does occur this will lead to a disruptive failure of the joint
or termination (as the full system short circuit current is available to flow through the
failed accessory) and may lead to an outage and power disruption. Such a failure
presents both a safety risk on site and introduces a significant delay to commissioning of the circuit while the affected components are replaced.
A DC oversheath test should also be carried out to ensure the cable system and its
accessories are insulated from earth.
6.3.2
Condition Monitoring
As indicated in Cigré TB 420 Generic Guidelines for Life Time Condition Assessment of HV Assets and Related Knowledge Rules, it is recommended that a good
database of information is established for each piece of equipment as it ages. Useful
information on the aging process during the full service life includes loading,
maintenance test results, fault history, general ambient and environmental conditions
and details of any site incidents.
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Fig. 6.17 On site Commissioning Test (in this set up three mobile tests sets needed simultaneously,
because of cable length)
Fig. 6.18 Discharge tracks
on cable PE outer serving due
to a defect. The discharge
tracks are a consequence of
fault localisation pulses
To effectively manage the aging of HV cable accessories, a structured methodology to analyse and prevent in-service failures is recommended. A suggestion for
such methodology is given in Cigré TB 420, clause 4.2. The final step in this
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E. Bergin
methodology is to gather the outputs from this process into a management strategy
which can be used for:
• Preventative maintenance,
• Decisions on equipment change-out
• Improvement in the specification, design or manufacture of new equipment.
Regarding preventative maintenance, there are many possible approaches to
monitoring the condition of terminations and non-buried joints. These vary from
visual inspection to on-line monitoring or regular testing while out of service, etc.
The monitoring to be carried out depends on:
•
•
•
•
•
•
•
•
•
•
The importance of the circuit
The history of the circuit and its accessories
The potential repair time
The potential cost of the outage
Potential cost of the damage
Effect on reputation
Potential damage from the failure
Effectiveness of the monitoring system adopted
Availability of monitoring tools and trained personnel
Cost of monitoring.
A list of current Condition Monitoring Tools is detailed in 6.Appendix 5. To assist
in the selection of a monitoring tool, each tool is described under a number of
headings including:• Experience – the level of working experience of each condition monitoring tool is
categorized as either well established (“W”) or under development (“D”).
• Effectiveness – one diagnostic monitoring tool may be considered (based on
costs, time and results) as more effective than another in finding damages or
degradations that will lead eventually to system failure; categorized here as useful
(“U”) and less useful (“L”).
• Level of expertise required – whether high or low level expertise is required i.e. a
technician/engineer trained in the particular tool being used or is a general
operative sufficient to operate the tool.
• Cost.
6.4
Recommendations
The aim of the WG has been to produce a Cigré TB that could be used by designers,
manufacturers, contractors and utilities to increase the integrity of terminations and
non-buried joints. Many approaches to this subject are possible, depending on the
factors outlined in Sect. 6.3.2 above. Two cases need to be considered:
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
297
Fig. 6.19 Example of
condition monitoring
technique: The X-ray photo of
cable outdoor termination
used to check any internal
displacement of the
top-connector
• where the accessories are on an existing cable circuit
• where the accessories are to be installed on a new cable circuit.
6.4.1
Existing Circuits
For existing circuits the following considerations apply:•
•
•
•
•
•
•
•
•
•
The importance of the circuit
The history of the circuit and its accessories
The potential repair time
The potential cost of the outage
Potential damage from the failure
Potential cost of the damage
Effect on reputation
Effectiveness of the monitoring system adopted
Availability of monitoring tools and trained personnel
Cost of monitoring.
6.4.2
New Circuits
If a new circuit is being installed then it seems appropriate to use proven
composite terminations (unfilled, if possible) and proven joints. The designs
should comply with IEC 60840 and 62067 as far as PQ and Type testing, Routine
and Site Test are concerned. There should be a full QC system in the factory for
both cables and accessories. Of course both joints and terminations should be
298
E. Bergin
installed fully in accordance with the manufacturer’s instructions, and in accordance with Cigré TB 476.
When new accessories are being installed a decision will have to be made on what
condition monitoring, if any, is necessary. Refer to recommendations of Sect. 6.3.2.
6.5
Conclusions
The following conclusions resulted from the work carried out by this working group:
• The survey completed by this WG has shown that disruptive discharge has been
experienced in terminations and non-buried joints.
• Utilities are concerned about these discharges.
• In the case of installing new cable systems, utilities should try to adopt designs
that either do not experience disruptive discharge and/or that have been tested to
ensure the impact is kept to a minimum.
• Full quality control procedures should be employed during the manufacture,
delivery, storage and the installation process.
• Jointers should be fully certified, have experience of the accessory to be installed
and their work should be checked/monitored/ inspected.
• All materials and jointing tools used should be appropriate for the work, be in
good condition, have been correctly stored and be within their expiry dates.
• The site conditions should be suitable with respect to space, safety, dust, pollution, humidity and temperature.
• On-site testing at an elevated voltage level, as prescribed in the IEC standards, is
strongly recommended during commissioning.
• A risk analysis should be done to determine the corrective actions required for
existing accessories, which have experienced disruptive discharge or it is
suspected they may do so in the future. This can vary from leaving the accessory
in service to partial or full replacement. Whether it is decided to go for full or
partial replacement, steps 3 to 8 above should be followed.
• If it is decided to do condition monitoring on existing or new circuits, then the
following items need to be considered
– The importance of the circuit
– The history of the circuit and its accessories
– The potential repair time
– The potential cost of the outage
– Potential cost of the damage
– Effect on reputation
– Potential damage from the failure
– Effectiveness of the monitoring system adopted
– Availability of monitoring tools and trained personnel
– Cost of monitoring
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
299
Appendix 1: Terms of Reference
Study Committee No: B1
WORKING BODY FORM
Group No: WG B1.29
Name of Convener: Eugene Bergin (Irl)
TITLE of the Working Group: Guidelines for maintaining the integrity of XLPE transmission cable accessories
Background:
The work is motivated by the occurrence of disruptive failures of cable end terminations, with consequent risks for personal
and material loss and damage.
Terms of Reference:
The scope shall be limited to land XLPE cable systems at 110 kV and above. Priority shall be given to outdoor and oil-immersed terminations, but also joints (that are not directly buried) shall be considered.
The work shall concentrate on recent incidents, but near misses shall also be included in the analysis.
The WG shall:
Review recent experience with failures of outdoor a
Review the consequences of termination failures for cables within substations and outside.
Examine the role of design, assembly and quality co
res
Examine the role of testing (development, type, routine & after-laying) and condition monitoring in minimising the incidence
or severity of termination failures
At the SC B1 meeting in 2010, the WG shall provide recommendations on possible extensions of work into joints (not directly
view at the B1 annual meeting in 2011.
Deliverables:
An Executive Summary article for Electra
A full report to be published as a TB
A Tutorial
Created: 2008
Duration: 3 years
Convener e-mail: bergin_eugene@yahoo.co.uk
WG members from: AU, BE, BR, CA, FR, DE, IN, IT, JP, KR, NL, NO, ES, CH, UK, US
Other stakeholding SC’s: B2, B3, C3
Approval by TC Chairman:
Date:
2008
Appendix 2: Bibliography/References
IEC Standards
IEC 60840 Ed 3 Power cables with extruded insulation and their accessories for rated
voltages above 30 kV (Um ¼ 36 kV) up to 150 kV (Um ¼ 170 kV) –Test
methods and requirements
300
E. Bergin
IEC 62067 Ed 2 Power cables with extruded insulation and their accessories for rated
voltages above 150 kV (Um ¼ 170 kV) up to 500 kV (Um ¼ 550 kV) – Test
methods and requirements
IEC 62217 Ed. 1: Polymeric insulators for indoor and outdoor use with a nominal voltage
greater than 1 000 V – General definitions, test methods and acceptance criteria.
IEC 61462 Ed. 1.0: Composite insulators – Hollow pressurized and unpressurized
insulators for use in electrical equipment with rated voltage greater than 1000 V –
Definitions, test methods, acceptance criteria and design recommendations
IEC 62271:High voltage switchgear and control gear – Part 209: Cable connections for
gas-insulated metal-enclosed switchgear for rated voltages above 52 kV – Fluidfilled and extruded insulation cables – Fluid-filled and dry-type cable-terminations
IEC 61039: General Classification of insulating liquids
IEC 60815–1 TS Ed. 1.0: Selection and dimensioning of high-voltage insulators for
polluted conditions – Part 1: Definitions, information and general principles
IEC 60836 Ed 2.0 b 2005 Specification for unused silicon insulating liquids for
electrotechnical purposes.
IEC 61109 Ed 2 Insulators for overhead lines – Composite suspension and tension
insulators for AC. systems with a nominal voltage greater than 1 000 V –
Definitions, test methods and acceptance criteria
CIGRE
Title of Electra Paper
Electra No.
243
Update of Service experience of HV underground and submarine cable
systems
235
Statistics on AC underground cables in power networks
210
Current cable practises in Power Utilities (A report on the recent AORC
Panel Regional Workshop in Malaysia)
204
General overview on experience feedback methods
141.1
Service experience of cables with laminated protective covering.
137
Survey of the service performance on HV AC cables.
212
Thermal ratings of HV cable accessories
203
Interfaces between HV extruded cables and accessories
TB
Title of TB
220
502
High Voltage On Site Testing with Partial Discharge Measurement
476
Cable Accessory Workmanship on Extruded High Voltage Cables
455
Aspects for the Application of Composite Insulators
420
Generic Guidelines for Life Time Condition Assessment of HVAssets and
Related Knowledge Rules
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
379
338
303
279
211
210
177
89
301
Update of Service experience of HV underground and submarine cable
systems
Statistics on AC underground cables in power networks
Revision of Qualification Procedures for HV and EHV AC Extruded
Underground Cable
Systems
Maintenance of HV Cables and Accessories
Preparation of guidelines for collection and handling of reliability data
Interfaces between HV extruded cables and accessories
Accessories for HV cables with extruded insulation
Accessories for HV extruded cable. Types of accessories and terminology
Title of Session Paper
Session Paper No.
21–01 Studies of Impurities and Voids in Cross-linked Polyethylene Insulated
Cables. Pre-fabricated Terminations.
21–02 Plastic insulated cable with voltage dependent core screen.
Jicable
Jicable 2011 paper A.3.7 “Return of Experience of 380 kV Power Cable Failures”
from Sander MEIJER (TenneT TSO), Johan SMIT, Xiaolin CHEN (Delft University of Technology), Wilfried FISCHER (50 Hertz Transmission GmbH),
Luigi COLLA (Terna S.p.A.)
Jicable 2011 paper A.5.4 “Remedial action and further quality assuring measures
after a failure in a 400 kV GIS cable termination” from Frank JAKOB, Frank
KOWALOWSKI, Claus KUHN, Wilfried FISCHER (50 Hertz Transmission
GmbH), Sigurdur A. HANSEN (Südkabel GmbH)
Jicable 2011 paper A.5.3 “Dry terminations for high voltage cable systems” from
Pascal STREIT (NEXANS)
Jicable 2003 paper A.6.2 “Anti-explosion protection for HV porcelain and composite terminations” from Gahungu, Cardinaels, Streit, Rollier (Nexans)
Jicable 2003 paper A.6.4 “New dry outdoor terminations for HV extruded cables”
from DEJEAN (PIRELLI France), QUAGGIA, PARMIGIANI (PIRELLI Italy),
GOEHLICH (Technical University of Berlin);.
Jicable 1999 paper A.5.4 “Development of synthetic and composite terminations for
HV and EHV extruded cables” (LE PURIANS from EDF R&D and JUNG from
EDF CNIR – RTE
Jicable 1995 paper A.3.2 “Composite EHV terminations for extruded cables”
(ARGAUT, LUTON from SILEC and JOULIE, PARRAUD from SEDIVER.
302
E. Bergin
Appendix 3: Reminder Chapter 5/TB 476
TB 476 Cable Accessory Workmanship on Extruded High Voltage Cables Oct 2011
Table of Contents
1 Summary
4
2 Introduction
4
3 Scope
6
3.1 Inclusions
6
3.2 Exclusions
6
4 Related Literature and Terminology
6
5 General risks and skills
8
6 Technical risks and required specific skills
10
6.1 Conductors
10
6.1.1 Conductor preparation
10
6.1.2 Compression
11
6.1.3 MIG/TIG Welding
12
6.1.4 Thermit Weld
12
6.1.5 Mechanical Connection
13
6.2 Insulation Preparation
15
6.2.1 Straightening
15
6.2.2 Stripping of insulation screen
16
6.2.3 Preparing the end of the insulation screen
18
6.2.4 Smoothening the insulation surface
19
6.2.5 Cleaning of insulation
20
6.2.6 Shrinkage
21
6.2.7 Lubrication
21
6.3 Metallic sheath
22
6.3.1 Welded Aluminium Sheath (WAS)
22
6.3.2 Corrugated Sheaths: Aluminium (CAS); Copper (CCS); Stainless Steel 25
(CSS)
6.3.3 Lead Sheath
28
6.3.4 Laminated sheaths: Aluminium Polyethylene Laminate (APL); Copper 30
Polyethylene Laminate (CPL)
6.4 Oversheath
32
6.4.1 Case of graphite coating
32
6.4.2 Case of extruded and bonded semiconducting layer
32
6.4.3 Low Smoke, Zero Halogen, Enhanced Flame Performance Sheaths
32
6.5 Installation of joint electric field control components
33
6.5.1 Slip on prefabricated joint
34
6.5.2 Expansion joints
37
6.5.3 Field Taped Joints
40
6.5.4 Field Molded Joints (Extruded or taped)
41
6.5.5 Heatshrink sleeve joint
41
6.5.6 Prefabricated composite type joint
42
6.5.7 Plug-in joint
43
6.5.8 Pre-molded three piece joint
44
6.6 Installation of termination electric field control components
45
6.6.1 Slip-on prefabricated field control components
45
6.6.2 Plug-in terminations
45
6.6.3 Taped Terminations
47
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
6.6.4 Heatshrink sleeve insulated terminations
6.6.5 Prefabricated composite dry terminations
6.7 Outer Protection of Joints
6.7.1 Polymeric outer protection by taping and/or heatshrink tubes
6.7.2 Outer Protection Assembly
6.7.3 Filling compounds for joint protections (joint boxes)
6.8 Filling of Terminations
6.9 Handling of Accessories
6.9.1 Supporting of accessory
6.9.2 Lifting of accessories
6.9.3 Special bonding configurations and link box installation
6.9.4 Sensor connections
6.9.5 Fibre optics
7 Skills Assessment
7.1 Aspects to be tested
7.2 Methods of qualification
7.2.1 Theoretical
7.2.2 Training on the job and observation
7.2.3 Testing – Electrical & Mechanical
7.3 Certification
7.4 Duration of certification
7.5 Upskilling
7.6 New Accessory type
8 Set Up
8.1 Organisation of jointing location
8.2 Positioning of Joint
8.3 Environmental Conditions
8.4 Cable End Inspection
8.5 Verification of Each Step
8.6 Measuring of Diameters, Ovality, Concentricity, Position
8.7 Safety and Health
8.8 Environmental Aspects
8.9 Quality Insurance
9 Bibliography
303
48
48
49
49
50
51
52
53
53
54
56
56
57
58
58
58
58
58
59
59
60
60
60
61
61
61
61
61
62
62
62
62
62
63
304
E. Bergin
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
305
Appendix 4: Short Circuit Tests
The possibility of two types of fault has to be considered – a fault external to the
accessory and a fault inside the accessory. Both faults will have very different
impacts on the accessory. The external fault may cause rapid heating of the conductor and result in a build up of pressure, if there is fluid or gas present in the accessory.
The internal fault results in fault current flowing through the insulation of the
accessory with high energy being dissipated in the insulation and filling medium
and this may cause large thermo-mechanical and pressure changes inside the
accessory.
Low Energy External Fault (Through-fault i.e. Breakdown Outside
the Accessory)
In the case of a system fault in another part of the electrical system external to the
accessory, the fault current passes through the conductor of the termination or joint.
Testing for such a case is carried out on terminations, joints (buried and
non-buried) installed as in service. The test installation shall be in accordance the
requirements of the specification and rules of each System Operator. This test should
be performed on terminations and joints connected by the specified cables, which
have either already gone through a type test or have gone through at least ten thermal
cycles.
The aim is to study the effects of a simulated external fault on the accessories,
including a check that pressure relief devices in terminations do not break during an
external short-circuit.
Simulation of the Fault
The accessory shall be installed in a suitable circuit to permit the fault current to flow
through the accessory.
Position of the Fault
The fault shall be external to the accessory being tested
External Fault Withstand Test
The test is performed with AC. In order to prevent fade-out of the electrical arcing,
the test will be performed with a symmetrical start-up on a voltage crest. The current
is injected from the cable to the accessory. The test voltage shall be at least 20 kV.
Examples are given in the Table 1 and each country will have its own set of values
depending on system configurations and fault conditions (Table 6.6).
Due to safety regulations, testing terminations that contain SF6 gas is no longer
allowed, as some gas by-products that may be generated by internal arcing are
harmful. Replacing SF6 with air (or nitrogen) has to be carefully considered, since
there are a lot of differences between arcs in SF6 and air. WG A3.20 is currently
carrying out studies on this question.
306
E. Bergin
Table 6.6 Short Circuit Levels at Different Operating Voltages
France
Voltage
kV U(Um)
Short-Circuit Parameters
Three-phase Short-circuit Intensity and
Single-Phase Short-circuit
duration
Intensity, duration,
63 (72,5)
a) 20 kA – 1 s
8 kA – 1,7 s – 0,2 s
b) 31,5 kA – 0,5 s
90 (100)
a) 20 kA – 1 s
10,3 kA – 1,7 s – 0,2 s
b) 31,5 kA – 0,5 s
225 (245)
31,5 kA – 0,5 s
31,5 kA – 0,5 s – 0,16 s
400 (420)
a) 63 kA – 0,5 s
a) 63 kA – 0,5 s – 0,07 s
b) 40 kA – 0,5 s
b) 40 kA – 0,5 s – 0,06 s
NOTE – Cases a) and b) depend on the grid characteristics and short-circuit power of the grid.
Ireland
Voltage
Short-Circuit Parameters
kV U(Um)
Three-phase Short-circuit Intensity and
Single-Phase Short-circuit
duration
Intensity, duration,
110 (123)
a) 31.5 kA – 1.0 s
a) 31.5 kA – 1.0 s
b) 40.0 kA – 1.0 s
b) 40.0 kA – 1.0 s
220 (245)
40 kA – 1.0 s
40 kA – 1.0 s
400 (420)
50kA – 1.0 s
50kA – 1.0 s
NOTE –
a) outside Dublin
b) in Dublin
Cases
Netherlands
Voltage
Short circuit parameters
kV
Three-phase Short –circuit Intensity and
Single-phase Short-Circuit
U (Um)
duration
Intensity, duration
50 (72.5)
9 kA – 0.5 sec
9 kA – 0.5 sec
15 kA – 1.0 sec
12.5 kA – 1.0 sec
25 kA – 1.0 sec
15 kA – 1.0 sec
110 (123)
30 kA – 0.5 sec
25 kA – 0.5 sec
40 kA – 1.0 sec
25 kA – 1.0 sec
150 (170)
30 kA – 0.5 sec
15 kA – 0.5 sec
40 kA – 1.0 sec
30 kA – 1.0 sec
50 kA – 1.0 sec
40 kA – 1. 0 sec
220 (245)
40 kA – 1.0 sec
27 kA – 1.0 sec
380 (420)
50 kA – 0.5 sec
50 kA – 0.5 sec
50 kA – 1.0 sec
50 kA – 1.0 sec
63 kA – 0.5 sec
63 kA – 1.0 sec
63 kA – 1.0 sec
The short-circuit levels are depending on the protection settings, imposed by the grid owner, and the
position of the cable system in the grid: close to a power plant or more remote
Requirements
On completion of the test, the pressure relief shall be observed to have operated
correctly. The whole test shall be recorded and filmed with a high-speed camera
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
307
(at least 1000 images per second) in order to witness and analyse the behaviour and
reaction of the termination and fixing installation devices.
High Energy Internal Fault (Internal Fault i.e. Breakdown Inside
the Accessory)
The test is carried out on a termination or joint installed as in service. The
installation shall be in accordance with the requirements of the specification and
rules of each System Operator. The aim is to study the external effects generated
by the accessory during the simulation of an internal arc fault. This test is intended
to check that the accessory does not disruptively eject components that might
cause external damage.
Simulation of the Fault
An internal fault is initiated by drilling a hole in the main insulation of the cable
within the termination or joint. A 1.5 mm2 copper wire shall connect the conductor to
the metallic screen/sheath or to a metallic piece itself connected to the screen/sheath.
Position of the Fault
In the case of a termination or joint having a stress cone, the fault is initiated by
drilling a hole at the top of the stress cone to the conductor in order to connect the
1.5mm2 copper wire.
Internal Fault Withstand Test
The test is performed with AC. In order to prevent from the fade-out of the electrical
arcing, the test will be performed with a symmetrical start-up on a voltage crest. The
rms. value and duration of the phase-to-earth short-circuit are given in the table
above. The current is injected from the cable to the termination or joint. The test
voltage shall at least 20 kV. Due to safety regulations, testing accessories which
contain SF6 is not allowed any more, as some by-products that may be generated in
case of arcing are considered harmful. Replacing SF6 by air (or nitrogen) has to be
considered carefully, since there are a lot of differences between arcs in SF6 and air.
Requirements
On completion of the test, no solid debris shall be observed at a distance of more than
3 metres from the termination or joint. The whole test shall be recorded and filmed
with a high-speed camera (at least 1000 images per second) in order to witness and
analyse the behaviour and reaction of the termination or joint and fixing installation
devices.
308
E. Bergin
Appendix 5: Condition Monitoring Techniques for Terminations
and Non-buried Joints
Condition monitoring techniques for terminations and associated auxiliary components are summarized in the tables in this Appendix under the following
headings:
Condition
Details the specific diagnostic tool for monitoring the
monitoring tool
termination/auxiliary components
Component
Identifies the component to which the monitoring tool can be
used on
Event/Cause
Application of the ‘condition monitoring tool’ reduce the
detected
probability of the here mentioned event that cause the cable
system failure, damage or degradation
On/off-line
Condition monitoring techniques are categorized as capable
of being done either on-line (cable system in service) or
off-line (cable system must be switched out)
Experience
The level of working experience of each condition
monitoring tool is categorized as either well established (‘W’)
or under development (‘D’).
Effectiveness
One diagnostic monitoring tool is considered as more
effective in finding damages or degradations that will lead
eventually to system failure than other tools, considering
costs and time versus result, categorized here as useful (‘U’)
and less useful (‘L’).
Frequency
Suggested interval of application of the monitoring tool
versus the cable life time cycle.
Please note that most monitoring tools will be selected based
on the service experience of the termination type and hence
the frequency.
Primary/secondary Primary tests are considered as the minimal test one shall
test
perform on a cable system after it has been put into service.
Secondary tests will be selected to monitor or discriminate
terminations with (suspected) specific defects, based on
(service) experience.
Cost
Indication of cost per test. Range: minor costs < +, ++, ++
+ > considerable costs. These costs are for the test only cost
and do not include cost of preparatory work, outages and
other associated expenses.
Expertise
Indication of required skills to perform the test. Range: less
skilled personal < +, ++, +++ > skilled personal
Reference
Reference source of the monitoring technique
Dielectric loss Terminations,
angle testa
non buried
joints
PD testing
Terminations,
(various
non buried
methods, such joints
as: acoustic,
UHF, Radio
interference,
voltage test)
2
3
Terminations,
non buried
joints, cable
Serving test
(DC test)
Component
1
Condition
Monitoring
No. Tool
Detecting
assembly
errors, low
contact
pressure at
interface,
shrink back of
cable
insulation,
contamination
of internal
insulation fluid
and/or gas due
to aging or
Ingress of
water in
insulation area
Pollution on
support
insulators or
screen
separations
D
W
Off- W
line/
On- D
line
Offline
Offline
U
L
U
Depending
on service
experience
Depending
on service
experience
Annual
On/
Event or Cause OffDetected
Line Experience Effectiveness Frequency
Short Circuit Levels at Different Operating Voltages
P
S
P
Primary/
Secondary
Test
++
(on-line)
+++
(off-line)
+++
+
Cost
+++
+++
+
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
(continued)
CIGRÉ TB
279, Table 6.4,
item 5
CIGRÉ TB
279, Table 6.4,
item 3
CIGRÉ TB
279, Table 6.4,
item 2
Expertise Reference.
6
309
Visual
Terminations,
inspection
non buried
with visible or joints
UV light
6
Terminations,
non buried
joints
X-ray
5
Terminations,
fluid filled
non buried
joints
Chemical and
Physical
analysis of
insulating
fluid, such as:
DGA, Tan
delta, Water
content,
Particles etc.
Component
4
Condition
Monitoring
No. Tool
Offline
Surface
pollution,
mechanical
damage,
uncontrolled
Online
Movement of
Offcable due to
line
thermal cycling
or poor
clamping
Contamination
of internal
insulating
fluid.
leaking,
insulator
tracking,
W
W
W
U
L
U
Annual
Depending
on service
experience
Annual
On/
Event or Cause OffDetected
Line Experience Effectiveness Frequency
Short Circuit Levels at Different Operating Voltages (continued)
P
S
P
Primary/
Secondary
Test
+
++
++
++
CIGRÉ TB
279, Table 6.4,
item 8
CIGRÉ TB
279, Table 6.4,
item 7
CIGRÉ TB
279, Table 6.4,
item 6
Expertise Reference.
+
+++
(N.B. does
not include
the costs of
taking the
sample)
Cost
310
E. Bergin
Visual
inspection
with IR on
current
carrying
components
Leakage
current
measurement
7
8
Terminations
Terminations,
non buried
joints
Insulator
surface
pollution,
surface
tracking or
damage
As with Item
6 above plus
detecting
possible
hotspots on
top-connector
and earthing
circuit
movement of
cable, cable
clamping,
tracking marks
on outdoor
insulators,
ferrule
retraction,
leakages,
corrosion,
animal attack,
vandalism.
Online
Online
w
w
L
U
Depending
on service
experience
5 yearly
s
s
+++
+
++
++
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
(continued)
CIGRÉ TB
279, Table ▶ 5.4,
item 25
CIGRÉ TB
279, Table 6.4,
item 8
6
311
Surface
wetting
characteristics
(STRI
method)b
Continuous
measurement
of fluid or gas
pressures
and/or low
pressure
alarms
10
11
Auxiliary
Terminations
Test at
Terminations,
elevated
non buried
voltage: AC,
joints
VLF, DC with
or without
DLA (Item 2)
and/or PD
(Item 3).
Component
9
Condition
Monitoring
No. Tool
Indication of
falling fluid /
gas pressure
Extrinsic
surface
pollution on
outdoor
polymeric
insulators
Main
insulation /
stress cone/
interface
defects
Online
Offline
Offline
W
W
w
U
L
U
p
Primary/
Secondary
Test
Continuous S
Depending S
on location
Depending
on service
experience
On/
Event or Cause OffDetected
Line Experience Effectiveness Frequency
Short Circuit Levels at Different Operating Voltages (continued)
+
+
+++
Cost
+
++
+++
CIGRÉ TB
279, Table ▶ 5.4,
item 23
CIGRÉ TB
279, Table ▶ 5.4,
item 26
IEEÉ St
48, clause 8.6
(DC), IEC 60840,
IEC62067
Expertise Reference.
312
E. Bergin
Visual
inspection
Voltage test on Earthing and Failure of SVL OffSVL
cross bonding to operate at
line
boxes.
rated voltage
15
16
Testing alarm
settings and
signals for
fluid/gas
pressure
monitoring
Earthing and Water ingress
cross bonding in link box,
boxes.
Condition of
any insulating
compounds,
Link
arrangement
Auxiliary
Testing of
fluid/gas
monitoring
equipment
Offline
Offline
Online
14
Leakage of
internal
insulating
fluid/gas from
termination
SF6 sniffers or Auxiliary
cameras
Online
13
Leakage of
internal
insulating
fluid/gas from
termination
Regular gauge Auxiliary
maintenance
and
calibration.
12
W
W
W
W
W
L
L
L
L
L
Depending
on service
experience
(usually
Annual
Annual
Annual
Annual
S
p
p
s
s
+
+
+
++
+
+
+
++
+
+
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
(continued)
CIGRÉ TB
279, Table 6.4,
item 10
CIGRÉ TB
279, Table ▶ 5.4,
item 32
CIGRÉ TB
279, Table ▶ 5.4,
item 31
CIGRÉ TB
279, Table ▶ 5.4,
item 23
CIGRÉ TB
279, Table ▶ 5.4,
item 23
6
313
Excessive
temperature
rise
Off
or
on
line
Integrity of
Offearthing circuit line
W
W
U
L
L
P
Continuous s
As per 16
Continuous S
Primary/
Secondary
Test
++
+
+++
Cost
Distinction between cable and termination might be a problem
STRI hydrophobicity classification guide provides a coarse value of the wetting status, reference is made here to IEC TS 62073
Cable and
joint
Optical fibre
19
b
a
Auxiliary
Measurement
of earthing
system
electrical
resistance
18
D
done on
same
outage as
serving
test)
On/
Event or Cause OffDetected
Line Experience Effectiveness Frequency
Earthing and Failure of SVL Oncross bonding to operate at
line
boxes.
rated voltage
Continuous
SVL
monitoring
Component
17
Condition
Monitoring
No. Tool
Short Circuit Levels at Different Operating Voltages (continued)
+++
+
+++
TB 247
Expertise Reference.
314
E. Bergin
6
Guidelines for Maintaining the Integrity of Extruded Cable Accessories
315
Eugene Bergin received a Bachelor of Engineering degree from
the University College Dublin. He had over 30 years experience in
the area of HV cables and has worked in many countries – China,
Japan, Korea, Bahrain, Dubai, Saudi Arabia, Turkey, France,
Germany, Sweden, etc. He has been a Member of Cigré for over
35 years and served as a Member, Secretary, and Convener of
many Working Groups. He received the Cigré Technical Committee Award in 2000 and the Cigré Distinguished Member Award in
2004. In his most recent commitments, he was Convener of both
the Customer Advisory Group and the Trenchless Technology
Working Group B1.48. Eugene was in the final stage of publication of the report of this Working Group on Trenchless Technologies (TB 770) when he passed away peacefully in October 2018.
He is missed by all his colleagues as a great professional and a
warm-hearted friend.
7
Feasibility of a Common, Dry Type Plug-in
Interface for GIS and Power Cables above
52 kV
Pierre Mirebeau
Contents
7.1 Introduction and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.2.1 General Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.2.2 Definitions and Terms (According to IEC 62271-209) . . . . . . . . . . . . . . . . . . . . . . . . . .
7.2.3 Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3 Experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.1 GIS Cable Terminations Installation Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.2 Experience of Dry Type Insulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.4 Design of Dry Type GIS Terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.4.1 Differences in Design of Barrier Insulator, Inner Cone Type . . . . . . . . . . . . . . . . . . . .
7.4.2 Differences in Design of Barrier Insulator, Outer Cone Type . . . . . . . . . . . . . . . . . . .
7.4.3 Requirements for Standardization of a Common Interface . . . . . . . . . . . . . . . . . . . . . .
7.5 Where the Plug-in Concept Could Be Applicable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.5.1 Geometrical Installation Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.5.2 Safety Practices and Constraints during Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.5.3 Testing Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.5.4 Conclusion Regarding Testing Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.6 Qualification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.6.1 State of the Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.6.2 Where the Plug-in Common Interface Could be Applicable . . . . . . . . . . . . . . . . . . . .
7.6.3 Qualification of new Insulator or Stress Cone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.7 Feasibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.7.1 Definition Feasibility (Cost Involved) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.7.2 Qualification Feasibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.8 Market Acceptance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.8.1 Current Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
319
320
321
321
321
325
325
325
331
334
335
335
336
339
339
350
351
353
354
354
362
362
362
362
363
364
364
Pierre Mirebeau has retired.
P. Mirebeau (*)
Villebon sur Yvette, France
e-mail: Pierre.mirebeau@sfr.fr
© Springer Nature Switzerland AG 2021
P. Argaut (ed.), Accessories for HV and EHV Extruded Cables, CIGRE Green Books,
https://doi.org/10.1007/978-3-030-39466-0_7
317
318
P. Mirebeau
7.8.2 Future Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.8.3 Where the Plug-in Common Interface Could be Recommended . . . . . . . . . . . . . . . .
7.9 Conclusion and Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
364
366
366
367
Abstract
Since 1986 the connection between GIS substations and cables has been managed
by a dimensional standard establishing electrical and mechanical interchangeability between cable terminations and gas insulated metal enclosed switchgear.
Within this framework termination suppliers design their own components:
insulator, stress cone (for the two available options inner cone and outer cone) and
the connection inside the termination.
The responsibility limit between the switchgear manufacturer and the cable
termination manufacturer is at the interface SF6/insulator.
Considering the large number of substations and planning difficulties due to
the fact that the cable system is not usually defined at the time of switchgear
manufacture, a joint working group has been set up by Cigré within committees
B1 and B3. The group has to investigate the possibility of a standardised common
interface insulator for the dry type and plug-in cable termination, which could be
supplied independently from the remaining termination components.
Starting from review of GIS cable termination designs and actual installation
practices for all voltage levels, the joint working group has studied:
• Operational experience in common interface design, for medium voltage and
for a specific utility
• Constraints in terms of civil works, space, weight of cables and terminations
• Compliance with standards
• Implications of the common interface insulator for the market
• Qualification requirements
• Applicable range (voltage and size)
• Estimated cost for testing and qualitative advantages of the common interface
(financial benefit versus development and qualification costs was not
evaluated)
• New limits of responsibility (insulator/stress cone and insulator/SF6)
• Market trend.
Taking into account all the above, as per the TOR of the group, WG B1-B3.33
advises Study Committees B1 and B3 to set up a new working group with the
following Terms of Reference.
The Working group should recommend a functional design of an insulator
with a common interface with the following scope of work:
• Voltage is 145 kV AC
• Current is 1000A, short circuit 40 kA 1 sec
• Cross sections are 1000 mm2 Cu or 1600 mm2 Al
7
Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
319
• Technology has to be defined (inner or outer cone), with a detailed evaluation
of technical advantages/disadvantages of the two technologies.
• The number of sizes has to be defined; the short circuit current can be altered
for the smallest sizes.
• Dimensions of insulator components have to be defined (current connection,
electrical design and properties, mechanical design and properties).
• The type and dimension of the main current connection has to be defined
• Consider the consequence of a termination failure.
• Consider upgrading of the cable link for higher current loads.
• Consider installation constraints, with a special focus on the basement
dimensions.
• The design has to meet the requirements of IEC 62271-209 and IEC 60840
• The initial and cross qualification processes.
The stress cone design and material, the lubricant and the design of the compression
device should be left to the discretion of the accessory manufacturer within the limits
of the standardised cable terminations properties.
Cigré TB 303 and the work of WG B1.44 and WG B1.46 should be taken into
account.
7.1
Introduction and Scope
The interface between High Voltage cable and switchgear is defined by IEC
62271-209.
In particular IEC 62271-209 defines two types of dry-type cable connections for
gas insulated switchgear above 52 kV. The limit of supply of the cable termination
manufacturer is the insulator. Type A connection incorporates elastomeric electrical
stress control component inside the insulating barrier. For type B, the elastomeric
electrical stress control component is located externally. IEC 62271-209 covers
specifically the connection assembly with a separating insulating barrier between
the cable insulation and the gas of the switchgear, which is the case of dry terminations. It does not address specifically the plug in issues.
Regarding Medium Voltage, EN 50181 Standard was published in 1997
describing “Plug-in type bushings above 1 kV up to 36 kV for equipment other
than liquid filled transformers” This document gave full details of bushings
which were fitted to power equipment (such as switchgear) to make a cable
connection to the equipment. The insulator could be customized to suit the design
of the equipment on that side, but was required to have standardized dimensions
on the cable side, such that a “separable connector” (plug in cable/stress cone
assembly as per the definitions of chapter 2.1) could be plugged in on the cable
side. The separable connector could then be supplied by one of several possible
suppliers.
The current version of EN 50181 was published in 2010. In this version the upper
limit of the applicable voltage range was raised to 52 kV.
320
P. Mirebeau
With the above background interest has been raised to extend the principle of a
common insulator interface to higher voltages with the potential benefits that cable
connections from different manufacturers would be interchangeable in a single insulator.
Investigation of this proposal was undertaken within Cigré, by forming a joint
working group (JWG) between Study Committees B1 (cables) and B3 (switchgear).
The working group JWG B1-B3.33 was formed and has produced the current
document.
7.1.1
Scope
The scope of the work of JWG B1-B3.33 is to consider the feasibility of a common
dry-type interface for GIS connections for AC extruded cable systems for voltages
above 52 kV, considering the following aspects:
• Examine the conditions around the switchgear and installation issues, including
the supporting system (also called site issues)
• Consider the impact of large cross sections
• Consider safety prectices during works
• Consider the testing procedures for GIS/Terminations and cables at the factory
and on site (overlapping or missing items).
• Propose measures to reduce the potential consequences of the GIS insulation
failure.
• Propose measures to reduce the potential consequences of the cable termination
insulation failure1
• Review the existing standards addressing the qualifications and extension of
qualification procedures applicable to GIS terminations.
• Define the relevant qualification procedures needed if any.
• Identify the limit of suppliers’ responsibility.
• Estimate the overall technical and practical feasibility of the common design
definition and qualification, insulator manufacturers' qualification and the cable
manufacturers' qualification and the cost involved.
• Once the feasibility window has been determined, survey the market (manufacturers and end users)
• Recommend or not to go to a second step with the launching of a new WG B1-B3.
XX to go in detail into the design of the standard components (shape, dimensions,
properties, . . .).
A WG “B1.29 Guidelines for maintaining the integrity of XLPE cable accessories” was decided in
2009. The group considered that this question is in B1-29 scope and is not to be addressed here.
Report from B1.29 is TB 560 published in December 2013 and published as ▶ Chap. 6, “Guidelines
for Maintaining the Integrity of Extruded Cable Accessories” of this Book.
1
7
Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
7.2
Definitions
7.2.1
General Layout
321
The general layout of the dry type GIS cable terminations as described in IEC 62271209 is shown Figs. 7.1 and 7.2.
7.2.2
Definitions and Terms (According to IEC 62271-209)
The definitions and terms of the different components of the dry type GIS cable
terminations as described in IEC 62271-209 are shown Figs. 7.2, 7.3, and 7.4.
7.2.2.1 Cable-Termination (IEC 62271-209)
Equipment fitted to the end of a cable to ensure electrical connection with other parts
of the system and to maintain the insulation up to the point of connection. Two types
are described in this standard.
7.2.2.1.1 Fluid-Filled Cable-Termination (IEC 62271-209)
Cable-termination which comprises a separating insulating barrier between the cable
insulation and the gas insulation of switchgear. The cable-termination includes an
insulating fluid as part of the cable connection assembly.
Fig. 7.1 General layout of dry GIS termination (in ref to IEC 62271-209)
322
P. Mirebeau
Fig. 7.2 Dry-type cable connection assembly – Typical arrangement (IEC 62271-209)
GIS main circuit end terminal
Connection interface
Plug-in connector of insulator
Insulator assembly
Insulator
Cable connection enclosure
Flange (if needed)
Plug-in connector of cable
Cable/stress cone
assembly
Stress cone
Cable gland
Cable
Fig. 7.3 Identification of the different parts of GIS termination, inner cone type design
7
Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
323
Connection interface
Insulator assembly
Cable connection enclosure
Insulator
Plug-in connector of insulator
Stress cone
Plug-in connector of cable
Cable/stress cone
assembly
Cable gland
Cable
Fig. 7.4 Identification of the different parts of GIS termination, outer cone type design
7.2.2.1.2 Dry-Type Cable-Termination (IEC 62271-209)
Cable-termination which comprises an elastomeric electrical stress control component in intimate contact with a separating insulating barrier (insulator) between the
cable insulation and the gas insulation of the switchgear. The cable-termination does
not require any insulating fluid.
7.2.2.2 Plug-in Cable Termination
Cable termination where cable/stress cone assembly can be engaged into the insulator assembly that is already installed into sealed GIS enclosure.
7.2.2.2.1 Locked Plug-in Type Cable Termination
Plug-in cable termination where conductor of the cable is interlocked with the
insulator assembly and cannot be removed without disassembling insulator assembly
from the GIS enclosure.
324
P. Mirebeau
7.2.2.2.2 Plug-in, Plug-out Type Cable Termination
Plug-in cable termination where the plug-in assembly may be removed from the
barrier insulator assembly without disassembling the insulator assembly from the
GIS enclosure.
7.2.2.2.3 Locking Plug-in, Plug-out Type Cable Termination
Plug-in cable termination where conductor of the cable is interlocked with the
insulator assembly and can be removed without disassembling the insulator assembly from the GIS enclosure.
7.2.2.3 Insulator Assembly
Assembly of insulator, plug-in connector of insulator and flange if needed.
7.2.2.4 Insulator
Separates insulating fluid (SF6) of GIS enclosure from the cable/stress cone
assembly.
7.2.2.5 Plug-in Connector of Insulator
Provides connection to GIS main circuit end terminal and to plug-in connector of
cable.
7.2.2.6 Plug-in Connector of Cable
Provides connection between cable conductor and plug-in connector of insulator.
7.2.2.7 Main-Circuit End Terminal (IEC 62271-209 and Compliant
with IEEE 1300)
Part of the main circuit of a gas-insulated metal enclosed switchgear forming part of
the connection interface.
7.2.2.8 Cable Connection Enclosure (IEC 62271-209 and Compliant
with IEEE 1300)
Part of the gas-insulated metal-enclosed switchgear which houses the cabletermination and the main-circuit end terminal.
7.2.2.9 Cable Connection Assembly (IEC 62271-209 and Compliant
with IEEE 1300)
Combination of a cable-termination, a cable connection enclosure and a main-circuit
end terminal, which mechanically and electrically connects the cable to the
gas-insulated metal enclosed switchgear.
7.2.2.10 Cable System (IEC 62271-209)
Cable with installed accessories.
Cable System (IEC 62271-209)
Cable with installed accessories.
7
Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
7.2.3
325
Units
7.2.3.1 Pressure
All pressure values in this document are given in bar as relative pressure.
7.2.3.2 Rated Voltages (IEC 60840 and 62271)
The symbols U0, U and Um are used to designate the rated voltages of cables and
accessories where these symbols have the meanings given in IEC 60183:
U0 ¼ the rated r.m.s. power-frequency voltage between each conductor and screen or
sheath for which cables and accessories are designed
U ¼ the rated r.m.s. power-frequency voltage between any two conductors for which
cables and accessories are designed
Um ¼ the maximum r.m.s. power-frequency voltage between any two conductors for
which cables and accessories are designed. It is the highest voltage that can be
sustained under normal operating conditions at any time and at any point in a
system. It excludes temporary voltage variations due to fault conditions and the
sudden disconnection of large loads.
Unless specified differently all voltages mentioned in this brochure are considering
Um values.
7.3
Experience
7.3.1
GIS Cable Terminations Installation Examples
The following pictures show some examples of installation. They include all kinds
of GIS terminations.
7.3.1.1 Um 362 ~ 550 kV
7.3.1.1.1 Vertical Installations
Vertical installation with cables entering from below is the most widely used. The
presence of a basement is of importance (Figs. 7.5 and 7.6).
• In case of no basement, the support structure must be high enough to comply with
the bending radius.
• When there is a proper sized basement, there is more freedom regarding the cable
termination implementation.
7.3.1.1.2 Horizontal Installations
Horizontal installation is selected when there is no basement and limited height.
Horizontal snaking is performed to lower the conductor thrust on the insulator
(Figs. 7.7 and 7.8).
326
P. Mirebeau
Fig. 7.5 GIS vertical arrangement examples
7.3.1.1.3 Inclined Installations
Inclined installation can be chosen as a trade-off between height and bending radius,
when there is no basement (Fig. 7.9).
7
Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
Fig. 7.6 Installation works,
placing GIS enclosure over
the 1600 mm2 Cu 345 kV
cable termination
Fig. 7.7 GIS horizontal arrangement examples
327
P. Mirebeau
Fig. 7.8 GIS horizontal
arrangement study example
(before clamping
implementation design)
5000
328
44590
33090
EL. 1523.50
installation under 30° angle, 400kV XLPE cable, 250
4750
4750
30°
EL. 1522.10
FEEDER 1
REACTOR 1
FEEDER 2
REACTOR 2
Fig. 7.9 GIS inclined arrangement examples
7.3.1.2 Um 245 ~ 300 kV
Vertical installation with cables entering from below is the most widely used. The
presence of a basement is of importance.
7.3.1.2.1 Vertical Installation
Vertical installation is the most widespread; generally cables are installed from
below (Fig. 7.10).
7
Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
329
Fig. 7.10 Libya 245 kV
vertical outdoor installation
800 mm2, no basement (not
plug-in)
Sometimes cables are installed from above (Fig. 7.11).
7.3.1.3 Um 123 ~ 170 kV
7.3.1.3.1 Vertical Installation
Almost all 123–170 kV installations are in vertical arrangement (Figs. 7.12 and 7.13).
Note the restricted space to fit the termination, and once installed, no room to
position the Surge Voltage Limiters.
7.3.1.3.2 Horizontal Installation
Figures 7.14 and 7.15.
7.3.1.4 Um 72.5 ~ 100 kV
7.3.1.4.1 Vertical Installation
Note on the left picture the restricted room for installation works that is performed
through the basement concrete floor (Fig. 7.16).
330
Fig. 7.11 245 kV vertical indoor installation, 1400 mm2 (not plug-in)
Fig. 7.12 145 kV vertical outdoor installation 800 mm2
P. Mirebeau
7
Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
331
Fig. 7.13 Plug in type 123 ~ 170 kV vertical indoor installations
Fig. 7.14 145 kV horizontal installation 500 mm2 plug-in (compact GIS)
7.3.2
Experience of Dry Type Insulator
7.3.2.1 History of Dry Plug-in Termination
Dry type insulators were introduced first in Germany at 170 kV level according to
Fig. 7.17.
332
P. Mirebeau
Fig. 7.15 Installation works Plug-in of cable into dry type GIS termination (outer cone model)
Fig. 7.16 72.5 kV vertical installations
7.3.2.2 German Experience of Plug-in Plug-out Interchangeable GIS
Termination
A large German utility has experienced a common interface with two epoxy suppliers and two cable makers for 110 kV cables.
Projects were based on standard cables:
• 630 mm2 and 800 mm2 in one city (dimensions fixed as per KG4023
specification),
• 640 mm2 to 1000 mm2 in another city.
7
Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
333
Cross section/mm2
2500
2010
2008
2000
2004
2002
2000
1000
800
1996
1998
145
170
300
550
Fig. 7.17 Year of introduction of dry type GIS termination as a function of voltage and cable cross
section in Germany
The electric stress was (and still remains) conservative: 17 mm insulation wall
thickness gives stresses lower than currently used similar cables.
Development History
The goal was to ease the planning of the interface components between the GIS and
cable suppliers though the specification of a standard connection.
First Step 1997, Planning Design
Cable manufacturer (A) was giving the insulator to the GIS manufacturer.
Then the cable/stress cone assembly was plugged in on site
As there were only standard cable types (including standard dimensions) the
utility went further to the full standardized termination (insulator and stress cone).
Second Step 1998, Product Qualification
One single cable manufacturer (A) had a termination ready.
Third Step 1999, Market Opening
The utility qualified a second cable termination manufacturer (B) for the same
insulator dimensions.
Then a long term test was performed with:
• 4 GIS manufacturers
• 2 cable termination manufacturers (A and B)
334
P. Mirebeau
• 2 insulator manufacturers (A and C)
• There were cross qualifications among suppliers (but not all combinations).
Currently, to qualify a new supplier the utility gives a list of components to be
used including insulators, and the cable supplier has to perform a type test.
There are 90 terminations in in the area of the utility.
On the network, termination plug-out occurred only a few times (for fault location
purposes).
There has not been any termination breakdown up to now, and the utility did not
face a responsibility issue in case of breakdown.
The cable and termination dimensions and design have not changed up to now
(no electric stress increase).
7.3.2.3 USA Experience
In USA a large utility from the east coast has a very positive experience with plugin type 115 kV vertically installed terminations. These XLPE to GIS, 3500 kcmil,
36 single phase termination units installed in 2008 have provided the company
with a trouble and maintenance free service. The terminations are part of two
115 kV interconnection circuits that separately connect a 115 kV air insulated
substation and a generating facility to a major 345 kV GIS substation. Two transformers have been installed in between these UG lines to step up the voltages from
115 kV to 345 kV.
All of these terminations have been installed outdoors, with provision of suitable
additional ground clearances on their bases. This extra space at the bottom provided
the utility with flexibility of fitting the cable terminations inside their GIS cable
enclosure. The installation was much easier and quicker in comparison with fixed
type conventional GIS terminations.
The insulator and cable/stress cone assembly came from a single manufacturer.
The termination is of locked plug-in type.
The USA has no experience of common interface design or use.
7.4
Design of Dry Type GIS Terminations
Cable and GIS manufacturers had met together in the early 80’s to write a technical
specification which establishes electrical and mechanical interchangeability between
cable-terminations and the gas-insulated metal-enclosed switchgear and determines
the limits of supply. This resulted in 1986 in the first edition of the Technical
Specification IEC 859. Now updated and transformed in international standard
IEC 62271-209.
In the frame of this technical specification, each manufacturer developed, with its
own technology and solution, products that comply with the interchangeability
requirements, for the specified inner and outer cone types.
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7.4.1
335
Differences in Design of Barrier Insulator, Inner Cone Type
All barrier insulators comply with the dimensions and requirements of IEC 62271209, however there are differences in the connection part, the plug in connector, the
high voltage screen, the insulator material, geometry, finish and the shield break
design which are represented in Fig. 7.18.
7.4.2
Differences in Design of Barrier Insulator, Outer Cone Type
Similar to the inner cone design, all barriers insulators comply with the dimensions
and requirements of IEC 62271-209, however there are differences in the connection
part, the plug in connector, the high voltage screen, the insulator material, geometry,
finish and the shield break design which are represented in Fig. 7.19.
Fig. 7.18 Design of barrier insulator – inner cone type
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Fig. 7.19 Design of barrier insulator – outer cone type
7.4.3
Requirements for Standardization of a Common Interface
This paragraph deals with the requirements that are to be set in addition to current
standards; they are not intended to replace them.
A common interface implies a common inner surface of the insulator.
If a full interchangeability has to be provided, the connector shielding has to be
common as well because the radius at the bottom of the electrode and the distance to
the interface affects the field distribution at the rubber body interface. As a consequence the minimum epoxy thickness is defined.
To comply with IEC 62271-209, each voltage class requires a specific insulator
(voltage classes are 72.5 to 100 kV, 123 to 170 kV, 245 to 300 kV, and 362 to
550 kV).
For a given voltage class, depending on the cable termination design several
insulator sizes might be needed to cover all cross sections.
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Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
337
7.4.3.1 Insulator
For the standardisation of each insulator, the following requirements should be
defined.
7.4.3.1.1 Dimensions and Tolerances
• Compliance with 62271-209 Fig. 5
• Inner cone or outer cone model
• Plug-in connector of insulator
• Lock -in system (if any)
• High Voltage screen (connector shielding)
• Insulator and shape of cone, smoothness
• Insulation shield break ring (if integrated in the insulator).
• Ground screen electrode (if any)
• Fixing of cable/stress cone assembly.
7.4.3.1.2 Dielectric Parameters
• Dielectric properties of insulator (permittivity, tan δ)
• Dielectric performance requirement (electrical withstand level, PD level)
• Insulation shield break ring (if integrated in the insulator).
The voltage requirements of the insulation shield break are the same as the ones of
the sheath sectionalising insulation of joints in IEC 60840 and IEC 62067 appendix
G. Paragraph G4.3. G.4.3.1 gives the DC voltage level and G.4.3.2 gives the
lightning impulse voltage level in table G.1 column “each part to earth/bonding
leads 3 m”.
• Other standards and specifications may specify higher requirements.
• Resistance to SF6 by-products, if applicable.
7.4.3.1.3 Mechanical Parameters
• Fixing for the pressure device (springs) and cable gland attachment (geometry
and strength) ! tensile tests to agree on
• Resistance to internal pressure.
• Resistance to internal fault (refer to brochure WG B1-29)
• Design maximum SF6 outside pressure
• The design maximum SF6 outside pressure is defined by IEC 62271-209 paragraph 6.1: 8.5 bar abs. and the type test level is according to paragraph 6.104 of
IEC 62271-203 (pressure test on partitions)
• Resistance to cantilever force according to paragraph 6.2 of IEC 62271-209
• Mechanical properties of epoxy : hardness, elongation, tensile strength, modulus,
maximum permissible temperature, type of test and test level to be agreed
• Smoothness of the epoxy/stress cone interface (test to be defined)
• Test at limit temperatures according to paragraph 6.106.2 of IEC 62271-203
(insulator thermal performance)
• Quality of connection interface according to paragraph 5.4 of IEC 62271-209,
• Quality of connector interface, to be defined.
• Tightness test according to paragraph 6.106.3 of IEC 62271-203.
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7.4.3.1.4 Routine Test
• Voltage test and PD measurement test according to paragraph 7.1.101 & 7.1.102 of
IEC 62271-203 the pressure being the minimum functional pressure for insulation
as per IEC 62271_209 Fig. 1, with the deviation range of paragraph 8.2.1.
• Tightness test according to paragraph 7.4 of IEC 62271-203
• Design and visual checks according to Fig. 5 of IEC 62271-209
• Pressure test according to paragraph 7.104 of IEC 62271-203.
7.4.3.1.5 Type Test and Prequalification Test
• Type Test of insulator according to GIS standard (see above) and type test of the
entire termination according to accessory standard (IEC 60840 and 62067).
• Type test of connector interface, test to be defined.
• Pre-Qualification test of entire termination, for voltages covered by IEC 62067.
7.4.3.2 Stress Cone
The cable accessory manufacturer will have to comply with the dimensions and
tolerances which will be defined by the insulator standard paragraph Dimension and
Tolerances.
7.4.3.2.1 Design Considerations
• The lubricant should be compatible with the epoxy (this is presently the responsibility of the cable manufacturer) ! compatibility test to be defined
• The arrangement has to apply a pressure that is lower than the maximum internal
pressure of the insulator.
• The electrical stress induced in the insulator must be within the acceptable range
of insulator (electric field calculation to be provided).
7.4.3.2.2 Routine Test
• Routine test values of the stress cone. (e.g. Voltage test and PD measurement test)
according to IEC 60840 and IEC 62067.
7.4.3.2.3 Type Test and Prequalification Test
• Type Test of the entire termination according to accessory standard (IEC 60840
and 62067).
• Pre-Qualification test of entire termination, for voltages covered by IEC 62067 or
for voltages covered by IEC 60840 in the case where the stress at the cable
insulation screen is higher than 4 kV/mm.
7.4.3.3 Plug in Connector and Other Parts of the Termination
7.4.3.3.1 Type Test
• Plug in connector must be Type tested of according to the recommendations of the
works of Cigré WG B1-46 “Conductor Connectors: Mechanical and Electrical
Test”.
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339
Connection and other parts of the termination should be in the supply scope of the
stress cone manufacturer, because they depend strongly on the cable conductor and
screen design.
7.5
Where the Plug-in Concept Could Be Applicable
7.5.1
Geometrical Installation Constraints
7.5.1.1 GIS Termination Installation Procedures
We distinguish 2 cases of metal enclosure installation,
1. Metal enclosure installed after cable termination installation
2. Metal enclosure already on place before termination installation and two types of
cable termination installation
(a) Stress cone plugged in the preinstalled insulator in the cable termination
enclosure
(b) Insulator fitted on the stress cone, then assembly installed in the GIS metal
enclosure.
These 4 cases are sketched (Fig. 7.20)
Advantages and Constraints of the Different Types of Installation
Solution 1a
• GIS metal enclosure can be factory tested
• Requires a temporary protection around the cable/stress cone assembly (mechanical protection, moisture protection, etc., always required unless metal enclosure
is installed immediately after termination assembly)
• Requires free space above metal enclosure (could require a higher ceiling)
• For safety reasons, reduced pressure inside GIS adjacent gas compartment during
cable termination installation work.
• Needs both installers for final assembly (both of them have major work to do)
• Cable termination enclosure must be disassembled on site.
• Gas operation must be performed prior and after assembly.
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Fig. 7.20 Types of installation procedure
Solution 1b
• GIS metal enclosure cannot be factory or site tested with the insulator
• Could require a temporary protection around the cable termination (mechanical
protection, moisture protection, . . ., depending of environmental conditions,
stand-by duration and risk of impact during handling)
• Requires free space above metal enclosure (could require a higher ceiling)
• For safety reasons, reduced pressure inside GIS adjacent gas compartment during
cable termination installation work.
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Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
341
• Needs both installers for final assembly (cable termination installer has minor
work, which would be to remove eventual protection, adjust cable termination
height, install SVLs)
• Gas operation must be performed after assembly.
Solution 2a
• GIS connection parts could be installed prior cable termination.
• GIS metal enclosure can be factory tested (high voltage + gas tightness test)
including insulator assembly.
• Could require more space under metal enclosure (cable bending for termination
installation)
• For safety reasons, reduced pressure inside metal enclosure during termination
plug-in.
• Does not need both installers at the same time (but GIS installer or customer
would have to come after termination installation to fill the metal enclosure at
rated pressure).
Solution 2b
• GIS metal enclosure cannot be factory or site tested with the insulator
• Could require more space under metal enclosure (cable bending for termination
installation)
• For safety reasons, reduced pressure inside GIS adjacent gas compartment during
cable termination installation work.
• Needs both installers for final assembly
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• Gas work must be performed after assembly.
All these solutions are presented as vertical installation, but they are also applicable for horizontal installation. In such case only civil work types will be different,
but space constraints will remain the same.
Solution 2a is the subject of this brochure.
However:
Solution 1a, is not fully satisfactory for the GIS manufacturer as the GIS has to be
opened during installation
Solutions 1b and 2b are not in the scope of the present brochure as they don’t
consider a common interface.
Solutions 1.a and 1.b give much less civil work constraints as the cable termination
can be realised in final position and in such case no room is necessary to move the
cable. As a disadvantage if no free space is available there is no possibility to have
some cable overlength for eventual repair or rerouting of the link in the
switchgear.
7.5.1.2 Civil Work Constraints
From paragraph 7.5.1.2 we present what are the distance requirements for solution 2.
a., knowing that for such solution it is not possible to avoid a large free space for
cable snaking in order to plug the termination in.
All calculated values are based on minimum bending radius. On a practical basis,
these values have to be increased to ensure a realistic proper installation (for instance
free spaces or distances may need to be increased up to 20%). In addition to this
description a free length has to be considered in the case of a flexible installation as it
is needed during line operation to release thermo-mechanical stresses on the cable
terminations.
7.5.1.2.1
Height Between the Bottom of Metal Enclosure/Epoxy Insulator
and Lower Floor
The height between the bottom of metal enclosure/epoxy insulator and the lower
floor must be at least the termination length (which is more than epoxy insulator
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Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
343
height) + the straight length of cable under the termination (at least 1 m where cable
clamps will be installed) + the minimum cable bending radius (20 D) see note2.
Often, it will be worth considering the largest cable size for the minimum
permanent bending radius, as a utility could need to upgrade its substation or install
additional GIS modules with larger cables.
Here is an example (Fig. 7.21):
• Diameter of cable to be used for the current project ¼ 100 mm
• Diameter of largest cable which could be used (for future eventual upgrading) ¼
120 mm.
So the height between floor and bottom of GIS enclosure has to be increased by
420 mm to accommodate potentially future larger cables (Fig. 7.22).
straight cable legth
termination height
H min (project)
D
20
2
0
D=
12
420
D=
10
0
H min (optimal)
Fig. 7.21 Height vs. cable
diameter
Installation cable radius based on cable manufacturers recommendation (Nexans catalogue, ERA
technology report) for aluminium or lead sheath
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Fig. 7.22 Typical view of a
basement installation
Fig. 7.23 Horizontal length for cable snaking
7.5.1.2.2 Free Space for Cable Snaking Necessary for Plug-in Operation
Horizontal Cable Snaking – Vertical Plug-in
This drawing shows that in order to allow termination insertion, it is necessary to
have a minimum length available for cable bending (usually horizontal or vertical)
(Fig. 7.23).
Vertical Cable Snaking – Vertical Plug-in
When the cable is laid in ducts the plug-in operation can be applied when the
distance between the base plate and the duct is large enough to make a vertical
snaking (Fig. 7.24).
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345
Fig. 7.24 Vertical length for
cable snaking
7.5.1.2.3
Free Space for Cable Snaking Necessary in Case of an Intermediate
Floor
In this paragraph we describe the snaking length for plug-in operation.
In case the termination has to be built on the lower floor, the available space
between lower and intermediate floors is very critical.
Figure 7.25 shows a theoretical cable arrangement in a basement to plug in a
terminationwith:
• D: cable diameter
• H bas.: minimum basement height ¼ 20D + D (practically 2 m minimum)
• L bas.: minimum free cable length in basement according to H bas. allowing a
maximum vertical snaking
• Ls: available length due to cable snaking.
The summary Table 7.1 (rounded values), is based on typical cables with an
aluminium foil screen bonded to the outer sheath:
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Fig. 7.25 Cable arrangement in a basement for termination plug in operation
Table 7.1 Snaking vs. free space
Cable type / Uo
D (mm)
Weight (kg/m)
H bas. (m)
L bas. (m)
Ls (m)
Weight of cable
to move (kg)
Cable 1
630 mm2
Al 63 kV
65
4.5
1.36
5.9
0.93
33
Cable 2
630 mm2
Cu 110 kV
80
9.6
1.68
7.3
1.14
86
Cable 3
1000 mm2
Cu 220 kV
100
17
2.10
9.1
1.43
190
Cable 4
1600 mm2
Cu 220 kV
120
23
2.52
10.9
1.71
310
Cable 5
2500 mm2
Cu 500 kV
150
40
3.15
13.6
2.14
680
If we consider that minimum basement height (H bas.) is 2 m, the available cable
length will increase for smaller cables, as long as free cable length (L bas.) can be
made slightly longer.
For example, considering Cable 1 from Table 7.1, and the arrangement of
Fig. 7.26 the above table values are modified as per Table 7.2.
From this example we can see that with basement length (L bas.) only 55 cm
longer, available cable length (Ls) increases from 0.93 to 1.77 m.
The necessary length in basement also depends where and how the cable termination
is prepared (horizontal preparation on lower floor, vertical above intermediate floor . . .)
7.5.1.2.4 Floor Hole Size when Cable Is Crossing an Intermediate Floor
There are different parameters that need to be taken into consideration.
Distance Between Bottom of Metal Enclosure/Epoxy Insulator and Intermediate
Floor
In some case the bottom of the metal enclosure is located within the floor hole.
Under such circumstances the diameter of the floor hole has to facilitate the cable
termination installation works and shall not just cover the dimensional requirements
of the GIS cable enclosure (Fig. 7.27).
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Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
347
Fig. 7.26 2 m high basement for small diameter cable snaking
Table 7.2
Cable type
D (mm)
Weight (kg/m)
H bas. (m)
L bas. (m)
Ls (m)
Weight of cable to move (kg)
Cable 1
630 mm2 Al 63 kV
65
4.5
2.00
6.45
1.77
43
Closed ferrous magnetic loops should not be introduced around the single phase
power cables by items such as external steelwork, and concrete reinforcement.
Size of Floor Hole (in Line with the Termination)
When the cable termination can be prepared on the intermediate floor, there is no
additional requirement due to the plug-in concept.
When the cable termination has to be prepared on the lower floor, a larger hole is
needed, depending of the type of termination (3-phase – single phase), and the SVL
position,
For a single phase termination, the hole has to be at least equal to external
diameter of the base of the epoxy insulator + extra space depending on the SVL
position, size and rated voltage (voltage clearance).
Figures 7.28 and 7.29 show an example of floor hole size study for a 72/100 kV
3-phase GIS metal enclosure, with a distance of 150 mm between bottom of metal
enclosure and intermediate floor.
The use of 15 kV SVL requires specific arrangement (SVL are in green).
• Distance between SVL and earth or metallic parts: min. 130 mm
• Distance between 2 SVL: min. 160 mm.
348
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Fig. 7.27 Tri-phase GIS
termination installation
Fig. 7.28 Profile view of
15 kV SVL installation
The two dimensions vertical distance of the bottom of the metal enclosure and
diameter of the floor hole are somehow linked. Whenever the vertical distance gets
narrow (e.g. below 500 mm) the size of the floor hole should be increased in order to
facilitate the mechanical installation and construction during insertion of the cable/
stress cone assembly from below. This leads to additional constraints on the metal
enclosure metallic support structure design.
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Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
349
Fig. 7.29 Bottom view of SVL installation
Cable stiffness increases when temperature decreases. At low temperature, plug
in operations are not feasible unless the cable has been heated.
If cable temperature is lower than +5 C, it has to be heated over this temperature.
The structure to support the cable in the basement must also allow for the
installation operations, which need large forces, especially for large cross sections
of cables and/or cold temperatures.
It is worth remembering that fixing of lifting tools etc. to the metal GIS enclosure
or its related components is not permitted.
7.5.1.3 Conclusions Regarding Geometrical Installation Constraints
Conclusion from geometrical constraint on solution 2a with the table space-weightcondition
Advantages and disadvantages of the different installation conditions are
summarised in Table 7.3.
The installation survey shows that the case 2a is the only one where the plug-in
concept can be considered.
In this case, the evaluation of geometrical constraint for termination preparation
and plug-in shows that the main controlling parameters are the cable diameter,
weight, and the available space.
Regardless of the civil works, the plug-in concept looks easy to implement for
smaller and lighter cables. i.e. less than 100 mm in diameter and 15 kg/m.
For large size and heavy cables, the constraints rapidly become more severe.
Refer to Table 7.4, where the practical cases are written with green letters, difficult
ones with orange letters, and almost impossible ones with red letters.
However, the plug-in is always possible if it has been taken into account at the
design stage of the civil works as it may require additional installation procedures
and efforts, adapted handling means and extended free space.
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Table 7.3
Type of installation a
Strong coordination between
cable termination and GIS
installers.
Necessity to disassemble the
Cable termination enclosure.
Increased probability to damage
the stress cone.
Reduced civil works
No advantage for further
standardization of the insulator
Case
1
Type of installation b
Always possible.
Reduced civil works
Need for coordination
between cable termination
and GIS installers.
Not plug-in procedure.
No advantage for further
standardization of the
insulator
Possible with restrictions:
Available space for moving
the cable
Necessary strength for lifting
the cable.
Not plug-in procedure.
Same civil works as 2a
No advantage for further
standardization of the
insulator
Possible with restrictions:
Align stress cone and insulator
axis during insertion
Available space for moving the
cable Necessary strength for
lifting the cable
Case
2
Further standardization of the
insulator can be evaluated
Table 7.4
Cable type / Uo
D (mm)
Weight (kg/m)
H bas. (m) (at least 2 m)
L bas. (m)
Ls (m)
Weight of cable to move (kg)
Comments
Cable 1
Cable 2
Cable 3
Cable 4
Cable 5
63kV
65
4.5
2.00
6.45
1.77
43
110kV
80
9.6
2.00
7.60
1.53
100
220 kV
100
17
2.10
9.1
1.43
190
220 kV
120
23
2.52
10.9
1.71
310
500 kV
150
40
3.15
13.6
2.14
680
*depending
on site
*depending
on site
with
- D: cable diameter
- H bas.: minimum basement height = 20D + D (practically 2 m minimum)
- L bas.: minimum free cable length in basement according to H bas. allowing a maximum vertical snaking
- Ls: available length due to cable snaking
nge letters, almost impossible red letters.
7.5.2
Safety Practices and Constraints during Installation
These recommendations are specific to GIS plug in cable terminations and come in
addition to normal practices in the electric civil works environment
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351
7.5.2.1 Voltage
• DISCONNECT THE VOLTAGE! Two open gaps are needed, for instance circuit
breaker and line disconnector
• Earth the part between the circuit breaker and the outgoing disconnector switch
with the earthing switch.
7.5.2.2 Gas Pressure during Installation
During GIS manufacturing, installation and delivery:
All insulators are pretested, tested in modules or complete in factory, and on site
after installation.
This requires adjusting the compartment pressures several times during the
different phases of the GIS delivery.
•
•
•
•
The design pressure is 7.5 bars relative (reference to IEC 62271-209).
During transportation, the pressure is decreased to 0,5 bar
During works, the pressure in adjacent compartments is decreased to 0.5 bar.
The customer or an authorized third party can perform the pressure decrease and
refill. There may be legal regulation regarding authorized persons.
• Supervision performed by experienced people or GIS manufacturer is
recommended.
• SF6 maintenance equipment is available at the customer premises.
• Decrease of pressure is specified in the operating/maintenance manual.
During the plug-in of the cable termination:
Uncontrolled forces or mistakes during the plug-in operation are more dangerous
with high gas pressure.
Similar to the work practice on the GIS compartments, the Cigré WG recommends decreasing the pressure of the cable box to 0.5 bars relative for the above
safety reason during the termination installation.
Note that during the manufacturing of insulator and termination stress cone, it is
common practice to first perform the pressure test of the insulator according to IEC
62271-203 and the maximum pressure of IEC 62271-209, then to perform the
dielectric test of the stress cone. During the installation of the stress cone, the
pressure in the cable box must be reduced to 0,5 bar.
7.5.3
Testing Constraints
All insulators and stress cones have to be tested.
7.5.3.1 Tests on Insulator Before Supply
At insulator manufacturer (or at the GIS manufacturer facility by agreement between
GIS and insulator manufacturers):
Dimensions and tolerances according to paragraph Dimensions and Tolerances of
Sect. 7.4.3.1.1
352
•
•
•
•
•
P. Mirebeau
Compliance with IEC 62271-209 Fig. 5,
Plug-in connector of insulator,
Lock-in system (if any),
Insulator and shape of cone, smoothness,
Insulation shield break ring (if integrated in the insulator).
Routine tests according to paragraph Routine Test of Sect. 7.4.3.1.4.
• Voltage test and PD measurement test according to paragraph 7.1.101 & 7.1.102 of
IEC 62271-203, the pressure being the minimum functional pressure for insulation
as per IEC 62271_209 Fig. 1, with the deviation range of paragraph 8.2.1,
• Tightness test according to paragraph 7.4 of IEC 62271-203,
• Design and visual checks according to Fig. 5 of IEC 62271-209,
• Pressure test according to paragraph 7.104 of IEC 62271-203.
7.5.3.2 Tests of the Stress Cone on a Cable Termination Assembly
with a Host Insulator
By accessory manufacturer: as per paragraph 9 of IEC 60840 or IEC 62067.
7.5.3.3 Tests After Installation
GIS
Without installed cable, test is according to IEC 62271-203 or ANSI C 37.122-2010.
The common interface insulator causes no special issue except the test of the
insulator, which is already prescribed in IEC 62271-209 paragraph 8.1 when it is
pre-installed during GIS manufacturing.
Cable
The cable system shall be tested after installation according to paragraph 8.3 of IEC
62271-209.
When the termination is not plug-in type, it is fitted inside the GIS enclosure.
Different testing arrangements can be implemented:
• A SF6 to air bushing has to be temporarily installed on the GIS after a disconnected area. See Fig. 7.30.
• A termination is available at the other end (outdoor termination or SF6/air
bushing). This is used to test the cable without emptying the cable box. If the
GIS busbar is not disconnected, there may be impact on the GIS enclosure in case
of termination failure.
When the termination can be plugged in
Different testing arrangements can be implemented:
• The GIS has a SF6/air bushing. It can be used for cable after installation test (for
cases above 245 kV – below 245 kV there is usually no bushing as part of the
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Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
353
Fig. 7.30 Example of after
installation test equipment
GIS) without emptying the cable box. If the GIS busbar is not disconnected, there
may be impact on the GIS enclosure in case of termination failure.
• A termination is available at the other end (outdoor termination or SF6/air
bushing). This is used to test the cable without emptying the cable box. If the
GIS busbar is not disconnected, there may be impact on the GIS enclosure in case
of termination failure.
• GIS to GIS link or no termination available. The cable box must be open, or use of
a “dummy” accessory before plug in. The final arrangement and the epoxy busbar
cone inside the GIS cable termination are not tested.
• GIS to GIS; as an alternative to the bullet point above, install a voltage lead
outside of the insulator. Depending on the GIS design, it can be a temporary GIS
termination, which is later on removed.
The test of the cable system via GIS should be made in agreement with the GIS
manufacturer.
7.5.4
Conclusion Regarding Testing Constraints
Due to the weight of the complete cable and the handling issues in the case where
there is no available termination for performing after installation test without moving
the cable, the cross section should be less than 1000 mm2 Cu or 1600 mm2 Al.
354
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7.6
Qualification
7.6.1
State of the Art
7.6.1.1 Medium Voltage Standards
There are 2 current standards EN 50180 and mainly EN 50181 (European standards
from CENELEC) which standardize the interface profile.
Connectors in Medium Voltage are similar to stress cones in our brochure.
EN 50180:2010: Bushings above 1 kV up to 52 kV and from 250 A to 3.15 kA for
liquid filled transformers.
Introduction
The object of this European Standard is to specify the requirements to ensure
interchangeability of bushings having highest voltages above 1 kV up to 52 kV
and rated currents from 250 A up to 3150 A for insulating liquid filled
transformers.
Scope (Chapter 1)
This European Standard is applicable to ceramic and resin insulated bushings
having highest voltages above 1 kV up to 52 kV, rated currents from 250 A up to
3150 A and frequencies from 15 Hz up to 60 Hz for insulating liquid filled
transformers.
This standard establishes essential dimensions, to ensure interchangeability of
bushings and to ensure adequate mounting and interchangeability of mating plug-in
separable connectors of equivalent ratings.
EN 50181:2010: Plug-in type bushings above 1 kV up to 52 kV and from 250 A
to 2.50 kA for equipment other than liquid filled transformers.
Introduction
The object of this European Standard is to specify the requirements to ensure
interchangeability of bushings for maximum voltages above 1 kV up to 52 kV and
rated currents from 250 A to 2500 A for equipment other than insulating liquid filled
transformers.
Scope (Chapter 1)
This European Standard is applicable to insulated bushings for maximum voltages above 1 kV up to 52 kV, rated currents from 250 A up to 2500 A and
frequencies from 15 Hz up to 60 Hz for equipment other than liquid filled
transformers.
This European Standard establishes essential dimensions, to ensure adequate
mounting and interchangeability of mating plug-in separable connectors of equivalent ratings.
Definitions in EN 50181:2010 are not in line with ones of this brochure. Some
examples are given hereunder.
7
Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
355
Plug in Type Bushing (Chapter 3.1)
Bushing one end of which is immersed in an insulating medium which has customized dimensions according to insulation requirements for the specific application and
the other end designed to receive a separable insulated cable connector without
which the bushing cannot function
Separable Connector (Chapter 3.2)
Fully insulated termination permitting the connection and disconnection of the cable
to and from the mating plug-in type bushing
Interface Type (Chapter 3.3)
Bushing dimensions that insure mechanical and electrical interchangeability of
bushing and separable connector of similar rating and type.
NOTE: Each interface type is designated by a letter or a number.
Bail Holder (Chapter 3.4)
Fixture which facilitates anchoring of an externally mounted device (called the bail)
designed to prevent undesirable separation of a separable connector and a bushing.
7.6.1.2 Medium Voltage Qualification Experience
Qualifications were carried according to market needs.
Most connector suppliers are also bushing suppliers, not necessarily to be
installed together.
No crossed qualifications are required.
Bushing material is not mentioned in EN 50181 (and mentioned as porcelain or
resin in EN 50180), but an elastomeric bushing should not be considered as a
possible solution according to these interchangeability standards.
As long as the interface is in accordance with the standard, the most critical point
concerns the lubricant to be used at the interface.
Some utilities have been facing problems of disconnection with silicone connectors which absorb the lubricant and stick to the bushing. Consequently a disconnection often leads to damage of such connectors.
Hence suppliers have to provide the associated lubricant which is compatible with
their connector (EPDM or Silicon Rubber) and considered neutral regarding compatibility with the bushing resin.
In case of fault, an examination is usually performed in order to identify the fault
source. However in MV the material cost remains very low compared to examination
or other investigations costs, so it is not worth engaging further investigations to
determine responsibilities. Usually the connector manufacturer supplies the replacement parts.
Unplugging could be necessary for temporary link installation (main purpose), or
in case of fault (fault location, repair . . .), but it is almost never used.
Lessons Learned from Qualification and Installation Experience
There are important points to validate:
356
P. Mirebeau
• Compatibility between connector and lubricant
• Conductor connection
• Insulator resin choice, which determines its electrical performance, but also on its
molding process or machining ability, mainly to ensure a well-controlled interface
roughness.
7.6.1.3 High Voltage Standards
Interface Standards
Table 7.5.
Cable System Standards
The Table 7.6 shows the most common applicable standards depending on the
different countries.
Table 7.5
GIS TERMINATIONS FOR EXTRUDED CABLES
COLLATION OF RELEVANT STANDARDS
Country
Standard Title
List of Type Tests (TT)
Country
Standard
Title
International
and EN
IEC
622712092007
USA
IEEE
13002011
High-voltage
switchgear and
controlgear
-Part
209: Cable
connections for
gas-insulated
metal-enclosed
switchgear for
rated voltages
above 52 kV.
Fluid filled and
extruded
insulation
cables Fluidfilled and
dry-type cableterminations
Guide for
Cable
Connections
for Gas
Insulated
Substations
Terminations
alone
List
List of PQ
of
Extension
PQ
Tests
Tests
As part of cable
systems only
As part
of cable
systems
This standard is an interface standards gives
recommended arrangements for dielectric tests
on GIS terminations. The dielectric tests for type
and PQ tests are specified in relevant IEC
standards for particular type of cable. It makes
reference for insulators to routine tests specified
in IEC 62271-203.
This guide is carbon copy of IEC 62271-2092007 in regard to GIS connections for extruded
cables. In addition it specifies dimensional
requirements for GIS connections for laminated
cables.
Standard
IEC 60840-2011
IEC 62067-2011
Country
International
International
Power cables with
extruded insulation and
their accessories for
rated voltages above
150 kV (Um ¼ 170 kV)
up to 500 kV (Um ¼
550 kV) – Test methods
and requirements
Title
Power cables with
extruded insulation and
their accessories for
rated voltages above
30 kV (Um ¼ 36 kV) up
to 150 kV (Um ¼
170 kV) – Test methods
and requirements
GIS TERMINATIONS FOR EXTRUDED CABLES
COLLATION OF RELEVANT STANDARDS
Table 7.6
Terminations are type
tested as part of cable
system only.
List of Type Tests (TT)
Terminations alone
• PD amb
• 20 cycles at 2U0 (8 h
heating, min 2 h @95–
100 C for EPR and
XLPE)
• PD amb
• PD hot
• Hot BIL followed by
2.5U0 15 min
• Visual inspection
4 kV/mm at insulation
screen.
• PD amb
• 20 cycles at 2U0 (8 h
heating, min 2 h @ 95–
100 C for EPR and
XLPE) PD amb
• PD hot
• SIV hot (for Um 300 kV)
• Hot BIL followed by
As part of cable systems
• PD amb
• 20 cycles at 2U0 (8 h
heating, min 2 h @ 95–
100 C for EPR and
XLPE) PD amb
• PD hot
• Hot BIL followed by
2.5U0 15 min
• Visual inspection
>4 kV/mm at insulation
screen.
Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
(continued)
List of PQ
Extension
List of PQ Tests
Tests
As part of cable systems only
• PD amb
• 180 cycles at 1.7U0
• Hot BIL (if done on
•
entire test rig)
60 cycles,
• Visual inspection
no voltage
• 20 cycles
at 2U0
• PD amb
• PD hot
• Hot BIL
followed
by 2.5U0
15 min
• Visual
inspection
4 kV/mm at insulation screen.
min 180 cycles at 1.7U0 • PD amb
(1 year test)
•
• Hot BIL (if done on
60 cycles,
entire test rig)
no voltage
• Visual inspections
• 20 cycles
at 2U0
• PD amb
• PD hot
• SIV hot
7
357
Standard
Cigré TB 303
Country
International
Changes in a qualified
cable system
Title
GIS TERMINATIONS FOR EXTRUDED CABLES
COLLATION OF RELEVANT STANDARDS
Table 7.6 (continued)
Change of insulator
material for indoor or
outdoor terminations. –
> new TT
Change of insulator
design or manufacturer
of GIS/Transformer
insulator -> newTT
Change in the
formulation of the stress
cone compound but with
the same base polymer –
> EQ Change of the
base polymer (EPR,
Silicone,...) of the stress
cone –> EQ
List of Type Tests (TT)
Terminations alone
As part of cable systems
2.5U0 15 min
• Visual inspection
(for Um 300 kV)
• Hot BIL
followed
by 2.5U0
15 min
• Visual
inspection
List of PQ
Extension
List of PQ Tests
Tests
As part of cable systems only
358
P. Mirebeau
IEEE 48-2009
AEIC-CS9-06
Association of
Edison
Illuminating
Companies
representting
Utilities
USA
USA
Specification for
Extruded Insulation
Power Cables and their
Accessories Rated
Above 46 kV
Through 345 kV AC
IEEE Standard for Test
Procedures and
Requirements for
Alternating- Current
Cable Terminations
Used on Shielded
Cables Having
Laminated Insulation
Rated 2.5 kV through
765 kV oi Extruded
Insulation Rated 2.5 kV
through 500 kV
• PD amb
• 3.5-3.9U0AC, 1 min
• DC, 15 min
• Cold BIL
• Hot BIL
• PD amb
• 30 cycles at 2U0 (each
cycle min 6 h at
emergency temp +0/
5 C (105 C for
XLPE and 130 C for
EPR, cooling process
specific)
• PD amb
• 2.5U0 AC, 6 h
• Cold BIL
• Cold SIL (for 345 kV
and above)
• PD amb
• Visual inspection
Per IEEE 48
Not
considered
• For class 170 kV: per
IEC60840 (if required
by purchaser spec)
• For class >170 kV: per
62067
• Additional 90 cycles at
emergency temp +0/
5 C (105 C for
XLPE and 130 C for
EPR) are required
• For class 170 kV:
per IEC60840
(if required by purchaser
spec)
• For class >170 kV: per
62067
The load cycling test for
both classes should be
done at emergency temp
+0/5 C (105 C for
XLPE
and 130 C for EPR)
Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
(continued)
Not
considered
Not considered
Not considered
7
359
Standard
JEC-3408-1997
RTE Spec
No. 214 ind.3
full current ref.:
NT-IMRCNERDL-ML2010-00214
(+amendments
of 14 Oct 2011
and 4 Apr 2012)
Country
Japan
France
RTE specification
Single phase cables and
accessories for
underground links from
63 kV to 400 kV AC
Title
High voltage tests on
XLPE insulated cables
and their accessories for
rated voltage from
11 kV up to 275 kV
GIS TERMINATIONS FOR EXTRUDED CABLES
COLLATION OF RELEVANT STANDARDS
Table 7.6 (continued)
GIS cable terminations
have to be in accordance
with IEC 62271-209
This specification is
based on IEC 60840 &
62067.
+ additional tests on
base insulating ring:
lightning impulse test
(for 63, 90 & 225 kV ¼
50 kV; for 400 kV ¼
62.5 kV) – AC test
under rain condition (all
voltages ¼ 20 kV for
15 min)
List of Type Tests (TT)
Terminations alone
As part of cable systems
• 30 days daily cycling at 90 C or 105 C, at 1.48
times max. phase-to-ground cable voltage (U0) or
• 1 h hot AC at 2.53 E0 or 1 h cold AC at 3.04 E0
• Hot or cold lightning Impulse, 3+, 3 shots
List of PQ
Extension
List of PQ Tests
Tests
As part of cable systems only
• 1/2 year daily cycling
Not
at 90 C or 105 C, at
considered
1.32 U0
• Hot or cold lightning
impulse, 3+, 3 shots
• 10 min hot or cold AC
PQ test 180 cycles,
6000h for voltages
150 kV,
1 year for 245 kV and
420 kV.
360
P. Mirebeau
7
Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
361
Table 7.7 Guide to the selection of tests because of modifications to an accessory within the same
family in a prequalified EHV cable system
Modification
Component
Terminations:
Outdoor
Indoor
Metal
enclosed
+ SF6
+
Oil-immersed
Type of modification
Higher electrical stress
design of stress cone
(or smaller metal clad for
GIS or transformer
terminations)
Change in nature of Filling
medium (e.g. oil to gas. . .)
Change in the formulation
of the stress cone
compound but with the
same base polymer
Change of the base
polymer (EPR, Silicone,
...) of the stress cone
Change of insulator
material for indoor or
outdoor terminations.
Change of insulator design
or manufacturer of
GIS/Transformer insulator
Ma
Pa
Da
V
V
V
V2)
V2)
V2)
V2)
V
V
DLa
V
IEC 62067 Ed.1
Clause number
TPQ- EQtest test
test
–
–
(xx)1)
–
–
(xx)1)
–
–
(xx)1)
–
–
(xx)
12
–
–
12
–
–
When can be demonstrated that the thermo mechanical aspects have no significant influence on the
performances of the termination a
Type Test may be sufficient.
In case of elastomeric insulators (“silicone” or “EPR”) climatic and pollution test according to IEC
61109 Annex C should be considered
(xx) Clause to be added in the standard
a
M, change in material; P, change in manufacturing process; D, change in design (construction); DL,
change in electrical design stress level
In every case voltages >170 kV are worth a full system consideration. Voltages
170 kV are either considered as a commodity (example: China, Middle East,
Thailand), or considered as a system (example: France, Italy, some end users in
USA).
Cigre Brochure: Revision of Qualification Procedures for HV and EHV AC
Extruded Underground Cable Systems
Cigré TB 303 deals with extension of qualification. Interchangeability leads to a type test.
Table 7.7 is an extract of Table 2.4 of TB 303:
GIS Partition and Insulator Standards
The insulator specification is part of the IEC standard 62271-203 “Gas-insulated
metal-enclosed switchgear for rated voltages above 52 kV” where most important
362
P. Mirebeau
parts of the outdated EN 50089 “Cast resin partitions for metal-enclosed gas-filled
high-voltage switchgear and controlgear” (1994) have been included.
• Type test (Chapter 6.1 and 6.104)
– Tightness test
– Voltage test including PD measurement
– Burst test (with a burst pressure result >3 design pressure)
– Thermal performance
• Routine tests (chapter 7.1, 7.4 and 7.104)
– Visual inspection
– AC voltage test including PD measurement
– Pressure test (2 design pressure/1 min.)
– Tightness test.
7.6.2
Where the Plug-in Common Interface Could be Applicable
Due to the qualification issues and specially the need for prequalification, the
common interface should be restricted to voltages up to and including 170 kV.
The detailed technology and the number of sizes will be defined by the next Cigré
working group.
7.6.3
Qualification of new Insulator or Stress Cone
We consider here terminations for voltage 170 kV.
When insulator, stress cone and termination assembly have been qualified
according to paragraph 4.3, the qualification of a new insulator with the same stress
cone or a different stress cone with the same insulator needs a Type Test of the
termination assembly.
The details of the Type Test arrangement as well as the range of approval need to
be defined by the next Cigre working group (see Sect. 7.9).
7.7
Feasibility
In this section, the conclusions from sections 7.6: “the common interface should be
restricted to voltages up to and including 170kV” and 7.5 “Due to the weight of
the complete cable and the handling issues, the cross section should be less than
1000 mm2 Cu or 1600 mm2 Al” are taken into account.
The cost of different development phases are addressed below.
7.7.1
Definition Feasibility (Cost Involved)
Definition and production of the plug in system
Due to variations in the manufacturing processes as a function of different suppliers, the design and manufacturing costs cannot be addressed by the working group.
7
Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
363
Definition and production of insulator:
• Design of the geometry: Cigré WG to come (see Terms Of Reference at the end of
the brochure)
• Engineering
• Mould design
• Eachinery
• Prototypes.
All this work needs several man-years
Definition and production of stress cones:
• The work needed to design, engineer, prototype stress cones. The cost is between
two to five times more than for the insulator, depending on the stress cone sizes
that are needed per voltage level (according to the core diameters).
7.7.2
Qualification Feasibility
The qualification has to be performed according to the standardisation requirements
(paragraph 4.3):
The market acceptance study (paragraph 8) shows that the customer will accept
only combinations stress cone/insulator that have been tested as a system.
The cost of the necessary tests is approximately:
Initial component and system qualification:
Insulator
• Development tests are about 100 k€
• The Type Test of paragraph 7.4.3.2 cost about 200 k€ (test of connector not
included)
• A preliminary Type Test is about 200 k€
Stress Cone
• Development tests are about 100 k€ at the supplier premises
• The Type Test of paragraph 7.4.3.1 is about 200 k€ including laboratory costs,
cable and accessory, installation works.
System
• A type test is needed (no prequalification because of the voltage level) i.e. 200 k€.
• If the cable stresses at the insulation screen is larger than 4 kV/mm (ref. IEC
60840) a prequalification test is required. This cost about 400 k€.
Cross Qualification (paragraph 6.2)
• Due to market acceptance, a type test is needed for all combinations. It costs about
200 k€ per combination.
364
P. Mirebeau
• When a stress cone has been prequalified and the insulator is from a different
manufacturer, a new prequalification test is not necessary as the stresses on
the insulator are not influenced by the insulation screen stress of the cable.
7.8
Market Acceptance
7.8.1
Current Status
For voltages above 170 kV full qualification of the cable system is required. Each
link is bought as a system (refer to IEC 62067).
For voltages up to 138 kV, There are two opposite trends: some customers move
to the system approach, others go to commodity approach: cable and accessories are
bought separately.
170 kV is a special case where the cable system stresses can be similar to the
245 kV level and the cable cross section is larger. For this voltage, the system
approach prevails.
When the cable termination supplier is not chosen at the time the GIS has to be
delivered (around 70% of cases), the GIS is not pre equipped with the insulator and
the last compartment is not tested. It has to be open at the cable installation time.
There are gas works and risk of pollution.
7.8.2
Future Status
For voltages lower than 170 kV, if stress cones and insulators are provided by different
manufacturers, there is one more limit of responsibility barrier as compared to the cable
system case. It is the stress cone – insulator interface. In case of failure, the responsibility for the failure is less easy to address than at the insulator/SF6 interface. End users
are concerned by this change as there is no clear limit of responsibility.
All combinations of stress cone/insulator must be tested.
If the cable accessory is installed by a third party contracted by the end user, there
is one more layer of responsibility. Improper cable clamping, contamination, or
pressure spring compression may lead to defect and further complicate allocation
of responsibility in case of a fault.
The end user can limit the complication of responsibility by giving the contract to
a limited number of parties.
The main benefits are that more flexibility is given to the end user and overall
logistics costs are reduced.
Note: The financial balance of common interface benefits versus the design
development and qualification costs was not investigated.
Market acceptance drivers are given in the hereunder table (Table 7.8).
7
Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
365
Table 7.8
In favour of
interchangeability
Qualification
Routine test of
insulator and
rubber
Routine test of
termination
assembly
Routine test of
GIS
manufacturing
Planning
–
Installation on
GIS
Cable enclosure fully
tested. (presently fully
tested only when the
termination supplier is
selected together with
GIS)
Engineering of cable
and GIS independent.
Easier logistics for GIS
manufacturer.
Higher flexibility for
the end user
Less storage – less
logistics – easier
planning
No opening of GIS on
site and pre-tested (true
for any pre-installation
of insulator, whatever
the interface)
Installation of
cable
termination
Spare parts
Comment
Final termination
assembly not routine
tested.
Costs
Cost
manufacturing
(insulator and
rubber)
Cost GIS
manufacturing
Detrimental to
interchangeability
Cost of a cross
qualifications of
insulators and stress
cones
–
More difficult and
costly logistics for the
cable accessory
manufacturer.
In practice the cables
are ordered later than
GIS.
Cable system design:
less optimised due to
variability
of components. (ref.
Vattenfall experience
3.2.2). Cable cost can
be affected.
New investments and
qualification to
perform due to new
design of insulator and
stress cone (paragraph
7).
The termination can
only be installed when
the GIS is on site
More space needed to
plug in (see 5.1) as
compared to 5.1.1 case
1 situation. This could
impact civil
works cost.
Installation should
avoid any torsion on
the cable.
Easier logistics
(continued)
366
P. Mirebeau
Table 7.8 (continued)
Utility &
industrial users
impact
Spare parts
Flexibility for
choice of cable
supplier in case
of upgrading
Responsibility
allocation
After
installation test
of the cable
system with
GIS
termination.
7.8.3
In favour of
interchangeability
Easier
Higher
Detrimental to
interchangeability
More difficult with
more parties.
Responsibility
allocation in case of
problem.
Comment
To be in the
application range of
insulator
End user should
minimize the number
of parties.
The test must be
performed through the
high voltage bus bar of
the GIS or from the
remote end outdoor
termination.
Where the Plug-in Common Interface Could
be Recommended
As coming from the market acceptance drivers the common interface should be
limited to the commodity market:
• Voltage 145 kV and less.
• Current 1000 A and less
• Short circuit 40 kA during 1 s and less.
7.9
Conclusion and Recommendations
Taking into account the above considerations and specially the market trend in some
countries towards a commoditisation of the High Voltage cables lower or equal to
145 kV, the working group thinks that there is room in these voltage levels for a
standard design in parallel with the present designs. As per the TOR of the group,
B1.B3-33 recommends Study Committees B1 and B3 to set up a new working group
with the following Terms of Reference.
The Working group should recommend a functional design of an insulator with a
common interface with the following scope of work:
7
Feasibility of a Common, Dry Type Plug-in Interface for GIS and Power. . .
•
•
•
•
Voltage is 145 kV AC (Um)
Current is 1000 A, short circuit 40 kA 1 s.
Cross sections are 1000 mm2 Cu or 1600 mm2 Al
Technology has to be defined (inner or outer cone), with a detailed evaluation of
technical advantages/disadvantages of the two technologies.
The number of sizes has to be defined, the short circuit current can be altered for
the smallest sizes.
Dimensions of insulator components have to be defined (current connection,
electric design and properties, mechanical design and properties).
The type and dimension of the main current connection has to be defined
Consider the consequence of a termination failure.
Consider the upgrading of the cable link for higher current loads.
Consider the installation constraints, with a special focus on the basement
dimensions.
The design has to meet the requirements of IEC 62271-209 and IEC 60840
Define the initial and cross qualification processes.
•
•
•
•
•
•
•
•
367
The stress cone design and material, the lubricant and the design of the compression
device should be left to the discretion of the accessory manufacturer within the limits
of the standardised insulator properties.
Cigré TB 303 and the work of WG B1.44 and WG B1.46 should be taken into
account.
Acknowledgments The Working Group wishes to thank T. Klein (DE), D. Kunze (DE) and
M. Obst (DE) for their active support.
References
All standards that are in the documents:
Cigré TB 303 (Chapter 4)
Cigré WG B1.29: Guidelines for maintaining the integrity of XLPE cable (Chapter 6)
Cigré WG B1.46: Conductor Connectors: Mechanical and Electrical Test (Chapter 10)
Pierre Mirebeau, who graduated from the “École Supérieure de
Physique et Chimie Industrielles” (Paris), has headed high-voltage
R&D for Nexans over the past 25 years. As a Member of Cigré since
2005, he contributed to a variety of subjects, including testing of DC
extruded cables, life management of buried AC lines, advanced
designs of laminated metallic coverings, dry type interfaces for
Gas-Insulated Switchgear and power cables, and the environmental
impact of cable links. In recognition to this work, he was granted the
Technical Committee Award for 2011. He is an Active Member of
the International Electrotechnical Commission (IEC) standardization
body, and the Institute of Electrical and Electronics Engineers
(IEEE), where his presentations on development techniques for
368
P. Mirebeau
HVDC Links with synthetic insulation in 2001 and his collaborative
(IEEE + IEC) presentation on cable terminations for gas insulated
switchgears in 2006 were awarded “best presentation.” He also holds
several important patents relating to lead-alloy composition, cable
designs, and polymer material composition. He is the Liaison Member between IEC TC 20 and Cigré B1 (both regarding insulated
cables), and between CIBRE B1 and Cigré B3 (substations and
electrical installations).
8
Test Procedures for HV Transition Joints
for Rated Voltages 30 kV up to 500 kV
Marco Marelli
Contents
8.1
8.2
8.3
8.4
8.5
8.6
8.7
8.8
8.9
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.1.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.1.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.1.3 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.1.4 Condition Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Normative References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Definition of Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.1 Development Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.2 Routine Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.3 Sample Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.4 Type Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.5 Prequalification Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.6 Electrical Test after Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Test Cables and Transition Joint Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Development Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.5.1 Electrical Development Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.5.2 Non-Electrical Development Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Routine Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.6.1 Extruded Cable Side of the Transition Joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.6.2 Paper Cable Side of the Transition Joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sample Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Type Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.8.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.8.2 Range of Type Test Approval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.8.3 Type Test Arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.8.4 Type Test Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Prequalification Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.9.1 General and Range of Prequalification Test Approval . . . . . . . . . . . . . . . . . . . . . . . . .
8.9.2 Prequalification Test Arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
370
370
370
371
372
372
373
373
373
373
373
373
374
374
374
374
374
375
375
375
375
376
376
376
377
379
382
382
383
M. Marelli (*)
Prysmian Group, System Engineering, Land and Submarine HV and EHV AC/DC Power Cable
Systems and Telecom Cable Systems, Milano, Italy
e-mail: marco.marelli@prysmiangroup.com
© Springer Nature Switzerland AG 2021
P. Argaut (ed.), Accessories for HV and EHV Extruded Cables, CIGRE Green Books,
https://doi.org/10.1007/978-3-030-39466-0_8
369
370
M. Marelli
8.9.3 Prequalification Test Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Electrical Test after Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.10.1 DC Voltage Test of the Oversheath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.10.2 AC Voltage Test of the Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Appendix A Considerations for Transition Joints for Other Types of Paper Cable . . . . . . . . . . .
A.1 Cables to IEC 60141-2: – Internal Gas-Pressure Cables and their Accessories
for Alternating Voltages up to 275 kV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A.2 IEC 60141-3: – External Gas- Pressure (Gas Compression) Cables and their
Accessories for Alternating Voltages up to 275 kV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A.3 IEC 60141-4: – Oil-Impregnated Paper-Insulated High Pressure Oil- Filled Pipe-Type
Cables and their Accessories for Alternating Voltages up to and Including 400 kV . . . . . .
Appendix B Design Features, Performance and Necessity for Performing Type Tests
for Transition Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.1 Back-to-Back Transition Joint with Two Insulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.2 Back-to-Back Transition Joint with One Insulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.3 Composite Type Transition Joint (Three-Core, Single Core) . . . . . . . . . . . . . . . . . . . . . . . . .
B.4 Single-Core or Three-Core Type with Bushing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.5 Methodology for Assessing Test Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Appendix C List of Type and Prequalification Tests of Cable Systems . . . . . . . . . . . . . . . . . . . . . . .
Appendix D Transition Joint Experience Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Appendix E Terms of Reference for WG B1-24 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.10
8.1
Introduction
8.1.1
General
384
385
386
386
387
387
388
389
390
391
392
393
394
395
395
395
399
400
This chapter is the editorial and graphical revision of the Cigré TB 415, prepared by
the WG B1.24 and published in June 2010.
8.1.2
Background
The use of extruded cables is increasing for transmission and distribution circuits in
preference to cables with paper insulation (either kraft paper or polypropylene paper
laminate). The number of manufacturers of paper cable is also decreasing, therefore
the availability of such cables for repair works or re-routing will be very limited in
the near future. Consequently it is becoming more common for a length of extruded
cable to be introduced into a paper cable circuit requiring transition joints for the
interconnection of the two cable types.
Cigré set up WG B1.24 to review this subject and issue a report including:
• A review of existing designs of transition joints.
• A review of the existing international standards and the extent to which they
cover the testing of transition joints.
8
Test Procedures for HV Transition Joints for Rated Voltages 30 kV up to. . .
371
• Recommendations about aligning voltage levels to those specified in IEC
Standards.
• Definition of test regimes for transition joints for routine, sample, type, prequalification and after installation tests. This Chap. 8 is the report of WG B1.24
published as Cigré TB 415.
8.1.3
Scope
The purpose of these new recommendations is to give general guidance for tests on
high voltage transition joints. These recommendations are valid for transition joints
between paper-insulated low pressure oil filled cables and extruded insulation cables
with rated voltage from 30 kV up to 500 kV. Transition joints for single core cables
as well as 3-core cables are covered. The use of these recommendations in relation to
other paper cable types, e.g. high pressure oil filled or gas pressure types is addressed
in Appendix A.
Note: The 30 kV voltage level is included in order to cover the full range of
cables covered by IEC 60141
Different types of transition joints are used to connect oil-filled to extruded
insulation high voltage cables, such as:
• Back-to-back transition joint
• Composite transition joint.
Tests on joints between cables with similar type of insulation are not considered in
this document, even if they are used between cables with different conductors or
different screens.
Although the application of high voltage transition joints for interconnection of
different cable systems is likely to increase, the quantity of transition joints compared to the quantity of standard accessories required will be low. There will also be
a large variety of cable constructions which have to be connected using transition
joints.
The number of type tests may be limited due to the availability of suitable paper
insulated cables, thus guidance is given about the range of approval.
Comments on the need for a long term prequalification test are also made.
Wherever well known and type tested components are used, for instance symmetric back-to-back transition joint designs (e.g. comprising two SF6 terminations in
a common chamber), a type test and prequalification test of the combination may be
omitted.
372
8.1.4
M. Marelli
Condition Assessment
In many cases the existing oil-filled cable on which a transition joint will be installed
will have been in service for many years and hence diagnostic tests may be advisable
to assess the cable condition. A full review of such procedures is given in reference
(Cigré Electra 1998).
In the event that the cable is found to be in as-new condition then it would
generally be considered unnecessary to carry out any special diagnostic tests after
installation of a transition joint.
Practices for maintenance of HV cable circuits are described in reference (Cigré
TB 279) and are not considered further in this report.
8.2
Normative References
The following documents are indispensable for the application of this document. For
dated references, only the edition cited applies. For undated references, the latest
edition of the referenced document (including any amendments) applies.
• IEC 60141 Test on oil-filled and gas-pressure cables and their accessories.
– Part 1: Oil-filled, paper-insulated, metal-sheathed cables and their accessories
for alternating voltages up to and including 400 kV
– Part 2:Internal gas-pressure cables and their accessories for alternating voltages up to 275 kV
– Part 3: External gas-pressure (gas compression) cables and their accessories
for alternating voltages up to 275 kV
– Part 4: Oil-impregnated paper-insulated high pressure oil-filled pipe-type
cables and their accessories for alternating voltages up to and including
400 kV
• IEC 60229 Electric cables – Tests on extruded oversheaths with a special protective function
• IEC 60230 Impulse tests on cables and their accessories
• IEC 60840 Power cables with extruded insulation and their accessories for rated
voltages above 30 kV (Um ¼ 36 kV) up to 150 kV (Um ¼ 170 kV) – Test
methods and requirements.
• IEC 60885-3 Electrical test methods for electric cables. Part 3: Test methods for
partial discharge measurements on lengths of extruded power cables
• IEC 62067 Power cables with extruded insulation and their accessories for rated
voltages above 150 kV (Um ¼ 170 kV) up to 500 kV (Um ¼ 550 kV) – Test
methods and requirements.
• EN 50299 Oil-immersed cable connection assemblies for transformers and reactors having highest voltage for equipment Um from 72,5 kV to 550 kV.
8
Test Procedures for HV Transition Joints for Rated Voltages 30 kV up to. . .
8.3
Definition of Tests
8.3.1
Development Tests
373
Internal tests made by the manufacturer before a new transition joint is type tested
and taken into service. Details of such development tests are proprietary and shall be
determined by the manufacturer.
8.3.2
Routine Test
Tests made by the manufacturer on each manufactured component to check that the
component meets the specified requirements.
8.3.3
Sample Test
Tests made by the manufacturer on samples of components taken from a complete
accessory, at a specified frequency, so as to verify that the finished product meets the
specified requirements.
8.3.4
Type Test
Tests made before supplying on a general commercial basis a type of accessory
covered by this recommendation, in order to demonstrate satisfactory performance
characteristics to meet the intended application.
Note: Once successfully completed, these tests need not be repeated, unless
changes are made in the accessory with respect to materials, manufacturing
process, design or design electrical stress levels, which might adversely
change the performance characteristics.
8.3.5
Prequalification Test
Tests made before supplying on a general commercial basis a type of accessory
covered by this recommendation, in order to demonstrate satisfactory long term
performance of the accessory.
Note 1: The prequalification test need only be carried out once unless there
is a substantial change in the accessory with respect to material,
manufacturing process, design or design electrical stress levels.
(continued)
374
M. Marelli
Note 2: A substantial change is defined as that which might adversely
affect the performance of the accessory. The supplier should provide a
detailed case, including test evidence, if modifications are introduced,
which are claimed not to constitute a substantial change.
8.3.6
Electrical Test after Installation
Tests made to demonstrate the integrity of the cable system as installed.
8.4
Test Cables and Transition Joint Characteristics
For the purpose of carrying out tests described in this document and recording the
results, the cables and accessory shall be identified. The relevant characteristics as
given in IEC 60141-1, IEC 60840 and IEC 62067 shall be known or declared.
8.5
Development Tests
Development tests are carried out to prove the main electrical and non-electrical
characteristics of the transition joint.
Details of such development tests shall be at the discretion of the manufacturer,
examples of possible tests are given in the following clauses.
8.5.1
Electrical Development Tests
Electrical development tests can be adopted from the type test recommendations of this
document, but may have increased test voltage levels. The duration of withstand tests as
well as the number of impulses during impulse voltage test may be increased, too.
Examples for electrical development tests:
• AC voltage test
• Partial discharge test
• Lightning impulse voltage test.
If new types of conductor connections are used as part of the transition joint design,
the necessity for development tests of such connections should also be considered.
8.5.2
Non-Electrical Development Tests
Non-electrical development tests are considered to demonstrate the sufficient tightness of the external transition joint housing as well as the pressure maintaining
barrier insulators between the different insulating fluids.
8
Test Procedures for HV Transition Joints for Rated Voltages 30 kV up to. . .
375
During operation joint housings and barrier insulators are subjected to hydraulic
pressure. Barrier insulators and related sealing systems may also be subjected to
vacuum during the installation process. (Vacuum processing is often used during
assembly work on paper-insulated cable accessories).
Examples for non-electrical development tests:
• Pressure test
• Vacuum leak test
• Thermo-mechanical test.
8.6
Routine Test
8.6.1
Extruded Cable Side of the Transition Joint
The prefabricated stress control component of a transition joint for U >30 kV
(Um >36 kV) shall undergo partial discharge and voltage tests according to IEC
60840 or IEC 62067 using a test arrangement which may be chosen from the following:
a) On a transition joint installed on a cable.
b) By using a host accessory into which a component of a transition joint is
substituted for test.
c) By using a simulated accessory rig (in place of a cable) in which the electrical
stress environment of a main insulation component is reproduced.
In cases b) and c) the test voltage shall be selected to obtain electrical stresses at least
the same as those on the component in a complete transition joint when subjected to
the test voltages specified.
Note: The prefabricated stress control component of a transition joint
consists of the components that come in direct contact with the cable
insulation and are necessary to control the electric stress distribution in
the accessory.
8.6.2
Paper Cable Side of the Transition Joint
The hydraulic tests specified in IEC 60141 shall be made on each accessory to which
the relevant clauses apply.
8.7
Sample Test
Due to the small numbers of transition joints which are expected to be supplied under
single orders, sample tests will not normally be appropriate.
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M. Marelli
Note: In special cases sample tests may be agreed between manufacturer
and customer.
8.8
Type Test
8.8.1
General
The tests specified in this clause are intended to demonstrate the satisfactory
performance of transition joints.
The type test may be omitted:
• As defined in the Range of Type Test Approval (see 8.8.2) or
• If the transition joint is a combination of existing type tested accessories.
• An example is a back-to-back transition joint.
In the case of three-core cables or three-core transition joints then if the cables and
cores within the joint are fully screened then it is permitted to carry out the electrical
type tests on one core only, or on a single core joint of similar electrical design.
Reference to Appendix B may be made to assist in determining the need for type
tests.
A summary of type tests on transition joints is given in Appendix C.
Note 1: If suitable paper-insulated cable is unavailable, type testing will not
be possible, thus approval of a transition joint design is dependant on
agreement between manufacturer and customer, subject to consideration
of any relevant test data.
Note 2: In the event that breakdown occurs in the paper-insulated cable or
within the joint and the primary cause is attributable to the quality of the
paper-insulated cable then approval of a transition joint design is dependant
on agreement between manufacturer and customer, taking into account the
extent of tests passed and any other relevant test data.
8.8.2
Range of Type Test Approval
When a type test has been successfully performed on a transition joint for connecting
cables of specific conductor cross-sections, and of the same rated voltage and
construction, the type approval shall be considered as valid for a transition joint
within the scope of these test recommendations with other conductor cross-sections,
rated voltages and with other cables provided that all the conditions of a) to c) are met:
(a) The voltage group is not higher than that of the tested transition joint.
8
Test Procedures for HV Transition Joints for Rated Voltages 30 kV up to. . .
377
Note: In this context, transition joints of the same rated voltage group are
those of rated voltages having a common value of Um, highest voltage for
equipment, and the same test voltage levels as given in Table 8.1.
(b) The transition joint has the same or similar construction to that of the tested
transition joint.
Note: Transition joints of similar construction are those of the same type and
manufacturing process of stress control elements and major insulation
components. Repetition of the electrical type tests is not necessary on
account of the differences of the cable insulation material, of the conductor
or connector type or material, or of the protective outer covering, unless
these are likely to have a significant effect on the results of the test.
(c) The calculated nominal electrical stresses within the main insulation parts of the
transition joint and at the cable and accessory interfaces do not exceed those of
the tested transition joint, or equal or higher electrical stresses at the relevant
locations are well proven in other accessories.
Note: Larger conductor cross-sections than tested are allowed within this
limitation.
A type test certificate signed by the representative of a competent witnessing
body, or a report by the manufacturer giving the test results and signed by the
appropriate qualified officer, or a type test certificate issued by an independent test
laboratory, shall be acceptable as evidence of type testing.
8.8.3
Type Test Arrangement
The transition joint shall comply with the tests specified in 8.8.4.1 and 8.8.4.2. The
minimum length of free cable between accessories shall be 5 m.
One sample of each transition joint type shall be tested.
The accessory shall be assembled on the cables in the manner specified by the
manufacturer’s instructions, with the grade and quantity of materials supplied,
including lubricants and insulating fluids if any. There should be provision for
measuring internal pressure of insulating fluid in the lapped cable compartment
during the test.
In units that are intended to operate with internal oil pressure, whether such
pressure is from the cable system or a separate source, the maximum pressure during
the test must not exceed the minimum design operating pressure +25%. If the
U
Kv
30–33
45–47
60–69
110–
115
132–
138
150–
161
220–
230
275–
287
330–
345
380–
400
500
1
Rated
voltage
Uo
kV
18
26
36
64
76
87
127
160
190
220
290
145
170
245
300
362
420
550
3
Value of Uo for
determination
of test voltages
2
Highest
voltage
for
equipment
Um
kV
36
52
72.5
123
Table 8.1 Test Voltages
435
330
285
240
190
131
114
4
Partial
discharge
measurement
of 8.8.4.3
1,5Uo
kV
27
39
54
96
580
440
380
320
254
174
152
5
Heating
cycle
voltage test
of 8.8.4.4
2Uo
kV
36
52
72
128
493
374
323
272
216
148
129
6
Heating
cycle
voltage test
of 8.9.3.3
1,7Uo
Kv
30
44
61
109
750
1050
–
–
1175
1050
950
1550
1425
1175
1050
650
–
850
kV
170
250
325
550
8
Lightning impulse
voltage test of
8.8.4.5 and
8.9.3.4
kV
–
–
–
–
7
Switching
impulse
voltage test of
8.8.4.5
580
440
380
320
254
218
190
2Uo
kV
36
65
90
160
9
AC Voltage test after
impulse voltage test of
8.8.4.5 and 8.9.3.4
378
M. Marelli
8
Test Procedures for HV Transition Joints for Rated Voltages 30 kV up to. . .
379
accessory includes an SF6 gas filled compartment then the gas pressure must be set
so that at 20 C the pressure is no greater than the minimal functional pressure for
insulation specified for the accessory +0.02 MPa.
Neither the cables nor the accessories shall be subjected to any form of conditioning not specified in the manufacturer’s instructions which might modify the
electrical, thermal or mechanical performance.
During tests a) to f) of 8.8.4.2, it is advisable to test joints with their outer
protection fitted. If it can be shown that the outer protection does not influence the
performance of the joint insulation, e.g. there are no thermo-mechanical or compatibility effects, the protection need not be fitted.
8.8.4
Type Test Procedure
8.8.4.1 Test Voltage Values
Test voltages shall be in accordance with the values given in the appropriate column
of Table 8.1. Prior to the type tests of the transition joint, the insulation thickness of
the extruded cable used shall be measured and the test voltage values adjusted, if
necessary, as stated in IEC 60840 or IEC 62067. In case of difficulty in achieving
impulse and ac test voltages for paper cable the test values may be agreed upon
between manufacturer and customer.
Note: If suitable oil filled cable of the required insulation thickness is not
available then it is allowed to use a cable with a greater insulation thickness
and to reduce the insulation thickness in the region where the joint is to be
installed to the required level. As an alternative it is also allowed to adjust the
test voltages in order to achieve the required electrical stress values.
8.8.4.2 Tests and Sequence of Tests
Transition joints shall be subjected to the following sequence:
(a) Partial discharge measurement at ambient temperature (see 8.8.4.3).
(b) Heating cycle voltage test (see 8.8.4.4).
(c) Partial discharge measurements (see 8.8.4.3).
• At ambient temperature and
• At high temperature
The measurements shall be carried out after the final cycle of item b) above or,
alternatively, after the lightning impulse voltage test in item d) below.
(d) Switching impulse voltage test (required for Um 300 kV, see 8.8.4.5).
(e) Lightning impulse voltage test followed by a power frequency voltage test (see
8.8.4.5).
(f) Partial discharge measurements, if not previously carried out in item c) above.
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M. Marelli
(g) Tests of outer protection for buried joints (see 8.8.4.6).
(h) Pressure leak test: this test can be carried out on a separate sample of the
transition joint. All components encapsulating the paper-insulated cable need
to be assembled and a pressure and leak test performed (see 8.8.4.7).
(i) Examination of the transition joint after completion of the above tests (see
8.8.4.8).
8.8.4.3 Partial Discharge Measurements
The measurements shall be performed in accordance with IEC 60885-3, the sensitivity being 5 pC or better. Measured values are for information purposes only.
The test voltage shall be raised gradually to and held at 1,75Uo for 10 s and then
slowly reduced to 1,5Uo (see Table 8.1).
When performed at high temperature, the test shall be carried out on the assembly
which shall be heated until the cable conductors reach a steady temperature 0 K to
10 K above the maximum conductor temperature(s) in normal operation. The
conductor temperature shall be maintained within the stated temperature limits for
at least 2 h.
8.8.4.4 Heating Cycle Voltage Test
Even though the extruded and oil filled cables may be of the same cross-section and
voltage it is likely that the thermal characteristics of the cables are very different.
Thus it is unlikely to be possible to heat the test assembly so that both cables achieve
their required temperature, using conductor current alone. It is thus acceptable to use
conductor current with the addition of heater tapes, thermal insulation or current
heating of the sheath of one or both of the cables in order to ensure that the required
temperatures are reached for both cables.
See IEC 60840 or IEC 62067 for determination of actual cable conductor
temperatures.
The assembly shall be heated until the cable conductor in each case reaches a
steady temperature 0 K to 10 K above the maximum conductor temperature in
normal operation as specified in the relevant cable standard.
The heating shall be applied for at least 8 h. The conductor temperatures shall be
maintained within the stated temperature limits for at least 2 h of each heating
period. This shall be followed by at least 16 h of natural cooling.
The extruded cable shall cool to within the temperature defined for the type test
heating cycle voltage test in IEC 60840 or IEC 62067. The conductor current during
the last 2 h of each heating period shall be recorded.
The cycle of heating and cooling shall be carried out 20 times.
During the whole of the test period a voltage of 2Uo shall be applied to the
assembly.
Interruption of the test is allowed provided 20 complete heating cycles in total
under voltage are completed.
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Test Procedures for HV Transition Joints for Rated Voltages 30 kV up to. . .
381
Note: Heating cycles with a conductor temperature higher than 10 K above the
maximum conductor temperature in normal operation are considered valid.
8.8.4.5 Impulse Voltage Tests
8.8.4.5.1 Switching Impulse Voltage Test
A switching impulse voltage test shall be carried out on transition joints of voltage
Um 300 kV.
The assembly shall be heated as stated in Sect. 8.8.4.4, until the cable conductors
reach a steady temperature 0 K to 10 K above the maximum conductor temperatures
in normal operation. These temperatures shall be maintained within the stated
temperature limits for at least 2 h.
Note: If, for practical reasons, the test temperature cannot be reached,
additional thermal insulation may be applied. The impulse voltage shall be
applied according to the procedure given in IEC 60230 with standard
switching impulse withstand voltage levels according to Table 8.1. The
transition joint shall withstand without failure 10 positive and 10 negative
voltage impulses.
8.8.4.5.2
Lightning Impulse Voltage Test Followed by a Power Frequency
Voltage Test
The assembly shall be heated as stated in Sect. 8.8.4.4, until the cable conductors
reach a steady temperature 0 K to 10 K above the maximum conductor temperatures
in normal operation. These temperatures shall be maintained within the stated
temperature limits for at least 2 h.
The impulse voltage shall be applied according to the procedure given in IEC
60230 with standard lightning impulse withstand voltage levels according to
Table 8.1. The transition joint shall withstand without failure 10 positive and
10 negative voltage impulses.
After the lightning impulse voltage test, the assembly shall be subjected to a
power frequency voltage test at 2Uo for 15 min (see Table 8.1). At the discretion of
the manufacturer, this power frequency voltage test may be carried out either during
the cooling period or at ambient temperature.
No breakdown of the transition joint shall occur.
8.8.4.6 Tests of Outer Protection for Buried Joints
These tests shall be performed according to IEC 60840 or IEC 62067 as appropriate,
unless already covered by the range of approval for these tests as specified in the
relevant standard.
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8.8.4.7 Pressure Leak Test
8.8.4.7.1 Leak Test
The vacuum leak test is to be performed as per manufacturer’s instructions when
applicable.
8.8.4.7.2 Pressure Test
Apply 2 times rated internal pressure for 1 h. Leakage shall be detected at the end of
this period by visual examination of the test specimen and by pressure drop. This test
may be performed at the end of the type tests.
No leak or rupture shall occur.
8.8.4.8 Examination
Examination of the transition joint, whenever possible, by dismantling, with normal
or corrected vision without magnification, shall reveal no signs of deterioration
which could affect the system in service operation (e.g. electrical degradation,
corrosion, harmful shrinkage or leakage, in particular across any seal separating
the extruded and oil filled cables).
8.9
Prequalification Test
8.9.1
General and Range of Prequalification Test Approval
The tests specified in this clause are intended to demonstrate the satisfactory long
term performance of transition joints.
The prequalification test may be omitted:
• If the transition joint is a combination of existing type tested paper-insulated and
prequalification tested extruded insulation accessories.
• If a transition joint of the same design has been prequalified for higher rated voltages.
• For those accessories suitable for cables with insulation screen stress less than or
equal to 4,0 kV/mm covered by IEC 60840.
• If the manufacturer can demonstrate good service experience with transition
joints of the same family with equal or higher calculated electrical stresses on
the insulation screen of the extruded cable and in the main insulation.
• If the manufacturer has fulfilled the requirements of an equivalent long term test
following a national or customer specification on similar transition joints.
It is recommended that prequalification of a new design of transition joint can be
achieved by carrying out tests based on IEC 62067 prequalification test (▶ Chap. 4,
“Qualification Procedures for HV and EHV AC Extruded Underground Cable
Systems” of this book) but may be installed in a laboratory as per the recommendations made in Cigré TB 303 for extension of a prequalification test. The details of this
test are described in Sects. 8.9.2 and 8.9.3.
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Test Procedures for HV Transition Joints for Rated Voltages 30 kV up to. . .
383
A prequalification test certificate signed by the representative of a competent
witnessing body, of a report by the manufacturer giving the test results and signed
by the appropriate qualified officer, or a prequalification test certificate issued by an
independent test laboratory shall be acceptable as evidence of prequalification testing.
Note 1: If the manufacturer so wishes then a transition joint can be included
in a full prequalification test to IEC 60840 or IEC 62067, in which case no
additional prequalification testing will be required. In this test the transition
joint must be placed in a rigid installation condition as this is generally the
most onerous.
Note 2: If suitable paper-insulated cable is unavailable, type testing will not
be possible, thus approval of a transition joint design is dependant on
agreement between manufacturer and customer, subject to consideration
of any relevant test data.
Note 3: In the event that breakdown occurs in the paper-insulated cable or
within the joint and the primary cause is attributable to the quality of the
paper-insulated cable then approval of a transition joint design is dependant
on agreement between manufacturer and customer, taking into account the
extent of tests passed and any other relevant test data.
8.9.2
Prequalification Test Arrangement
The minimum length of free cable between accessories shall be 5 m. One sample of
each transition joint type shall be tested.
The accessory shall be assembled on the cables in the manner specified by the
manufacturer’s instructions, with the grade and quantity of materials supplied,
including lubricants and insulating fluids if any. There should be provision for
measuring internal pressure of insulating fluid in the lapped cable compartment
during the test.
In units that are intended to operate with internal oil pressure, whether such
pressure is from the cable system or a separate source, the maximum pressure during
the test must not exceed the minimum design operating pressure +25%. If the
accessory includes a gas filled compartment then the gas pressure must be set so
that at 20 C the pressure is no greater than the minimal functional pressure for
insulation specified for the accessory +0,02 MPa.
If the prequalification of the transition joint is to qualify the joint for use both in
flexible and in rigid installations, the joint shall be installed in a rigid configuration.
Otherwise the joint shall be installed in a flexible configuration.
If the joint is installed for test in a rigid configuration, the manufacturer of the
joint shall consider the aspects of the design which might affect operation in a
flexible installation and subject to agreement between manufacturer and customer
the prequalification shall apply to both rigid and flexible installations.
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Neither the cables nor the accessories shall be subjected to any form of conditioning not specified in the manufacturer’s instructions which might modify the
electrical, thermal or mechanical performance.
8.9.3
Prequalification Test Procedure
8.9.3.1 Test Voltage Values
Test voltages shall be in accordance with the values given in the appropriate column
of Table 8.1. Prior to the prequalification tests of the transition joint, the insulation
thickness of the extruded cable used shall be measured and the test voltage values
adjusted, if necessary, as stated in IEC 60840 or IEC 62067. In case of difficulty in
achieving impulse and ac test voltages for paper cable the test values may be agreed
upon between manufacturer and customer.
Note: If suitable oil filled cable of the required insulation thickness is not
available then it is allowed to use a cable with a greater insulation thickness
and to reduce the insulation thickness in the region where the joint is to be
installed to the required level.
8.9.3.2 Tests and Sequence of Tests
The normal sequence of the prequalification tests shall be as follows:
• Installation of the transition joint which is subject to the prequalification on the
relevant cables.
• Heating cycle voltage test (see 8.9.3.3).
• Lightning impulse voltage test (see 8.9.3.4).
• Examination of the cable system with cable and accessories shall be carried out
after completion of the tests above (see 8.9.3.5).
8.9.3.3 Heating Cycle Voltage Test
Even though the extruded and oil filled cables may be of the same cross-section and
voltage it is likely that the thermal characteristics of the cables are very different.
Thus it is unlikely to be possible to heat the test assembly so that both cables achieve
their required temperature, using conductor current alone. It is thus acceptable to use
conductor current with the addition of heater tapes, thermal insulation or current
heating of the sheath of one or both of the cables in order to ensure that the required
temperatures are reached for both cables. See IEC 60840 or IEC 62067 for determination of actual cable conductor temperatures.
The assembly shall be heated until the cable conductors reach a steady temperature 0 K to 10 K above the maximum conductor temperature(s) in normal operation.
Note: If the conductor temperature exceeds the upper limit the test is still valid.
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Test Procedures for HV Transition Joints for Rated Voltages 30 kV up to. . .
385
The heating shall be applied for at least 8 h. The conductor temperatures shall be
maintained within the stated temperature limits for at least 2 h of each heating period.
This shall be followed by at least 16 h of natural cooling. The conductor current
during the last 2 h of each heating period shall be recorded.
The cycle of heating and cooling shall be carried out 180 times.
A voltage of 1.7Uo (see Table 8.1) shall be applied to the assembly during the
whole of the test period.
Interruption of the test is allowed provided 180 complete heating cycles in total
under voltage are completed.
Note 1: The test period is determined by the time required to complete
thermal cycles and will be a minimum of 180 days.
Note 2: Heating cycles with a conductor temperature higher than 10 K above
the maximum conductor temperature in normal operation are considered
valid.
Note 3: Partial discharge measurements are recommended to provide an
early warning of possible degradation and to enable the possibility of a
repair before failure.
8.9.3.4 Lightning Impulse Voltage Test
The assembly shall be heated as stated in the preceding section, until the cable
conductor reaches a steady temperature 0 K to 10 K above the maximum conductor
temperature in normal operation.
The conductor temperature shall be maintained within the stated temperature
limits for at least 2 h.
The lightning impulse voltage shall be applied according to the procedure given
in IEC 60230.
The assembly shall withstand without failure or flashover 10 positive and 10 negative voltage impulses of the appropriate value given in Table 8.1.
No breakdown of the insulation or flashover shall occur.
8.9.3.5 Examination
Examination of the transition joint, whenever possible, by dismantling, with normal
or corrected vision without magnification, shall reveal no signs of deterioration
which could affect the system in service operation (e.g. electrical degradation,
corrosion, harmful shrinkage or leakage, in particular across any seal separating
the extruded and oil filled cables).
8.10
Electrical Test after Installation
Tests on newly installed transition joints are carried out when the installation of the
cable and its accessories has been completed.
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M. Marelli
If required the new cable section with extruded insulation may be tested
separately according to its relevant standard before the transition joint is
installed.
The test voltages recommended for general use are given in Table 8.2, however
test regimes should be evaluated on an individual basis to take into account the
condition of an existing cable system.
A d.c. oversheath test according to clause 8.10.1 and an a.c. insulation test
according to clause 8.10.2 are recommended.
8.10.1 DC Voltage Test of the Oversheath
8.10.1.1 New Cable Section with Extruded Insulation
The voltage level and duration specified in clause 5 of IEC 60229 shall be applied
between each metal sheath or concentric wires or tapes and the ground.
8.10.1.2 Existing Cable Section (Paper-Insulated)
The voltage level and duration of the test should follow the local practice.
Note: Where it is required to test the oversheath of the two cable sections
separately it is recommended to install a sheath sectionalised transition joint.
8.10.2 AC Voltage Test of the Insulation
The a.c. test voltage to be applied shall be subject to agreement between the
purchaser and contractor. The waveform shall be substantially sinusoidal and the
frequency shall normally be between 20 Hz and 300 Hz. However if the capacitance
of the cable is such that this cannot be achieved, then subject to agreement between
purchaser and contractor, the minimum frequency may be reduced to 10 Hz. A
voltage according to Table 8.2 shall be applied for 1 h.
Note: For installations, which have been in use, lower voltages and/or
shorter durations may be used. Values should be determined, taking into
account the age, environment, history of breakdowns and the purpose of
carrying out the tests.
Alternatively, a voltage of Uo may be applied for 24 h.
In addition to the a.c. voltage test, partial discharge measurements may be carried
out, especially on the extruded cable part of the transition joint. The result should be
recorded for information and future reference.
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Test Procedures for HV Transition Joints for Rated Voltages 30 kV up to. . .
387
Table 8.2 AC Test Voltages after Installation
Rated voltage
(kV)
30–33
45–47
60–69
110–115
132–138
150–161
220–230
275–287
330–345
380–400
500
Value of U0
(kV)
18
26
36
64
76
87
127
160
190
220
290
Existing cable 5 years
(kV)
36 (2Uo)
52 (2Uo)
72 (2Uo)
128 (2Uo)
132 (1,73Uo)
150 (1,73Uo)
180 (1,4Uo)
210 (1,3Uo)
250 (1,3Uo)
260 (1,2Uo)
320 (1,1Uo)
Existing cable >5 years (see
note) (kV)
29 (1,6Uo)
42 (1,6Uo)
58 (1,6Uo)
103 (1,6Uo)
106 (1,4Uo)
122 (1,4Uo)
152 (1,2Uo)
192 (1,2Uo)
228 (1,2Uo)
260 (1,2Uo)
320 (1,1Uo)
Note: the threshold of 5 years is indicative only; test regimes should be evaluated on an individual
basis to take into account the condition of an existing cable system and local practices where these
exist
Appendix A Considerations for Transition Joints for Other Types
of Paper Cable
The main body of this document specifically addresses transition joints connecting
low pressure oil filled cables and extruded cables. The extruded cable types are those
covered by IEC 60840 and IEC 62067.
However three other main types of paper cable exist and are covered by IEC
60141 parts 2, 3 and 4. Specific differences which should be taken into account
when testing transition joints for use on these types of cables are given in this
Appendix.
A.1 Cables to IEC 60141-2: – Internal Gas-Pressure Cables and their
Accessories for Alternating Voltages up to 275 kV
Routine Test: – A hydraulic test as specified in the main body of this report should
be carried out. In addition a gas leak test is required for the casing on the paper cable
side of the joint at maximum operating pressure for 24 h. There shall be no leakage.
AC Test Voltages for Heating Cycle Voltage Tests: – Test voltages with heating
cycles are not specified in IEC 60141. The test voltages given in the main body of
this report may be used. However the manufacturer should consider the values to be
applied in relation to the known performance of the particular cable and adjust the
AC test voltages if appropriate.
Lightning Impulse Test and AC Voltage Test After Impulse Voltage Test: –
As specified in IEC 60141-2 the lightning impulse test voltage is calculated
according to the formula:
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• Test voltage ¼ 6Uo + 40 kV
and the AC test voltage according to:
• Test voltage ¼ 1,7Uo + 10 kV
This results in the following values reported in Table 8.3.
Note: These test voltages are lower than those specified in the main body of
this document.
After installation test: the test may be carried out at Uo for 24 h. If a one hour
AC test is proposed then the condition of the cable should be taken into account in
determining the voltage. Nevertheless the test voltage should not exceed the value
specified in Table 8.2 of the main document.
A.2 IEC 60141-3: – External Gas- Pressure (Gas Compression) Cables
and their Accessories for Alternating Voltages up to 275 kV
Routine Test: – A hydraulic test as specified in the main body of this report should
be carried out. In addition the following tests to IEC 60141-3 are required where
applicable:
• A gas leak test is required for the casing on the paper cable side of the joint, if it is
exposed to gas pressure in service, at maximum operating pressure for 24 h. There
shall be no leakage.
Table 8.3 Test Voltages, case of internal gas-pressure cables
1
Rated
voltage
U
kV
30–33
45–47
60–69
110–115
132–138
150–161
220 to 230
275 to 287
2
Highest
voltage for
equipment
Um
kV
36
52
72,5
123
145
170
245
300
3
Value of Uo for
determination of
test voltages
Uo
kV
18
26
36
64
76
87
127
160
8
Impulse voltage
test of 8.8.4.5
and 8.9.4.4
6Uo + 40
kV
148
196
256
424
496
562
802
1000
9
AC Voltage test after
impulse voltage test of
8.8.4.5 and 8.9.4.4
1,73Uo +10
kV
41
55
72
121
141
161
230
287
8
Test Procedures for HV Transition Joints for Rated Voltages 30 kV up to. . .
389
• If the accessory is subjected in normal service to small transient differences
between oil pressure and gas pressure then the interface between the oil and gas
regions shall be subjected to a gas pressure difference of 3 bar for 1 h. There shall
be no leakage.
AC Test Voltages For Heating Cycle Voltage Tests: – Test voltages with
heating cycles are not specified in IEC 60141. The test voltages given in the main
body of this report may be used. However the manufacturer should consider the
values to be applied in relation to the known performance of the particular cable and
adjust the AC test voltages if appropriate.
Lightning Impulse Test And AC Voltage Test After Impulse Voltage Test: –
As specified in IEC 60141-3 the lightning impulse test voltage is calculated
according to the formula:
• Test voltage ¼ 6Uo + 40 kV
and the AC test voltage according to:
• Test voltage ¼ 1,7Uo + 10 kV
This results in the following values reported in Table 8.4.
Note: These test voltages are lower than those specified in the main body of
this document.
After installation test: the test may be carried out at Uo for 24 h. If a one hour
AC test is proposed then the condition of the cable should be taken into account in
determining the voltage. Nevertheless the test voltage should not exceed the value
specified in Table 8.2 of the main document.
A.3 IEC 60141-4: – Oil-Impregnated Paper-Insulated High Pressure
Oil- Filled Pipe-Type Cables and their Accessories for Alternating
Voltages up to and Including 400 kV
Routine Test: – It is recommended that a hydraulic test in accordance with IEC
60141-1 is carried out on the fluid filled side of the transition joint. There shall be no
leakage.
AC Test Voltages For Heating Cycle Voltage Tests: – Test voltages with
heating cycles are not specified in IEC 60141. The test voltages given in the main
body of this report may be used. However the manufacturer should consider the
values to be applied in relation to the known performance of the particular cable and
adjust the AC test voltages if appropriate.
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Table 8.4 Test Voltages, case of external gas-pressure (gas compression) cables
1
Rated
voltage
U
kV
30–33
45–47
60–69
110–
115
132–
138
150–
161
220 to
230
275 to
287
2
Highest
voltage for
equipment
Um
kV
36
52
72,5
123
3
Value of Uo for
determination of
test voltages
Uo
kV
18
26
36
64
8
Impulse voltage
test of 8.8.4.5
and 8.9.4.4
6Uo + 40
kV
148
196
256
424
9
AC Voltage test after
impulse voltage test of
8.8.4.5 and 8.9.4.4
1,73Uo +10
kV
41
55
72
121
145
76
496
141
170
87
562
161
245
127
802
230
300
160
1000
287
Lightning Impulse Test And AC Voltage Test After Impulse Voltage Test: –
As specified in IEC 60141-4 the lightning impulse test voltage is defined by the
manufacturer of the cable. In practice the lightning impulse voltages given in
Table 8.2 of this report are those normally used. The value of test voltage given in
Table 8.2 for the AC voltage test after impulse voltage test is also recommended to
be used.
These values are recommended subject to agreement and consideration of the
condition of the cable used for the test.
After installation test: the test procedure as given in the main body of this
document is recommended.
Appendix B Design Features, Performance and Necessity
for Performing Type Tests for Transition Joints
Transition joints might be either of innovative design, in which case the full scale
development and type tests need to be performed or the joints might be constructed
of well known and type tested components, in which case development and type
tests are not necessary.
This Appendix is a general description of constructional principles of some
common types of transition joint (Cigré TB 89), with drawings and principal design
8
Test Procedures for HV Transition Joints for Rated Voltages 30 kV up to. . .
391
features and is meant to give a general understanding and guidance to those studying
this subject for the first time (See ▶ Chapter 1 of this book).
In the last section of this Appendix a methodology is described which may be
employed to assess the need for testing a particular new design.
B.1 Back-to-Back Transition Joint with Two Insulators
The transition joint as shown in Fig. 8.1 comprises either:
• Two GIS terminations in a common joint shell or
• Two oil immersed terminations in a common joint shell.
The terminations are in back-to-back arrangement and connected with a short
length of busbar. In the case of GIS terminations the joint shell is filled by insulating
gas (either with SF6 gas or mixture of SF6 gas and nitrogen). In the case of oil
immersed terminations either cable oil, transformer oil or other insulating oil is used.
Features
Extruded and paper cable terminations are identical to terminations used in either
SF6 switchgear or transformer applications and therefore further approval testing
should not be necessary.
Current carrying connection between two terminations may be specific to transition joint, in which case this may need separate evaluation.
The electrical field design in the central region may be specific to the transition
joint, however this may be assessed by electric field calculations if adequate test data
is available.
In the case of gas, a gas supply is required, and in case of oil the oil may be
connected to the cable oil system or alternatively a header tank of some type could be
used. Both systems would normally require some sort of fluid loss alarm.
Joint shell
Gas or liquid immersed terminations
Fixing flange
Insulated flange
End metalwork
Plumb
Insulator
Conductor stalk
Gas or insulating liquid
Connector
Corona shields
Fig. 8.1 Single phase back-to-back transition joint with (2) insulators
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In the case of oil immersed terminations the chamber required may be very large,
see EN 50299.
In special cases, the busbar connection can be designed so that the two cables may
be disconnected allowing independent high voltage commissioning tests on the two
cables.
B.2 Back-to-Back Transition Joint with One Insulator
Figure 8.2 shows example of the GIS or oil immersed type termination with rigid,
epoxy or porcelain, insulator on the paper-insulated cable side. The insulator anchors
cable conductors and centres the corona shield within the joint shell filled with
insulating fluid (SF6 gas, mixture of SF6 and nitrogen or insulating oil). The insulator
of the GIS/transformer termination is the barrier between insulating liquid of the
paper-insulated cable and the insulating oil of the joint shell.
The extruded cable end is terminated by a stress cone, which is directly immersed
in the insulating fluid of the joint. It is necessary to seal the strands and sheath of the
extruded cable conductor to prevent loss of insulating fluid.
The arrangement of the joint with the rigid insulator at the extruded cable side can
be utilized too. In this case the joint shell is filled with insulating liquid of the paper
cable and the stress cone of the paper cable is directly immersed into this liquid.
Features
The terminations with and without rigid insulator are identical to terminations
used in either SF6 switchgear or transformer applications.
Current carrying connection between two terminations may be specific to transition joint.
Corona shield (individual or collective) may be specific to transition joint.
An oil reservoir might be required to control thermal expansion/compression of
the insulating fluid.
Joint shell
Gas or liquid immersed terminations
Stress cone
Conductor seal
Fixing flange
Insulated flange
End metalwork
Plumb
Insulator
Gas or insulating liquid
Connector Corona shields
Conductor stalk
Fig. 8.2 Single phase back-to-back transition joint with one insulator
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Test Procedures for HV Transition Joints for Rated Voltages 30 kV up to. . .
393
B.3 Composite Type Transition Joint (Three-Core, Single Core)
The composite type transition joint shown in Fig. 8.3 features central barrier, usually
made of cast thermoset resin, which closely resembles the stop joint barrier
employed to segregate pressure between single core liquid-filled cables. The barrier
is cylindrical with an embedded metallic HV electrode, which is sealed to the
conductor connection to form a seal between the two sides of the joint.
The stress control on the paper cable is made of hand applied oil-impregnated
paper tapes or a combination of hand applied paper tapes and thermoset resin stress
cone. In the case of single core cables there is a channel at the connector to permit
insulating liquid from the cable conductor duct to be fed into the joint shell on the
paper cable side. For three core cables the oil feed comes directly from the core
separation position near the end of the cable sheath.
The extruded cable side of the transition joint is similar to a dry-type GIS
termination, the stress cone and springs normally being identical to those used in
GIS terminations. The elastomeric stress cone is sandwiched between the cable
insulation and central barrier and the interface pressures are maintained by the
springs.
Features
A common thermoset resin barrier with an embedded corona shield may be
specific for use in the transition joint.
The stress cone for the extruded cable may be identical to that used in dry-type
terminations.
The paper cable side may be identical to a stop joint in which case testing of the
stop joint will be applicable.
In the case of the extruded cable side, testing of similar dry type accessories may
be considered in conjunction with electrical stress calculations.
Oil or gas filled
paper cable
Fluid feed union
Paper insulation
Cast thermoset resin stress cone
Cast thermoset resin barrier
HV electrode
Ferrule
Polymeric extruded cables
Plumb
Plumb
Oil or gas
Joint shell
Insulated flange
Compression device
Semiconducting
elastomer
Insulated elastomer
Fig. 8.3 Single phase composite, fed-type transition joint
Elastomeric
moulded stress
cone
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M. Marelli
The current carrying connection between two cables may be specific to the
transition joint.
B.4 Single-Core or Three-Core Type with Bushing
The same electrical design applies to single or three core versions of this joint.
A central barrier plate with a single bushing or multiple bushings separates lapped
cable joint side from the side with extruded cable. The barrier and bushings that are
usually made of premoulded thermoset resin are designed to withstand operating and
test pressures required for the lapped cable.
The bushing is connected to the extruded cable in the form of extruded cable joint
that can be of various designs, such as taped insulation, premoulded elastomeric
body, heat shrink sleeve, etc. The joint on the paper cable side is usually insulated
with either impregnated plain or crepe paper tapes.
The joint shell on the paper cable side is filled with the insulating liquid of the
paper cable.
Features
Thermoset resin bushing may be similar to one used in stop joints.
On the paper cable side the design is usually identical to a stop joint and thus
previous testing of a stop joint may be applicable.
Interface of insulation with the bushing on the extruded side is specific to
transition joint, however standard premoulded components or taping methods may
be used.
The current carrying connection between the bushing and paper cable is usually the
same as in the stop joint. Likewise, current carrying connection between bushing and
extruded cable may be the same as the connection in extruded cable joint. In these
cases testing of these items will already have been carried out for the standard joints.
Electrical testing of a single core can be considered valid for three core designs,
only thermomechanical and pressure characteristics of the casings need to be
considered when moving from single to three core versions (Fig. 8.4).
Oil or gas filled cable
Paper insulation
Insulated conductor rod
Cast thermoset resin bushing
Insulation (tape etc.)
Polymeric extruded cables
Plumb
Plumb
Barrier plate
Oil or gas
Spacer
Joint shell
Fig. 8.4 Three-core transition joint with the bushing
Insulated flange
8
Test Procedures for HV Transition Joints for Rated Voltages 30 kV up to. . .
395
B.5 Methodology for Assessing Test Requirements
In assessing the need for type and/or prequalification tests it is first necessary to
consider the proposed design and to evaluate which parts of the accessory are similar
to established accessories or parts of established accessories (for example the oil
filled side of a transition joint might resemble an established stop joint). Then, based
on available knowledge or lack of knowledge of performance of the particular design
feature, the confidence in performance in certain test conditions should be evaluated.
This can be done by considering the range of service and related test conditions
which have to be met. The following table gives an example for this for a fictitious
design. The need for test can then be judged based on the number of entries on the
“Type Test Required” column.
Appendix C List of Type and Prequalification Tests of Cable
Systems
Type tests of transition joints are covered by paragraph 8.8 (Table 8.5).
Table 8.6 gives a summary and references for type testing of transition joints.
Prequalification tests of transition joints are covered by paragraph 8.9.
Table 8.7 gives a summary and references for prequalification testing of these
transition joints.
Appendix D Transition Joint Experience Data
Part of the terms of reference of WG B1-24 was to review the range of transition
joints currently available. To this end the WG has carried out a survey amongst its
members to investigate the types of transition joint used, their availability and
number in service in the members’ countries.
The results of this survey are presented in the following table (Table 8.8):
396
M. Marelli
Table 8.5 Example of evaluation of need for performing certain type tests of novel transition joint
Condition (examples –
others might be chosen in
practice)
PD initiation
Breakdown at AC
withstand voltage
Breakdown at DC
withstand voltage
Breakdown at impulse
withstand, at ambient
Breakdown at impulse
withstand, hot
Ionization initiation in
paper insulation
Confidence
Level
High Low
X
X
Type Test
Required?
Yes No
X
X
Reason for confidence-level rank &
remarks (typical comment shown as
an example)
X
X
Thermoset resin barrier is new
X
X
X
X
X
X
Voltage
breakdown in
oil (or gas) in
shell
Voltage
breakdown in
termination
Thermal
runaway of
centre
connector
Mechanical or thermal
failure during short-time
current test
X
X
X
X
X
X
X
X
Breakdown at AC
withstand voltage after
short-time current test
Mechanical or thermal
failure of ground
connections during shorttime current test
Voltage breakdown of the
shield break during load
cycling in water
Pressure and leak test
X
X
Load
cycling
Electrical stress in paper insulation
is influenced by the stress cone
design. Test is not required if PD
level is acceptable.
Thermoset resin barrier is new
Manufacturer to evaluate necessity
of performing these tests as
development tests based on past
experience.
X
X
Metallic shield restoration has been
individually tested
X
X
Jacket restoration and shield-break
have been individually tested
X
X
Material and dimensions of the shell
and the sealing system are critical for
pressure and leak test. No test is
required if previously tested on
similar design
8
Test Procedures for HV Transition Joints for Rated Voltages 30 kV up to. . .
397
Table 8.6 Type tests on transition joints
Item
a
b
c
d
e
f
g
h
i
j
k
l
Test
General
Range of type approval
Type test arrangement
Test voltage values
Tests and sequence of tests
Partial discharge measurements
Heating cycle voltage test
Switching impulse voltage test (for Um 300 kV)
Lightning impulse voltage test followed by power frequency voltage test
Leak test
Pressure test
Examination
Clauses
8.8.1
8.8.2
8.8.3
8.8.4.1
8.8.4.2
8.8.4.3
8.8.4.4
8.8.4.5.1
8.8.4.5.2
8.8.4.7.1
8.8.4.7.2
8.8.4.7
Table 8.7 Prequalification tests on transition joints
Item
a
b
c
d
e
e
f
Test
General and range of prequalification test approval
Prequalification test arrangement
Test voltage values
Tests and sequence of tests
Heating cycle voltage test
Lightning impulse voltage test
Examination
Clauses
8.9.1
8.9.2
8.9.3.1
8.9.3.2
8.9.3.3
8.9.3.4
8.9.3.5
Table 8.8
Yes
Yes
Yes
No
No
No
No
Yes
Yes
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
3C HP Gas to SC XLPE
SC LPOF to SC XLPE
3C LPOF to SC XLPE
3C IPG to 3C Pipe XLPE
3C GC to 3C Pipe XLPE
3C IPG Gas to SC XLPE
3C GC to SC XLPE
SC LPOF to SC XLPE
3C LPOF to SC XLPE
3C HP Gas to 3C Pipe XLPE
3C HP Gas to SC XLPE
3C MIND to SC XLPE
SC LPOF to SC XLPE/EPR
SC LPOF to SC XLPE
3C LPOF to SC XLPE
SC LPOF to SC XLPE
3C LPOF to 3 SC XLPE
3C MIND to 3 SC XLPE
SC LPOF to SC XLPE
3C LPOF to SC XLPE
SC LPOF to SC XLPE
3C LPOF to SC XLPE
SC IPG to SC XLPE
3C IPG to SC XLPE
SC LPOF to SC XLPE
3C HPOF to SC XLPE
3C IPG to SC XLPE
5
0
0
0
0
3
30
0
0
80
0
100
300
5
51
12
15
4
500
250
20
0
Unknown
Unknown
Unknown
1
0
0
0
0
0
0
0
No. in service
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
No
Yes
No
No
Yes
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
Yes
Yes
Yes
No
No
110-219kV
Available
5
7
2
40
40
0
1
2
1
0
27
30
0
51
0
0
10
0
65
75
30
0
10-20
20-30
<10
0
200
84
0
3
<25
0
0
No. in
service
0
0
0
6
13
3
No
0
Yes
3
(Back-to-back)
No
0
No
0
No
0
No
0
No
0
Yes
0
No
0
No
0
No
0
No
0
No
0
Yes
<10
No
0
No
0
No
0
No
0
No
0
No
0
Yes
0
No
0
No
0
No
0
No
0
No
0
No
0
No
No
Yes
Yes
Yes
Yes
220-314kV
AvailNo. in
service
able
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
Yes
No
No
No
No
No
No
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
No
0
No
0
Yes
0
No
0
No
0
Yes
6
(Back-to-back)
No
0
No
0
315-500kV
AvailNo. in
able
service
Note: Data were collected between January 2007 and November 2008 and were not updated during or after WG activity: those reported should be considered as “historical”
reference only
USA
UK
Sweden
Netherlands
Italy
Japan
Ireland
Germany
Yes
Yes
Yes
Yes
No
Yes
SC LPOF to SC XLPE
SC LPOF to SC XLPE
SC LPOF to SC XLPE
SC LPOF to SC XLPE
3C HPOF to SC XLPE
SC LPOF to SC XLPE
Australia
Belgium
Canada
China
France
30-109kV
Available
Type of Transition Joint
(SC = single core;
3C = 3 core)
Country
398
M. Marelli
8
Test Procedures for HV Transition Joints for Rated Voltages 30 kV up to. . .
399
Appendix E Terms of Reference for WG B1-24
Group No: WG B1.24
Name of Convener: Marco MARELLI (ITA)
TITLE of the Group: Test procedures for HV transition joints
Background:
Extruded cable is increasingly being used for transmission and distribution
circuits in preference to cables with lapped insulation. It is becoming more
common for a length of extruded cable to be introduced into a lapped cable
circuit, when the latter is repaired or diverted. International cable specifications
are generally written to cover a specific insulation technology e.g. IEC 60840
applies to cables with extruded insulation and their accessories. Applications
that involve cables with more than one insulation system are not usually
considered. The test regimes differ between lapped paper and extruded polymeric insulation; for example an AC after laying test might be used with
extruded cable and a DC test with paper cable.
Terms of Reference:
• To review the range of transition joints currently available
• To review the existing international standards and the extent to which they
cover the testing of transition joints
• Align voltage levels to those specified in IEC Standards for extruded cable
systems
• To propose test regimes for transition joints and their associated cables.
Type, routine, sample and after-laying tests should be considered
Scope of Work:
The WG should take into account ac cables and accessories for rated voltages
above 30 kV up to 500 kV. Transition joints in submarine or DC cable systems are
not considered. Priority should be given to jointing paper cables with extruded
cables, in particular SCFF cables and XLPE cables. All forms of testing should be
considered. Priority shall be given to after-laying and type tests.
Deliverables:
The WG should provide recommendations on type, routine, sample tests for
transition joints.
The WG should provide a recommendation on site testing of transition joints.
The WG will also provide an Electra article and a tutorial for presentation at
Cigré conferences and workshops.
Created: 2006, Duration: 3 years
Members: Australia, Belgium, Canada, China, Denmark, France, Germany, India, Ireland, Italy, Japan, Korea, The Netherlands, Sweden, United
Kingdom, United States.
Approval by TC Chairman: Klaus Frohlich
Date: Nov. 12, 2006
400
M. Marelli
References
Cigré Electra no. 176, February 1998 Diagnostic Methods for HV Paper Cables and Accessories
Cigré Paper B1-301 Qualification of transition joint between oil – filled paper insulated cable and
XLPE insulated cable for the 150 kV Belgian network (Liemans, D., Mella, J., Gille, A.,
Szczepanski, C., Mampaey, B.) (2008)
Cigré Paper B1-303 HV-EHV transition joints: a solution to optimize the cable route (Courset, L.,
Hondaa, P., Argaut, P., Bénard, L., Mirebeau, P.) (2008)
Cigré TB 279 Maintenance for HV Cables and Accessories
Cigré TB 303 Revision of Qualification Procedures for HV and EHV AC Extruded Underground
Cable Systems (Chapter 4 of this book)
Cigré TB 89 Accessories for HV Extruded Cables (Chapter 1 of this book)
IEE Conference Publication No. 382, Page 267 The HV transition joints (Gahungu, F., Francois, D.,
Darcy, A., Becker, J., Brouet, J., Couturier, J., Mella, J.) (1993)
IEEE 404–2006 Extruded and Laminated Dielectric Shielded Cable Joints Rated 2500 V to 500000 V
IEEE 48–1996 Standard Test Procedures and Requirements for Alternating-Current Cable Terminations 2.5 kV Through 765 kV
JICABLE Paper A.5.3 A range of transition joints for 33 kV to 132 kV polymeric cables (Attwood,
J., Gregory, B., Svoma, R.) (1991)
JICABLE Paper C.5.1.14 Compact transition joints for up 154 kV Power cable (Niinobe, H.,
Yokoyama, S., Toraki, Y., Kaneko, S.) (2007)
JICABLE Paper C.5.1.15 Upgrading quality of 275 kV Y-branch pre-fabricated transition joints
(Nakanishi, T.) (2007)
Marco Marelli has a Master’s degree in Electrical Engineering.
He developed his career in Prysmian where he is currently Head of
System Engineering in the Projects BU, with responsibilities on
power and telecommunication cable systems. His expertise covers
in particular HV/EHV and Submarine Cable Systems, both AC
and DC. He spent indeed more than 20 years doing design and
engineering works for large projects worldwide including some of
those recognized as milestones in the cable industry. His work
within Cigré as SC B1 Member, Convener of Working Groups,
and Special Reporter at the General Session has been recognized
with the “TC Award” in 2010 and the “Distinguished Member
Award” in 2012. He is author of several papers and has been part
of several technical and scientific committees. Since August 2016,
Marco is the Chairperson of Cigré Study Committee B1 “Insulated
Cables.”
9
Thermal Ratings of HV Cable Accessories
Henk Geene and Reinhard Schroth
Contents
9.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.3 Thermal Ratings of Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.3.1 Basic Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.3.2 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.4 Thermo-mechanical Ratings of Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.4.1 Basic Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.4.2 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.5 Systems Design Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.5.1 Thermal Ratings of Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.5.2 Thermo-mechanical Ratings of Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Annexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Annex 1. Thermal Calculations in HV and EHV Cables and Joints . . . . . . . . . . . . . . . . . . . . . . . . . . .
Example 1: Dynamic Temperature Calculations in a 132 kV Cable and Joint . . . . . . . . . . . .
Example 2: Thermal Behavior of a 400 kV Joint during IEC Loading Cycles in Air . . . .
Annex 2. Overview of International Standards on Thermal Aspects of Accessories
(as a Result of a Questionnaire under the Members of the Task Force) . . . . . . . . . . . . . . . . . . . . . . .
Annex 3. Guide to Aid Development Engineers for Testing the Thermal Properties
of Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
402
402
403
403
404
405
405
406
406
406
406
407
408
408
408
410
412
415
415
Reinhard Schroth has retired.
This work from TF 21.10 has been introduced in Electra 212 (February 2004). This Chapter is the
final report of the Task Force
H. Geene (*)
Prysmian Group, Product Management HV Accessories, The Hague Area, Netherlands
e-mail: henk.geene@prysmiangroup.com
R. Schroth
Berlin, Germany
e-mail: reinhard.schroth@gmx.de
© Springer Nature Switzerland AG 2021
P. Argaut (ed.), Accessories for HV and EHV Extruded Cables, CIGRE Green Books,
https://doi.org/10.1007/978-3-030-39466-0_9
401
402
H. Geene and R. Schroth
Test Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415
Thermal Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Annex 4. Guide to Aid Design Engineers in the Correct Design of Systems: Thermal
and Thermo-mechanical Aspects of Accessory Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cable Systems: Way of Laying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Rigid Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flexible Systems: Cable Horizontally Snaked or Vertically Waved . . . . . . . . . . . . . . . . . . . . . . .
Semi-flexible Systems: Cable Constrained . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.1
416
416
416
416
416
417
417
417
417
Summary
On request of IEC TC 20 a Task Force TF 21(B1)-10 was launched by SC 21 in 2001
with the scope to review whether or not existing HV cable test specifications would
appropriately specify and verify the crucial thermal and thermo-mechanical characteristics of accessories. TF B1-10 finished its work on schedule in 2003 with the
following conclusions:
• Thermal ratings of accessories need not be specified separately from cables, as
they are considered identical due to the presence of cable inside the accessory.
• The successful completion of IEC thermal tests at a complete cable system can be
considered as simultaneous verification of the adequate thermal design of both,
cables and accessories, provided that comparable or higher conductor temperatures as rated for the cable are achieved inside joints. These test conditions shall
be realized by applying only cable conductor current heating.
• The thermal performance of terminations in normal operation is not considered
critical; therefore they do not have to reach the rated temperature for the cable
during test.
• External thermo-mechanical forces can be reproduced in the IEC prequalification
test only for the specific installation conditions applied.
• The thermal limits of accessories and external thermo-mechanical forces in service
operation cannot be reproduced comprehensively by standardized tests, but have to
be taken into account for each individual case by the systems design engineering.
The abstract of the work was published in Electra No 212 February 2004.
9.2
Introduction
It is common practice to base the calculation of the current carrying capacity of
HV/EHV underground transmission lines on the thermal ratings of the cable, taking
into account the losses in the cable and the heat transfer to its environment.
9
Thermal Ratings of HV Cable Accessories
403
International standards as IEC specifications 60840 Ed.3 and 62067 Ed.1 have
defined the thermal ratings of extruded HV/EHV cables by their maximum cable
conductor temperatures for different insulations. The thermal ratings of accessories
are not explicitly mentioned as they were generally considered to have equal or
better levels than those of the cable.
Questions have been raised, whether and how the thermal and thermo-mechanical
ratings of accessories, i.e. terminations and joints, should be defined and how these
should be taken into account in the design of cable systems.
In 2001 a Task Force TF 21-10 was established with the following scope:
• To specify the terms “thermal and thermo-mechanical ratings” of accessories
• To review existing test specifications with regard to appropriate verification of
thermal and thermo-mechanical performance of accessories
• To consider, if applicable, improved or new test procedures for thermal and
thermo-mechanical verification of accessories
• To prepare recommendations to IEC, whether and how specific thermal and
thermo-mechanical tests should be combined with and/or integrated into existing
test specifications for extruded HV and EHV cables (e.g. IEC 60840 Ed.3 and IEC
62067 Ed.1)
• To prepare guidelines how to apply the findings of basic laboratory tests to the
multitude of practical configurations.
9.3
Thermal Ratings of Accessories
The thermal rating of an accessory is defined as “the maximum temperature of the
conductor or conductor connector contained within the accessory (whichever is the
higher) allowed in normal operation”.
9.3.1
Basic Considerations
• Thermal ratings of extruded HV/EHV cables are defined in IEC specifications
60840 and 62067 Ed. 1by maximum cable conductor temperatures for different
insulations.
• Thermal ratings of accessories are not explicitly mentioned as they were generally
considered to have equal or better thermal ratings than those of the cable.
• Thermal aspects are verified in IEC specifications by heating cycle voltage tests
and by prequalification tests on complete EHV cable systems (cable +
accessories).
• The heating current in the test loop is defined by the maximum temperature in the
cable conductor remote from the accessories.
• Thermal designs of accessories are extremely diverse and within the responsibility of each manufacturer.
404
H. Geene and R. Schroth
• Terminations installed in normal conditions are not considered as a hot spot for
the cable due to more effective heat transfer to the environment (e.g. air circulation for outdoor terminations, axial conductor heat transfer in GIS and transformer terminations).
• In steady state test conditions (i.e. when a single cable is installed in air in a test
loop) joints will develop higher conductor temperatures than the remote cable,
due to their larger dimensions (Annex 1).
• Longer thermal time constants for joints may result in lower conductor temperature in the first part of a heating period than for the cable, but higher temperatures
at the end of the heating period, followed by delayed cooling after disconnecting
the current (Annex 1).
• Depending on the time constants and duration of the cooling period, joints may
not cool down completely to the ambient temperature, resulting in a gradual
increase of conductor temperatures in subsequent cycles (Annex 1).
• Additional thermal insulation may extend the thermal time constant for the cable.
• Most existing standards require current heating for cable and accessories
(Annex 2).
9.3.2
Conclusions
• Thermal ratings of accessories need not be specified separately from cables, as
they are considered identical due to the presence of cable inside the accessory.
• Common test specifications can only assess the basic thermal performance of
accessories, rather than compliance with rated cable conductor temperatures.
• Many joints have worse heat dissipation characteristics than cables, thus developing during thermal IEC tests higher internal conductor temperatures than the
remote cables.
• Higher than rated conductor (insulation) temperatures are not allowed inside
accessories during service operation.
• For type/prequalification tests it is acceptable for maximum temperature in
accessories to be higher than in the cable. The successful completion of IEC
thermal tests on a complete cable system can be considered as simultaneous
verification of the adequate thermal design of both cables and accessories,
provided that comparable or higher conductor temperatures as rated for the
cable are achieved inside joints.
• The thermal performance of terminations in normal operation is not considered
critical; therefore they do not have to reach the rated temperature for the cable
during test.
• Conductor heating by means of current should be applied during type and
prequalification tests. No external means of heating or sheath current heating
should be applied, as this will tend to reduce the conductor temperature within a
joint in comparison to the temperature of the remote cable conductor.
• Some cable systems with additional thermal insulation may require extended
heating (and cooling) cycles.
9
Thermal Ratings of HV Cable Accessories
9.4
405
Thermo-mechanical Ratings of Accessories
The thermo-mechanical rating of an accessory is defined as “the ability of the
accessory to withstand mechanical forces, which are developed due to operation of
the accessory and associated cable at the maximum temperature allowed in normal
operation. The forces are internal and external. Only the level of external forces is
specified, being symmetrical and asymmetrical conductor forces (arising from the
connected cables)” (Fig. 9.1).
9.4.1
Basic Considerations
Thermo-mechanical ratings of accessories are neither mentioned nor explicitly
specified in IEC specifications. Thermo-mechanical forces in accessories can originate from:
• Components inside the accessories: internal forces.
• External sources, mainly cable: external forces.
• Internal thermo-mechanical forces (expansion, retraction, pressure etc.) are
reproduced in actual thermal IEC tests, provided that maximum (rated) conductor
temperatures (cycles) are adequately achieved.
• External thermo-mechanical forces on accessories are induced by external components and their installation. Depending on the test arrangements used, specific
external thermo-mechanical forces can be reproduced by IEC prequalification
tests. These, however, cannot be representative for the complete variety of
possible service installations.
• The definition of the mechanical withstand strength of each individual accessory
against external forces is with the manufacturer.
Fig. 9.1 Measurement of
thermo-mechanical forces
406
H. Geene and R. Schroth
This strength is determined by “mechanical” components such as insulators,
anchor joint casings, etc.
• It is considered sufficient to verify the adequate mechanical strength of such
components by separate certificates rather than testing of complete accessories.
9.4.2
Conclusions
• Internal thermo-mechanical forces can adequately be verified by thermal IEC
tests, provided that maximum conductor temperatures are adequately achieved.
• External (thermo-) mechanical forces, in special installation conditions, cannot be
reproduced comprehensively in standardized tests.
• Maximum admissible symmetrical and/or asymmetrical forces are indicated by
accessories manufacturers and attested by certificates rather than verified at
complete individual accessories.
• Thermo-mechanical ratings of accessories need not be specified explicitly in IEC
specifications, but left as a subject of agreement between customer and
manufacturer.
9.5
Systems Design Aspects
9.5.1
Thermal Ratings of Accessories
Thermal limits of accessories in service operation, (i.e. obeying maximum rated
cable conductor temperatures in accessories too) have to be secured by systems
design engineering taking into account:
• The accessory’s basic thermal characteristics provided by the manufacturer
(Annex 3).
• Appropriate installations such as wider phase spacing (Fig. 9.2), special backfill,
ventilation of manholes, etc. (Annex 4).
• Severe environmental conditions for terminations (e.g. hot climates, transformer
terminations in hot oil).
9.5.2
Thermo-mechanical Ratings of Accessories
External thermo-mechanical (and other mechanical) forces on accessories have to be
considered by systems design engineering taking into account:
• The value of admissible mechanical forces acting on the accessory, to be provided
by the accessory’s supplier.
9
Thermal Ratings of HV Cable Accessories
407
Fig. 9.2 Joints in manholes,
installed with wider spacing
• The thermo-mechanical characteristics (e.g. bending moments, allowable thrust)
of the cables involved, to be provided by the cable’s supplier.
• The actual installation conditions (Annex 4).
9.6
Conclusions
Thermal ratings of accessories need not be specified separately from cables, as they
are considered identical due to the presence of cable inside the accessory.
The thermal performance of terminations in normal operation is not to be
considered critical; therefore they do not have to reach the rated temperature for
the cable during test.
The successful completion of IEC thermal tests at the complete cable
system can be considered as simultaneous verification of the adequate thermal
design of both, cables and accessories, provided that comparable or higher
conductor temperatures as rated for the cable are achieved inside joints. These
test conditions will be achieved by applying cable conductor current heating
only.
For the heating of cables and accessories during type test, the following clause is
recommended to IEC:
For IEC 62067 Ed.1 clause 12.4.7 becomes:
The cable shall have a U-bend with a diameter as specified in 12.4.4.
The assembly shall be heated by conductor current until the cable conductor
reaches a steady temperature 5 C to 10 C above the maximum conductor temperature in normal operation. No additional external heating or heating by sheath
current shall be allowed. If for practical reasons the test temperature cannot be
reached, additional thermal insulation can be applied, which then must be described
in the test report.
408
H. Geene and R. Schroth
The heating shall be applied for at least 8 h. The conductor temperature shall be
maintained within the stated temperature limits for at least 2 h of each heating
period. This shall be followed by at least 16 h of natural cooling to a conductor
temperature within 15 C of ambient temperature, with a maximum of 45 C. The
conductor current during the last 2 h of each heating period shall be recorded.
The cycle of heating and cooling shall be carried out 20 times.
In the case of IEC60840/Ed3/CDV clause 12.3.6:
The same wording is recommended as given above except that “12.4.4” is
changed to “12.3.3” and “within 15 C of ambient” is replaced by “within 10 C
of ambient” in accordance with the existing wording.
For the Impulse voltage test and “hot” partial discharge test, the same method of
heating shall be applied.
External (thermo-) mechanical forces in normal installation condition may be
reproduced in the prequalification test for EHV systems. However, external
(thermo-) mechanical (and other mechanical) forces, in special installation conditions, cannot be reproduced comprehensively in standardized tests and should therefore be considered by systems design engineering.
Completely new generation of accessories (e.g. dry outdoor terminations) might
need further considerations, regarding thermal and thermomechanical aspects.
Annexes
1. Thermal calculations in HV and EHV cables and joints
Example 1: dynamic temperature calculations in a 132 kV cable and joint
Example 2: thermal behavior of a 400 kV joint during IEC loading cycles in air
2. Overview of international standards on thermal aspects of accessories
3. Guide to aid development engineers for testing the thermal properties of joints
4. Guide to aid design engineers in the correct design of systems: thermal and
thermo-mechanical aspects of accessory performance
Annex 1. Thermal Calculations in HV and EHV Cables and Joints
Example 1: Dynamic Temperature Calculations in a 132 kV Cable
and Joint
Joints and cables have different thermal properties. The basic differences can be
expressed in:
• Thermal resistances
• Thermal time constants
9
Thermal Ratings of HV Cable Accessories
409
Model for calculations
2m
Φa
Φa
Φr
Φr
Tj
Tc
Tc
Tc: conductor temperature in the cable
Tj: connector temperature in the joint
Φr: radial heat flow
Φa: axial heat flow.
To verify the differences in the joint and cable temperature during one heating
cycle, dynamical calculations were made for an 800mm2 132 kV XLPE cable.
First, the heating current is calculated to obtain a stable cable conductor temperature of 95 C. Based on the heating current, the temperature was calculated inside
the joint and cable for a period of 10 h after switching on the current. The results are
given in Fig. 9.3 at a conductor heating current of 1800A.
110
100
Temperature (°C)
90
80
70
60
50
40
30
20
10
0
0
1
2
3
4
5
6
7
Time (hours)
Joint
Cable
Fig. 9.3 Typical heating curve of a 132 kV 800 mm2 Cu cable and joint
8
9
10
410
H. Geene and R. Schroth
Conclusion
In stationary conditions, the joint reached a higher temperature than the cable, as a
result of higher thermal resistance of the joint. In the first 6 hours of the heating
cycle, the temperature in the joint is lower than in the cable due to the longer thermal
time constant of the joint.
Example 2: Thermal Behavior of a 400 kV Joint during IEC Loading
Cycles in Air
Introduction
In order to evaluate the temperature difference between a 400 kV cable and the
relevant premoulded joint during the heating cycle voltage test, specified in IEC
60840 Ed. 3 and 62067 Ed.1, thermal calculations have been carried out using the
finite element method.
The test loop assumed for the calculation is installed in air and includes 20 m of
cable and a 400 kV premoulded joint complete with its anticorrosion protection. The
length of cable is such that the presence of the joint does not affect the asymptotic
temperature of the cable.
Due to the use of the FEM method, the joint is subdivided in finite elements where
both radial and longitudinal heat transmission is taken into account.
During the heating cycle test the cable conductor is heated by conductor current in
order to reach in 6 hours a conductor temperature of 95 C (far from the joint),
followed by 2 hours where the current is reduced in order to maintain the cable
conductor temperature between 95 C and 100 C, then the current is switched off
for 16 hours still maintaining the voltage on. This cycle under constant voltage of
2 Uo is repeated for 20 times. The calculation has been made for 400 kV XLPE
cables with a 1600 mm2 and a 2500 mm2 copper conductor. Both conductor losses
and dielectric losses have been considered in the calculation.
Loading Cycle Temperature Profile Calculation
2500 mm2 Cu 400 kV cable and joint
During the loading cycles a constant current of about 3450 A is circulated in the
conductor, so that a temperature of 95 C is reached in the cable conductor after
6 hours, starting from a uniform ambient temperature of 20 C. Then the current is
reduced in order to maintain the temperature in the cable conductor between 95 C
and 100 C for 2 hours. Subsequently the conductor current is switched off for
16 hours.
The results of the calculations of the cable and joint daily cycles are shown in
Fig. 9.4.
It can be observed that initially the joint ferrule temperature is slightly lower
than 95 C, then it increases and reaches a stable value of about 101 C after four
cycles.
9
Thermal Ratings of HV Cable Accessories
411
110
100
Temperature (°C)
90
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
80
90
100
Time (hours)
Joint
Cable
Fig. 9.4 Loading cycles (8 hours on, 16 hours off) on a 400 kV 2500 mm2 Cu cable and joint
110
100
Temperature (°C)
90
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
80
90
100
Time (hours)
Joint
Cable
Fig. 9.5 Loading cycles (8 hours on, 16 hours off) on a 400 kV 2500 mm2 Cu cable and joint
1600 mm2 Cu 400 kV Cable and Joint
The initial conductor current in order to bring the cable conductor temperature to
95 C after 6 hours (including dielectric losses) is of about 2500 A. The results of the
joint and cable load cycle calculation are shown in Fig. 9.5.
412
H. Geene and R. Schroth
It can be observed that the temperature of the joint has the same behavior as in
Fig. 9.4, i.e. the periodic asymptotic temperature in the joint is reached after 4 cycles,
but its value is a little smaller (99 C instead of 101 C).
Conclusions
During IEC loading cycles, with only conductor current heating, the joint ferrule
temperature of a 400 kV joint follows the cable conductor temperature with a certain
delay due to the higher thermal time constant of the joint compared to the cable.
However, after about 4 cycles also the joint reaches stable periodic conditions
with a maximum temperature generally slightly higher than that of the cable
conductor.
These conclusions depend on the design of the joint. Joints longer than the one
considered in these calculations or with thicker insulation would present a higher
time constant, so that stable cycle conditions for the joint would be reached after
more than 4 cycles, but certainly within the 20 IEC cycles.
The higher periodic temperature in the joint is also due to the fact that, during the
type test, the joint is provided with the thick outer protection foreseen for the
underground installation (as in the case of these calculations), while for actual
installations in air the casing is normally unprotected.
Annex 2. Overview of International Standards on Thermal Aspects
of Accessories (as a Result of a Questionnaire under
the Members of the Task Force)
Standards, relevant statements on thermal ratings and testing of accessories
Standard
Contents and comments
BS 7912 (UK)
BS 7912 (Implementation of HD 632): the method for heat cycling
assemblies containing accessories is “The assembly shall be heated until the
cable conductor reaches a steady temperature 5 C to 10 C above the
maximum conductor temperature in normal operation. The heating
arrangements shall be selected so that the cable conductor attains the
temperature specified in this sub clause, remote from the accessories and as far
as practicable, also within the accessories.”
EATS 09-16
EATS 09-16 is the more widely used document which effectively expands on
(UK)
the requirements of the above BS. The latest revision of this, which is still in
draft form at the time of the publication of this report, states:
“The load cycle test shall be carried out as in clause 16.4 of BS 7912 except
that the details of heating given in the last two sentences (i.e. the 2 sentences
quoted from BS 7912 above) shall be replaced by the following:
The heating arrangements shall be selected so that the cable conductor attains
the temperature specified above, remote from the accessories, and as far as
practicable, the conductor temperature in accessories shall reach at least the
rated temperature of the accessory plus 5 C to 10 C.
The rated temperature of the accessory shall have been declared previously by
the supplier (the value shall be no lower than the maximum cable conductor
temperature in normal operation).
(continued)
9
Thermal Ratings of HV Cable Accessories
413
Standards, relevant statements on thermal ratings and testing of accessories
Standard
Contents and comments
NEN 3629
(Netherlands)
IEEE 48-1990
(USA)
IEEE
404-1993
(USA)
Alternatively, the test installation shall be heated by conductor current alone,
until the cable conductor remote from the accessories reaches a steady
temperature of 5 C to 10 C above the maximum cable conductor temperature
in normal operation. No thermal insulation or means of cooling or further
forms of heating shall be used.”
Thermal properties
According to this standard, in normal operation a conductor temperature of
max 90 C and during short-circuit (duration max 5 sec) of 250 C is
acceptable acceptable.
Heating cycle voltage test with 30 cycles.
IEEE standard test procedures and requirements for high-voltage alternatingcurrent cable terminations
4. Rating
Note: regarding the continuous current rating (ampacity). The application of
various types of cable terminations requires engineering consideration as to
the ampacity of the completed installation. A cable termination by itself
cannot be assigned a design or nominal current or ampacity rating since this
parameter is completely dependent upon the type of cable insulation, the
maximum allowable cable conductor temperature for the type of cable
insulation involved, and the anticipated maximum ambient temperature of the
medium surrounding the termination...
The supplier of cable terminating devices or material should be consulted for
the ampacity of the design for the intended application with specific type and
size of cable.
7.4.2 Cyclic aging test
(Conductor heating is required. There shall be no current in the cable metallic
shield.)
7.4.2.3
During the current-on period, the cable conductor temperature midway
between the terminations shall be within 5 C of the cable’s maximum rated
emergency operating temperature for a period of 6 h.
Note: the cyclic aging test is not intended to establish current rating for a
termination (see Sect. 9.4. Rating)
IEEE standard for cable joints for use with extruded dielectric cable rated
5000–138000 V and cable joints for use with laminated dielectric cable rated
2500–50000 V
4.2 Unusual service conditions
The manufactures should be consulted for recommendations.
5.2 Current ratings
The current rating of the cable joint shall be equal to or greater than the current
rating of the cables for which the cable joint is designed.
5.3 Temperature limitations
The joint shall be designed for operating with the conductor and connector within
the joint at the same maximum temperature limitations as those for the conductors
of the cables being joined.
7.7 Cyclic aging test for extruded dielectric and transition joints
7.7.2 Extruded cable joints rated 46–138 kV
(Joints are tested in water and dry. Conductor heating is required.)
There shall be no current in the cable metallic shield.
The following information shall be recorded in the test report:
(continued)
414
H. Geene and R. Schroth
Standards, relevant statements on thermal ratings and testing of accessories
Standard
Contents and comments
SEN 24 14
34 (Sweden)
SS 424 14 17
(Sweden)
NF C 33-061
September
1999 (France)
NF C 33-062
September
1999 (France)
a) The maximum temperature of the outside of the joint housing in water
b) The maximum temperature of the outside of the joint housing in air
c) The temperature of the outside surface of the cable in air
The temperature at which the joint is qualified
Joints and terminations, rated voltage 1–420 kV. Testing
Valid since May 1977. Expired 1998. Not replaced by any other Swedish
standards.
“...type tests shall be carried out with the largest size of cable conductor...”
“...shall be loaded with the highest permissible current...and sufficiently long
time to reach temperature equilibrium”.
“The rise...must not assume values that can damage the materials used, or
endanger the environment (fire risk).”
“Cyclic load tests...shall be carried out on terminations...criteria in the cable
standard shall then apply.”
“Testing of a complete cable joint...shall be carried out in accordance with
the...cable”
Power cables – XLPE-insulated cables with extruded over sheath and rated
voltage 12–420 kV – Testing Load cycling:
Conductor temperature: 100–105 C. Achieved by a suitable method
(no specifications)
Heating during at least 8 h and natural cooling during at least 16 h. The
conductor temperature shall be between 100 C and 105 C during the last 2 h
of the heating period.
Insulated cables and their accessories
§ 6 Type tests:
for power systems.
“...In case of temperature of the
Joints for single-core cables with
conductor is specified, its value
polymeric extruded insulation for rated shall be obtained by circulation of
voltages above 30 kV (Um ¼ 36 kV)
adequate current in the cable
up to 500 kV (Um ¼ 525 kV)
conductor”
“For tests requiring an increase of
Insulated cables and their accessories
the cable conductor temperature,
for power systems
this temperature can be obtained, if
SF6 insulated metal enclosed
necessary, by thermal insulation of
terminations for single-core cables
with polymeric extruded insulation for the cable, in order not to induce a
current ampacity either too high or
rated voltages above 30 kV
too low, non representative of
(Um ¼ 36 kV) up to 500 kV
normal operation.”
(Um ¼ 525 kV)
Long term test:
Thermal cycles:
Cycle time: 8 h of heating and 16 h
of cooling. Current applied to raise
the conductor to a temperature up
to 0 C to 10 C higher than the
maximum normal operating
temperature, for the first
167 cycles and up to 0 C to 5 C
higher than the maximum
emergency overload temperature,
during the remaining 83 cycles.
(continued)
9
Thermal Ratings of HV Cable Accessories
415
Standards, relevant statements on thermal ratings and testing of accessories
Standard
Contents and comments
NF C 33-063
Insulated cables and their accessories for power systems
September
Outdoor terminations, with porcelain insulator, for single-core cables with
1999 (France)
polymeric extruded insulation for rated voltages above 30 kV (Um ¼ 36 kV)
up to 500 kV (Um ¼ 525 kV)
NF C 33-064
Insulated cables and their accessories for power systems
September
Indoor or outdoor polymeric terminations, without porcelain insulator
1999 (France)
for single-core cables with polymeric extruded insulation for rated voltages
above 30 kV (Um ¼ 36 kV) up to 150 kV (Um ¼ 170 kV)
§ 6 Type tests: idem above.
C 33-065
Insulated cables and their accessories
Long term test
February 2001 for power systems
Thermal cycles:
(France)
Self supporting outdoor polymeric
Cycle time: 8 h of heating and 16 h
terminations or terminations with a
of cooling.
composite housing, without
Current applied to raise the
porcelain insulator for single-core
conductor to a temperature up to
cables with polymeric extruded
10 C higher than the maximum
insulation for rated voltages above
normal operating temperature
150 kV (Um ¼ 170 kV) up to 500 kV
(Um ¼ 550 kV)
with a tolerance of +/4 C
Annex 3. Guide to Aid Development Engineers for Testing
the Thermal Properties of Joints
Introduction
The aim of the guide is to give the development engineer some recommendations on
how to measure the thermal characteristics of a prefabricated joint in transient and
steady state conditions.
Test Installation
The test loop has to contain at least 15 m of cable and one joint. The distance
between the joint and cable ends has to be at least 5 m. No direct contact of the cable
or joint with the lab floor is allowed. It is important that cable and joint should be
subjected to the same thermal ambient conditions. No additional thermal insulation
should be applied.
Thermocouples (or other temperature sensors) should be installed in the following positions:
• At the cable, at least 5 m from the joint and 5 m from the cable end,
– On the conductor
– On the metallic sheath
– On plastic outer sheath
416
H. Geene and R. Schroth
• At the joint in the middle,
– On connector in the joint
– On metallic casing or metallic screen
– On insulating cover
• Near to the test loop to record the ambient temperature.
Thermal Test
The heating current shall be applied for at least 24 h until the cable conductor, remote
from the accessories, reaches a steady temperature of at least 5 C above the
maximum conductor temperature in normal operation for the cable. During the
entire heating period, the temperatures shall be recorded. No other means than
current heating shall be used.
Test Results
From the recorded heating curves the following characteristics can be calculated:
• The thermal resistance between conductor and outer covering of the joint
(deduced from the ratio between the steady state temperatures)
• The thermal resistance between the conductor and outer covering of the cable
(deduced from the ratio between the steady state temperatures)
• Thermal time constant of the cable
• Thermal time constant of the joint.
Annex 4. Guide to Aid Design Engineers in the Correct Design
of Systems: Thermal and Thermo-mechanical Aspects
of Accessory Performance
Introduction
The aim of the guide is to give the design engineer some recommendations regarding
important thermal and thermo-mechanical characteristics to check on accessories.
When possible or appropriate, the guide indicates the way to control or measure
the described characteristics.
References
This guide has been established taking into account the recommendations and
guidelines included in the following documents:
Cigré WG 21-09: Electra No. 140, February 1992
Considerations of ageing factors in extruded insulation cables
Cigré WG 21-17: TB 194, October 2001 Construction, laying and installation
techniques for extruded and self contained fluid filled cable
systems
9
Thermal Ratings of HV Cable Accessories
Cigré WG 21-06:
417
TB 177, February 2001 Accessories for HV cables with
extruded insulation, Sect. 2: A guide to the selection of
accessories (▶ Chap. 2, “ A Guide to the Selection of
Accessories” of this book).
Cable Systems: Way of Laying
Thermal and thermo-mechanical properties of accessories are directly linked to the
way of laying of the cable they equip.
Cables can be laid in the following environments, which are classified as rigid,
flexible or semi-flexible systems. Induced thermo-mechanical thrust on accessories
depends strongly of this classification as described more precisely in the Cigré TB
published by WG 21-17 (TB 194).
Rigid Systems
•
•
•
•
Laid direct and buried in ground
Troughs
Tower/shaft (close cleats)
Jointing chamber (close cleats).
Flexible Systems: Cable Horizontally Snaked or Vertically Waved
•
•
•
•
Tunnel
Above ground
Tower/shaft
Jointing chamber.
Semi-flexible Systems: Cable Constrained
• Bridge
• Unfilled ducts.
The cable system including the accessories has to sustain any of the thermal or
thermo-mechanical constraints, which could happen under:
• Normal operation
• Transient operation: Short-circuit (phase to phase or phase to earth)
• Overload
• Earthquake.
Table 9.1 summarises main properties to take into account by the design engineer
to avoid any failure linked to a bad design regarding thermal or thermo-mechanical
properties.
Overload
Steady-state
operation
Same constraints as above for
steady-state operation but
higher level of constraints
Radial thermal expansion of the
cable components
Maximum temperature
(surroundings of cable or
accessories)
Vibrations
Constraints
Mechanical forces linked to
snaking Longitudinal dilatation
of the cable – axial thrust
(conductor thermo-mechanical
thrust) and retraction
Cable components retraction
(insulation, metallic screen,
outer sheath)
X
Mechanical
X
X
Thermal
Constraints Classification
Support design, flexible link
from power apparatus and
terminations
Same as previously described
for steady state operation.
Adjustment of level of
constraint and test duration
To be known and taken into
account for the design
Short-term and long term test
including accessories with
thermal cycles and a
representative configuration of
laying and clamping.
Design of the clamp
X
X
Test to perform/ characteristics
to control
Calculations of the thrust (see
WG 21-17) or specific tests
made by the cable
manufacturer
Thermo –
mechanical
X
Table 9.1 Characteristics to control or tests to perform for assessing the reliability of accessories on cable systems
Test report has to be clear
about the way of laying
(in particular for the
prequalification test)
IEC tests
418
H. Geene and R. Schroth
X
X
X
X
X
X
X
X
X
A specific care has to be taken
for the transition part between
2 different ways of laying as
described in the Cigré TB from
WG 21-17 – p 86
• Calculations
• Tests
• Cleating design
Note: effects due to short-circuits have not been included in the table but it should be noted that when designing a cable link it is necessary to take into account
the behavior under short circuit conditions
Transition between flexible and
rigid systems (buried)
Angle of installation of
terminations
Transition between ducts and
manholes
Transition between flexible and
rigid systems (open air)
Transformers (raised
temperature. . .)
Outdoor termination
Solar radiation
Special
environments
Others
Machanical properties of the
support
Earthquake
9
Thermal Ratings of HV Cable Accessories
419
420
H. Geene and R. Schroth
Henk Geene has a Master’s degree in Electrical Engineering
from the Technical University in Eindhoven, the Netherlands.
Shortly after graduation, he joined the Dutch cable manufacturer NKF (nowadays part of the Prysmian Group) where he
started as an engineer to develop High and Extra High Voltage
cable accessories. Currently, he is responsible for product management and sales of the Prysmian high voltage accessories.
He is past Dutch Member of Cigré Study Committee D1,
Convener TF15/21 “interfaces in HV cable accessories,” Convener TF21.10 “thermal ratings of HV cable accessories,” participated as a Member in several Cigré Working Groups, and is
currently Chairman of the IEEE Insulated Conductors Committee (ICC).
He is author of several papers and publications on a wide range
of subjects in the field of high voltage cable accessories and
their interaction with other components in the cable systems.
Reinhard Schroth was born in 1942 in Berlin. He was graduated as Engineer in High Voltage and Electrical Power Engineering from the University of Berlin. Reinhard took various
management functions in Siemens Power Cables (Berlin), and
Pirelli Cables, PKS, (Germany). He joined Cigré as Individual
Member in 1984. In Cigré, he has been Member and Convener
of many Working Bodies since 1985. He was German National
Member of SC 21/B1 from 1996 to 2002 and was also German
Member of IEC TC 20/ WG 16 “Power cables.” Reinhard
chaired SC B1 from 2002 to 2006. He received the TC Award
in 1993, the Distinguished Member Award in 2004, and the
Honorary Member Award in 2006. He is author of numerous
international publications and participated several times in
Jicable Technical Committee.
Test Regimes for HV and EHV Cable
Connectors
10
Milan Uzelac
Contents
10.1
10.2
10.3
10.4
10.5
Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.1.1 Terms of Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.1.2 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.1.3 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cable Conductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.2.1 Basic Cable Conductor Types and Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.2.2 Materials for Cable Conductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.2.3 Fillers (Compounds, Yarns, Cloth, Powder, . . .) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.2.4 Construction of Cable Conductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Connectors for HV/EHV Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.3.1 Basic Theory of Current Carrying Cable-Connections . . . . . . . . . . . . . . . . . . . . . .
10.3.2 Connector Construction and Types for HV and EHV Extruded Cables . . . . .
10.3.3 Diagnostics for Cable Connector Condition Assessment . . . . . . . . . . . . . . . . . . . .
Cable Connectors in Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.4.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.4.2 Mechanical Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.4.3 Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.4.4 Cable Connectors in Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.4.5 Cable Connectors in Outdoor Terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.4.6 Cable Connectors in Equipment Type Terminations . . . . . . . . . . . . . . . . . . . . . . . . .
10.4.7 Connections to the Cable Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation of Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.5.1 Installation Instruction Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.5.2 Cable Conductor Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.5.3 Mechanical Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.5.4 Crimp Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.5.5 Exothermic Welding Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.5.6 MIG or TIG Welding Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
425
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426
426
427
427
428
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456
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459
460
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462
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M. Uzelac (*)
G&W Electric Co, R&D, HV Cable Accessories, Bolingbrook, USA
e-mail: muzelac@gwelec.com
© Springer Nature Switzerland AG 2021
P. Argaut (ed.), Accessories for HV and EHV Extruded Cables, CIGRE Green Books,
https://doi.org/10.1007/978-3-030-39466-0_10
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M. Uzelac
10.6
469
469
471
Experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.6.1 Utility Presentations at WG Meetings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.6.2 Worldwide Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.7
Existing Test Methods, Requirements, and Assessment in Cable Connector
Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.7.1 Medium Voltage Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.7.2 Additional Tests on MV Connectors/Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.7.3 Existing Practice in Testing HV/EHV Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.8
Test Regimes for Cable Connector/Conductor Combinations in HV AND EHV
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.8.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.8.2 WG Recommendations for Testing Connectors for HV and EHV Cables . . .
10.8.3 Range of Applicability of Development Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.8.4 Test Loop for Heat Cycling and Temperature Stability Tests
for Development Tests with Conductor Sizes Above 1200 mm2 . . . . . . . . . . .
10.8.5 Recommended Development Test Sequence with Conductor Sizes Above
1200 mm2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.8.6 Test Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.9
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Terms of Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Comparison of IEC and IEEE Type Test Requirements for Extruded Cables
and Accessories for Voltages up to 245 kV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Comparison of IEC and IEEE Type Test Requirements for Extruded Cables
and Accessories for Voltages 245 kV and above . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Background Behind Range of APPLICABility and Proposed Development Tests . . . . . . . . . . .
476
477
481
486
490
490
494
495
498
498
500
503
504
507
508
508
513
Executive Summary
The current IEC 61238-1-3 [1] standard applies to connectors for medium voltage
(MV) cables up to 30 kV (Um ¼ 36 kV). There is no IEC standard for connectors for
cables for high voltage (HV) and extra high voltage (EHV) networks. The IEC standards
for testing HV/EHV cable systems/accessories (IEC 60840 and IEC 62067 correspondingly) do not specify separate tests for qualifying only connectors. The task of CIGRE
WG B1.46 was to propose test regimes for connectors for cables above 30 kV, with
focus on larger conductor sizes typically used in HV/EHV cable systems.
The type tests specified in IEC 61238-1-3 consider connectors to be commodity items.
Such connectors may be, and in some cases, are used and installed in MV cable
accessories without consent from the cable accessory manufacturer. Inappropriate use
and improper installation of MV connectors have been the cause of numerous failures in
MV networks, especially in systems with high and intermittent loads such as wind farms.
In HV/EHV applications where the system approach is dominant, connectors are
considered to be an integral part of the cable system. The design, development
testing, and in many cases installation of such connectors are under strict control of
the cable system/accessory manufacturer who takes full responsibility for the performance of each component in a particular project, including connectors. This is
one of the reasons why there have been a very small number of failures that can be
attributed to the malfunction of the connectors in HV/EHV networks, compared to
MV. Although for HV/EHV systems the connectors are not challenged often to their
rated values, there is a trend to utilize cable systems closer to their maximum rating.
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423
In current practice, the tests on HV/EHV connectors are done as development
tests performed at the discretion of the cable system/accessory manufacturer and
further verified by type testing and prequalification (PQ) testing (where required) of
the cable systems/accessories per IEC 60840 or IEC 62067. Some users have their
own specifications for connector qualification, in which cases the manufacturer
performs additional tests to satisfy those requirements.
Some of the tests specified in IEC 61238-1-3 are neither practical nor applicable
for large size cable conductors. For example, it is not practical to raise the temperature of the conductor during the SC test to 250 C, as it would require a current far
beyond the maximum short circuit rating of the underground networks. Also, the
time to carry out 1000 thermal cycles is much longer for large conductors in typical
use for HV/EHV systems which would lead to unreasonably long test times. Due to
variety of conductor designs within one nominal size in HV/EHV applications, tests
need to be done for each connector/conductor combination.
Results from the survey on field experience with HV/EHV cable connectors and
from utility presentations at the WG meetings show very good performance of these
connectors in the network. Such performance supports the fact that testing procedures for development of connectors in combination with type/PQ testing of the
cable systems/accessories as per relevant standards used for HV/EHV cable systems
have been appropriate.
A new test sequence is recommended to provide guidance in development tests
for verifying new conductor/connector combinations or changes in connector/conductor combinations in already qualified HV/EHV cable systems. These include
short circuit and heat cycle stability tests per the suggestions in CIGRE TB
303, Annex 5.4, “Functional Analysis” for the Metallic Connection of joints and
terminations” [29]. TB 303 is presented in ▶ Chap. 4, “Qualification Procedures for
HV and EHV AC Extruded Underground Cable Systems” of this book.
Although the proposed development test sequence and test methods are based on
combined practice and experience in development and qualification testing of both
HV/EHV and MV connectors, the sequence is new and not yet tried on a large
scale. The sequence and test methods are presented by the WG for evaluation purposes
at this stage. The type tests for HV/EHV connectors are not recommended at this point
of time.
Section 10.1 provides background information. As the current standard for cable
connectors applies only to MV cables, the WG 16 of IEC TC20 is considering
extending the scope to HV/EHV cable connectors. Thus, technical evaluation by
experts in the area of connectors and HV and EHV cable systems is necessary and
TC20 agreed to pass the work to CIGRE.
Section 10.2 describes cable conductor designs that are the most commonly used
in HV and EHV cables. The variety of conductor designs and materials starting from
solid aluminum to stranded round or segmental aluminum and copper, bare or
insulated individual strands, filled or not filled conductors, variety of filling compounds and solid materials, and so on present a challenge for design of connectors.
Not all connectors are suitable for all conductor designs; hence, the focus in
development testing of the connectors is on the connector/conductor combination,
rather than on individual connectors and conductors.
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M. Uzelac
Section 10.3 gives a short introduction into the connection theory. It also describes
design of the most commonly used connectors in HV/EHV cable networks. Compression (crimp) connectors are still the most commonly used but mechanical connectors are gaining popularity due to simple field installation. Other connector types
like MIG (Metal Inert Gas) welded and TIG (Tungsten Inert Gas) welded, exothermically welded, clamp connectors, and others are all used in special applications.
Section 10.4 talks about cable connectors in accessories where the connectors
may be exposed to significant thermal and mechanical stresses. Expansion and
contraction of cable conductors during normal and abnormal (e.g., short circuit)
operation may generate significant thrust and tensile forces on cable connectors.
Encapsulation of connectors with components of cable accessories changes the
thermal environment from that when connector is tested on a bare conductor. Finally,
connections to the cable connectors in HV/EHV terminations and transition joints
are exposed to the same thermo-mechanical stress. These connections have not been
specifically addressed in any of the standards.
Section 10.5 considers the installation of connectors. Many failures of connectors in
the MV cable systems are contributed to either improper installation or improper use of
the connectors. Use of proper tools and strict following of instructions for connector
installation is essential for proper connector operation as outlined in ▶ Chaps. 5, “Cable
Accessory Workmanship on Extruded High Voltage Cables” and ▶ 6, “Guidelines for
Maintaining the Integrity of Extruded Cable Accessories” of this book. This section
provides more in-depth information on installation of various connector types.
Section 10.6 discusses field experience. The working group launched a CIGRE
sponsored survey on experience with cable connectors in HV/EHV systems. In
addition, representatives from major utilities were invited to present their experience
in the WG meetings. The survey was answered by 34 utilities from 12 countries and
presentations at the working group meetings were done by three major utilities from
USA, France, and Germany. Field experience is very good. No failures were
reported on connectors in HV/EHV terminations. The few failures reported on
through connectors (joint connectors) were attributed to installation error.
Section 10.7 describes existing test methods for cable connectors. The MV
connectors are tested per IEC61239-1-3, while the HV/EHV connectors are tested
per proprietary test procedures set forth by cable system/accessory manufacturers
and, in some cases, by user’s requirements.
Section 10.8 contains proposals for development tests of HV/EHV connectors. All
manufacturers of HV/EHV cable systems perform certain tests on connectors at their
own discretion before doing Type and PQ (when required) tests on accessories/systems.
Most follow existing IEC and ANSI Standards for MV connectors but with some
deviations from the standard, especially when it comes to connectors for large size
conductors. The WG has made an effort to “standardize” these development tests and
define test sequences and range of approval combining experience of cable system/
accessory manufactures, manufacturers of connectors for MVand HVapplications, and
experience of the laboratories in connector testing as well as the input from academia.
Section 10.9 lists conclusions of the work. Statements to acknowledge current
practice in development testing of connectors are included. The WG proposes a
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Test Regimes for HV and EHV Cable Connectors
425
sequence and a range of approval of development tests to be done on HV/EHV
connector/conductor combinations prior to use in type and PQ tests. It is proposed
that experience with the new test regime is collected and evaluated before an attempt
is made to introduce qualification testing of HV/EHV connectors in a new part of the
IEC Standard.
Section 10.10 is a list of useful and comprehensive references.
10.1
Background
Manufacturers of HV cable systems/accessories have to take into account the
following factors (among others) when designing and testing the connectors for
HV cable accessories:
• The dimensional and functional requirements of connectors, typically for larger
cable sizes
• The type of cable conductor construction
• Different circuit load patterns
• Short circuit levels
• Mechanical stresses due to tensile and thrust forces
• Systems/accessories
Thus, when WG16 of IEC TC20 commenced work on revision of the current
IEC61238-1-3 standard a part 4 was reserved for HV cable connectors and is
planned for the future. Technical evaluation by experts in the area was necessary
and TC20 agreed to pass the work to CIGRE. Study Committee B1 of CIGRE set up
WG B1.46 to review this subject and issue report with the terms of reference and
scope given below.
10.1.1 Terms of Reference
• Review: Existing conductor types and sizes; The range and types of cable
conductor connectors; The types of connection systems used in joints and terminations; Existing national and international standards and the extent to which they
cover the testing of connectors; Any work been done by CIGRE, CIRED,
JICABLE, and other; Extent of service experience so far for different connector
types (prepare survey and invite users to the WG meetings to share their experience); Extent of experience in type testing MV cable connectors; Extend of
experience in testing HV?EHV cable connectors (PQ tests, type tests failure
mode tests. . .); Customer’s needs.
• Analyses: Operation on high loaded systems where conductors are approaching
or temporarily exceeding maximum conductor operating temperature. Academia
input on physical properties of connector material vs. temperature and mechanical
stress; Thermo-mechanical performance of connectors under cycling loads;
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M. Uzelac
Performance of connectors in short circuit conditions, taking into account thermal
and dynamic forces and actual network ratings; Performance of connectors
installed in cable joints and terminations.
• Propose: Thermal and mechanical test regimes for connectors for HV and EHV
cables with special attention be given to connectors for large size cables; type,
routine, and sample tests including mechanical, cycling, and resistance stability
tests; consider practicality of the short circuit test for large-size conductors and
test loop arrangement; WG should be free to consider mechanical tests (e.g.,
tensile, thrust forces. . .) in order to evaluate mechanical strength of connection
and physical properties of connector itself; WG should be free to consider
separate or integral test sequences combining mechanical, cycling, short-circuit,
and resistance stability (assessment) acting on the same samples; evaluate necessity of performing type tests on connectors that already successfully passed
qualification tests per IEC 60840; WG should consider range of type test
approval.
10.1.2 Scope
The conductor connectors for HV and EHV applications are to be considered. The
WG will make recommendation to include or not connectors for MV applications.
The connectors for extruded cables are of prime interest. The connectors for
submarine cables are not in the scope of the WG.
The WG should consider the tests that reflect mutual impact between connectors,
cable conductors, and accessories.
10.1.3 Terminology
The following terminology is used in this TB, following that used in IEC 61238-1-3
which is also generally in line with IEC 60050, International Electrotechnical
Vocabulary (IEV) – Chap. 461: Electric Cables.
10.1.3.1 Connector (of Cables)
Metallic device for connecting a conductor to an equipment terminal or for
connecting two or more conductors to each other (IEV 461-17-03, modified).
10.1.3.2 Through Connector
Metallic device for connecting two consecutive lengths of conductor (IEV 461-1704).
10.1.3.3 Terminal Lug
Metallic device to connect a cable conductor to other electrical equipment (IEV
461-17-01).
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427
10.1.3.4 Barrel (of Terminal Lug, of Connector, etc.)
Part of a device into which the conductor to be connected is introduced (IEV 461-1706).
10.1.3.5 Reference Conductor
Length of unjointed bare conductor or conductor with the insulation removed, which
is included in the test loop and which enables the reference temperature and
reference resistance to be determined.
10.1.3.6 Compression Jointing
Method of securing a connector to a conductor by using a special tool to produce
permanent deformation of the connector and the conductor.
10.1.3.7 Mechanical Jointing
Method of securing a connector to a conductor, for example by means of a bolt or
screw acting on the latter or by alternative methods.
10.1.3.8 Median Connector
Connector which during the first heat cycle records the third highest temperature of
the six connectors in the test loop per IEC 61238-1-3 type tests up to 1200 mm2 or
the second highest temperature of the four connectors in the test loop for connector
development tests with conductor sizes exceeding 1200 mm2.
10.2
Cable Conductors
Current experience and practices are outlined in this section. It includes review of
cable conductor and cable connector state of the art designs, existing national and
IEC standards, users experience with connectors both in medium voltage and high
voltage application, the extent of testing connectors by manufacturers, users, and
independent laboratories and so on.
10.2.1 Basic Cable Conductor Types and Sizes
In general conductors in high voltage XLPE cables are made of solid or stranded
copper, aluminum, or aluminum alloy for fixed installations. In terms of the conductor cross-section the electrically effective value, rather than the geometric cross
section, is used. It is represented by the measured resistance of the conductor.
General design parameters of conductors are:
• Specified and required resistance.
• Type of conductor (solid, stranded, Milliken) in terms of production and laying of
cables.
• Conductor material (aluminum, copper).
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M. Uzelac
•
•
•
•
Weight of conductor in terms of limits of stranding machines.
Nature of surface of wires (bare, oxidized, coated, e.g., enameled).
Use of fillers, yarns, and tapes for special purposes (filling, water tightness).
Length and direction of strands for mechanical stability of the conductor. The
conductors described in IEC 60228 are specified as square millimeter (metric)
sizes. North America and other regions of the world use conductor sizes with
characteristics according to the American Wire Gauge (AWG) – kcmil system.
• Special measures taken and designs to reduce skin effect.
• Compactness of conductors in compliance with requirements and considering the
mechanical properties of the wires.
For high voltage cables conductors usually consist of stranded single wires or in
some cases of just a solid conductor. General design parameters of wires are:
• Thickness of the wires representing the required resistance of the wire.
• Variation of thickness of the wires to the required cross-sections under consideration of existing production facilities.
• Coating of wires, for example, oxidized or enameled surface.
• Tensile strength of the wires corresponding to requirements of the standards under
consideration of the forces during stranding.
10.2.2 Materials for Cable Conductors
In terms of the used conductor material wires or profiles are applied. The material for
wires and profiles of conductors is specified in IEC 60228 and it can be made from:
•
•
•
•
Plain copper
Metal-coated annealed copper
Aluminum
Aluminum alloy
In order to block the radial conductivity sometimes insulated wires are used with
copper. Aluminum is very ignoble and the surface reacts at room temperature with
air and water immediately to an aluminum oxide layer.
Since the very beginning of production of cables, copper has been known for its
unique and useful properties. The chemical element copper is in the periodic table,
together with gold and silver in group 11 and the fourth period between the elements
nickel and zinc [11]. Its good conductivity and ductility make copper well proven
material for high voltage cable conductors. Copper is a malleable metal, stretchable
and under cold conditions a deformable material with an excellent conductivity.
Copper with a level of purity (99.95%) is used, which enables the production of fine
wires down to a diameter of 10 microns.
Aluminum, in contrast to copper, has a lower density, but conductors made from
aluminum need a larger cross section than their counterparts of copper because of
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Test Regimes for HV and EHV Cable Connectors
429
their lower conductivity. Aluminum creeps at high temperatures and high pressures
(cold flow) due to changes its shape in the micron range and in combination with
moisture or nobler metals is aluminum electrochemically negative and therefore
highly susceptible to corrosion.
In general, the surface of aluminum is oxidized. Aluminum oxide is difficult to
remove and has high electrical resistance.
However, the surface of a conductor with oxidized of enameled layer may be
treated in a special way as requested in the work instruction manual for the
connector.
Table 10.1 shows typical properties of copper and aluminum.
According to the mass density, the weight of an equivalent conductor crosssection of copper to aluminum is:
– 1 kg Cu ~ 0.3 kg Al
According to the conductivity, the equivalent conductor cross-section of copper
to aluminum is:
– 1 mm2 Cu ~ 1.6 mm2 Al
The conductivity/weight relationship is:
– 1 Sm2/kg Cu ~ 2 Sm2/kg Al
In general aluminum is lighter and lower in cost, but to achieve the same
conductivity, a larger conductor cross-section must be used. But considering the
better conductivity/weight relationship and lower costs for raw material of aluminum, the relationship between copper and aluminum is approximately 6:1 at the
same transmission capacity.
Therefore, the replacement of copper by aluminum, which has a lower price, is
becoming a developing trend in the cable industry.
However, the significant greenhouse gas emission during aluminum production
may restrict this development, because aluminum has more carbon (CO2) emission
in contrast with copper.
Table 10.1 Properties of materials for cable conductors
Property
Resistance to fracture
Tensile strength at 1% strain
Conductivity
Specific resistance
Temperature coefficient of electrical resistance
Density
Tin-coat
Unit
(N/mm2)
(N/mm2)
(Sm/mm2)
(Ohmmm2/m)
(1E-6/K)
(kg/dm3)
()
Copper
220–270
120–200
58.5
0.0171
3900–4000
8.93
Applicable
Aluminum
120–140
40–50
35.85
0.0279
3900–4000
2.7
Limited
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M. Uzelac
Another and just as important aspect is that increasing the cross section of
conductors for cables can significantly increase electrical energy efficiency. Incorporating a higher cross section can save a huge amount of greenhouse gas emissions
(CO2) due to lower losses in the cable. At the same time, the energy savings achieved
will, in the vast majority of cases, lead to lower costs over the life cycle of the system.
In this matter, IEC 60287 sets out a method for the selection of a cable size taking
into account the initial investments and the future costs of energy losses during the
anticipated operational life of the cable. Matters such as maintenance, energy losses
in forced cooling systems, and time of day energy costs have not been included in
this standard. All conductor sizes have an economic current range for given installation conditions [12].
In terms of life time assessment, it has been shown that in general the difference
between copper and aluminum cables over their entire lifetime is not as significant as
generally thought. The cost for raw copper material is about 3.5–4 times higher than
aluminum but looking at lifetime costs, and within the uncertainties of LCCA over
the long cable lifetime, both solutions can be considered equivalent [13].
In general, there are different types of wires in use, for example, round solid or
round enameled solid as shown in Fig. 10.1. Enameled wires are applied only with
copper conductors. In high voltage extruded cables, typically round and solid wires
are used.
Due to the manufacturing process in which the wires inside of a conductor are
compacted, an individual deformation of single wires is a typical result after
production. Especially the outer surface of the outer layer receives a strong
d
d
d D
Basecoat
d
D-d=increase
1mm
Cu
bare
Cu
oxidized
(thickness 1 µm)
Cu
enameled
(D-d)/2 = approx. 10 µm
Fig. 10.1 Types of solid bare round wires: oxidized or enamelled
Al
bare
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Test Regimes for HV and EHV Cable Connectors
431
Fig. 10.2 Compacting and deformation of wires after stranding
deformation. For smaller cross sections of conductors, the outer surface has to be
more compacted and smoothened as shown in Fig. 10.2.
10.2.3 Fillers (Compounds, Yarns, Cloth, Powder, . . .)
Often semi-conductive or insulating tapes are embedded in layers inside of stranded
conductors either to provide water blocking or to separate segments. The conductor
itself is covered by semi-conductive tapes achieving a uniform and smooth surface.
In the case of water blocking, the tapes are swellable. Fillers may be used instead
of water blocking tapes. Some connector designs may require filler materials to be
removed, to be specified by the connector manufacturer.
In some cases, and especially in the case of conductor constructions with equal
segments, gaps or dips in the outer surface between the segments are smoothed with
fillers.
10.2.4 Construction of Cable Conductors
Conductors are either round or sectoral in shape. They are realized with solid metal,
stranded wires. Up to 1000 mm2 the minimum number of wires in the conductor is
specified. For larger cross sections, the minimum number of wires for these sizes is
not specified. These sizes are usually constructed as a “Milliken” conductor with
4, 5, or 6 equal segments, which is designed to reduce the skin effect, and thus
improving the value of the ac resistance of the conductor.
432
M. Uzelac
For smaller cross-sections, both stranded and solid conductors can be used. In a
few cases, solid aluminum conductors are used up to 1600 mm2. For larger conductors, the increased bending force limits the use of solid conductors.
10.2.4.1 Insulated Strands and Sectors
For high-current conductors with large cross sections, special measures are required
to limit additional eddy current losses. The current rating of AC cables depends on
the AC resistance of the conductor. The AC resistance is higher than the DC
resistance due to the skin effect. The skin effect is based on the behavior of the
eddy current depth depending on frequency f, conductivity, and permittivity of the
material and causes eddy current losses. For this reason, “Milliken” conductors
are used.
A “Milliken” conductor is a stranded conductor comprising an assembly of
shaped stranded conductors, with each segment lightly insulated from each other.
The individual strands may be either insulated (e.g., enameled or oxidized) or bare.
In general layers of conductors can be constructed with uni-directional or
bi-directional wires. The degree of stranding defines the length of one twist of
each layer of conductor. In Fig. 10.3 the principle of a bi-directional stranding is
shown by the small arrows indicating the direction of twist of the layers.
According to the design, construction, and requirements regarding the conductivity of conductors, they are compacted more or less during production.
Different types of conductors are shown in Fig. 10.4.
Typical conductors for high voltage XLPE cables are round stranded or Milliken
conductors with equal segments. Round conductors are typically used for aluminum
conductors up to 2000 mm2, copper conductors up to 1200 mm2. Milliken conductors with equal segments are typically used for both aluminum and copper conductors between 1600 mm2 and 3200 mm2 or larger.
In Fig. 10.5 different types of conductor constructions for high voltage XLPE
cables are shown.
Fig. 10.3 Bi-directional
stranding direction
10
Test Regimes for HV and EHV Cable Connectors
Round, solid
Round, stranded
4, 5 or 6 equal segments
(Milliken)
4, 5 or 6 equal segments
hollow (Milliken)
with or without core
433
Round stranded
compacted
Round, with profiled
strands
Fig. 10.4 Cable conductor types
round, Al solid
round, stranded
compacted Cu
6 equal copper
segments (Milliken)
6 equal Aluminium
segments (Milliken)
Fig. 10.5 Examples of different types of cable conductors
10.2.4.2 Influence of Cable Construction on Design and Dimensions
of Connector
The size of the conductor and the choice of the conductor material is a result of
ampacity calculation. The connectors must match ampacity requirements of the
cables. The size of cable conductor, its material, and construction have major
influence on the design of the cable connector.
The connector dimensions and its design are also influenced, in some cases, by
the diameter over cable insulation. For example, it is preferred that connector OD
matches cable insulation OD when used in the slip-on joints. Since the thickness
(and diameter) of cable insulation depend on the voltage level, it may not be
achieved that connector OD matches insulation OD as illustrated in Fig. 10.6.
434
M. Uzelac
60 kV, 2500 mm2
Cable insulation wall: 10 mm
220 kV, 2500 mm 2
Cable insulation wall: 20 mm
500 kV, 2500 mm 2
Cable insulation wall: 30 mm
Fig. 10.6 Mechanical connector for HV and EHV joints for extruded cables with the same
conductor size but different voltage level
Table 10.2 Typical thickness of XLPE cable insulation
Voltage level U (kV)
Insulation thickness (mm)
10
3.4
20
5.5
30
8
60
10
110
15
220
20
345
25
400
28
500
30
The typical values for the cable insulation wall thickness are shown in the
Table 10.2.
10.3
Connectors for HV/EHV Cables
The cable connector transfers electrical current from cable conductor to substation
equipment or to another cable length or section. It is imperative that the contact
resistance between connector and cable conductor remains stable during the lifetime
of a cable accessory. An increase of contact resistance beyond an acceptable limit
causes an increase of connector temperature which may result in failure of the
accessory (e.g., by thermal runaway).
In operation, cable connectors are subjected to thermal and mechanical stresses
which depend on many factors, for example, nominal and intermittent circuit load,
short circuit current value and duration, the size, material and construction of the
cable conductor, voltage level, type of accessories used in a particular project, level
of thrust and tensile forces, cable route, just to mention few. The manufacturer of an
HV cable system/accessory must take into account all these factors when making a
decision on which type of cable connectors and which installation method of the
connectors are the most appropriate to use in accessories for a specific project. Some
connector designs for HV/EHV cables are described in this section.
Many cable accessory manufacturers make their own connectors and in some
cases connector installation tools. The connectors are specifically designed to meet
their requirements and constraints of design of an HV/EHV accessory and cable.
Some cable accessory manufacturers purchase connectors from connector manufacturers, but then again to meet strict requirements of the designs of a particular cable
accessory and cable. Mixing and matching of cable accessories and connectors,
which sometimes is the case in MV applications, is not possible in HV/EHV
applications.
In the absence of the industry standards for testing connectors for HV cables, the
manufacturers of cable the systems/accessories perform tests on connector/
10
Test Regimes for HV and EHV Cable Connectors
435
conductor combinations at their own discretion as development tests. These tests are
combination of applicable requirements from industry standards for MV connectors
and manufacturer’s own experience. Once they are satisfied with the results of
development tests, the connectors are installed in accessories which in turn are tested
to the requirements of type and prequalification (where required) tests of IEC 60840
(for HV) and IEC 62067 (for EHV) Standards. The requirements for the type tests of
the cable system/accessory include 20 load cycles at maximum operating temperature of the cable plus 5–10 K. For the prequalification, the number of cycles is 180 at
maximum operating temperature plus 0–5 K.
10.3.1 Basic Theory of Current Carrying Cable-Connections
This section explains a very basic concept of the contact surfaces and theory in
calculation of contact resistance. Refer to Sect. 10.10, Bibliography/References, for
comprehensive references on the subject.
• A-spots: On a microscopic level, each contact surface consists of peaks and
valleys. When two connecting surfaces come together, valleys and peaks of one
connection surface randomly match those of the other connection surface. Direct
contact is only obtained in few points, so-called A-spots, as shown in Fig. 10.7a.
The restriction of current flow to these contact points constitutes a contact
resistance. Contamination, corrosion, aging, and other effects influence the spread
of A-spots. The goal of a connector is to create as many A-points to the cable
conductor as possible and that A-spots are not affected in operation by temperature, corrosion, vibration, the tension, and thrust forces of the cable conductor
and so on.
• When the force is applied to two connecting surfaces (Fig. 10.7b), connecting
surfaces are deformed and impurity layers broken resulting in increased number
of “A” spots and lower connection resistance.
• Figure 10.8 shows a simplified representation of the structure of A-spots. The
total “apparent” contact area is in fact much larger than the true area which is
F =0
F >0
Impurity layer
conductor 1
A-spots
conductor 1
A-spots
Current-flow through A-spots
conductor 2
a) No external force applied to conductors. Only
few micro contacts (A-spots) due to surface
roughness
conductor 2
b) External force applied. The A-spots are
deformed and impurity layers are broken at higher
force
Fig. 10.7 A-Spots with and without compression force
436
M. Uzelac
Key:
As
A t1
A t3
A i1 A m1 A q A i2
A i4 A m2 A i5
Ai3 = A t2
As
apparent contact area
At
load bearing contact area
Ai
insulating contact area
Aq
quasi conducting contact area
Am
conducting contact area
and As >> At > Am
n…number of A-spots
Fig. 10.8 Definition of the different contact areas in a real connection
Conductor 1
Area of homogeneous
current-flown material RM1
Constriction of the current
flow line at the a-spot
RC
Conductor 2
Area of homogeneous
current-flown material
RM2
R M1
RC
RJ
R M2
Fig. 10.9 Resistivity equivalent circuit of a connection (schematic drawing – microcontact)
mechanically loaded which is again larger than the area which is electrically
conducting. Within the A-spots there are conducting areas, where the metal of the
conductors is in true contact, quasi conducting areas where some surface impurity
layer is still present, giving limited conductivity, and insulating areas which are in
mechanical contact but provide no significant conduction.
• Sphere and ellipsoid model [14]: this is a development of the A-spot model. Holm
considered that the A-spots cause a “restriction” of current flow in the vicinity of
the contact, see the red lines in Fig. 10.9, representing the current flow in a single
A-spot contact between two cylinders. An increase in resistance compared to that
for a solid rod is considered to be caused by the increase in current density close to
the A-spots.
Equivalent Network for Connections with Stranded Conductors
Equivalent circuit with infinitesimal resistances: Fig. 10.10 shows a schematic of an
element of current flow from a connector body, through a microcontact and then via
the cable conductor. A simple electrical model of a connection is provided by Möcks
10
Test Regimes for HV and EHV Cable Connectors
437
Fig. 10.10 Electrical network of compression type connection [19–21]
[21]. The model divides the connection in infinitesimal elements of the length dx,
each consisting of the material resistances R1 and R2 per unit length of the jointed
conductors and a resistivity Rq. This resistivity is assumed to be equally distributed
along the connection.
The Kirchhoff’s laws are applied to the circuit and a differential equation is
formed for the voltage ux. An expression for the joint resistance Rj is derived from
the solution of the differential equation [21]:
R þ R cosh ðαsÞ
ð R1 R2 Þ
R1
αs
2
tanh
R sþ
þ 1
Rj ¼
α
2
R1 þ R2 2
α sinh ðαsÞ
ð10:1Þ
with
rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
R1 þ R 2
α¼
Rq
ð10:2Þ
Equation (10.4) may be rearranged so that an expression for the ratio k0 is
obtained
0
1
pffiffiffiffiffi
a
2
A Rq
k0 ¼ @
þ
c tanh pcffiffiffiffi c sinh pcffiffiffiffi
Rq
Rq
ð10:3Þ
438
M. Uzelac
with
R1 R2
þ
R2 R1
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
c ¼ s K F ð R1 þ R2 Þ
a¼
If the resistivity Rq fulfills the condition in Eq. (10.4), Eq. (10.3) may be solved
for resistivity Rq analytically:
Rq s2 ðR1 þ R2 Þ
Rq ¼
h
c 0
k
a
i2
ð10:4Þ
ð10:5Þ
In case the condition in Eq. (10.4) is not fulfilled, Eq. (10.3) may only be solved
numerically. In both cases, a solution for the characteristic value Rq of a connection
may be calculated. For this purpose, the material resistances of conductor and sleeve
and the geometry of the compression connection must be known. The resistivity Rq
provides the opportunity to rate the electrical performance of a connection independently from the material resistances. Thus, the resistivity Rq is related to the contact
resistance of a connection directly. Of course, due to the constraints of the electrical
model it may only be applied for those types of connections that meet the following
conditions. The electrical model implies the assumption that the distribution of the
a-spots in the connection is almost homogenous in axial and radial direction. Of
course, the resistivity Rq integrates the influence of all a-spots in a connection
regardless of their actual size and location or whether there is more than one actual
contact surface. Thus, it cannot be separated, whether a rise in the resistivity Rq stems
from the a-spots between conductor and sleeve or from those a-spots between the
single strands. Nevertheless, the value of Rq is a suitable criterion to analyze and
compare the electrical behavior of different designs of compression connectors.
However, the derived ratio k’ still contains a part of the material resistances and is
therefore no autonomous criterion to rate the electrical performance of different
connections. Further conclusions can be found in [21].
10.3.1.1 Aging of Electrical Connections
Aging mechanisms (force reduction, chemical reactions, inter-diffusion, rubbing
wear, electro-migration) are discussed in the following references: [16, 17, 22, 25]
and the mechanisms and their effects are given in Table 10.3. The dominant aging
mechanism depends on type of connection.
10.3.1.2 Comparison of Material Properties
The Table 10.4 below lists basic properties of Al and Cu materials used in
manufacturing cable conductors.
– Oxide layers and their characteristics (Table 10.5)
10
Test Regimes for HV and EHV Cable Connectors
439
Table 10.3 Aging mechanisms of current-carrying connections [25]
Mechanism
Chemical reactions
Chemical interaction between conductor
material environment
Force reduction
Change in texture of material according to
temperature and mechanical stress
Rubbing wear
Change surface properties by relative
movement
Interdiffusion
Diffusion of different metals into each other
Electromigration
Directional material transport due to high
current density and current density gradient
Effect
Growth of high resistivity oxide or impurity
layers- galvanic corrosion at bimetal connections
➔Decrease of the conducting contact area, Rj"
Especially under extreme environmental
conditions (e.g., industrial atmosphere, high
humidity, salt fog)
Decrease of the joint force
➔Loss of the mechanical integrity of the
a-spots, mechanical strength#, RV", especially at
clamped or bolted connections (dominate force
closure)
Wear of coatings
➔Generation of rubbed-off particles which
sediment in the contact area, Rj"
Especially at plug-in connections
Growth of intermetallic compounds (IMP) with
different electrical and mechanical properties
➔Higher resistance at the contact area, Rj"
Depending on material combination
Formation of holes and accumulate of material at
irregularities of crystal structures ➔ higher
defect density
➔Decreasing of the a-spot ampacity, Rj"
Especially for direct current devices but also at
alternative current with high current density
Table 10.4 Material properties of copper and aluminum [24]
Property/material
κ in MS/m (20 C)
Cu-ETP
CW004A
Min. 57
Al 99.5
EN AW-1350A
34–36
αT in 1/K
Melting temperature ϑs in C
ρ in g/cm3
E in kN/mm2
Rp0.2 in N/mm2
0.00381
1083
8.93
110
Min. 180
0.004
ca. 660
2.71
65
–
Rm in N/mm2
Min. 250
Min. 60
H in HBW
65–90
Typ. 20
αL in 106 K1 (20–200) C
λ in W/Km
17.7
394
23.8
215–235
AlMgSi alloy
EN AW-6101B
30–34
(T6 30)
(T7 32)
0.004
ca. 660
2.70
69
Min. 160 (T6)
Min. 120 (T7)
Min. 215 (T6)
Min. 170 (T7)
70 (T6)
60 (T7)
23.4
215–225
440
M. Uzelac
Table 10.5 Properties of oxide layers [22]
Property/material
ϑs/ C
δ/g/cm3
κ/mm2/(Ω∙m)
H/HV
αL/1/(K∙106) (20–200) C
λ/W/(m∙K)
Cu-ETP
CW004A
1083
8.93
Min. 57
90
17.7
394
Al99.5
EN AW-1350A
660
2.71
34–36
21–48
23.8
215–235
Cu2O
1242
5.8–6.11
1.82∙1011
109–189
–
6.3–8
Al2O3
2050
3.97
1012–1014
1730–2060
6.2
40
Fig. 10.11 Typical compression connector for HV outdoor terminations
10.3.2 Connector Construction and Types for HV and EHV Extruded
Cables
Unlike connectors for medium voltage which are a commodity product, the connectors
for high voltage applications are carefully selected for a particular application in the
cable system. There are many designs of cable connectors for high voltage applications.
Some of those are described in this section. Compression type connectors are used most
commonly for HV cable accessories, but lately mechanical (shear-bolt) types are
gaining ground due to the ease of installation which does not require any special tools.
10.3.2.1 Compression Type Connectors
The most common cable connector in HV applications is compression type often referred
to as crimp type. The connector features a hollow cylindrical section, called the ferrule as
shown in Fig. 10.11 (see also ▶ Chap. 1, “Compendium of Accessory Types Used for AC
HV Extruded Cables”) of this book, barrel or sleeve. The cable conductor is fed into the
ferrule and the connection between connector and conductor is obtained by pressing the
ferrule outer diameter with the appropriate compression (or crimping) tool.
10.3.2.1.1 Compression Connector Design
The material of the connector matches that of conductor except that hardness of the
connector material has to be appropriate for the method of crimping. For example,
most aluminum crimp connectors are made from soft aluminum and are used on
conductors made of either hard or soft aluminum. Softer material is easier to
10
Test Regimes for HV and EHV Cable Connectors
441
compress and will not crack while being crimped. The connector designer has to take
into consideration the increase of material hardness during crimping operation.
The length of the ferrule and its inner and outer diameters depend on many factors
including conductor material, size, and crimping method.
Typically, the inner ferrule diameter is selected to be a tight fit to the bare
conductor diameter. The cross-sectional area of the connector does not necessarily
need to match effective area of the conductor. In general, the cross-section of
connectors for copper conductors is somewhat smaller than the effective area of
the conductors while aluminum connectors have significantly larger area than the
associated conductors. In the case of copper connectors, a smaller area is possible
due to a higher heat dissipation from the connector surface. In the case of aluminum
connectors, a larger area is required for mechanical reasons.
The length of the ferrule is very critical. It establishes the length of engagement
between the cable conductor and the connector. Some of the variables that influence
selection of the length of the ferrule include the crimping method, the size of the
crimping dies (if used), the number of crimps, the type of connector material, and the
conductor size, material, and construction. The longer the ferrule the better connection between the conductor and connector may be achieved. On the other hand, due
to constraints involving cable accessories, the goal of a connector manufacturer is to
make the ferrule as short as possible.
10.3.2.1.2 Crimping Tools
There is variety of crimping tools on the market, but it is crucial that only the
crimping tool that has been used in connector testing is also used for the field
installation. Many connector manufacturers make their own crimping tools. Some
accessory manufacturers who make their own connectors also make crimping tools.
There are different crimp tools for deep indent and circumferential die connector
designs.
The deep indent tool features either one, two or four rams (pins). The rams
penetrate connector compressing it to the conductor. Figure 10.12 shows the indent
crimping tool with four rams 90 apart.
The distance between and number of successive sets of indents as well as the depth of
indents are specified by the connector manufacturer. The depth of each indent is vital for
the quality of the connection and must meet requirement specified by connector
manufacturer. The depth of each indent is measured in the field after crimping.
The distance between the tips of opposing rams in the crimping tool head is
adjustable. This feature allows the tool to be used for a wide range of connector sizes.
Due to its universal usage and relatively easy handling, this tool has gained popularity in the USA.
The crimping tools that make circumferentially shaped crimps on large size
connectors feature a crimping head with interchangeable dies for variety of connector sizes. There are also die less crimping tools which are typically for use with
smaller size connectors.
The size of the crimping tool is determined by the force (in Tonnes) that is
imposed on the movable half of the crimping die. The “tonnage” of crimping tools
442
M. Uzelac
Fig. 10.12 Four-ram, deep-indent press and crimp connector for 2000 mm2 Cu cable
Fig. 10.13 200 ton press with hex-dies and crimp connector on 2500 mm2 Cu cable
varies from few tons to few hundred tons. Figure 10.13 shows a 200 ton crimping
tool used for the connector for a 2500 mm2 copper conductor.
The pressure of the die on the connector depends on the force, the width of the
crimping surface of the die, and shape of the die (hex, circular, oval. . .). A good
crimp is achieved when die is fully closed. In that case the crimped connector
under the die forms to the shape of the die. The die design usually allows for flow
of the metal.
Some connector manufacturers characterize crimp efficiency of specific die set by
the crimp ratio, which is the ratio between the area of closed die set and sum of
10
Test Regimes for HV and EHV Cable Connectors
443
effective cross section area of the cable conductor and connector ferule. The
following formula defines the crimp ratio.
CR ¼
Adie
100
ACond þ Aferule
The procedure for connector installation should be provided for each project. The
procedure should specify starting point of the crimp, the number and sequence of
crimps, the distance between crimps, rotation of the crimping head, and the necessity
for full closure of the dies. The procedure should also include preparation of the
conductor for crimping, for example, cleaning the conductor and necessity for
removing fillers and/or cleaning individual strands in case of strand filled or enameled conductors.
10.3.2.2 Mechanical Connectors (Shear-Bolt)
The reliability of conductor connections has historically depended on the skill and
experience of the jointer. The introduction of mechanical connectors has been
primarily to reduce the skill required and hence to minimize variability in the
connections and thus to improve reliability. Other features which are also beneficial:
• There is a reduction of the time to install the connection
• No special tools or equipment such as presses are required
• No heat or flames are involved, improving safety
The mechanical connectors are commonly referred to as “shear bolt” connectors,
the name indicating the key feature of such connectors which makes them much less
influenced by the skill of the jointer. The shear bolts (the number, size, and material
depending on the connector design and conductor size) are designed to break at a
specified torque value controlling the tightening torque of the bolts. Different types
of shear bolt are used. In some, the torque is determined by a reduced diameter
region of the bolt, where it breaks. In another type a special double bolt is used which
has a steel screw inside a brass body that is internally and externally threaded. In this
latter design the brass component breaks off flush with the surface of the connector
body minimizing any work necessary to produce a flush profile (which facilitates the
design of the joint body itself).
The connector body is usually internally grooved or threaded so that the cable
conductor is forced into contact with the crests of the thread giving a high local
contact pressure and a good electrical contact.
The connector body is frequently made of aluminum alloy, which guarantees high
elasticity of the cylindrically shaped body and mechanical resilience of internal
grooves or threats. These properties enable connector body to deform cable conductor and stabilize its movement in radial direction, thus achieving and maintaining
maximum thrust-forces introduced by the shear bolts.
The bore of the connector body is often tin-plated and lubricated and further
oxidation of the aluminum material is thus prevented. For tin-plating, the surface
444
M. Uzelac
oxide layer on the connector body is removed by dipping in a caustic bath. Tin is
very ductile. During installation of the conductor, the tin is pushed aside while the
peaks of the threads are cutting into the conductor surface. The lubricant remains in
the “valleys” of the threads or grooves of the body preventing further oxidation of
the just created metal contact areas between connector body and conductor.
Tin-plating of the threated holes for the shear-bolts in the connector body controls
the coefficient of friction during fastening of the shear bolts.
It may be required that for HV and EHV joints the outer diameter of the body of
the connector matches insulation diameter (see Fig. 10.6). Hence, the wall thickness
of shear-bolt connector bodies for HV and EHV joints is typically much bigger
comparing to MV-applications (Fig. 10.14). The thicker the connector wall the
longer is the length of a threaded hole for the shear bolt, and higher force from
shear bolt to conductor may be achieved. This increases design margin for the yield
strength and decreases possibility of relaxation of compression force in service.
It also has to be kept in mind, when designing shear bolt connectors, that the
bigger the conductors are, the higher radial forces must be applied to break oxide
layers of stranded aluminum conductors.
A given mechanical connector design may be adopted to a specific slip-on joint on
specific cables by modifying body of the connector and keeping the design and number
of shear bolts constant for a specified conductor. Features of such connector are:
• Outer diameter of the connector body closely matches the outer diameter of
prepared cable insulation to minimize the slip-on step.
By leaving almost no “air” between connector and the rubber body of the joint,
the heat transfer from connection through the connector and the joint is maximized and
Fig. 10.14 Four different
types of mechanical connector
10
Test Regimes for HV and EHV Cable Connectors
445
Fig. 10.15 A mechanical
connector on a 2500 mm2
Milliken conductor
By increasing the OD of connector body (to match cable insulation OD), the
electrical resistance of the connection is lowered.
• The inner diameter of the connector is tight fit to actual conductor in the project to
minimize the gap between cable conductor and connector body.
The design of the face of the shear bolt that presses on the cable conductor also
varies; some designs avoid rotation of the face against the conductor to prevent
strand damage, whereas others have direct contact from flat, curved, or conical ends.
Mechanical connectors with aluminum bodies can be used on both copper and
aluminum conductors although conclusions as to their long-term suitability for the
latter are not yet generally available [26].
The above features can be seen in Fig. 10.14, which is provided courtesy of
European Manufacturers.
Mechanical connectors are widely used for LV and MV accessories, sizes suitable
for conductors from 25 mm2 up to 630 or 1000 mm2 being widely available.
Development of designs suitable for HV conductors up to 2500 mm2 is also in
progress. To achieve satisfactory connection of such large conductors can require a
large number of shear bolts in a relatively long connector body. An example of a
2500 mm2 mechanical connector is shown in Fig. 10.15. The picture depicts
connector secured to cable conductors but the bolts need yet to be sheared off during
final installation.
10.3.2.3 MIG and TIG Weld Connectors
A creep phenomenon can take place as an effect of loading cycles when crimp-type
connectors are used for large size cable conductors. Current-cycling tests with
aluminum compression connectors with large aluminum conductors have shown
an increase of electrical resistance between cable conductor and connector after
several cycles. The creep leads to reduction of the contact pressure between connector and conductor, with a corresponding increase of the electrical resistance. This
causes increased losses and hence unstable thermal behavior, ultimately resulting in
thermal failure.
As a result, the preferred method of joining large aluminum conductors is
welding. The practice in the USA is to use welded connectors for aluminum
446
M. Uzelac
conductors above approximately 1250 kcmil (~630 mm2) while for smaller aluminum conductors a crimp connection is utilized.
Welded connections fuse two cable conductors (in case of cable joints) or cable
conductor and connector (in case of cable terminations) by application of molten
metal. Either the Metal Inert Gas (MIG) or Tungsten Inert Gas (TIG) welding
process is adopted in these cases. The MIG welding process, which generates less
heat during the welding operation, is commonly used in the USA for large aluminum
cable conductors.
Welded connections are also used for copper conductors with enameled strands. If
crimp connectors were used on these conductors, the enamel coating would need to
be removed from every strand, which is a quite elaborate and time-consuming
process.
As significant heat is generated during welding, care should be taken that cable
insulation is not overheated. It is necessary to dissipate excess heat to keep temperature of the adjacent conductor and surrounding cable insulation below a specified
value. Once the cable conductor reaches the maximum allowed temperature, the
welding operation has to be interrupted to let conductor cool down. This is why
installation of welded connections is more time consuming than for other connection
types. Only trained, highly skilled operators using appropriate welding and cooling
equipment can perform this task.
Efficient cooling speeds up the process. Use of heat-sink clamps in combination
with forced air or gas flow is the most common method. In some cases, water is used
as coolant for extruded cables. In case of oil filled cables, the cooling system is more
elaborate since it has to incorporate provision of vacuum application in order to
remove the oil from the strands in the weld area.
The strands of the cable conductor have to be thoroughly cleaned to remove any
insulating tapes or cable conductor filler material before welding. If these are not
removed, the weld is contaminated and becomes porous which results in reduced
conductivity and low mechanical strength of connection.
As shown, the procedure for welding power cable conductors is elaborate. That is
one of the reasons why commercial installations of underground cable with large
aluminum conductors only began after methods for field-welding the conductors
were developed and proven.
10.3.2.3.1 MIG Welded Connector for HV Joints
Two cable conductors can be welded to each other with or without use of a
connecting sleeve. The weld itself provides an electrical connection that is equivalent to the conductor and is not subject to instability during heat cycles due to
decrease of contact pressure. However, the tensile strength of the welded connector is significantly (50–60%) lower than the ultimate tensile strength of the
conductor due to annealing of the conductor near the weld. If necessary, mainly
for submarine cables, the tensile strength can be improved by round-compressing
the conductor and the weld (hardening process) and/or using a connecting sleeve,
which is crimped to both cable conductors to bridge the weld and provide
mechanical strength.
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Test Regimes for HV and EHV Cable Connectors
447
Fig. 10.16 Aluminium MIG-Weld Connector for HV cable terminations
The conductors to be joined are cut in a wedge shape, and then buttered with weld
metal, and the two “V” grooves are filled until the conductor diameter is reached. As
a result, this connection is flush with the conductor, which is necessary when the
joint must have a minimum diameter, such as in laminated paper cable joints.
10.3.2.3.2 MIG Welded Connectors for HV Terminations
Figure 10.16 shows a typical MIG weld connector for HV cable terminations where
a high tensile strength of the connection is required. The connector features a ferrule
to be crimped to the cable conductor and provide additional mechanical strength.
Electrical connection is established with molten metal applied between conductor
and connector through weld “windows” in the connector barrel.
The connector stalk (stud) is threaded and secured with a threaded hood at the
termination top plate, ensuring that the cable will not slip due to its own weight and
the weight of other termination components.
The cable conductor to be joined is cut in a wedge shape, and then buttered with
weld metal as shown in Fig. 10.17. The connector is slipped over the prepared
conductor and windows in the ferrule aligned with the wedge shaped and buttered
conductor. The two windows are filled until the connector diameter is reached. As a
result, this connection is flush with the connector. The weld provides an electrical
connection that is equivalent to the conductor. For additional pull out strength, the
ferrule is crimped to the conductor.
10.3.2.4 Exothermic Welded Connections
An exothermically welded connection is produced using a welding process that
employs molten metal to permanently join the conductors. They are widely used in
MV and some HV applications. The process employs an exothermic reaction of a
thermite composition to heat a metal powder together with the conductor and
conductor/ferrule to be joined. Thermite is a pyrotechnic composition of metal
powder, which serves as fuel, and metal oxide. It requires no external source of
heat or current. These connections can have excellent current-carrying and short
circuit capacity, do not loosen up in service, and do not corrode. They form a
permanent, low resistance connection, provide a molecular bond, and do not deteriorate with age.
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M. Uzelac
MIG weld Al connector
“V”-shape cut and “buttered”
cable conductor
Cutting and “buttering”
heat-sink jig
Welding heat-sink jig
Weld
Thermocouple location
Fig. 10.17 Steps in installation of MIG weld connector for HV cable termination
The exothermically welded connection requires lesser length of exposed connector from that required by other connector types, for example, crimp or mechanical
connector. Less than 100 mm of conductor needs to be exposed at each cable end.
Fillers and nonmetallic materials must be removed before making the connection.
Environmental conditions have to be considered when preparing and making a
connection. The handling of exothermic weld powder must be treated with care
and in accordance to manufacturer’s instructions.
Exothermically welded connections are applicable for all types of HV cable
conductors and materials:
• Round and stranded Al or Cu conductors
• Segmented Al or Cu conductors
• Solid Al or Cu conductors
Figure 10.18 shows different types and material combinations of exothermically
welded connections for HV cable terminations. Inside of the connector the area
should be melted homogenously without any cavities. Single wires should migrate
into the melted area transition-free and seamlessly.
Combinations and transition of different types of conductors and/or materials are
also possible. Figure 10.19a shows connection of two aluminum stranded conductors of different size.
After it is made, each exothermically welded connection must be visually
inspected at the site. The condition of the outer surface must comply with visual
inspection requirements of the connector manufacturer.
Relationship between connector quality and condition of the outer surface of the
connection has been established by manufacturer during development tests.
Figure 10.19b shows cut through the connector that successfully passed
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Test Regimes for HV and EHV Cable Connectors
449
Fig. 10.18 Aluminum and copper exothermically welded connector for HV cable terminations
Fig. 10.19 Aluminum and copper exothermically welded connections for HV cable joints
development tests. Notice that there are very few porosity holes inside the connector
as well as at the outside holes. Each connector manufacturer has their own criteria in
size and population of the porosity holes and depressions.
The equipment for making exothermically welded connection consists of crucible
made from graphite and unique ceramic fiber smoke filter system as shown in
Fig. 10.20. The filter prevents sparks and reduces generation of dust and other
emissions to acceptable level, even if used in unventilated manholes and cable tunnels.
The installation equipment is portable with no external source of power required.
10.3.2.5 Copper Brazing
Copper brazing is often used in submarine cable joints especially in factory joints
and repair joints because they must have almost same diameter as the cable before
the armor is applied. Compression type connector and mechanical (shear-bolt)
connector are not used for factory joints because they would add up to the diameter
and obstruct further manufacturing.
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Fig. 10.20 Equipment for making an exothermically welded connection
Like welding, brazing and soldering are important methods of thermally joining
metals. Both welding and brazing/soldering lead to the formation of a metallic joint;
however, the chemical composition of these joints differs. Whereas a welded joint
has the same chemical composition as that of the two identical parent metals being
joined, the use of a filler alloy in a brazing or soldering procedure means that the
brazed or soldered joint has a different chemical composition to that of the parent
materials. Brazing and soldering do not involve any melting of the parent material,
that is, of the surfaces to be joined. Instead, the work pieces are joined by introducing
an additional molten metal, the “filler metal,” possibly in combination with a flux
and/or in a protective gas atmosphere. Some of the advantages of brazing or
soldering compared to welding are:
• As less heat is applied in the joining process, brazed or soldered parts tend to
exhibit greater dimensional accuracy and less distortion.
• Multiple brazed/soldered joints can be created on a single work piece in a single
operation.
• Intricate assemblies can be brazed/soldered without damage.
• Brazed/soldered joints exhibit good thermal and electrical conductivity.
• As brazing/soldering directs less heat into the joint than welding, there is less
residual stress and distortion in the component.
The following points should, however, be noted: the strength of a brazed or
soldered joint is typically not as great as that of the parent material; the parent metal
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Test Regimes for HV and EHV Cable Connectors
451
and the braze/solder metal have different chemical potentials; there is a risk of
chemical corrosion due to the presence of flux residues; extensive preparatory and
after-treatment procedures are often required, such as degreasing, etching, removal
of flux residues.
The related joining techniques of brazing and soldering are distinguished in the
DIN ISO 857-2 standard by the liquid temperature of the filler metal used. In
soldering, the liquid temperature of the filler metal is below 450 C; in brazing it
is above 450 C.
Brazing is used if the joint will be subjected to high mechanical and thermal
stresses. When brazing copper, the filler metals of choice are brass brazing alloys,
copper-phosphorus, and silver brazing alloys. Silver brazing filler metals have lower
brazing temperatures, which reduces the risk of forming coarse grains and enables
faster brazing speeds. Copper brazing procedure is shown in Fig. 10.21.
In order to achieve a high-quality brazed joint between cable conductors, the
mating surfaces need to be carefully prepared. Surface preparation can involve
chemical, mechanical, or thermal cleaning procedures or a combination thereof.
The parts to be brazed must be clean and free from any residues that might inhibit
wetting, such as oxides, oil, grease, dirt, rust, paint, cutting fluids. In case of stranded
conductor, inner wires as well as outer wires of near mating surface of the conductor
should be cleaned carefully. The connecting mold can be mounted to position each
end of conductor properly. In order to avoid overheating of cable insulation, heatsink or cooling blocks of water or forced air or cooling gas are usually set up near the
insulation. The choice of an appropriate brazing process and suitable flux and filler
materials is critically important to produce conductor joint with sufficient mechanical properties. Conductors are brazed with a single brazing seam across the entire
diameter or layer by layer or segment by segment or wire by wire.
The quality of a brazing process depends on the skill and experience of the
operator. If the parent material and filler alloy are properly matched, and if the
joint is properly designed and made, a brazed joint can provide as a reliable join as
that achievable by welding. Brazing faults and defects such as flux burning,
de-wetting, discontinuities, cracks, porosity, incomplete fusion, or penetration and
nonmetallic inclusions must be avoided. Sometimes, in order to check brazing
Fig. 10.21 Copper brazing procedure
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M. Uzelac
quality, nondestructive testing such as X-ray or Ultrasonic can be executed
according to the manufacturer’s instruction.
10.3.2.6 Clamp Connectors
A clamp connector (Fig. 10.22) consists of two components, machined to fit bare
cable conductor of specific size. In some cases, it may cover several conductor sizes.
The inner surface of the connector often has grooves to increase number of connection points (“A”-spots). This design can be used for both aluminum and copper
conductors. Bolts in different numbers and position are used to apply pressure on the
conductor and are tightened to a specified torque. Tightening the bolts in sequence
specified in installation will insure proper d forces and doing so the conductor will
have a relatively even force from all sides. An advantage with this connector type is
that they do not require special tools.
It is absolute requirement that conductors are free of any foreign material.
Segmental or strand filled conductors or conductors with individually insulated
wires (enameled strands) must be thoroughly cleaned. The segments and then
individual wires must be spread out, cleaned, and then put back together as in
individual conductor (see Fig. 10.23).
This is very time-consuming operation, requires extreme patience and concentration
but needs to be properly done to insure lifetime performance of the clamp connectors.
10.3.2.7 Creuset Connector
The Creuset “crucible” welding process is a reliable method of making electrical
connections used to connect two cables with aluminum conductors.
In this process, granular metals of aluminum are dispensed into a graphite
crucible mold adapted to the cross section to connect and heated (Fig. 10.24).
A gas flame as source of energy is used to cause the fusion inside the crucible.
The mold is then removed and the weld is allowed to solidify. The process takes
seconds to complete.
Excessive heat is generated during welding process and care should be taken that
cable insulation is not overheated. Appropriate cooling system is used to dissipate
Fig. 10.22 Clamp type connector
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Test Regimes for HV and EHV Cable Connectors
453
Fig. 10.23 Cleaning of strand-fill segmental conductors
Fig. 10.24 Mold setup for Creuset connection
excess of heat and to maintain temperature of the conductor and surrounding cable
insulation below specified value.
Creuset welding produces connection with high performances as it is a perfect
molecular bond, the conductor is not broken, and there are no contact surfaces.
The integrity of the effective cross section of the conductor is unaltered. The final
result is shown in Fig. 10.25.
Only trained and qualified jointers using appropriate welding and cooling equipment can perform this kind of welding (see ▶ Chaps. 5, “Cable Accessory Workmanship on Extruded High Voltage Cables” and ▶ 6, “Guidelines for Maintaining
the Integrity of Extruded Cable Accessories”) of this book.
10.3.2.8 Grounding Cable Connectors
The good electrical contact between the metallic screen and the ground connection should
be effective during the complete life of the cable and particularly in the accessories.
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Fig. 10.25 Mold removed and finished “Creuset” weld after final cleaning
Particular attention has to be paid to the endurance of the ground connection at the
accessories, currents in the screen may be important, and the ability of the screen
connection must not to overheat during cycling should be checked.
The TB 446 (Advanced Design of Metal Laminated Coverings: Recommendations for Tests, Guide to Use, Operational Feedback) by WG B1.25 [35] describes
the three successful designs that are today covering the market:
Combined Design – combined mechanical and electrical properties
Separate design – separated mechanical and electrical properties
Separate semi-conductive design – separated electrical and water tightness properties with semi-conductive plastic-coated foil
Following are the most commonly used cable sheaths:
•
•
•
•
•
•
•
•
Lead sheath
Lead sheath with copper wires
Aluminum corrugated sheath
Aluminum smooth sheath
Aluminum laminated sheath
Copper wires + aluminum laminated
Copper wires + Cu laminated
Aluminum wires + aluminum laminated
Ground connectors must satisfy the following electrical functions:
•
•
•
•
•
•
•
Satisfy the short-circuit conditions, transfers short circuit current
Transfers currents circulating in cable screen
Collects capacitive current and induced currents
Fixation of earth potential
Evacuates short circuit current and circulating currents with both ends earthed
In case of disconnection from earth, electrical withstand between earth and screen
Suppression of screen currents with single end earthing or special bonding
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Test Regimes for HV and EHV Cable Connectors
455
Chemical functions:
• No corrosion of contact points
Thermal and mechanical properties:
• No degradation of connection and surrounding with thermal short circuit
In the case of a single phase short circuit, the current can flow through the metal
screen, the metal screen/grounding connection, the ground lead of the joint or the
termination.
Existing short circuit tests as per TB 446 [35] have been designed to test metal
screen/grounding connection in a simple way, electric parameters of this test have
been chosen to be such that the test capabilities are available in many laboratories at
an acceptable cost.
Test
Five short circuits shall be applied successively to the assembly:
• Before the short circuit test, the cable conductor shall be heated and stabilized for
at least 2 h at a temperature 90–95 C.
• The short circuits are separated by an interval of time long enough to cool down
the cable screen within 5 K of its initial temperature.
Rating
• The short circuit rating has to be determined by calculation.
• The maximum short circuit duration is 5 s.
• Asymmetry is free.
Result
Examination of the samples should reveal no cracks or separation of the metal foil
of laminated protective coverings or damage to other parts of the cable.
There shall be no sign of harmful deterioration of the cable/joint screen connection, neither at the cross-bonding leads nor at the grounding connections.
10.3.3 Diagnostics for Cable Connector Condition Assessment
Regular check of the temperature of termination connections is done by infra-red
(IR) cameras. Poor connection pressure due to improper installation or inappropriate
surface protection and treatment of contact surfaces between termination cable
connector and buss connector resulting in corrosion of contact surfaces are the issues
that will result in overheating of the connection. If not detected on time, the issue
may result in thermal runaway and physical damage of the connection resulting in
costly repair.
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The temperature of the connection of the molded rubber joint may be controlled
be fiber optic cable which may be laid over the joint body or over the housing in
which the joint is installed. The CIGRE TB 247 on Optimization of Power Transmission Capability of Underground Cable Systems Using Thermal Monitoring
shows current practice of laying FO cable over the joint in different countries [33].
CIGRE TB 756 “Thermal Monitoring of Cable Circuits and Grid Operators use of
Dynamic Rating Systems [36] by CIGRE WG B1.45” provides an update and a
comprehensive bibliography.
The X-ray method is mostly used in MV applications. This method shows proper
positioning of the cable connector inside the joint. Improper positioning of the
connector may cause dielectric failure. This method is also used to periodically
check for signs of cable distortion resulting from thermo-mechanical movement of
cables and joints in the HV pipe-type cable systems, resulting in thermo-mechanical
bending (TMB) of the cables, which eventually may cause electrical failure.
10.4
Cable Connectors in Accessories
10.4.1 General
Accessories are an essential part of HV cable system. They need to operate under the
same electrical conditions as the cable.
In relation to the connector system of the accessories, we can distinguish between
current load and mechanical load.
The current load is enforced by the operation current of the cable and can be
divided in normal load, emergency load (in some countries), and the load under short
circuit conditions, that is, short circuit currents.
The mechanical load or forces in the connector system can be divided in internal
and external forces. The internal forces, also called thermo-mechanical forces, are
generated by the thermal expansion of the cable due to operating and short circuit
currents. The external forces are generated by the environment of the cable system
and are, for example, the consequence of gravity, clamping, soil movements,
vibrations, etc.
Forces generated by gravity or thermo-mechanical movements of the system are
the so-called static forces. These forces act continuously under the influence of
gravity or have a cyclic behavior as a consequence of the load cycles, which usually
appear in a daily sequence. The forces usually start as pushing forces, so called thrust
forces, caused by the thermal expansion of the conductors, but will eventually also
generate pulling forces during no load or low load of the system.
Under the influence of the high thrust forces (in the order of tons) the conductor
starts to deform, distributed over the entire cable, making it effectively shorter. Once
the load decreases the thrust forces will go down and eventually generating pulling
forces. For this reason, the connector system has to be able to withstand both pushing
and pulling forces.
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Test Regimes for HV and EHV Cable Connectors
457
The main cause for the dynamic load of the system is short circuit forces passing
through the system. Due to the magnetic field, generated by the short circuit current,
forces are generated perpendicular on the cable. These forces, the so-called Lorentz
forces, can generate pushing and pulling forces and are usually of short duration (less
than 1 s).
Apart from the magnetic forces there is also the effect of the thermal expansion of
the conductor under the short circuit conditions. In case of HV systems, with usually
large conductor sizes, the temperature increase is low and the impact of the thermomechanical expansion negligible.
Short circuits can also have a very local impact on the connector system,
thermally and magnetically.
High contact resistance will cause high local dissipation and increasing temperatures. Because of this the mechanical properties of the conductor material can
change (annealing) lowering the contact pressure and increasing the contact
resistance.
The currents in the parallel conductor wires will cause a strong magnetic field and
related magnetic forces pushing the wires more closely. Also, this effect may
temporary lower the contact pressure with the connector, increasing the contact
resistance.
Detailed overview of the thermo-mechanical forces involved with large conductor XLPE cable system (1000 mm2 and above) is provided in CIGRE TB
669 “Mechanical Forces in Large Conductor Cross-Section XLPE Cables” [32].
Such forces can generate high axial thrust and tension and/or significant cycling
movements in the installed cable system. The designer of connectors for these cables
in HV and EHV applications has to take these forces into account and to incorporate
into development tests.
10.4.2 Mechanical Loads
The connectors for HV cables are exposed to significant mechanical forces during
assembly process of cable accessories due to movement of the cable and accessory
into their final position [32]. More importantly, connectors are exposed to thermomechanical forces in service generated by thermal expansion and contraction of the
cable due to variations of the load current or exposure to the short circuit current
[32]. In practice, the forces caused during the installation process are not problematical and are not usually limiting for an HV connector. However, the loads imposed
on the conductor due to changes in conductor temperature can be very significant.
After initial installation, the cable conductor is normally relaxed with little axial
mechanical force present. However, as the temperature increases the conductor
expands and, if the cable is rigidly installed [27], then axial thermal expansion is
prevented and instead a compressive force develops in the conductor (which is
evidenced as a thrust force from the conductor at the cable ends). If a rigidly installed
cable is heated rapidly to its full operating temperature on the first load cycle, then
relatively high forces can be developed. However, if expansion is fully prevented
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then the result is that relaxation of the maximum thrust occurs towards the maximum
conductor temperature, reducing the compressive force produced. However, a consequence of this relaxation is that a tensile force develops in the conductor when it
cools down to the initial installation temperature (or below). Typically, after a
number of cycles the compressive and tensile forces developed in a conductor
cycling over its full temperature range will be similar, and with values of approximately 50% of the maximum force that might be achievable in a single rapid cycle.
As far as the connector is concerned the conductor tensile force is the most critical
as it will tend to pull the conductor out of the connector. In the case of the conductor
compressive force then this is normally equal and opposite to the force from the next
cable length on the other side of a joint or in the case of a termination has to be
resisted by the connection of the connector to the body of the termination itself.
Thus, in terms of testing the performance of connectors only the tensile (pullout)
force from the conductor has to be considered.
In assessing the behavior under tension of a conductor to connector connection,
the tensile load that can be resisted with minimum movement has to be assessed.
10.4.3 Environment
Consideration of Environmental Conductor Size Optimization
Over the years, energy utilities have considerably increased their requirements to
consider the ecological environmental impact of electric cables in relation to their
service conditions. Environmental considerations should be included in both design
and redesign work with respect to the raw materials used, energy consumption and
emissions during production, end of life disposal or recycling, and in-service
performance. A specific guidance document has been published by IEC TC 20 in
2007 as the technical report IEC/TR 62125 “Environmental statement specific to
IEC TC 20 – Electric cables.” This guidance will be replaced by IEC 62125
Ed. 1 showing a qualitative checklist based approach for environmental impact
and quantitative approaches by using life cycle assessment (LCA) or an energy
cost based conductor size optimization (ECSO). The results obtained by applying
such methodologies can be used for external communication.
As recommended by IEC Guide 109, the basis of the assessment of productrelated environmental impact is Life Cycle Thinking. Environmental impact of a
product needs to be evaluated considering its whole life cycle and evaluating various
environmental indicators. LCA is a tool covering all life cycle stages (cradle to
grave). An LCA shall be carried out in accordance with the methodology of life cycle
assessment (LCA) specified in ISO 14040 and ISO 14044.
Environmental and energy cost based Conductor Size Optimization is taking into
account the cable’s life phases’ costs and reduction in power loss costs during use
phase and related costs of CO2 compared to the conventional sizing of highly loaded
cables with significant energy losses. ECSO takes specifically into account:
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Test Regimes for HV and EHV Cable Connectors
459
• Initial cost of investment including manufacturing, transportation, installation,
and final disposal costs
• Cost for CO2 emission during manufacturing, transportation, and installation and
final disposal
• Costs for Joule losses during anticipated life time
• Costs for CO2 emission during anticipated life time
There is an ecological and economical demand for more efficient operation of
electric cables and some information is available on suitable cable design parameters
to achieve lower losses. Unfortunately, diverse pressures from a number of interests
usually result in the need to compromise in this area. Lower transmission losses,
reduced heating effects, and, as a result, lower emission of greenhouse gases and
hence reduced carbon footprint might be achieved.
Energy losses during service are dominated either by the duration under load,
which could be many decades for HV cables in transmission or distribution networks, or by a combination of time under load and length of the network. The current
loads will create temperatures which might start ageing effects in insulation and
inside connections. A certain end temperature is needed to initiate such aging effects
and long lasting high temperatures might consume lifetime. The lower the current
loads are, the lower the reached temperature exposure of cable systems and, respectively, the lower the risk of limiting service lifetime will be. Balancing total costs of
ownership by additionally involving environmental aspects often shows that the
conservative approach, running a cable system at 40–60% nominal load, will create
optimal results and besides that limit the risk of connector failures. Cable system
qualification tests including connector development tests will simulate some worst
case conditions but will give only limited information about long time endurance and
life time expectation when running a cable system close to its nominal loads.
The Technical Brochure 689 “Life Cycle Assessment of Underground Cables” by
CIGRE WG B1.36 [37] provides guidance for the implementation of an eco-design
approach applied to underground cables, through the use of LCA methodology by giving
principles of LCA (standards, guides, historical approach), a state of the art regarding
studies and reports on this topic, a methodology to perform LCA on underground cables,
and an LCA case study. In conclusion the main results, highlights, and limits are discussed.
10.4.4 Cable Connectors in Joints
10.4.4.1 General
Joints are subjected to current load and mechanical forces.
The main consequence of the current load is the heating of the cable and
connector system, leading to elevated temperatures inside the joint. In continuous
operating conditions, temperatures exceeding the maximum operating temperature
of the extruded cable need to be avoided [30]. In this respect the conductivity of the
connector system and the thermal properties of the joint have to be considered.
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The connector system needs to withstand the mechanical forces that do exist in cable
systems, such as pushing (thrust), lateral and pulling forces. See Reference [32]. These
forces should not lead to instabilities in the performance of the connector system.
10.4.4.2 Thermal Rating of the Joint
The CIGRE TF 21 (B1)-10 reviewed if existing IEC Specifications for HV/EHV
extruded cables and their accessories appropriately specify and verify the crucial
thermal and thermo-mechanical characteristics of accessories. The thermal rating of
an accessory is defined as “the maximum temperature of the conductor or conductor
connector contained within the accessory (whichever is the higher) allowed in
normal operation.” The report of TF 21-10 is given under ▶ Chap. 9, “Thermal
Ratings of HV Cable Accessories” of this Book.
TF B1-10 finished its work on schedule in 2003 with the following conclusions
(see reference [30] and ▶ Chap. 9, “Thermal Ratings of HV Cable Accessories”):
• Thermal ratings of accessories need not be specified separately from cables, as
they are considered identical due to the presence of cable inside the accessory.
• The successful completion of IEC thermal tests at a complete cable system can be
considered as simultaneous verification of the adequate thermal design of both,
cables and accessories, provided that comparable or higher conductor temperatures as rated for the cable are achieved inside joints. These test conditions shall
be realized by applying only cable conductor current heating.
• The thermal performance of terminations in normal operation is not considered
critical; therefore, they do not have to reach the rated temperature for the cable
during test.
• External thermo-mechanical forces can be reproduced in the IEC prequalification
test only for the specific installation conditions applied.
• The thermal limits of accessories and external thermo-mechanical forces in
service operation cannot be reproduced comprehensively by standardized tests,
but have to be taken into account for each individual case by the systems design
engineering.
The Annex 1 of referenced document [30] shows thermal calculation for HV and
EHV extruded cable joint. It is shown that in stationary conditions, the cable conductor in the joint reaches a higher temperature than in the cable, because of higher
thermal resistance of the joint. In the first 6 h of the heating cycle, the temperature of
the cable conductor in the joint is lower than in the cable conductor outside the joint,
as shown in Fig. 10.26 and Fig. ▶ 9.3 in ▶ Chap. 9, “Thermal Ratings of HV Cable
Accessories” of this book, due to the longer thermal time constant of the joint.
10.4.5 Cable Connectors in Outdoor Terminations
In most of the termination designs, the connector is located in the top of the
termination. The connectors in terminations are usually large, compared to the
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Test Regimes for HV and EHV Cable Connectors
461
110
100
90
Temperature (˚C)
80
70
60
50
40
30
Joint
20
cable
10
0
0
1
2
3
4
5
6
Time (hours)
7
8
9
10
Fig. 10.26 Typical heating curve of 138 kV extruded cable and molded rubber joint
connectors in joints, and therefore usually not considered critical. Beside this, the
termination connectors are exposed to environmental conditions, which usually
represents effective cooling. Exposed section of connector has to be designed to
operate under different environmental conditions.
Important for termination connectors is its thermal stability and the resistance
against thermo- mechanical forces. The conductor below and inside the termination
will generate thrust forces during load, which might change to pulling forces in no
load conditions. Depending on the conductor arrangement inside the terminations,
the thrust force can result in cable bending causing cantilever loads.
The connector systems have to be able to handle all these forces.
10.4.6 Cable Connectors in Equipment Type Terminations
Equipment terminations, such as GIS and transformer terminations, can be divided
in open and closed top design (see ▶ Chap. 11, “Standard Design of a Common, Dry
Type Plug-in Interface for GIS and Power Cables up to 145 kV”).
In the open top design, the connector is mechanically fixed in the top of the
termination after installing the cable. This is usually a screw connection. This allows
the thermo-mechanical forces to the transferred to the termination insulator. Apart
from the connection with to the cable conductor, there is also an electrical contact
with the embedded electrode of the termination insulator. This contact is a metal/
metal contact based on adequate contact pressure.
In the closed top design, a metal enclosed top electrode is integrated in the
(epoxy) termination insulator. During installation, the cable is plugged into the
termination. The conductor of the cable is provided with a plug and the plug is
connected to the top electrode by means of multicontact system.
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For the connection with the conductor, similar conditions apply as for the joints
and outdoor terminations.
Plug-in contacts are based on a male/female connector system, connected through
a multicontact system, achieving continuous contact pressure.
In the equipment terminations, there are the locked and unlocked designs of the
connector system. In the locked design, the plug-in connector is fixed in the
termination, transferring the forces to the termination insulator.
In the unlocked design, the cable is fixed below the termination by means of
clamping. The clamping can be integrated in the termination design or installed
externally.
10.4.7 Connections to the Cable Connectors
10.4.7.1 General
Cable connectors are used for connecting two or more cable conductors to each other
inside the joint or connecting cable conductor to the terminal of the overhead line or
terminal of the equipment such as GIS, transformer. The construction, type, material,
and installation methods of connecting cable conductors to the cable connectors are
well explained other part of this report, so in this section, it will be described to
connect cable connectors to the terminal of overhead line or the equipment.
10.4.7.2 Outdoor Terminations
Outdoor termination connects the cable to either substation component or busbar or
to the overhead line. The connection of the cable conductor to the substation
component or overhead line is achieved.
10.4.7.3 Equipment Type Terminations (GIS and Oil Immersed)
Cable connections for gas-insulated switchgear (GIS) are defined by IEC 62271-209
[7] and oil-immersed cable connections for transformers and reactors are defined by
the relevant standard, EN 50299-1 [8] or EN 50299-2 [9]. Figures 10.27, 10.28, and
10.29 illustrate typical arrangements proposed in these documents.
The main circuit end terminal of GIS or transformer is generally connected to the
top conductor of the cable termination through screws at rated normal current up to
3150 A. In order to reduce electrical contact resistance, the normal current-carrying
contact surfaces of the connection interface are silver- or copper-coated or solid
copper and apply adequate screw torque during assembling according to the manufacture’s installation manual.
The mechanical forces on the cable termination caused by short-circuit may be
critical to the design of the cable connection system. Total dynamic forces generated
during short-circuit conditions consist of those generated within the cabletermination and those coming from the main circuit of the switchgear. For a threephase connection, the maximum additional force applied from the switchgear to the
connection interface transversely and then being transferred from the main circuit
end terminal shall not exceed 5 kN. For single-phase connections, taking into
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Test Regimes for HV and EHV Cable Connectors
463
Fig. 10.27 Fluid-filled cable connection assembly for GIS – typical arrangement ([7], Fig. 2)
Fig. 10.28 Dry-type cable connection assembly for GIS – typical arrangement ([7], Fig. 4)
account lack of symmetry, it is considered that this additional force is small.
However, a total mechanical force of 2 kN applied to the connection interface
transversely should be assumed. It is the responsibility of the manufacturer of the
switchgear to ensure that the specified forces are not exceeded.
For both single-phase and three-phase connections, additional forces and movements from the switchgear can be experienced due to temperature variations and
vibrations in service. These forces can act on both switchgear and cable-termination
464
M. Uzelac
Fig. 10.29 Cable connection assembly – transformer ([9], Fig. 1)
and depend largely on the switchgear layout, termination installation, cable design, and
the methods of mechanical support. The design of any support structure shall take into
account these forces and movements. It is particularly important that the support for the
switchgear shall not be affixed to the insulator collar and/or clamping flange.
The top conductor design of cable termination can be divided in open and closed
system whether embedded top metal part of insulator is open or closed. Figure 10.30
shows typical open and closed top connector systems.
In case of open top connector system, conductor connector is generally connected
to the embedded top metal part of insulator by screw connection. In order to prevent
gas (or oil) penetration from GIS (or transformer) to cable termination, additional
sealing systems are required between conductor connector and embedded top metal
part of the insulator. Because cable conductor, conductor connector, and embedded
metal part are all connected directly, the thermo-mechanical force due to thermal
expansion and extraction of the cable may affect to the insulator. To minimize this
affection, suitable clamping system is required inside the cable termination or near
the termination. During installation, cable with conductor connector inserted to the
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Test Regimes for HV and EHV Cable Connectors
465
Embedded top insert
Cable connector
Cable conductor
Insulator
(a) Open top
connector system
(b) Closed top
connector system
Fig. 10.30 Typical open and closed top connector system of cable termination
insulator together first and then cable termination is assembled to the GIS or
transformer generally. So, equipment (GIS or transformer) metal enclosure cannot
be factory tested with the insulator. During the final assembly, both installers
(equipment and cable termination) are needed and vacuuming and gas or oil filling
must be performed after final assembly.
In case of closed top connector system, conductor connector with cable is
plugged-in to the embedded top metal part by multicontact, spring, or tulip contact
system. The current-carrying surfaces of conductor connector, multicontact, and
embedded top metal parts are generally silver-coated. The dimensions of outer
diameter of multicontact and the inner diameter of the embedded top metal part
are important in order to maintain suitable contact pressure. Because embedded top
metal part is closed and normally leak test is performed as a routine test, additional
sealing system is not required and more reliable structure in a viewpoint of gas or oil
leakage compared with the open top connector system. There are two types of closed
top connector system. One is locked plug-in type and the other is unlocked plug-in
type. The plug of locked plug-in type cannot be removed without disassembling
insulator from the equipment enclosure, whereas the plug of unlocked plug-in type
can be removed without disassembling insulator from the equipment enclosure.
The thermo-mechanical force of cable may affect directly to the insulator or partly
be compensated according to the design of locked plug-in type; however, clamping
system inside the termination or near the termination is needed to minimize this
affection. Unlocked plug-in type can partly or fully be compensated according to
466
M. Uzelac
the design; however, clamping is essential because plug can easily be removed without
clamping during operation. In case of closed top connector system, insulator can be
preinstalled in the equipment enclosure and the cable with plug inserted later on site.
In this case, equipment metal enclosure can be factory tested including the insulator
including voltage test. During the final assembly, both installers (equipment and cable
termination) are not needed at the same time.
More information will be found in ▶ Chap. 11, “Standard Design of a Common,
Dry Type Plug-in Interface for GIS and Power Cables up to 145 kV” of the book.
10.5
Installation of Connectors
Proper cable conductor preparation and connector installation are crucial for a long
and successful field performance of cable systems. Many failures of medium voltage
accessories have been caused by thermal runaway because of poor connector
installation or/and poor conductor preparation. Most common mistakes are insufficient engagement of conductor into the connector ferrule, insufficient tightening of
the bolts in mechanical connectors, use of inappropriate crimping die for a press-type
connector, fail to remove water blocking material from filled conductors, when
required, or fail to remove insulating coatings from individual strands, when present.
Mandatory trainings in installation of HV/EHV cable accessories, including preparation of conductors and installation of connectors, increase awareness of importance of
proper installation and provides opportunity to check the skills of the splicers. Hence,
there are very few field failures of HV/EHV cable accessories due to connection failure.
10.5.1 Installation Instruction Manual
The manuals for installation of cable accessories (joints and terminations) either
describe steps in installation of connectors or refer to separate manual for connector
installation. Selection of installation tools and strict minding of steps described in
instructions is of essence.
The CIGRE TB 476 Cable Accessory Workmanship on Extruded High Voltage Cables
[31] which is the content of ▶ Chap. 5, “Cable Accessory Workmanship on Extruded
High Voltage Cables” of this book describes in detail technical risks and required skills for
preparation of conductors and installation of different types of connectors.
Only competent and trained personnel familiar with cables, accessories, and safe
operating practices should install accessories, both for testing and field assembly.
Cleanliness during the whole installation is of great importance.
10.5.2 Cable Conductor Preparation
Preparation of conductor is as important as installation of connector. It involves
cutting the conductor (in most cases it is required that conductor cut is square),
removing insulation and exposing cable conductor to specified length, removal of
10
Test Regimes for HV and EHV Cable Connectors
467
Fig. 10.31 Cleaning and crimping of filled 2500 mm2 Cu conductor
strand filling materials (powders, yarns, cloth. . .) if present, removal of coating from
individual strands when strand insulating conductors are used and cleaning exposed
conductor. The cable insulation must be protected from damage and metallic particles during all these steps.
Figure 10.31a shows example of preparation of segmental, strand filled cable
conductor. Individual strands from each segment must be flared out, cleaned from
the filler, and then put back together to form the segments of the same shape as in
original conductor. Considerable skill and training is required to perform this
operation. If not done properly, the strands may be damaged or conductor shape
and outer diameter changed such that connector would not fit.
10.5.3 Mechanical Connectors
This connector type uses bolts to apply pressure to the underlying conductor. It can
be used on both copper and aluminum conductors. Mechanical connectors do not
require special tools for installation and the skill level is relatively easy to achieve in
proper training, positioning of properly prepared conductor(s) into connector and
tightening the bolts is spelled out in instructions. Most connector designs are of the
shear-bolt type where the bolt is tightened until they shear. Other designs require
tightening of the bolts to specified value.
The tightening sequence must be followed as specified in instructions. Factory
applied lubricants (if present) are not to be removed.
The sharp points need to be removed and, if required, the holes filled after all the
bolts are tightened or sheared.
10.5.4 Crimp Connector
The most common connectors in HV applications are still of the crimp type.
Depending on the cable size and manufacturer, many crimping tool types are used.
They may be either with or without crimping dies.
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M. Uzelac
The die-less crimping tools feature one, two, or four rams (indenters). Rams put
deep indents in the ferrule and deform the ferrule and underlying conductor. The
die-less crimping tools are adjustable to take larger span of connector/cable conductor sizes.
The crimping tool with dies features the crimping head that accommodates dies
for different connector sizes. The dies are usually of circular or hexagonal shape but
other shapes, for example, ellipse, are also used. The width of the die differs
substantially between manufacturers.
Material of connector ferrule matches material of conductor: copper ferrules are
used on copper conductors and aluminum ferrules on aluminum conductors. Since
the cross-sectional area of aluminum ferrule is bigger than cross-sectional area of
conductor, the crimping dies for copper and aluminum connectors are different. The
aluminum ferrules tend to be longer than the copper ones, accommodating larger
number of crimps.
All the variables mentioned above are taken into account by cable accessory
manufacturer when the connector is designed and the crimping tool, crimping dies,
sequence, and number of crimps are specified. It is important that the cable accessory
manufacturer is consulted if different crimping tool or set of dies are intended to
be used.
10.5.5 Exothermic Welding Connector
Exothermic welding uses chemical reagents in a reusable crucible, placed above a
mold specifically designed for the conductors being welded.
This is a special technique and includes placing the correct quantity of reactants in
the crucible. It is necessary to take good care to avoid porosity and cavities in the
welding mass. This can come from the presence of moisture or filler in the conductor.
The setting of the gap between the conductors needs to be done carefully, then the
crucible and mold assembly is installed and filled before firing the reactants so they
drop into the mold, melting the ends of the conductors together. During this process,
the presence of any porosity should be noticeable.
It is important to follow the manufacturer’s instructions carefully and to be aware
of the risks, for example, high temperatures and toxic gases evolved during the
process.
10.5.6 MIG or TIG Welding Connector
The installer must be qualified and experienced for this kind of installation and
follow the instructions for the welding equipment.
This technique involves using arc welding in an inert gas with a feed wire of
copper or aluminum. The wire must be appropriate to the welding machine. The
conductor ends are cut diagonally to form a V shape when placed in the welding jig.
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Test Regimes for HV and EHV Cable Connectors
469
In a normal installation, overheating of insulation during welding must be
avoided. In a test situation this might not be a critical point. Heat sinks or forced
coolers are generally applied on both sides of the exposed conductor. Prior to
welding all enamel must be removed from enameled copper wires before MIG or
TIG welding is carried out. After welding is completed any sharp edges or points
must be removed from the connection.
10.6
Experience
The working group spent substantial time in gathering information on experience
with cable connectors in HV and EHV cable systems. The methods to get information were presentations by users at the WG meetings and world-wide survey.
10.6.1 Utility Presentations at WG Meetings
10.6.1.1 USA
Two major utilities from the USA shared their experiences. One of the utilities
addressed cable connectors in HV applications (69–345 kV) and the second one in
MV applications (up to 46 kV).
While there were only a few connector failures in 60 years history of HV
laminated cable connectors, there were no reported failures for connectors in over
20 years’ experience with HV XLPE cable systems.
Experience for MV cable connectors is not so good. The number of failures, and
in particular connector failures, in joints increased with introduction of wind farms.
Analysis of the failures indicated the cause generally to be the incorrect selection of
connectors.
10.6.1.2 Germany
The following is a short summary of the presentation by Christian Walter at the third
CIGRE B1.46 meeting in Winterbach, Germany, on 26 Nov 2014.
Mr. Christian Walter leads the technical team “HV cable systems” of “E.ON
Centre of competence grid and distributed energy” in the legal entity “Bayernwerk
AG” located in Bayreuth, Germany. As a global player, E.ON sources cable systems
worldwide.
Up to now their experience shows no connector failures. The load management
on cable systems is conservative due to the n-1 criterion and is reaching up to 50% of
the nominal rated load. For the implementation of new cable systems, measures have
been taken to improve the quality management systems to be able to run cable
systems at their calculated limits, adapted and verified for each single project,
especially when connecting wind farms and renewables.
Systems for distribution cables up to 110 kV are specified in a technical specification following in most parts test conditions for the next higher voltage level
132 kV according to Cenelec HD 632.
470
M. Uzelac
For future operation, the ampacity calculation according to IEC 60287 is verified
by DTS measurements taking into account the soil conditions while increasing loads.
Even joints will be equipped with optical fibers to determine the connector temperatures. In particular there will be an evaluation of the behavior of new cable systems
due to rapidly changing grid loads from nearly 0% up to 100% daily (in solar plants)
or weekly (in wind farms). There will also be a lifecycle evaluation process with
periodic PD and tan Delta measurements being made.
Cable-system delivery for a project is only accepted by a single contractor
representing the cable manufacturer, the accessory manufacturer, and the installation
company. During the qualification process, two type tests according to HD 632 have
to have been completed: One for a small aluminum conductor, for example,
630 mm2, and one for the biggest aluminum conductor, for example, 2500 mm2.
The cable conductor has to be according to IEC 60228 with the following designrestrictions: conductors to be compacted stranded circular (class 2). Solid conductors
made are not used. Conductors above 1200 mm2 shall be segmented (Milliken
conductor). Milliken designs shall have at least five segments. In future only cables
with aluminum conductors will be purchased. Due to increasing ampacity requirements, cross sections larger than 2500 mm2 may be needed in future projects.
Longitudinal water tightness of stranded conductors is required. Materials used
for that purpose shall not be toxic. A semi-conductive bonding tape shall be used to
prevent the inner semi-conductive layer penetrating the gaps between the conductor
wires.
To reduce installation failures, only mechanical connectors equipped with shear
bolts shall be used on stranded conductors. Due to a lack of test experience, no
compression connectors are in use. Welding of connections will no longer be
accepted due to an incomplete quality management system and for safety reasons
on site.
Because connector type tests for high voltage cable applications are not yet
specified, available type tests similar to IEC 61238-1-3 are requested with a minimum of 1000 heat cycles showing temperature stability with a min. 2500 A for
2500 mm2 aluminum. Currently just a few type tests can be shown on connectors for
big cross-sections. Short circuit withstand ability should be tested with a min. 40 kA/
1 s (3 phase). A mechanical tensile test with a min. 100 kN for 2500 mm2 will be
required. Aluminum should show no slippage and no elongation. As long as no
standardized types and designs for conductors and connectors are available a
qualification of each combination will be necessary.
To get at least limited comparability, a common type test specification for
connectors will be appreciated.
10.6.1.3 France
As the transmission engineering and expertise center for the EDF Group, the CIST
(Power System and Transmission Engineering Centre) shared its experience in
HV/EHV cable systems. It is the focus for all the specialist disciplines involved in
power transmission (power systems and transmission grids).
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Test Regimes for HV and EHV Cable Connectors
471
CIST supervises the construction and maintenance of electricity supply installations, from the generating plant to the power transmission grid operated by RTE
(French transmission system operator).
In France, it negotiates the conditions for connection to the grid; it operates at
voltages of 63 kV, 90 kV, 225 kV, and 400 kV.
Regarding HV cable systems, there were no failures in accessories related to
connectors in the last 10 years.
10.6.2 Worldwide Survey
A survey was sent to utilities in order to assess their cable system and the type of
problems encountered due to connector failures.
The following tables summarize the data collected.
Table 10.6 shows the number of utilities with the range of cable length per voltage
range at the present time, and the additional number of utilities that will fall in that
range. On the bottom of the table, we have the total length of cable per voltage range
for the surveyed utilities. In voltages above 220 kV, we will see an increase of over
35% of the installed base within the next 5 years.
Table 10.7 shows the number of utilities that use a range of conductor sizes at the
present time, and the additional number of utilities that will use these sizes in the next
5 years. Large sizes up to 1600 mm2 and above are used at all voltage levels. The
trend is to use larger size conductors in higher voltage systems.
Table 10.8 shows the number of utilities that use copper and aluminum conductors at the present time and the additional number of utilities that will use them in the
next 5 years. Copper is still mostly used for heavy loads, but aluminum is used as
well.
Table 10.9 shows the number of utilities that use the different types of outdoor
terminations of different voltage class. Oil filled type terminations are still used,
especially at higher voltages. Dry types are becoming more popular at up to 161 kV.
Table 10.10 shows the number of utilities that use different types of termination
vs. voltage class. Dry type terminations are mostly used nowadays, at other than the
highest voltage range.
Table 10.11 shows the number of utilities that use the different joint types
vs. voltage class. An outer housing is widely used, especially at higher voltages.
Table 10.12 shows the number of utilities that experienced connector failures on
accessories vs. Voltage class.
Table 10.13 shows the number of utilities that experienced connector failures
attributed to different causes vs. voltage class. Failures were reported on terminations, but more so in joints (at all voltage levels). Generally, the failures were due to
installation errors, but also from overheating.
Conclusions
• A good number of responses from the utilities (34 surveys from 12 countries)
were received.
Range (km)
1–10
11–25
26–50
51–100
101–250
251–500
501–999
1000+
Nominal cable system voltage (kV)
45–70
110–161
220–287
Now
Future
Now
Future
Now
1
3
4
7
4
1
1
1
2
1
1
2
3
5
5
1
1
1
2
2
4
3
3
7
1
3
1
1
6
3
3
1
Total cable system length in service (km). Surveyed utilities only
12108
9456
1840
Future
2
2
2
1
1
1
777
315–500
Now
4
2
2
1
1
1
Future
3
2
1
1
101
1
500+
Now
1
1
Table 10.6 Number of surveyed utilities that own cable systems and planned in the next 5 years. Total installed length (at surveyed utilities only)
Future
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M. Uzelac
Range (mm2)
<630
630–1000
1001–1600
>1600
Nominal cable system voltage (kV)
45–70
110–161
Now
Future
Now
8
5
16
12
4
23
9
2
18
8
2
13
Future
11
8
10
7
Table 10.7 Range of conductor sizes in service and in next 5 years
220–287
Now
4
7
12
12
Future
1
2
6
8
315–500
Now
1
1
3
6
1
3
8
Future
1
1
500+
Now
1
Future
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Test Regimes for HV and EHV Cable Connectors
473
Range (mm2)
Copper
Aluminum
Nominal cable system voltage (kV)
45–70
110–161
Now
Future
Now
7
8
25
3
1
3
Future
17
6
Table 10.8 Conductor material currently used and planned for future
220–287
Now
16
2
Future
10
1
315–500
Now
11
2
Future
7
1
500+
Now
Future
1
1
474
M. Uzelac
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Test Regimes for HV and EHV Cable Connectors
475
Table 10.9 Number of utilities that have outdoor terminations in service
Outdoor termination type
Oil filled
Dry type, not-supporting
Dry type with additional support insulator
Dry-type self-supporting
Nominal cable system voltage (kV)
45–70 110–161 220–287 315–500
14
23
16
10
1
4
2
7
3
5
4
1
500
2
Table 10.10 Number of utilities that have equipment-type terminations in service
Equipment termination type
Oil filled
Dry type, not plug in
Dry type, plug in
Nominal cable system voltage (kV)
45–70
110–161
220–287
6
9
8
10
14
10
12
22
7
315–500
10
4
2
500
Table 10.11 Number of utilities that have joints in service
Joint type
Without housing for outer protection
With Cu or fiberglass housing
Nominal cable system voltage (kV)
45–70
110–161
220–287
315–500
3
7
1
13
21
16
7
500
2
Table 10.12 Number of utilities that experienced connector failures in service
Accessory type
Outdoor terminations
Equipment type terminations
Joints
Nominal cable system voltage (kV)
45–70
110–161
220–287
10 no
20 no
13 no
2 yes
1 yes
17 no
23 no
10 no
1 yes
2 yes
10 no
14 no
11 no
1 yes
4 yes
2 yes
315–500
5 no
500
3 no
5 no
2 yes
3 no
315–500
500
Table 10.13 Cause of failures (number)
Cause of connector failure
Wrong design
Installation error
Overheating
Fillers
Push/pull force
Outer corrosion
Nominal cable system voltage (kV)
45–70
110–161
220–287
1
3
8
4
2
1
1
1
1
1
2
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M. Uzelac
• A substantial increase in higher voltage installations (up to 35% of current base
length) is expected within the next 5 years.
• An increase in the use of shear bolt (mechanical) connectors is foreseen.
• The failures reported are mainly in through connectors, due to installation errors.
• Bigger sizes of conductors are expected to be used in future projects.
• In high voltage cable systems, for copper conductors, the crimped or deep indent
type connections are predominant, while for aluminum conductors welded
connectors are widely used, with a trend towards the use of shear bolt
connectors.
10.7
Existing Test Methods, Requirements, and Assessment
in Cable Connector Testing
The principles for connecting connector to cable conductor are basically the same in
HV, EHV, and MV systems. Since type tests are standardized only for MV connectors, it is important to understand the issues encountered in the world of MV
connectors in order to specify test requirements for HV/EHV connectors.
Some differences between MV connections and HV connectors are:
• The cross-section range in MV is typically from 95 to 1000 mm2 and in HV from
185 to 3000 mm2 or even larger.
• MV connectors may be purchased separately from cable accessories, as commodity item, which is not the case in HV/EHV applications.
• Qualification of MV connectors is done per IEC 61238-1-3 standard. There is no
standard for qualification of HV/EHV connectors as separate components, outside the cable accessory.
• There is a difference in test requirements for components of cable systems
between MV and HV/EHV applications. The Cenelec standard for MV cables
HD620 (similar to IEC 60502-2) and Cenelec standard for MV cable accessories
HD 629.1 (similar to IEC 60502-4) specify test requirements separately for
cable components (cables and accessories), while the major focus in the IEC
standards 60840 and 62067 is on cable systems. For example, the test setup for a
PQ test of EHV cable systems is designed to pay special attention to thermomechanical aspects of cable accessories, while that is not the case in MV test
setups.
Sections 10.7.1 and 10.7.2 consider aspects of MV connectors. It summarizes test
requirements per IEC 61238-1-3 and additional test requirements specified by some
users in certain countries. Also, real-life examples of testing and use of MV
connectors are provided in this section.
Section 10.7.3 explains current practice in additional tests performed on connectors and accessories for HV/EHV cable systems.
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477
10.7.1 Medium Voltage Connectors
10.7.1.1 IEC 61238-1-3 Requirements
MV connectors of the mechanical and compression type are qualified per IEC
61238-1-3 standard. When a design of connector meets the requirements of this
standard, then it is expected that in service:
1. The resistance of the connection will remain stable.
2. The temperature of the connector will be of the same order or less than that of the
conductor.
3. The mechanical strength will be fit for the purpose.
4. If the intended use demands it, application of short-circuit currents will not affect
a) and b).
There are three test criteria for evaluation of MV connectors per this standard:
stability of temperature, stability of connection resistance, and mechanical strength.
The statistical method of assessing test results described in this standard is mainly
based on a compromise between the Italian Standard CEI 20-28 and the British
Standard BS 4579: Part 3.
The connection resistance and temperature stability are checked by performing
1000 heat cycles on the test loop consisting of six connectors and the corresponding
reference conductor, which is identical to that used in the connectors. The influence
of short circuit current on resistance and temperature stability is also checked. This
is done by interrupting temperature cycling after 200 cycles and applying a short
circuit current of certain intensity and duration.
The connectors are installed on bare cable conductors. The test loop shall be
installed in a location where the air is calm. The ambient temperature of the test
location shall be between 15 C and 30 C. The heat is generated by circulating ac
current in the test loop. The preferred method of measuring temperatures is using
thermocouples.
The temperature of the reference conductor, which is the control parameter of the
test, is determined in the first cycle of the test. The current is adjusted to bring
reference conductor to 120 C at equilibrium (the moment when the reference
conductor and the connectors do not vary in temperature by more than 2 K for
15 min). If at that time the connector with the third highest temperature (median
connector) is below 100 C, the current is further increased until the temperature of
median connector reaches 100 C at equilibrium, subject to the reference conductor
temperature not exceeding 140 C. Subsequent cycles are controlled by this reference conductor temperature.
During the cooling period, the reference conductor has to be cooled down to
35 C or below.
The criterion for temperature stability is that temperature of any of six connectors does not exceed temperature of reference conductor at any time during the test.
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M. Uzelac
The criterion for connection resistance is much more involved. Here, a statistical
method of evaluating the trend of electrical resistances was adopted. It requires
calculation of the connector resistance factor (k) for each connector each time the
resistance is measured. The measurement is done before cycling, immediately before
and after the short circuit test at cycle 200, after the 250th cycle and then after every
75 cycles (total 14 times from start to finish of heat cycling). A total 64 k values
(6 connectors 14 resistance measurements) are then used in the statistical analysis
to determine if the connector passed or failed the test.
Statistical parameters for k, to which the connectors are evaluated, are set in the
standard. The selection of assessment criteria and values was made after evaluating
test results and experience from different laboratories and countries. In short,
assessment criteria require that:
• Six specimens shall be similar in resistance at the beginning of the test. This is
assessed by calculating initial scatter δ between the six values of k before heat
cycling and shall not exceed the value 0.3.
• The resistance should not change extensively during test. This is assessed by
calculating:
– The mean scatter β between the six values of k averaged over the last
11 measurements which verifies that the connectors behave in the same way
and that they belong to the same “family.” The mean scatter β shall not exceed
the value 0.3.
– The change in resistance factor D, which shows the change of the resistance
factor k for each connector over the last 11 measurements. Statistical methods
are used to assess the probability that the change of resistance will not exceed
the specified value. The change in resistance factor D shall not exceed 0.15.
Note: These 11 readings start at the 250th cycle point, and then every 75 cycles
up to 1000 cycles.
• The resistances shall not change excessively as a result of the short-circuit test.
This is assessed by calculating the resistance factor ratio L, which shows the
relationship between the resistance at any stage of the measurements and the
initial resistance. The resistance factor ratio L shall not exceed 2.0.
The connection resistance factor k is ratio between the resistance of a connector
and an equivalent length of the conductor. The connection resistance itself cannot be
measured. Instead, it is derived from measured resistance of known length of reference
conductor and resistance measured between two points on the conductor with connector. Measuring points are on the cable conductor (or equalizer, where required) at
each side of connector. By knowing the length between measuring points and lengths
of cable at each side of the connector, the resistance of the connection is calculated by
subtracting the resistance of the conductor at each side of the connector from the
resistance of the equivalent length of conductor. The value obtained is then normalized
to temperature of 20 C. All measurements of resistance are made with direct current
(preferably 10% of the ac test current) and at ambient temperature.
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Test Regimes for HV and EHV Cable Connectors
479
The measuring accuracy of connection resistance is critical. Measured values
are very small, in the range of micro-ohms, which requires measuring equipment of
high accuracy (within 1% or 0.5 μΩ, whichever is the greater) and experienced
personnel. There are many resistance readings taken throughout the test (total 86)
and any incorrect reading affects analysis and may result in not qualifying a
connector, not because of its performance in the test, but due to erroneous measurements. Accurate readings are of particular importance for large-size connectors,
1000 mm2 and above. The electrical resistance of these conductors is even smaller
and requires more precise readings.
Measuring instrumentation should be calibrated and not changed for any of the
readings. The same measuring points should be used throughout the test, since
calculation always refers to the initial situation. Verification of the measuring points,
especially after the short-circuit test, is advised. It is recommended that the same
value of direct current is used throughout the test program. Bending or vibrations
during transport and handling may give rise to mechanical forces, which affect the
contact resistance of the test objects and should be avoided. In general, every effort
should be made to avoid spurious readings.
Equalizers at the measuring points of a stranded conductor are required to assure
all strands are at the same potential. If the strands are not galvanically connected a
potential between the strands develops during measurement of resistance resulting in
a measuring error. In addition, equalizers in the reference conductor ensure uniform
current distribution in conductor strands, Welded or soldered equalizers are most
commonly used. It is very important that the equalizers are not affected by heat or
movement and maintain acceptable stability throughout the test. There are 14 equalizers in a test loop for joint connectors and making all of them in acceptable quality is
highly challenging, particularly for large-size stranded cables. One bad equalizer can
cause a test failure.
The short-circuit test is intended to reproduce the thermal effects of high currents
only. In (6) short-circuit applications after 200th temperature cycle the current level
shall be such that it raises the bare reference conductors to a temperature between
250 C and 270 C. The standard recognizes that for cross-sectional areas exceeding
630 mm2 copper or 1000 mm2 aluminum, the specified maximum parameters (45 kA
and 5 s) are insufficient to reach 250 C.
The mechanical test is performed on three additional connectors. The purpose of
these tests is to ensure an acceptable mechanical strength for the connections to the
conductors of power cables. The result of mechanical test does not give any reliable
indication of the electrical quality of the connector.
The rate of application of the tensile load shall not exceed 10 N per square
millimeter of cross-sectional area and per second up to the value of tensile force
in Newton that is equal to 20 times cross sectional area for aluminum conductors and 40 times for copper. For both aluminum and copper conductors the
tensile force should not exceed 20,000 N. This force is then maintained for
1 min.
The criterion for the mechanical test is that neither connector slip.
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M. Uzelac
Range of Approval
In general, tests made on one type of connector/conductor combination apply to that
arrangement only. However, to limit the number of tests, using the same conductor
material, the following is permitted:
• A connector which can be used on stranded round conductors or on stranded
sector shaped conductors which have been rounded, is approved for both types if
satisfactory results are obtained on a compacted round conductor.
• A connector which covers a range of consecutive cross-sectional areas shall be
approved, if satisfactory results are obtained on the smallest and the largest crosssectional area.
• If a connector is a through connector for two conductors of different crosssectional areas, shapes, or materials, and if the jointing method and the connector
barrels used have already been tested separately for each cross-sectional area, no
additional test is necessary. If not, and if it is required for bimetallic through
connectors, additional tests shall be made using the conductor having the highest
temperature of the two conductors, as reference conductor.
• If a type test for a range taking mechanical connector is passed on the biggest
possible conductor cross-sectional area, this result is also valid for similar connector designs with the same material of the connector body but bigger outer
diameter provided that the design of the conductor clamping channel (inner
diameter, shape, etc.), quantity and design of clamping screws (torque, material,
size, shear-off characteristic, etc.) are identical.
• If a manufacturer can clearly demonstrate that common and relevant connector
design criteria were used for a family of connectors, conformity to this document
is achieved by successfully testing the largest, the smallest and two intermediate
connector sizes.
– Exception no.1: for a family of connectors consisting of five sizes, only the
largest connector, the smallest connector, and one connector of a representative intermediate size need to be tested.
– Exception no.2: for a family of connectors consisting of four sizes or less, only
the largest connector and the smallest connector need to be tested.
• If conformity to this document is achieved by successfully testing a connector on
dry conductor then approval is achieved for the same conductor used in an
impregnated paper insulated cable.
• For connectors where one or both sides are designed for a range of cross-sectional
areas, and a common clamping or crimping arrangement serves for the connection
of the different cross-sectional areas, then mechanical tests on conductors with the
largest and smallest cross-sectional areas shall be carried out according to Clause
7.
• If conformity to this document is achieved by successfully testing a mechanical
connector on round stranded aluminum conductors, this type test approval can be
applied to solid aluminum conductors of the same cross-sectional area(s).
• If conformity to this document is achieved by successful testing of a through
connector, this type test approval can apply to the barrel of a termination which
10
Test Regimes for HV and EHV Cable Connectors
481
uses the same design criteria. Approval of the complete termination can be
achieved if the termination connection does not influence the barrel performance,
proven through design parameters, drawings or through thermal verification test.
• If conformity to this document is achieved by successfully testing a connector on
a conductor with water blocking, approval is achieved for the same conductor
without any water blocking but not for the same conductor with different types of
water blocking.
10.7.2 Additional Tests on MV Connectors/Accessories
Some recent studies show an increase in the failure rate of MV joints in several
countries. It seems to be related to the increase of the load and new cycle types
(especially in the case of renewable generation, e.g., wind farms) and failures appear
in unusual conditions. The main contributor to those failures was identified as
thermo-mechanical force, which can induce an increase of the resistance of the
contacts, a bending of the conductors and a loss of water tightness, and pure thermal
effect.
The above aspects, except for the thermal effect, are not addressed in current
standards for MV connector and accessory testing. For example, in testing MV joint
or joint connector, the cables are not required to be fixed; therefore, no mechanical
forces are applied to the connector and the joint. The influence of the size of the
connector on the thermal behavior of the accessory is also not considered.
Axial force generated by temperature change of conductor may be calculated
[32]. Calculated values are very high. The values of axial forces measured in
laboratories are much lower from calculated but still significant. For example, a
theoretical force of more than 60 kN is calculated when temperature of a 630 mm2
aluminum conductor is increased for 60 C, while in the lab the force was measured
16 kN on fixed cable. Another interesting observation from these tests is that type of
cable conductor (stranded or solid) does not seem to influence the force.
Additional Requirements in Some Countries
In order to consider those aspects, some countries require additional tests for their
accessories.
• Test of the cable system (with the connector and cable as used by the company)
with additional cycles at a higher temperature (Belgium). The requirement is
50 cycles at 110 C and 2.5 U0 with a thermal analysis during the last cycle.
• Real condition test (France) – Robustness test.
Evaluation of Thermal Behavior (Belgium)
The goal of the test is to evaluate thermal behavior of the connector in real
conditions, in the joint installed on particular cable (the cable system approach).
The current is circulated in the test lop for cable conductor to reach different
temperature levels at location of TC5: 80 C, 95 C, 110 C, and 125 C. The
482
M. Uzelac
Fig. 10.32 Location of the thermocouples
temperatures of the cable conductor, cable connector, and the joint are measured at
each temperature level at locations shown in Fig. 10.32.
The requirements were set to:
• Temperature TC1 of the joint connector not to exceed temperature TC5 of cable
conductor at the point which is at least 1500 mm from the joint body.
• Temperatures TC2 and TC3 of cable core in the joint 10 mm away from either
side of connector not to exceed temperature TC5.
The value of this test is to find out which joint/connector/conductor systems are
suitable for the application. In some instances the system with a” large connector”
failed the test while the same system with the same joint body with a smaller
connector passed.
The temperature of the outer surface of the joint TC4 and the hot spot temperature
were recorded for engineering information.
Simulation of Heat Losses with an Artificial Connector (Belgium)
The goal of the test is to evaluate the thermal parameters of the joint body. The test
rig is relatively small. The test is realized by injecting controlled losses inside an
artificial connector by means of a resistive wire and temperature is measured at
different locations of the joint body. Two metal shells are placed above an electric
wire which is wound around a cable conductor in order to establish a thermal
connection. The test setup is shown in Figs. 10.33 and 10.34.
10.7.2.1 Additional Studies
Other tests are studied in order to check their ability to detect poor joints.
10.7.2.1.1 Mechanical Tests on Connectors
In the tests made in the past on aluminum connectors, different forces/stresses (see
Table 10.14) have been used and up to 200 push/pull cycles have been performed.
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Test Regimes for HV and EHV Cable Connectors
483
Fig. 10.33 Principle of the injection of losses
Fig. 10.34 Mounting of the wire and shells
Table 10.14 Stresses/forces
Lab measurement
Lab measurement
Applied force during testing
IEC 61238-1-3
IEC 61238-1-3
Cross section
240 mm2
630 mm2
240 mm2
240 mm2
630 mm2
F/mm2
27.92 N/mm2
28.41 N/mm2
18.75 N/mm2
40.00 N/mm2
40.00 N/mm2
F
6700 N
17,900 N
4500 N
9600 N
25,200 N
To evaluate the behavior of the conductor connections, a dedicated test setup was
built to allow for the application of higher forces and evaluation of the conductor
slippage.
The test specimen consists of two identical connectors
installed in the same way
pffiffiffiffi
on the conductor with a small distance (e.g., A with A ¼ cross section of the
conductor) between the edges of the connectors (Fig. 10.35).
This assembly is mounted to the test fixture by appropriate connection parts
installed on the barrel of the connectors. Several connector types – including
hexagonal and deep indent crimped contacts and screw type connectors – installed
on solid and stranded Al conductors of 240 mm2 and 630 mm2 were tested.
484
M. Uzelac
Fig. 10.35 Setup for testing mechanical endurance of connectors
Fig. 10.36 Typical mechanical cycle and typical test record
They were subjected to alternating push-pull force applications. The magnitude
of the applied forces was gradually increased in steps from about 25 to 40 N/mm2.
Applied force (N) – measured with a load cell – and relative displacement of the
contacts (mm) – measured with a miniature displacement sensor installed between
the contacts – were logged continuously. Mechanical stress (N/mm2) and energy
exchange (Nmm) were calculated from these data (see Fig. 10.36).
On some tested objects, the resistance between the connectors was measured
while cycled at about 20 N/mm2. A substantial resistance increase was observed at
the relaxation phase during force reversal. Samples that had not been prestressed did
not show this behavior indicates that an irreversible change had taken place during
the cycles with nonelastic deformation of the samples (Figs. 10.37 and 10.38).
This suggests that even momentary mechanical overloading – for example, by
conductor displacements in non-elastic cable arrangements – affects the contact
resistance, the effect of which remains after the stress has been removed. The
temperature increase could not be studied in this test setup however.
10.7.2.1.2 Water Ingress in Joint
The forces due to the expansion of the conductor may cause the joint to move and
bend putting pressure on the water seals. This situation can lead to water ingress
inside the joint. The test aims at reproducing the situation in the field when the cable
is blocked by the surrounding soil.
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Test Regimes for HV and EHV Cable Connectors
485
Fig. 10.37 Resistance of
240 mm2 connection
Fig. 10.38 Resistance of a
nontested 630 mm2
connection mechanically
tested before
The joint, with 5 m of cable connected to each side, is mounted in a fixture that
blocks lateral and longitudinal forces of the cables.
Cable cleats are installed every 30 cm for a length of 4 m on both sides of the
joint. On each side of the joint 1 m cable section is not blocked such that lateral
movement is possible in order to get a maximum stress on the water seals. The test
setup is shown in Fig. 10.39 and the expected behavior is described in Fig. 10.40.
There is a water filled plastic pipe installed around the cable joint with a diameter of
at least three times the diameter of the joint. The pipe is water sealed at both ends,
between the PVC pipe and the cable. Oversized silicon rubber (for flexibility under
mechanical stress) will be utilized as the seals. These seals exist and are commonly used
in current water penetration tests. Water will be entered using either an elevated water
vessel (for pressure build-up) or directly to a water pressure vessel in order to exert a
water pressure according to the desired standard or customer required pressure level.
The length of the pipe is 2 m plus the length of the joint so that the water seals
inside the pipe are located close to the cable cleats. This minimizes movement of the
cable inside the artificial seals which in its turn minimizes the chance of leakage at
486
M. Uzelac
Fig. 10.39 Test setup
Fig. 10.40 Expected
deformation of the blocked
cable
that location. Furthermore, this minimizes the effect of the plastic pipe on the cable
movement.
After the test setup has been fully built up at, the following testing procedure applies:
1. After the cable has been installed, the PVC pipe will be filled with water at the
required pressure. As soon as the pipe is filled a first sheath test is performed.
2. The assembly is left to soak for 24 h.
3. A second sheath test is performed at 10 kV DC, for 5 min.
4. The cable is subjected to 10 heating cycles as prescribed by IEC 61442, clause
9 [6]. No test voltage shall be applied. The water temperature will not be
controlled or measured.
5. A third sheath test is performed at 10 kV DC, for 5 min.
10.7.3 Existing Practice in Testing HV/EHV Connectors
Separate tests on connectors are not required in existing IEC Standards for HV/EHV
cable systems and accessories (62067 and 60840). However, details of connectors
used in accessories must be provided, together with information concerning type test
approval where applicable as per the following extract from IEC 62067 (or 60840):
Under “Accessory Characteristics” clause 7:
“b) conductor connections used within the accessories shall be correctly identified, where
applicable, with respect to
• assembly technique,
• tooling, dies and necessary setting,
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Test Regimes for HV and EHV Cable Connectors
487
• preparation of contact surfaces,
• type, reference number and any other identification of the connector,
• details of the type test approval of the connector if applicable;”
In practice, specific type testing of connectors per IEC61238-1-3 Standard has not
been carried out, except in cases of a specific customer request.
In the absence of IEC test requirements for HV/EHV connectors, manufacturers
of HV/EHV cable systems and accessories have been performing tests at their
discretion to evaluate performance of new connector designs. Different manufacturers have different test protocols but in essence those are combination of modified
requirements from IEC 61238-1-3 (MV connectors) or other national Standards, for
example, US Standard ANSI C119.4, Italian Standard CEI 20-28, and British
Standard BS 4579: Part 3 (now withdrawn); the network requirements, user’s
specifications, and manufacturers’ experience.
After being “qualified” in development tests, those connectors were further
checked in type and PQ tests of HV and EHV cable systems and accessories.
These tests were performed per IEC 60840 and IEC 62067 Standards.
10.7.3.1 Development Tests on HV/EHV Connectors
The temperature stability criteria without statistical evaluation of the connection
resistance are adopted by most manufacturers of HV/EHV cable accessories/systems
in development testing of HV/EHV connectors. This is particularly true for large size
connectors, for example, 2500 mm2 and higher, where making equalizers and
resistance measurements is extremely demanding and can have questionable end
results. If performed, the resistance measurement is used for engineering information
only and not as the qualification criterion.
The temperature stability is checked in temperature a cycling test. The number of
temperature cycles varies between manufacturers. The WG has made attempt to
“standardize” number of cycles based on the rational supported by the current
development testing of connectors, type and PQ tests of accessories and systems,
and field experience. A cable system manufacturer’s test arrangement for temperature cycling testing of connectors on large size conductors is shown in Fig. 10.41.
One of the tests that is often adopted by manufacturers is a pretension test. This
test simulates the tensile forces acting on connectors in field installations of
HV/EHV cable systems. This test is usually performed before heat cycling since
tension forces may influence performance of connectors in heat cycling and short
circuit testing. The tensile test in IEC 61238-1-3 is performed on separate connectors
and not on those that are part of the test loop for temperature cycling. Figure 10.42
shows one of the setups for the pretension test.
The short circuit current test is performed only on those connectors that may be
thermally or mechanically challenged under short circuit conditions.
Final verification of connector performance is achieved by performing type tests
and PQ tests (where applicable) on the cable systems/accessories according to IEC
60840 and IEC 62067.
488
M. Uzelac
Fig. 10.41 Preparation of the setup for temperature cycling in connector development test
Fig. 10.42 Pretension test on connectors
Some customers have proprietary system specifications, defining tests to be done
and results to be achieved, for connectors to be used in their network. The WG was
given access to some such system specifications from major utilities and their
requirements were considered and implemented in the new development test proposal wherever possible.
10.7.3.2 Type and Prequalification Tests for HV/EHV Cable Systems
and Accessories
Type tests are defined in IEC 62067 as: “tests made before supplying, on a general
commercial basis, a type of cable system covered by this standard, in order to
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Test Regimes for HV and EHV Cable Connectors
489
demonstrate satisfactory performance characteristics to meet the intended
application.”
In IEC 62067 (and 60840) the range of approval for cable system type tests is
given in clause 12.2 and specifies that the following condition is met with an
explanation in note 3:
“c): the cable and the accessories have the same or similar constructions as that of the tested
cable system(s)”.
“NOTE 3 cables and accessories of similar construction are those of the same type and
manufacturing process of insulation and semi-conducting screens. Repetition of the electrical type tests is not necessary on account of the differences in the conductor or connector
type or material or of the protective layers applied over the screened cores or over the main
insulation part of the accessory, unless these are likely to have a significant effect on the
results of the test. In some instances, it may be appropriate to repeat one or more of the type
tests (e.g. bending test, heating cycle test and/or compatibility test)”.
10.7.3.3 Work of CIGRE WG B1.06 Concerning Connectors
The WG has also considered the work of the CIGRE WG B1.06 on “Revision of
Qualification Procedures for HV and EHV AC Extruded Underground Cable Systems” [27] and ▶ Chap. 4, “Qualification Procedures for HV and EHV AC Extruded
Underground Cable Systems” of this Book. That WG proposed tests to requalify an
already prequalified EHV cable system, in case of less significant changes/modifications of components without doing the full set of type and PQ tests according to
the then active IEC Standard (edition 3 of IEC 60840 and edition 1 of IEC 62067).
Both PQ (not included in IEC 60840 ed.3) and type tests were reviewed, although
the PQ test received greatest attention, as it takes long time and is very costly.
In their work, WG B1.06 considered the influence of changes in material,
manufacturing process, design and stress level, of already qualified cable system
components and proposed “Extension of Prequalification” (EQ) tests to be
performed on such modified cable systems/components to qualify the changes.
Consequently, IEC accepted the proposals and issued new editions of the Standards
(edition 4 of IEC 60840 and edition 2 of IEC 62067). At their next major revision,
both standards were changed, incorporating the WG B1.06 proposals:
• IEC 60840 (edition 4, 2011): a PQ test was added, together with the EQ test, for
cables with high conductor screen or insulation screen stress.
• IEC 62067 (edition 2, 2011): the EQ test was added.
Tables 2.4 (for EHV cable systems) and 3.4 (for HV cable systems) in TB
303 [27], which are the guides to the selection of tests due to modifications of
cable system component in a prequalified HV cable system, do not give any
recommendation for tests in the case of change of connector or connector/conductor
combination and the current versions of IEC Standards (edition 4 of IEC 60840 and
edition 2 of IEC 62067) do not specify any test to be performed in the case of such a
modification.
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M. Uzelac
Annex 5.4 of TB 303 [27] though recommends the “Functional Analysis
Method” as means for a systematic assessment of the significance of changes/
modifications in components of a cable system and the tests to prove functionality
of the modified component. The analysis includes modifications of “Metallic connection and its eventual covering” for joints and “Metallic connection of conductor
to network” for terminations.
Tables 5.4.2 for joints and 5.4.3 for terminations from that Annex give a consideration of potential effects of the modification of critical components of the joints
and terminations and recommended testing for specific changes within accessories.
Excerpts from these two tables, relevant to connector/conductor combinations, are
given in Tables 10.15 and 10.16 below. Note that the comments relating to specific
IEC standards have been adjusted, where necessary, to reflect the current editions of
the standards.
The content of these two tables is quite similar. The significant comments are
made as follows:
• Heat cycles to IEC 61238-1-3 could be used as development tests in case of
mechanical connectors and where appropriate.
• Short circuit testing is considered, to at least at a level of the network requirement,
as a development test.
• In relation to demonstrating adequate mechanical properties, the comments
indicate that PQ tests were considered as adequate for this.
10.8
Test Regimes for Cable Connector/Conductor
Combinations in HV AND EHV Applications
10.8.1 General
The WG has considered the test methods described in the current Standard for MV
connectors (IEC 61238-1-3) and existing practice in testing and evaluation of
HV/EHV connectors performed by cable system/accessory manufacturers. The
general view is that test methods and test sequence from IEC 61238-1-3 should
not be applied for evaluation of cable connectors for HV and EHV cable systems.
During the maintenance cycle for the revision of IEC 61238-1-3 (MV cable
connectors), it was decided to limit the scope of the standard to a maximum
conductor size of 1200 mm2 mainly because verified test experience for larger size
conductor/connector combinations is not available for the time being. Generally
larger conductor sizes are in use in HV and EHV cable systems, currently up to
3500 mm2 with a tendency towards even larger sizes. The large cable sizes
(>1200 mm2), variety of conductor designs, and variety of designs of connectors
for HV/EHV cable accessories may lead to unrealistic test results and unnecessary
expense when test requirements from IEC 61238-1-3 are fully followed.
It is acknowledged by the WG that current practice adopted by manufacturers of
HV/EHV cable systems/accessories in testing and evaluation of connectors
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Test Regimes for HV and EHV Cable Connectors
491
Table 10.15 Updated and abbreviated excerpt of Table 5.4.2 on functional analysis when joint
component is changed (CIGRE TB 303/Chap. 4)
Function or
Test to check the
property
Specification/threat
functionality
Metallic connection and its eventual covering
Electrical
Transports nominal
Heat cycles on
continuity/
current without
connections. Use IEC
electrical
overheating
61238-1-3 when
resistivity
appropriate (¼ not
welded): Suggested as
Development test
Mechanical
properties
Thermal
function
Interface
with joint
semi-con
Supports short circuit
current and temperature
Short circuit test
following the network
needs: (Such test is part
of IEC 61238-1-3).
Suggested as
Development test
Supports longitudinal
tension and thrust forces
from cable conductor in
service. Prevents
twisting of conductor
during heat cycles
Dissipates correctly the
heat generated in the
connection and avoids
overheating in the center
of the joint
Heat cycles of cable
loop with joint installed:
Test requirements are
specified in Type and
PQ tests of IEC 60840
and 62067
Heat cycles of
connections per system
type tests in IEC 60840
and IEC 62067, but
without voltage +
Measurement of
temperature of
connector versus
conductor +
examination. Suggested
as Development test
Long- term test
(suggested as
development test or
PQ + examination)
Compatibility of the
possible used additives
with the semi-con of the
joint (grease, mastic,
water sealant)
Possible additives (grease, mastic, water sealant. . .)
Electrical
No negative influence
Heat cycles on
function
on the conductivity of
connections (see above)
the contact
Thermal
Supports the
Heat cycles of
properties
temperature of the
connections: see above.
Comments
Not required per IEC
60840 ed4 or 62067 ed2
The IEC 61238-1-3
presently applies only to
connectors for cables
30 kV and below but
could be useful for HV
connections
Short circuit test is not
required per IEC 60840
ed4 or 62067 ed2
The short circuit
temperature shall not be
at 250 C as required per
IEC 61238-1-3 but
derived from short
circuit currents selected
from IEC 61443
Are 20 cycles enough to
see the effects of
longitudinal forces?
See tensile strength of
welded connectors
If a reliable program to
calculate the
temperature profile in a
joint is available, it may
replace the test on cable
system
Test is also possible on
materials: semi-con
plates in air oven
exposed to the additives
(continued)
492
M. Uzelac
Table 10.15 (continued)
Function or
property
Chemical
properties
Specification/threat
connection during
service without
degradation
Gives some protection
against electrical
degradation of the
contact of the
connection
Test to check the
functionality
Comments
Examination of the
additive after cycling
Heat cycles of
connections: see above.
Examination of the
additive after cycling
Table 10.16 Updated and abbreviated excerpt of Table 5.4.2 on functional analysis when termination component is changed (CIGRE TB 303/Chap. 4)
Function or
Test to check the
property
Specification/threat
functionality
Metallic connection of conductor to network
Electrical
Transports nominal
Heat cycles on
continuity/
current without
connections. Use IEC
electrical
overheating
61238-1-3 when
resistivity
appropriate (¼ not
welded): Suggested as
Development test
Supports short circuit
Short circuit test
current and temperature
following the network
needs
Mechanical
properties
Supports compression/
extension efforts during
cycling of cable
conductor
Supports the thermal
short circuit efforts
Chemical
properties
Resistance to corrosion
Interface
with
network
Connection fits with
terminal lugs of network
interface (sliding
contacts, bimetallic
interfaces. . .)
Heat cycles per
requirements specified in
Type and PQ tests of IEC
60840 and 62067
Short circuit test
following the needs of
the network would be
useful as a development
test
Humidity and pollution
test as a development
test
Comments
Not required per IEC
60840 ed4 or 62067
ed2
Short circuit test is not
required per IEC
60840 ed4 or 62067
ed2
Short circuit test values
could be selected from
the data of IEC 60859
(now 62271-209).
System aspect
Long term PQ tests
missing in IEC 60840
ed3 (included in ed4)
No such test in HV
IEC specifications (for
cable systems and
accessories)
Matter for engineering
of network
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Test Regimes for HV and EHV Cable Connectors
493
(connector development tests), followed by type and PQ (where required) testing of
the cable system/accessories per IEC 60840 and IEC 62067 has been successful. The
survey of users of HV/EHV cable systems (see Sect. 10.6) shows positive field
experience with existing HV/EHV connectors.
Therefore, WG B1.46 has considered that the test methods and the assessment of
results per IEC 61238-1-3 should not be mandatory for cable connectors in HV/EHV
applications. Nevertheless, recommendations are given to cable system/accessory
manufacturers for connector development tests to ensure that the specific conductor/
connector combination will pass a type and (when required) PQ tests according to
the relevant HV/EHV standard and perform successfully in service.
Based on positive experience from development tests performed by cable system/
accessory manufacturers and other laboratories, the WG proposes that temperature
stability should be the criteria for passing connector development tests and omit
resistance stability requirement required per IEC 61238-1-3. Most of connector
development tests on large size cables, performed by HV/EHV cable system manufacturers, have been done without equalizers for resistance measurement. The test
criterion was only temperature stability. As previously stated, such connectors have
been successfully used in type and PQ testing of cable systems/accessories and have
excellent field record.
Some of the issues of implementing resistance stability criteria on large cable
conductors are: It is very difficult to make functional equalizers which remain stable
during the test on large cables (e.g., 2500 mm2 and above); the connection resistance
values are very small and there is question of maintaining required measuring
accuracy throughout the test; interpretation of resistance pass/fail criteria have
been some of the issues that lab personnel faced during testing large size connectors
per IEC 61238-1-3. On the other hand, measuring the temperature of connectors and
conductors and assessing temperature stability may be performed for any connector
type and any connector/conductor combination. In addition, temperature stability of
any connection system to the cable connector, for example, on sliding contacts in
plug-in cable terminations, may be evaluated, while the resistance stability criteria is
strictly limited to non-movable mechanical and compression connectors.
The short circuit withstand capability of connections in HV and EHV cables is so
far not covered by existing HV and EHV cable system/accessory type and PQ test
standards. In MV-applications test experience with IEC 61238-1-3 shows that
application of short-circuit shots may have a significant impact on the temperature
and/or resistance stability of the connection. In case of big conductor cross sections,
the short circuit current carrying capacity of the cable conductor itself is far beyond
the capability of available test facilities. Where short circuit testing is considered
necessary WG B1.46 is recommending the application of short circuit levels (current
and time) which are realistic, that is, related to actual service levels and future needs
in intended new HV/EHV cable system applications using such conductor/connector
combinations.
As the following proposed recommendations of WG B1.46 for connector development tests, although based on combined practice of several cable system and
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connector manufacturers, are new and not yet tried on a large scale, they are
presented for evaluation purposes at this stage.
10.8.2 WG Recommendations for Testing Connectors for HV
and EHV Cables
WG B1.46 concluded that current practice in verification of the performance of cable
connectors (connector/conductor combinations) in HV and EHV applications
resulted in positive field service. Existing practice is a combination of development
tests, currently performed at the full discretion of cable system/accessory manufactures, and type and PQ (where required) tests of cable systems/accessories. Based on
the collective experience of manufacturers of cable systems and accessories, connector manufacturers, and experience in testing both MV and HV connectors, the
WG recommends following:
• A separate type test for mechanical or compression connectors according to IEC
61238-1-3 is not required and not mandatory in HV/EHV applications for cable
systems and accessories complying with IEC 60840 or IEC 62067.
• Instead, a test regime as development tests for HV/EHV connector/conductor
combinations is recommended as follows.
10.8.2.1 Development Tests for Conductor Sizes up to and Including
1200 mm2
It is recommended that for cables which have conductor sizes up to and including
1200 mm2 that development tests of new connector/conductor combinations shall be
carried out per IEC 61238-1-3 but with modified short circuit requirements. If
connectors should only be used in HV/EHV applications, the short circuit current,
number of short circuits, and duration should be selected based on the short circuit
rating required for the accessory in service.
No additional development tests are required for connector/conductor combinations in HV/EHV applications that are already approved per IEC 61238-1-3 for MV
applications and followed the criteria mentioned in the range of applicability as
shown in the Sect. 10.8.3 for design-modifications of connector or conductor
compared to the tested combination.
10.8.2.2 Development Tests for Conductor Sizes Above 1200 mm2
The existing standards IEC 60840 and IEC 62067 do not require any specific tests
for change of connector type or conductor material or construction. Therefore, in
cases where such changes are significant, such as a change of material, or change in
conductor or connector design, then it is recommended that development tests are
undertaken before these are used in type and PQ (where required) tests. The
recommended development tests are described in the subsections below. They are
not only limited to mechanical or compression connectors like in IEC 61238-1-3 and
may also be used for other types of cable connectors described in Sect. 10.3.2. These
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tests can also be used for evaluation of other connections to cable connectors in cable
accessories, for example, aerial lugs, sliding connections in equipment type terminations, and so on.
See Sects. 10.8.4, 10.8.5, and 10.8.6 for proposed test loop, development test
sequence, and test methods.
10.8.3 Range of Applicability of Development Tests
In general, tests made on one type of HV/EHV connector/conductor combination
apply to that arrangement only. However, to limit the large number of tests which
would be necessary for the variety of existing HV/EHV cable conductor designs, it is
essential to develop criteria to predict that combinations of the same connector with
other conductors may produce comparable test results without performing tests for
every combination.
Based on current experience in testing and usage, the range of applicability for
development tests of other connector/conductor combination in HV/EHV applications is proposed as follows:
10.8.3.1 Covered Range of Nominal Cross-Sectional Areas of Conductor
If the test is carried out on a single cross section, the range covers 20% of the tested
cross-section. For example, if connector is tested on 2500 mm2 cable conductor of a
certain design and material, the connector may be used on a 2000 mm2 conductor,
and not vice versa.
If a manufacturer can clearly demonstrate that common and relevant connector
design criteria are used for a range of connectors for specified conductors having
different cross-sectional areas, then successfully performed development tests on the
largest and the smallest nominal cross-sectional area will additionally cover all
nominal cross-sectional areas in between for the same conductor design. For example, if connectors for 1200 mm2 and 2500 mm2 are tested, the connectors for
1600 mm2 and 2000 mm2 will also be covered without additional testing. In
addition, if the same connector/conductor combination is tested per IEC 61238-13 at 1000 mm2, the design can be used from 1000 mm2 to 2500 mm2.
10.8.3.2 Covered Range Based on Cable Insulation Material: Extruded
vs. Impregnated Paper
If a connector successfully passed development tests on a conductor used in extruded
insulation cables, then performed development test covers, additionally, applications
for the same conductor design and material used in impregnated paper insulated
cables.
10.8.3.3 Covered Range of Conductor Designs: Round Stranded
and Compacted
If a connector is successfully tested on a compacted round stranded conductor, then
performed development test also covers applications for the use on any round
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stranded conductor with the same or less number of strands and the same material
and class (e.g., within the same class according to IEC 60228, which is different for
stranded, fine stranded and flexible) or for conductors to be rounded and where all
nonconductive material(s) on and between strands are removed during installation of
the connector.
10.8.3.4 Covered Range of Conductor Designs: Conductors
with Insulated Segments or Strands or with Water-Blocking
Material and Conductors Without Those Materials
If a connector is successfully tested on a conductor using segment and/or strandinsulation materials and/or water-blocking materials without their removal, then
applicability is restricted to the same type, amount, and distribution of materials in
the conductor.
Successful development tests performed on conductors with those materials are
applicable for the same conductor designs without these materials or where these
materials are removed during installation of the connector.
10.8.3.5 Covered Range of Conductor Designs: Segmented and Milliken
Conductors
If connectors are successfully tested on segmented conductors with four, five, or six
equal segments, for example, with Milliken design according to IEC 60228 class
2, then performed development test also covers applications for segmented conductors, having less segments and for round stranded conductors of the same crosssectional area and material provided that all non-conductive material(s) on and
between strands are removed during installation of the connector.
10.8.3.6 Covered Connection Applications: Through Connectors
for the Joints for the Same and Different Size Cable Conductors
If connectors are successfully tested for different cross-sectional areas for specified
conductors, then performed development test also covers through connectors
connecting two conductors of different cross-sectional area within the range, provided that the same connector barrel designs are used and the connector body is
produced from one unjointed piece of metal.
10.8.3.7 Covered Connection Applications: Through Connectors
and Terminal Lug
If through connectors are successfully tested on specific conductor, then performed
development test also covers terminal lugs utilizing the same design of the barrel as
in tested through connector and on the same cable.
10.8.3.8 Covered Modifications of Mechanical Connectors in HV
and EHV Applications
Additional criteria have been worked out based on test experience with mechanical
connectors on large conductors:
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• If a mechanical connector is successfully tested on round stranded aluminum
conductors, performed development test also covers applications for solid aluminum conductors.
• If mechanical connectors are successfully tested on stranded conductors, then
performed development test also covers applications for conductors with the
same cross-sectional area but with different diameter to which this connectors
have to be adapted by decreasing the inner diameter of the connector barrel
accordingly, as long as other relevant design parameter for the clamping
channel (e.g., shape, grooves, surfaces), the clamping bolts (e.g., tightening
torque, material, dimensions, tolerances, surface, shear-off characteristic), and
connector body (e.g., material, tolerances, surface) are the same as in tested
connector.
• If mechanical connectors are successfully tested on conductors, then applicability
might be assumed for cable applications using the same conductors where the
outer diameter of the connector barrel should be increased to have approximately
the same thickness as the actual used cable insulation, as long as other relevant
design parameter for the clamping channel (e.g., shape, grooves, surfaces), the
clamping bolts (e.g., tightening torque, material, dimensions, tolerances, surface,
shear-off characteristic), and connector body (e.g., material, tolerances, surface)
are the same as in tested connector.
10.8.3.9 Covered Short Circuit Current Withstand Capability
If the connector/conductor combination successfully passed short circuit (SC) test,
then this test covers applications for such combinations where the Joule-Integral (I2t)
value is lower than or equal to that tested.
The test setup should fix the conductors in such way to allow for thermal
expansion of conductors and prevent radial movement in order to avoid any additional mechanical impact on the connectors due to flow of SC current.
If it is necessary to check the behavior of a connector/conductor combination
when exposed to dynamic forces, caused by asymmetric SC current, the precise
layout of the test loop must be specified. This may be different from above case,
where only the thermal effect of the SC is considered.
Generally, SC tests are not considered necessary for copper connectors on “bare”
copper conductors. Only in specific cases where the copper is not bare, for example,
uncleaned, enameled, or oxidized conductors or other insulation material and water
blocking material not to be removed during installation of the connector, are these
tests recommended.
For stranded aluminum conductors, SC tests are generally recommended in all
cases due to the existence of a surface oxide layer.
Other empirical verified criteria for comparing HV cable connector/conductor
combinations should be developed in future to cover other possible cable applications by successfully performed development tests. As soon as more test results are
available, shared for comparison, evaluated on a statistical basis, and agreed by
technical experts, they may be integrated into the set of commonly applicable “rules”
to widen the range of applicability given above.
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10.8.4 Test Loop for Heat Cycling and Temperature Stability Tests
for Development Tests with Conductor Sizes Above
1200 mm2
For each series of tests, at least four connectors shall be fitted in accordance with the
manufacturer’s instructions, on a bare conductor or on a conductor that has had the
insulation removed before assembly, to form a test loop together with the corresponding
reference conductor. The installation instructions and the tools recommended by the
connector manufacturer must be used for the preparation of the test assembly.
An example of the test loop is shown in Fig. 10.43. The figure indicates the
minimum length of exposed conductor on either side of the test object and the
minimum lateral distance between test objects and between conductors.
In this example, individual legs of the test loop with connectors may be easily
disassembled for transport to short circuit and mechanical test labs and reassembled
quickly when needed.
Connectors of the type to be tested are applied onto bare conductors of the appropriate size, material, and type for the connector/conductor combination under test.
Disconnecting terminals may be additional test objects (e.g., terminal lug). All conductors of the same cross-sectional area in the test loop shall be taken from the same length.
The test setup is applicable to all types of connector in combination with any
conductor design and material, not restricted to mechanical and compression
connectors.
10.8.5 Recommended Development Test Sequence with Conductor
Sizes Above 1200 mm2
The development tests for connectors to be used on conductors above 1200 mm2
should be performed in the proposed test sequence acting on the same samples to
Fig. 10.43 Test loop setup
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Test Regimes for HV and EHV Cable Connectors
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accumulate stresses and verify performance of the connector/conductor combination. The development test is to be considered as successfully passed, if the test
sequence in the given order is passed and all mentioned verification criteria are met.
Note: Resistance stability assessment is not recommended to be used as evaluation criterion for connector/conductor combinations on conductors with crosssection areas exceeding 1200 mm2.
10.8.5.1 Prestress
Preferably applied separately to each of the four legs of the test loop shown in Fig. 10.43.
Each leg consists of: disconnecting terminal lug–conductor–test connector–conductor–
disconnecting terminal lug.
(a) Tensile load test per method described in Sect. 10.8.6.1.
Each leg of the test loop should be subjected once to a mechanical tensile load
which is related to the nominal cross-section area and the conductor material:
The force value to be applied in axial direction is:
(i) 30 N/mm2 for copper conductors and
(ii) 20 N/mm2 for aluminum conductors
The tensile force not to exceed 80 kN for copper conductors and 50 kN for
aluminum.
(b) Six short circuit shots based on the maximum short circuit level of the cable
system in service per method described in Sect. 10.8.6.2.
After passing tests, a and b above the test samples should be assembled for heat
cycling as shown in Fig. 10.43. The test arrangement should be placed in one
horizontal plane in a test area where the air is calm, minimizing variations in
convection acting on the different specimens. Ambient temperature should be
maintained below 35 C during cooling. The test loop may be of any shape, if it is
arranged in such a way that there is no adverse effect from the floor, walls, and
ceiling.
10.8.5.2 Constant High-Current Temperature Stability Test
200 h with reference conductor temperature between 120 C and 140 C and target
temperatures of connectors 100 C should applied as described in Sect. 10.8.6.3. The
control parameter during the test is the temperature of reference conductor. The
temperature stability assessment should be performed as described in Sect. 10.8.6.3.
10.8.5.3 Heat Cycle Temperature Stability Test
200 heat cycles should be performed (no. of cycles per IEC 60840/62067, 20 for type
test plus 180 for PQ test). The cycle regimes are with reference conductor temperature from 120 C to 140 C as described in Sect. 10.8.6.4 and target connector
temperatures of 100 C. The control parameter during the test is the temperature of
reference conductor.
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Fig. 10.44 Temperature regime of a cycle
The temperature regime of the cycle should be such to ensure that targeted
connector temperatures are held stable within the target temperature range as
shown in Fig. 10.44.
At the end of the heating period, forced air cooling may be used. The reference
conductor must cool to within 10 K of ambient temperature before the next heating
cycle commences.
10.8.5.4 Tensile Strength Test on (3) New Connectors
60 N/mm2 for copper conductors and 40 N/mm2 for aluminum conductors (as per
current IEC 61238-1-3). The tensile force not to exceed 80 kN for copper conductors
and 50 kN for aluminum.
10.8.6 Test Methods
Following sections describe methods, assessment, and verification criteria of each
development test.
10.8.6.1 Tensile Load (Prestress) Test Method
The test should be carried out at ambient temperature.
Each leg of the test loop should be subjected once to a mechanical tensile load
which is related to the nominal cross-section area and the conductor material as
defined in Sect. 10.8.5.1 (a).
The rate of application of the load should not exceed 10 N/mm2 of the nominal
cross-sectional area per second and the maximum force will be maintained for 1 min.
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Test Regimes for HV and EHV Cable Connectors
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The test is considered as successfully passed if no visual slippage between
conductor, connector, and disconnecting terminal lugs will occur after test.
A stability verification by measurement of slippage is not recommended.
The applied forces should be included in the test report.
10.8.6.2 Short Circuit Current Test Method
Layout of the test loop: The recommended layout of the test setup for short-circuit
current tests is to use single phase test arrangements with one leg out of the test loop
from Fig. 10.43 with a concentric return as short as possible and/or a mechanically
stiff fixing of the test specimen to minimize mechanical forces and movement
induced by current flow through adjacent current carrying structures.
Short circuit shots: The short circuits shall be applied to each connector/conductor combination when preheated to 90 C and allowing cooling to between 90 C and
95 C in between short circuits. Preheating of the connector/conductor combination
can be done either by heating conductor by an a.c. current or by external heating
elements.
The short circuit current and duration defines the Joule-Integral to be applied and
should be selected based on the maximum short circuit level of the cable system in
service.
The current and time can be adjusted to achieve the required thermal energy level
given by the Joule-Integral, but the duration should not be greater than 5 s (in order
to achieve adiabatic heating) and the short circuit current and duration should not be
less than 25 kA, 1 s and not more than 45 kA, 5 s. The calculated end temperature of
the reference conductor to be tested with the Joule-Integral, for example, according
to IEC 61238-1-3 Annex D or IEC 60949, should not be above 250 C.
Verification: The test is considered as successfully passed if no obvious signs of
overheating can visually be detected. Temperature measurement of the connectors
and reference conductor during short circuit tests is not recommended but might be
recorded if measured. Starting temperatures of specimen, current and duration of
each short circuit shot should be included in the test report.
10.8.6.3 Constant High-Current Temperature Stability Test Method
Temperature measurement: The recommended method of temperature measurement is to use thermocouples. Temperature measurements should have device
uncertainty within 2 K. The temperature of the reference conductor should be
measured on the surface of the conductor or between the first layer of conductor
strands halfway between the disconnecting terminal lugs. The temperature of each
connector shall be measured on the connector surface in the middle of the connector.
The test method according to IEC 61238-1-3 Chap. 6.3.2 is selected to determine
the reference conductor temperature to be used and to identify the median connector
at equilibrium for the specific test-loop. The median connector in this test setup is
defined as the connector which during the first heating records the second highest
temperature of the four connectors in the test loop.
Heating: Current is circulated in the test loop, bringing the reference conductor to
120 C at equilibrium when temperatures of the reference conductor and the
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connectors do not vary, during application of current, by more than 2 K for 1 h. If at
that time the temperature of the median connector (the one with the second highest
temperature of all connectors in the test loop) is equal to or greater than 100 C, the
120 C of reference conductor temperature will be used as control parameter for duration
of the test. The minimum heating period to maintain temperature stability is 1 h.
If median conductor does not reach 100 C with reference conductor at 120 C,
then the current shall be increased until the median connector temperature reaches
100 C at equilibrium, subject to the reference conductor temperature not exceeding
140 C. Such determined reference conductor temperature θR, (120 C < θR
140 C) will be used as control parameter for duration of the test. This temperature
should be maintained within 5 K for 200 h.
Temperature readings for each connector and the reference conductor should be
taken 8 h after reaching equilibrium and then at least every 24 h.
Verification: Every recorded maximum temperature of each connector in each
measurement campaign should not exceed that of the reference conductor measured
at the same time by more than 5 K. Additionally the arithmetic mean value calculated
from all (four) connector temperatures in all (eight) measurement campaigns should
not exceed the highest temperature value of the reference conductor out of this record.
The test is considered as successfully passed if the verification criteria are met.
The data and the evaluation should be included in the test report.
10.8.6.4 Heat Cycle Temperature Stability Test Method
Temperature measurement: The same method for measuring temperature is used as
described in Sect. 10.8.6.3.
The temperature of the referenced conductor θR previously established in Sect.
10.8.6.3 is control parameter of the head cycle test. The median connector, the one
with the second highest temperature, is also identified in Sect. 10.8.6.3.
First cycle: The object of the first heat cycle is to determine the heat cycle
duration and temperature regime which will be used on the test loop for all subsequent heat cycles. Current is circulated in the loop until the main reference conductor
temperature reaches the value θR with a tolerance of 0, +6 K over 120 min period,
and the median connector temperature is stable within 2 K over a 15 min period at
the end of heating period t1 (see Fig. 10.44).
Note: See Appendix D for discussion on justification of using the longer,
120 min, exposure time comparing to that in IEC 61238-1-3.
At the beginning of the heat period t1, an elevated current up to 150% of the
heating current at equilibrium may be used to reduce the heating period. The current
shall thereafter be decreased or regulated to a value of the current at equilibrium to
ensure stable conditions during the median-connector control period. It may be
necessary to use more than one cycle to determine the temperature regime.
The heating period t1 is followed by a cooling period t2 to bring the temperatures
of all connectors and the reference conductor to values below ambient temperature.
It may be necessary in subsequent heat cycles to adjust t2 to ensure that the
temperature conditions are reached. If accelerated cooling is used, it shall act entire
test loop, and use air within ambient temperature limits. The total period t1 + t2
constitutes a heat cycle.
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Test Regimes for HV and EHV Cable Connectors
503
Subsequent cycles: The reference conductor temperature is the only control parameter, to reproduce the temperature regime for all subsequent cycles. In this way, the
fluctuation of the ambient temperature will not affect the temperature profile of the
reference conductor within the specified tolerances. The heating regime of the reference
conductor containing the characteristics of temperatures in time is shown in Fig. 10.43
and should be reproduced in subsequent cycles, while the median connector will not be
controlled anymore and may differ by more than 3 K compared to the initial situation.
Instead of cooling down below 35 C as done in the first cycle, it is recommended to
cool down at least to 10 K above ambient temperature before starting a new cycle.
Temperature measurements should be taken by using the method described in Sect.
10.8.6.3. The first measurement campaign should be collected after the 10th cycle, the
next campaigns then every 10 cycles. One measurement campaign consists in recording temperatures on each connector and the reference conductor taken every minute
during the last 15 min. of the heating period t1. The maximum measured connector
temperature in every measurement campaign should be recorded together with the
reference conductor temperature measured at the same time. A set of 20 measurement
campaigns with four pairs of connector/conductor combinations temperature values
will then be available for the assessment of temperature stability.
Heat-cycle temperature stability verification: Every recorded maximum temperature of each connector in each measurement campaign should not exceed that of the
reference conductor measured at the same time by more than 5 K. Additionally the
arithmetic mean value calculated from all (four) maximum connector temperatures
in all (20) measurement campaigns should be below the highest temperature value of
the reference conductor out of this record.
The test is considered as successfully passed if the verification criteria are met.
The data and the evaluation should be included in the test report.
10.8.6.5 Tensile Strength Test Method
The test should be carried out at ambient temperature.
The test shall be made on three additional connectors having the same combination of conductors and installation procedure as used for the electrical test.
The recommended conductor length, between connectors or between the connector and the tensile test machine jaws, is 500 mm.
The rate of application of the load shall not exceed 10 N per square millimeter of
nominal cross-sectional area per second and then up to the value as defined in Sect.
10.8.5.4, which is then maintained for 1 min.
The test is considered as successfully passed if not more than 3 mm slippage will
occur during the last minute of the test.
The applied forces should be included in the test report.
10.9
Conclusions
WG B1.46 has taken into account current practice in testing cable connectors for
HV/EHV cables that included: development testing on connectors currently performed
by cable system/accessory manufacturers at their own discretion; system/accessory type
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and PQ tests per IEC 60840 and 62067 Standards; existing positive experience with
HV/EHV cable connectors in service; existing requirements and experience in testing
MV connectors per IEC 61238-1-3 for MV connectors; and work of the CIGRE WG
B1.06 on Revision of Qualification Procedures for HV/EHV AC Cable Systems. The
WG came to the following conclusions:
• A separate type test for mechanical or compression connectors per IEC 61238-1-3
is not required and not mandatory in HV/EHV applications for cable systems and
accessories complying with IEC 60840 or IEC 62067.
• A separate development tests for HV/EHV connector/conductor combinations
followed by type/PQ tests on cable system/accessory is recommended.
• The connectors for HV/EHV cables that have been included in type and PQ tests
(where applicable) and have been used historically should continue to be used
without further separate component testing being required.
• Additional testing is also not required for connector/conductor combinations that have
not been used in service yet but successfully passed proposed development test for
connectors and type and PQ tests (where applicable) for cable systems/accessories.
• If separate connector development or type tests have been made according to
other specifications these tests are not required to be repeated according to this
recommendation.
• Recommendations have been made for development tests and the range of
approval for new connector/conductor combinations in accordance with proposals made in Annex 5.4 of TB 303, taking into account the existing IEC
standard for MV connectors and experience from manufacturers and users.
• The WG proposes a sequence of development tests for HV/EHV connector/
conductor combinations based on current practice in development testing of
HV/EHV connector and type testing of MV connectors.
• To avoid the need to test every size and type of connector, details are given of the
range of approval that is valid for different test scenarios (e.g., large and small
sizes tested to also cover intermediate sizes).
• Involved parties are invited to collect and share experience with the here proposed
development tests of new connector/conductor combinations to verify practical
use of proposed procedure and assessment before a further standardization of type
testing of HV and EHV cable connectors is considered.
10.10 References
1. IEC 61238-1-3:2018 Compression and mechanical connectors for power cables
– part 1-3: test methods and requirements for compression and mechanical
connectors for power cables for rated voltages above 1 kV (Um ¼ 1.2 kV) up
to 30 kV (Um ¼ 36 kV) tested on non-insulated conductors
2. IEC 60840 Power cables with extruded insulation and their accessories for rated
voltages above 30 kV (Um ¼ 36 kV) up to 150 kV (Um ¼ 170 kV) – Test
methods and requirements
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Test Regimes for HV and EHV Cable Connectors
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3. IEC 62067 Power cables with extruded insulation and their accessories for rated
voltages above 150 kV (Um ¼ 170 kV) up to 500 kV (Um ¼ 550 kV) – Test
methods and requirements
4. IEC 60050 (461) International Electrotechnical Vocabulary (IEV) –
Chap. 461: Electric cables
5. IEC 60228 Conductors of insulated cables
6. IEC 61442 Test methods for accessories for power cables with rated voltages
from 6 kV (Um ¼ 7.2 kV) up to 36 kV (Um ¼ 42 kV)
7. IEC 62271-209, 2007: High-voltage switchgear and controlgear – Part
209: Cable connections for gas-insulated switchgear for rated voltages above
52 kV – Fluid filled and extruded insulation cables – Fluid filled and dry-type
cable-terminations
8. EN 50299-1, 2014: Oil-immersed cable connection assemblies for transformers
and reactors having highest voltage for equipment Um from 72.5 kV to 550 kV.
Fluid-filled cable terminations
9. EN 50299-2, 2014: Oil-immersed cable connection assemblies for transformers
and reactors having highest voltage for equipment Um from 72.5 kV to 550 kV.
Dry-type cable terminations
10. IEC TR 62125 Environmental statement specific to TC 20. Electric cables
11. IUPAC Periodic Table of the Elements 22/11/16. https://iupac.org/what-we-do/
periodic-table-of-elements
12. IEC 60287-3-2 Ed.2: Electric cables – calculation of the current rating – part
3-2: sections on operating conditions – economic optimization of power cable
size
13. BOONE Wim, KACKER Arnav, BAL Remco “Copper or aluminium cable
conductors, broadly compared in a life-cycle perspective” JiCable Conference
2015
14. Holm R.: Electric Contacts-Theory and Applications. Springer-Verlag 2000.
ISBN 3-540-03875-2.
15. Vinaricky, E.: Elektrische Kontakte, Werkstoffe und Anwendungen. 2. Auflage:
Springer-Verlag 2002. ISBN 3-540-42431-8.
16. Böhme, H.: Mittelspannungstechnik-Schaltanlagen berechnen und entwerfen.
2. stark bearbeitete Auflage Berlin: Verlag Technik 2005. ISBN 3-341-01495-0.
17. Hildmann, C. Schlegel, S.; Lücke, N.; Großmann, S.: Vergleich genormter
elektrischer Alterungsprüfungen für Verbindungen der Elektroenergietechnik
mit Erkenntnissen aktueller wissenschaftlicher Untersuchungen. Connectors
Symposium, Lemgo, 2015
18. Braunovic, M.: Aluminium connections: legacies of the past. Tagungsbd. 40th
IEEE Holm Conference on Electrical Contacts. 17.10-19.10.1994, Chicago,
S. 1–31.
19. Naybour, R. D.; Farrell, T.: Degradation mechanisms of mechanical connectors
on aluminium conductors. Proceedings of the Institution of Electrical Engineers,
1973, vol. 120, no. 2, S. 273–280.
20. Braunovic, M.: Effect of Current Cycling on Contact Resistance, Force, and
Temperature of Bolted Aluminium-to-Aluminium Connectors of High
506
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
M. Uzelac
Ampacity. IEEE Transactions on Components, Hybrids, and Manufacturing
Technology, 1981, vol. 4, issue 1, S. 57–69.
Möcks, L.: Die Stromverteilung in der Starkstromklemme. Elektrie, 1995, vol.
49, no. 8/9, S. 299–303
Hildmann, C.; Schlegel, S.; Großmann, S.; Dockhorn, T.: Investigations on the
long-term behaviour of current carrying fittings for high temperature low sag
conductors. 23rd International Conference on Electricity Distribution (CIRED),
Lyon, 2015
Hildmann, C.: Zum elektrischen Kontakt- und Langzeitverhalten von Pressverbindungen mit konventionellen und Hochtemperatur-Leiterseilen mit
geringem Durchhang. Dissertation, TU Dresden, 2016 (http://nbn-resolving.
de/urn:nbn:de:bsz:14-qucosa-222889).
Hildmann, C.; Grossmann, S.; Dockhorn, T.: The initial contact stress in Aluminium compression connections with high temperature low sag conductors.
Tagungsbd. 27th International Conference on Electrical Contacts (ICEC), 22.26.06.2014, Dresden, S. 557562.
Pfeifer, S.: Einfluss intermetallischer Phasen der Systeme Al-Cu und Al-Ag auf
den Widerstand von elektrischen Verbindungen im Temperaturbereich von
90 C bis 200 C, Dissertation, TU Dresden, in press.
Europacable Services Ltd., Great Britain, MECHANICAL SHEAR-BOLT
CONNECTORS: A “Best Fit” Solution for Jointing Cable Conductors, 2016
CIGRE TB 194 Construction, Laying and Installation Techniques for Extruded
and Self-Contained Fluid Filled Cable Systems, WG 21.17, October 2001
Lücke, N.; Schlegel, S.; Grossmann, S.: Vergleich von Werkstoffen auf Basis
von Cu und Al sowie Trends bei deren Anwendung in der Elektroenergietechnik. Metall, 67. Jahrgang, 11/2013.
CIGRE TB 303 Revision of Qualification Procedures for HV and EHV AC
Extruded Underground Cable Systems., WG B1.06, August 2006
Electra 212_4 Thermal Ratings of HV Cable Accessories, TF 21(B1)-10
CIGRE TB 476 Cable Accessory Workmanship on Extruded High Voltage
Cables, WG B1.22, October 2011
CIGRE TB 669 Mechanical Forces in Large Conductor Cross-Section XLPE
Cables, WG B1.34
CIGRE TB 247 Optimization of Power Transmission Capability of Underground Cable Systems Using Thermal Monitoring, WG B1.02, February 2004
Quaggia, D at all, Mechanical Connectors used inside M.V. Accessories: a
system approach, Paper E9.5, Jicable 2015
CIGRE TB 446 Advanced Design of Metal Laminated Coverings: Recommendation for Tests, Guide for Use, Operational Feedback, WG B1.25,
February 2011.
CIGRE TB 756 Thermal Monitoring of Cable Circuits and grid Operators’ Use
of Dynamic rating Systems, WG B1.45, February 2019.
CIGRE TB 689 Life Cycle Assessment of Underground Cables, WG B1.36,
May 2017
10
Test Regimes for HV and EHV Cable Connectors
507
Terms of Reference
Scope, Deliverables, and Proposed Time Schedule of the Group
Background
During the meeting held in San Francisco on March 5 and 6, 2012, the SAG
(Strategic Advisory Group) of SCB1 discussed what could be the next items to be
studied by the Study Committee. One of the topics was: “Conductor joint strength
(mechanical for long HV cables) + thermal test for connectors”.
Current IEC 61238-1-3 standard applies to connectors for medium voltage cables.
There is no IEC standard for connectors for HV cables. The procedures from IEC
61238-1-3 along with manufacturer and user specifications have been used to type
test HV cable connectors. The thermal, mechanical, and resistance stability tests
specified in current standard are applicable to HV but some requirements are specific
to high voltage applications. These include dimensional and functional requirements
of connectors within HV cable accessories, typically larger cable sizes, versatility of
the conductor constructions as well as different circuit load patterns, short circuit
levels and mechanical stresses due to tensile and thrust loads.
The IEC WG16 of the TC20 commenced work on revision of current IEC612381-3 standard. During this work, some members of WG16 expressed interest that the
scope of this standard is extended to high voltage cable application. The TF in charge
of the revision believes this work needs to be done by a dedicated group of high
voltage experts.
At the Study Committee B1 meeting held in Paris on August 28 and 29, 2012, it
was agreed that a task force be established to consider if further guidance was needed
on the testing of connectors for HV cable accessories. It was also decided in the
meeting that the topics should be expended to cover mechanical loads, not only
thermal to include all connectors, not just mechanical and to include termination
connectors, not only for the joints.
Scope
To review
• The range and types of connectors currently available
• Existing international standards and the extent to which they cover the testing of
connectors
• Any work been done by CIGRE, CIRED, JICABLE. . .
• Extent of service experience so far for different connector types
• Customer needs
To analyze
• Operation on high loaded systems where conductors are approaching or temporarily exceeding maximum conductor operating temperature
• Thermo-mechanical performance of connectors under cycling loads
508
M. Uzelac
• Performance of connectors in short circuit conditions, taking into account thermal
and dynamic forces and actual network ratings
• Performance of connectors installed in cable joints and terminations
To propose thermal and mechanical test regimes for connectors for HV and EHV
cables with special attention be given to connectors for large size cables.
• Type, routine, and sample tests including mechanical, cycling, and resistance
stability tests
• Consider practicality of the short circuit test for large-size conductors and test
loop arrangement
• WG should be free to consider mechanical tests (e.g., tensile, thrust forces. . .) in
order to evaluate mechanical strength of connection and physical properties of
connector itself
• WG should be free to consider separate or integral test sequences combining
mechanical, cycling, short-circuit, and resistance stability (assessment) acting on
the same samples
• Extent of connector type test experience so far (for different connector types)
• Evaluate necessity of performing type tests on connectors that already successfully passed qualification tests per IEC 60840
• WG should consider range of type test approval
The WG should consider the tests that reflect mutual impact between connectors,
cable conductors and accessories.
The conductor connectors for HV and EHV applications are to be considered. The
WG will make recommendation to include or not connectors for MV applications.
Deliverables
Technical Brochure with summary in Electra and Tutorial
Comparison of IEC and IEEE Type Test Requirements for Extruded
Cables and Accessories for Voltages up to 245 kV
See Table 10.17
Comparison of IEC and IEEE Type Test Requirements for Extruded
Cables and Accessories for Voltages 245 kV and above
See Table 10.18
Partial discharge test at high
temperature
Partial discharge test at
ambient temperature (after
final cycle or after lightning
impulse voltage test in item
i)
Lightning impulse voltage
test followed by power
frequency voltage test
AC voltage 1 min dry
withstand
AC voltage 10 s wet
withstand
DC voltage 15 min dry
withstand
Heating cycle voltage test
Test
Bending test
Partial discharge test at
ambient temperature
AC withstand voltage
650 kV, 10+/
10, at
Tcmin ¼ 95 C
20 cycles at
Tcmin ¼ 95 C,
2Uo
5 pC at 1.5Uo, at
Tcmin ¼ 95 C
5 pC at 1.5Uo
12.4.4
–
12.4.4
12.4.7
12.4.4
12.4.4
12.4.7
12.4.7
12.4.4
12.4.6
12.4.6
12.4.6
Clauses IEC 60840 up to 245 kV
Type tests on cable systems, cables, accessories
Test values
(applicable to
Cable
accessories)
systems Cables Accessories
5 pC at 1.5Uo
12.4.3
12.4.3
–
12.4.4
12.4.4
12.4.4
650 kV, 10+/10,
at
Tcmin ¼ 105 C
30 cycles at
Tcmin ¼ 105 C,
2Uo
5 pC at 1.5Uo
(120 kV)
5 pC at 1.5Uo
(120 kV)
315 kV, 15 min
3Uo (240 kV),
15 min
5 pC at 1.5Uo
(120 kV)
7.7.3
7.6.1
7.6.1
7.9.2
7.7.2
7.7.1
Joints
7.6.1
IEEE Std 404-1993 for
joints 138 kV
650 kV, 10+/10,
at
Tcmin ¼ 105 C
30 cycles at
Tcmin ¼ 105 C,
2Uo
5 pC at 1.5Uo
(120 kV)
5 pC at 1.5Uo
(120 kV)
315 kV, 15 min
275 kV, 10 sec
310 kV, 1 min
5 pC at 1.5Uo
(120 kV)
Test Regimes for HV and EHV Cable Connectors
(continued)
8.4.1.6
8.4.1.1
8.4.1.1
8.4.2 item c
8.4.1.5
8.4.1.2/
8.4.1.4
8.4.1.3
Terminations
8.4.1.1
IEEE Std 48-1990 for terminations
138 kV
Table 10.17 Comparison of IEC and IEEE Type Test Requirements for Extruded Cables and Accessories for Voltages up to 245 kV
10
509
Test
Partial discharge test at high
temperature (if not carried
out after item g) above)
AC voltage 6 h dry
withstand
Partial discharge test at
ambient temperature (if not
carried out after item g)
above)
Tests of outer protection for
joints
Table 10.17 (continued)
12.4.4
Annex
G
5 pC at 1.5Uo
1m
watercolumn,
20 cycles, DC
and BIL test
12.4.4
Annex G
12.4.4
–
Clauses IEC 60840 up to 245 kV
Type tests on cable systems, cables, accessories
Test values
(applicable to
Cable
accessories)
systems Cables Accessories
–
12.4.4
5 pC at 1.5Uo, at 12.4.4
Tcmin ¼ 95 C
Sectionalizer
(if applicable)
2.5Uo (200 kV),
6h
5 pC at 1.5Uo
(120 kV)
5 pC at 1.5Uo
(120 kV)
7.11
7.6.1
7.1
Joints
7.6.1
IEEE Std 404-1993 for
joints 138 kV
2.5Uo (200 kV),
6h
5 pC at 1.5Uo
(120 kV)
5 pC at 1.5Uo
(120 kV)
8.4.1.1
8.4.1.7
Terminations
8.4.1.1
IEEE Std 48-1990 for terminations
138 kV
510
M. Uzelac
Partial discharge test at ambient temperature
(after final cycle or after lightning impulse
voltage test in item i)
Lightning impulse voltage test followed by power
frequency voltage test
Partial discharge test at high temperature
1050 kV, 10+/10,
at Tcmin ¼ 95 C
12.4.7.2
12.4.4
12.4.4
12.4.5
12.4.6
1050 kV, 10+/
10, at
Tcmin ¼ 105 C
5 pC at 1.5Uo
(200 kV)
30 cycles at
Tcmin ¼ 105 C,
2Uo
5 pC at 1.5Uo
(120 kV)
5 pC at 1.5Uo
(200 kV)
1050 kV, 10+/
10, at
Tcmin ¼ 105 C
5 pC at 1.5Uo
(200 kV)
7.7.3
7.6.1
7.6.1
7.6.1
30 cycles at
Tcmin ¼ 105 C,
2Uo
5 pC at 1.5Uo
(120 kV)
5 pC at 1.5Uo
(200 kV)
7.9.2
7.7.2
445 kV, 10 sec
525 kV, 15 min
525 kV, 15 min
5 pC at 1.5Uo
(200 kV)
AC voltage 10 s wet withstand
DC voltage 15 min dry withstand
Tan δ measurement
Heating cycle voltage test
7.7.1
Joints
7.6.1
460 kV, 1 min
5 pC at 1.5Uo
(200 kV)
3Uo (400 kV),
15 min
AC voltage 1 min dry withstand
Bending test
Partial discharge test at ambient temperature
AC withstand voltage
20 cycles at
Tcmin ¼ 95 C,
2Uo
5 pC at 1.5Uo, at
Tcmin ¼ 95 C
5 pC at 1.5Uo
IEC 62067 230 kV
Type tests on cable systems
only
Clauses
Cable
systems
5 pC at 1.5Uo
12.4.3
12.4.4
(continued)
8.4.1.1
8.4.1.6
8.4.1.1
8.4.1.1
8.4.2 item c
8.4.1.2/
8.4.1.4
8.4.1.3
8.4.1.5
Terminations
8.4.1.1
IEEE Std 48-1990 for terminations
Clauses
Table 10.18 Comparison of IEC and IEEE Type Test Requirements for Extruded Cables and Accessories for Voltages 245 kV and above
IEEE Std 404-1993 for joints
Clauses
Test Regimes for HV and EHV Cable Connectors
Test
10
511
Partial discharge test at high temperature (if not
carried out after item h above)
Tests of outer protection of buried joints
Test
Table 10.18 (continued)
5 pC at 1.5Uo, at
Tcmin ¼ 95 C
1 m watercolumn,
20 cycles, DC and
BIL test
Annex
G
12.4.4
IEC 62067 230 kV
Type tests on cable systems
only
Clauses
Cable
systems
2.5Uo (332 kV),
6h
5 pC at 1.5Uo
(200 kV)
Sectionalizer
(if applicable)
7.11
7.6.1
Joints
7.1
IEEE Std 404-1993 for joints
Clauses
2.5Uo (332 kV),
6h
5 pC at 1.5Uo
(200 kV)
8.4.1.1
Terminations
8.4.1.7
IEEE Std 48-1990 for terminations
Clauses
512
M. Uzelac
10
Test Regimes for HV and EHV Cable Connectors
513
Background Behind Range of APPLICABility and Proposed
Development Tests
The following table gives a brief explanation of the background behind some
recommendations for covering other applications by a successfully performed
development test.
8.1 General and 8.3 Range of
applicability of development tests
8.3.2 Covered range based on cable
insulation material: extruded
vs. impregnated paper insulation
Collected experience show that an
interpolation is possible between the
smallest and the biggest positive test
results of a connector/conductor
combination as long as principle
parameter of the connector design and
the conductor design are equal and only
the nominal conductor cross-sectional
area is changed
As the tests in IEC 61238-1-3 are more
severe than that recommended for
connections in HV/EHV applications
and the smallest a member of the
connector family have been successfully
tested according this standard, then it is
assumed that the design is suitable for
sizes below 1200 mm2 and interpolation
down to that tested size might be
possible
Tests on “fluid filled” conductors
produced comparable test results as on
“dry” conductors. Wet material may
drop out of stranded conductors during
heating in bare conductors. The fluid
will prevent additional oxidation on the
conductor strands. Therefore it was
decided to test only in “dry” conditions
to cover worst case. In contradiction
some tests on impregnated aluminum
conductors taken out after decades of
service did not pass the test. After
further investigations it was decided to
restrict the tests to new conductors made
out of one continuously produced
conductor length. This observation
leads to the conclusion that connections
to “historic” cables and replacement of
514
8.3.3 Covered range of conductor
designs: round stranded and compacted
conductors
M. Uzelac
joints might not have the same
performance level as in complete new
cable installations. The unknown
degradation of aluminum conductor
material will not be a reproducible test
criterion
A compacted round stranded conductor
is considered to be the most critical
conductor, because the strands are
shaped and strain-hardened during
manufacturing and all air in between is
removed. Therefore, a connector needs
to apply higher radial forces to create
radial and axial deformation of strands
to remove oxide layers on each surface
and create the necessary contact
pressure between the metallic parts for
achieving a low and stable electric
contact resistance. The more layers and
strands, the higher this deformation
should be to get an impact on most of
the strands fixed inside the connector
barrel. Where nonmetallic material will
not be removed prior to installation,
these layers have additionally to be
pierced and pushed aside while
installing the connector to get a pure
metallic contact between the strands of
the conductor. Where all strands are
brushed and cleaned in the area of a
connection, the conductor has to be
rebuilt in a round shape which allows
the correct placement inside the
connector without overstressing the
strands by bending and reducing the
effective conductor cross-sectional area
Experience show that mechanical
connectors which are tested on stranded
conductors will never have a problem to
pass a test on solid conductors of that
nominal size which fits into the
connector barrel. Intrinsic watertight
solid conductors are available in
aluminum for the use in power cables,
10
Test Regimes for HV and EHV Cable Connectors
515
for example, up to 1600 mm2. Solid
conductors of copper of big sizes are not
in use for power cables in typical
distribution networks. Mechanical
connectors are assumed to apply the
same radial force via torque limited
screws, no matter how the dimension,
shape, and hardness of a used conductor
will be. But compression connectors
may not fulfill this rule, as usually
depending on the dimension and
hardness of the conductor inside the
fixed deformation of the connector/
conductor combination introduced by
the tool and die. The dominating
phenomenon in tests of connectors on
aluminum conductors is the penetration
of the oxide layers on its surfaces.
Besides the solid conductor, which has
its surface only outside, the stranded
conductor has additional oxide-layers
on each strand. The hardness
(or softness) of aluminum used in solid
conductors allows axial mechanical
tensile strength up to 40 N/mm2
multiplied by the size in mm2 as the
maximum applicable value in Newton.
At approximately 50 N/mm2 applied
axial tensile load value an irreversible
elongation of the solid conductor will
start, making it thinner and longer which
might have an influence on the partial
discharge level due to insufficient
coupling to the inner semi-conductive
layer of the cable insulation. The usual
hardness of aluminum material used for
solid conductors seems to be “soft”
enough for the bending and laying of the
cable and “hard” enough that no further
“cold flow” is starting inside installed
connectors. Test experience show that in
case of compression connector different
sleeves and/or different compression
layout has to be used for stranded and
516
8.3.4 Water blocking material
8.3.5 Use of segment- or strand
insulation in the conductor
M. Uzelac
for solid conductors of the same
nominal cross-sectional area
The use of water blocking material is
normally not specified or standardized
in material, and distribution inside a
connector. It is usually made of an
electrically nonconductive or
low-conductive material and has to be
pushed aside by the connector during
installation to guarantee a stable contact
behavior to be investigated in a
connection test. Similar considerations
are applicable to “contact grease”
normally applied inside compression
connectors for aluminum conductors.
Although there might be metallic
ingredients of these compounds, it has
to be pushed aside to guarantee direct
metallic contact between conductor
strands and to the connector.
Compounds are primarily used to
prevent the contacts from further
oxidation after installation and are not
able to carry the required currents
The use of nonconductive materials
inside conductors might be
advantageous to achieve low
AC-resistance values and handle skinand proximity effects of current
distribution inside conductors with large
cross-sectional areas. At cable ends and
in conductor connections it is necessary
to inject the current almost
homogeneously in each conductive
structure. This can be done either by
manually removing all nonconductive
material from the contact zone or by
pushing aside during closing of the
connector. Conductors of the same size
and material as tested might be used
with one connector as long as less or no
nonconductive materials are used. This
statement is applicable for compression
and for mechanical connectors
10
Test Regimes for HV and EHV Cable Connectors
8.3.6 Through connectors in joints for
connecting different cable sizes
517
The most common approach for using a
mechanical or compression connector
family for the widest range of
application is to remove all
nonconductive material on and inside a
conductor at least at the zone to be
placed inside the connector barrel as to
be described in the installation
procedure of the connector. But this
installation procedure might be time
consuming and expected results might
be depending on the working skills of
fitters and the quality of their work.
Rebuilding a segmented, stranded
conductor to a round shape of almost the
same diameter to fit into the connector
barrel with parallel strands, not
overstressed by bending and rearranging
by not losing too much material, is
hardly reproducible
So there might be economic and quality
assurance considerations to use
connectors which are able to perform
stable without removing nonconductive
materials of the conductor during
installation of the connector. The
disadvantage is that each change in
combination using a different conductor
design has to be verified by tests
Almost all connector barrels, no matter
if used for compression connector or for
mechanical connector families are made
from one specific material. For
connecting two of these barrels in a
through connector jointing two equal or
different conductors, usually one
connector body is formed out of the
same material without an additional
join-patch in between. This will
guarantee that the connector itself will
have no additional internal transition
resistance which might need a “risk
assessment” due to production,
installation or expected deterioration
518
8.3.7 Termination lug connectors
M. Uzelac
during service. Most of the “reduction
connectors” jointing two different
conductors are built in this way. In some
cases, it might be necessary to joint two
connector barrels made of different
material, for example, like in
compression connectors for jointing
aluminum conductors to copper
conductors. For jointing such different
materials, for example, friction welding
is used and the manufacturing method in
this special application can be regarded
as a family and might therefore be tested
if significant influence of this internal,
prefabricated joint in the connector body
might be expected. As most of the
jointed different conductors should be
serial loaded during this test, the
“weakest” conductor is limiting test
currents
There are also cases where two
connector barrels in one connector body
of the same material are separable by a
mechanical connection, for example, to
ease installation in specific accessories.
The test performance of this additional
internal connector joint besides the
conductor connections might also be
investigated like bimetallic through
connectors
The thermal situation at cable
termination ends is normally less critical
than inside joints of HV/EHV-cable
accessories. Therefore, additional
connector tests at termination bolts or on
cable lugs are not necessary, as long as
the same connector design criteria at
connector barrels are used as
successfully tested for through
connectors used for joints on the same
conductors. Some users are requesting
combined tests including the clamping
arrangement to the overhead line
connection. But in most of the
10
Test Regimes for HV and EHV Cable Connectors
8.3.8 Mechanical connectors –
adjustment of dimensions to suit
application
519
applications the current carrying
capacity of the equipment-connection is
higher than the nominal current of the
connected cable and there is no need for
additional tests. Metal parts and their
coatings as well as means and
arrangements to secure the termination
end to other equipment should be able to
withstand specified corrosive
atmospheres without losing contact
pressure. Universal applicable tests are
not defined up to now, due to the variety
of interfaces and environmental
conditions at terminations
The diameter of a stranded conductor of
a cable is seldom a known and
guaranteed characteristic when selecting
a cable for a specific project and
designing the accessories. For example,
in case of aluminum conductors of class
2 according to IEC 60228 there is an
informal guidance for minimum and
maximum diameter for sizes up to
630 mm2 with a variation of 3.8 mm for
this nominal cross-sectional area. A
connector should be able to handle such
dimensional differences without loss of
performance. As in some HV/EHVaccessories it is advantageous to control
eccentricity of installed connectors, it
might be necessary to modify the inner
diameter of a mechanical or
compression connector to handle this
nonstandardized dimensional difference
of conductors within one nominal crosssectional area. To be covered by
previous test approval of connector and
conductor, it is allowed to decrease the
inner diameter. Therefore, a test of the
mechanical connector/conductor
combination should cover worst case
condition with the smallest volume of
the connector body or the largest inner
diameter of the connector barrel
520
8.3.9 Thermal short circuit tests
M. Uzelac
For example, in slip-on joints it is
advantageous to have almost no
diameter difference or “step” between
prepared cable insulation and connector
outer surface to avoid damage at the
expanded insulation part while axially
moved during installation and to have a
good heat transmission by direct and
intense connection between installed
connector and elastic insulation part of
the joint. To achieve this, a connector
should be adapted to have the same
wall-thickness as the primary cable
insulation in each application. For a test
of a connector on a conductor, the worst
case should be selected, which is given
by the lowest heat dissipation in the test
setup in bare condition, respectively, the
smallest surface of the connector body,
the lowest mass and, respectively, the
smallest outer diameter
The thermal impact of short-circuit
current tests on connections is
adequately represented by the JouleIntegral applied during adiabatic tests by
avoiding any additional dynamic and/or
mechanical impact due to current-flow
in the specific test setup
Mainly the initial temperature shock
between “hot” conductor and “cold”
connector creates a mechanical stress
inside the connector due to different
thermal expansion of involved
materials, which might shift the “microcontact-spots” to other regions of the
connection. This is considered to be the
major effect on connections to be
checked in adiabatic single phase shortcircuit tests
Experience shows that the integrated
short-circuit tests in type tests, for
example, according to IEC 61238-1-3,
will have a clear impact on test results.
But for bigger sizes the created
10
Test Regimes for HV and EHV Cable Connectors
8.3.9 Dynamic short circuit test validity
is limited to the test-setup
521
temperature rise of short-circuit tests is
very limited and created additional
stresses due to different thermal
expansion inside the connector/
conductor combination will be limited
accordingly. Especially for big copper
conductors less effect can be seen on the
test results of already qualified
connectors. So it might be allowed to
skip this test procedure, mostly done in a
different test laboratory with additional
mechanical stress for test setup by
dismantling, moving, and rebuilding
after tests
Although calculation with a shortcircuit current of 45 kA applied for 5 s
show that the overall temperature rise
will be not more than 30 K when
starting from 90 C, which is the same
or less as applied during heat cycling,
the heat created in the single contact
spots between conductor layers and
connector body during short-circuit tests
is much higher than during heat cycles.
This cannot be measured from outside,
but it might have an influence on poor
designed connectors
Experience shows that short-circuit tests
shall be mandatory for all connectors for
stranded aluminum conductors. The
more strands and layers, the higher the
risk of insufficient deformation during
connector installation and the higher the
risk of local overheating of single
contact spots due to higher current
densities of the remaining strands in the
current path will be
Some users prefer to apply higher
currents for shorter times to get the same
energy-input by the Joule-Integral or use
an asymmetric test current specifying a
certain peak-value or peak-factor. But as
higher currents will lead to additional
mechanical forces created from the
522
8.5.1 (a) Tensile load test
M. Uzelac
magnetic field of all current carrying
parts in the test-setup, test results are
specific for this test arrangement and its
mechanical fixations. The validity of the
test is limited to the used test
arrangement only. Users have to check
whether expected worst case conditions
in practical cable installations will be
covered
The purpose of the test is to ensure an
acceptable basic mechanical strength to
stresses which may occur during the
erection of a cable system by handling
already installed connectors on cable
conductors
There is no mechanical type test
specified in this development test
recommendation to be performed
separately on additional new samples
like described in IEC 61238-1-3
Chap. 7. Mechanical type tests and
electrical type tests are strictly separated
in IEC 61238-1-3 while the mechanical
load test specified in Sect. 8.2.5 is an
integral part of each development test
sequence. Therefore, the applied values
for this combined mechanical and
electrical test are lower. The aim is to
create a realistic prestress to simulate
usual installation conditions for a cable
system before any current will be
applied
The mechanical performance of a
connector/conductor combination is
usually verified with a single axial
pulling test in each assigned
combination separately on new samples.
The breaking load value of the
combination should be sufficiently high
above the withstand ability value of this
connection, which is 40 N/mm2 for
aluminum and 60 N/mm2 for copper
multiplied by the nominal size of the
conductor in mm2. It is assumed that
10
Test Regimes for HV and EHV Cable Connectors
8.5.1 (b) Short circuit tests
523
usual occurring push-pull-forces in
cable installations, created by changing
thermal expansion due to fluctuant
currents, can be handled without
changing the performance of this
connector/conductor combination. It is
also assumed that the cable installation
will avoid nonaxial bending forces
acting on the bearing point of the
connection. Tests in MV installations
simulating such bending forces in cable
accessory tests show that the electrical
performance is sufficient, if electrical
and mechanical tests of connections
according IEC 61238-1-3 are passed
and installation is done properly
The purpose of this test is to ensure
basic short circuit current withstand
ability to usual HV and EHV cable
network service conditions for the
intended application
Advantage is that only “realistic”
conditions are tested in available test
facilities in case of conductors
exceeding 1200 mm2 and there is up to
now no other international recognized
standard requiring short circuit tests in
HV and EHV cable systems and/or with
their accessories
Disadvantage is that the complete test
sequence should be repeated in case of
higher required short circuit values
occurring in service
The purpose of the test is not to test
connectors at 250 C conductor end
temperature with max. 45 kA, 5 s for
comparing performance-limits of
different connector/conductor
combinations among each other like
done in IEC 61238-1-3
A passed dynamic short circuit test
using asymmetric short circuit peak
current covers, besides the thermal
criteria additionally all applications
524
8.5 2, 8.6.3 Constant high-current
temperature stability test
M. Uzelac
where the same or lower maximum
Lorentz-forces may occur. If the layout
of the test loop and current flow through
adjacent parts is specified by
dimensions, the same configuration is
covered in practical applications
The purpose of this test is to create
additional ageing stress on the already
pre-stressed samples by applying
maximum allowed temperatures to the
test loop during a long time, created by
an almost constant heating current, far
beyond nominal currents in cable
systems. Before applying the materialexpansions and -relaxations created by
heat cycling, the constant application of
high temperatures and high currents
creates worst case conditions following
Arrhenius’ law. This stress
accumulation and the temperature limits
below 140 C are selected to avoid
changes in involved material
characteristics, especially for aluminum
During 200 h thus determined
equilibrium should be maintained
within 5 K using the reference
conductor as control parameter, in order
to keep the temperature constant. In this
way, the fluctuation of the ambient
temperature will not affect the
temperature of the reference conductor
within the specified tolerances
Temperature measurements should be
taken by using the method described in
e). The first measurement campaign
should be collected 8 h after reaching
equilibrium, the next campaigns then
every 24 h. One measurement campaign
consists in recording temperatures on
each connector and the reference
conductor taken every minute. If the
temperature readings during 15 min do
not vary by more than 2 K, the
measurement campaign can be stopped.
10
Test Regimes for HV and EHV Cable Connectors
8.5.3, 8.6.4 Heat cycle temperature
stability test
525
If not, the measurement campaign
should be continued until the 2 K-band
during 15 min is achieved for every
connector. The maximum measured
connector temperature in every
measurement campaign should be
recorded together with the reference
conductor temperature measured at the
same time. A set of eight measurement
campaigns with four pairs of connector/
conductor temperature values will then
be available for the assessment of
temperature stability
The purpose of this final test in the
sequence is to verify, if the such
pre-stressed conductor/connector
combination will be able to pass a cable
system qualification including 20 heat
cycles for type test plus 180 heat cycles
for PQ test with 8 h at rated operating
current followed by at least 16 h without
current per IEC 60840/62067. The heatcycle temperature-time regime
recommended here is much shorter,
because performed on a test loop with
uninsulated conductors, similar to the
test loop and method used in IEC
61238-1-3. This allows to use higher
heating currents and end temperatures
(because the cable insulation will not
limit any more) and speed up heating
and cooling times by keeping a high
temperature stability phase on the
reference conductor of at least 120 min.
In IEC 61238-1-3 this high temperature
stability phase is around 15 min while
the connector temperature should be
hold for 10 min at the maximum level.
The accumulated exposure time at
elevated temperature stage is balanced
in this test recommendation to be
comparable as well with IEC 60840/
62067 (for 200 cycles on longer
duration but lower temperatures) and
526
8.5.2 and 8.5.3 Temperature stability
criteria
M. Uzelac
with IEC 61238-1-3 (for 1000 cycles
with much shorter duration)
Regarding the test procedure this
proposed development test follows
strictly IEC 61238-1-3 in order to use
the same requirements for performing
the test and by using the same concept
of “reference method”. That means, that
the test can be done by using different
parameter if adequate, as long as it is
provided that the test will create the
same or comparable results. Only in
case of doubt, the reference method
should be used for comparison
The first aim of the high-current
temperature stability and heat-cycle
temperature stability tests is to show that
the temperatures of the connectors are
always below the temperature of the
reference conductor measured at the
same time during current flow in
“constant conditions” assuming no
changes in the heating current acting as
heat source, in heat transfer in involved
materials, in the radiation on material
surfaces of the test setup, in convection
of air flow in the test chamber and in the
ambient temperature during these
relatively long tests. The second aim is
to show that there is no detectable
increase of temperatures when
comparing initial situation to the
situation at the end of test, to prove that
possible connector resistance increase
inside will have no impact on the
measured temperatures on the surface of
connectors. But these assumed
“constant conditions” can hardly be
reproduced and it depends on the skills
of lab stuff to balance stability between
“hot” test setup and “cold” chamber
while differences in natural convection
might influence temperature of
specimen in different positions inside
10
Test Regimes for HV and EHV Cable Connectors
8.5 2, 8.5.3, 8.6.3, 8.6.4 Temperature
measurement
527
the chamber. Therefore a tolerance for
individual readings of 5 K is introduced
and all connectors of the same design
are “pooled” by the mean values to
verify stability compared to the
reference conductor to avoid, that the
connectors will be designed to be too
close to the limit where they might be
warmer as the reference conductor.
Nevertheless, the set temperature
criteria in this recommendation for
development tests seem to be
demanding and future shared test
experience will show if selected criteria
should be kept
Due to skin-effects in conductors above
1200 mm2 created when using
a.c. heating currents, there are a higher
surface temperatures than inside the
conductor and due to proximity effects
in the test loop setup, there might be
higher temperatures at surfaces adjacent
to other current carrying parts. This can
be observed when using d.c. heating
currents, which will create lower
temperatures when applying the same
value of current. When using
a.c. current heating these effects cannot
be avoided and are minimized as long as
surface temperature measuring spots are
at conductor and connector surfaces
with adequate distance to each other
528
M. Uzelac
Milan Uzelac graduated from Electro-Technical University of
Belgrade, Serbia, and joined Minel-Elektrooprema, Belgrade, as
a design engineer, senior design engineer, and the head of R&D
Department.
Milan relocated to United States in 1989 and joined G&W
Electric Company, Chicago, as an R&D engineer and product
manager. Currently, he is chief R&D engineer. His responsibility
has been the development and design of accessories for extruded
and laminated high and extra-high voltage cables.
Milan is active in IEEE working groups for developing industry
standards for high voltage cable accessories (IEEE 48 and 404).
He chaired IEEE WG for IEEE 1300 Standard for cable connections in gas-insulated switchgear.
He has served as a member of several CIGRE working groups
considering HV cable systems and was convener of CIGRE WG
on connectors for HV cables.
He was author of several papers and tutorials on high voltage
cable accessories and is co-author of EPRI Underground Transmission Systems Reference Book.
Standard Design of a Common, Dry Type
Plug-in Interf