DZS 907-1 : 2015
ISC
Edition1
Draft for Public Comment
Zambian Standard
ELECTRICITY DISTRIBUTION INFRASTRUCTURE - APPLICATION
GUIDE
Part 1:
Construction (Design, Selection, Installation and Commissioning)
This draft standard is for public enquiry only.
It must not be used or referred to as a Zambian
Standard
ZAMBIA BUREAU OF STANDARDS
DZS 907-1:2015
DATE OF PUBLICATION
This Zambian Standard has been published under the authority of the Standards Council of the
Zambia Bureau of Standards on ……………….
ZAMBIA BUREAU OF STANDARDS
The Zambia Bureau of Standards is the Statutory National Standards Body for Zambia
established under an Act of Parliament, the Standards Act, Cap 416 of 1994 of the Laws of
Zambia for the preparation and promulgation of Zambian Standards.
REVISION OF ZAMBIAN STANDARDS
Zambian Standards are revised, when necessary, by the issue of either amendments or of revised
editions. It is important that users of Zambian Standards should ascertain that they are in
possession of the latest amendments or editions.
CONTRACT REQUIREMENTS
A Zambian standard does not purport to include all the necessary provisions of a contract. Users
of Zambian standards are responsible for their correct application.
TECHNICAL COMMITTEE RESPONSIBLE
This Zambian Standard was prepared by the Technical Committee TC 5/7 on Electricity
Distribution Infrastructure upon which the following organizations were represented:
Copperbelt Energy Corporation Plc (CEC)
Energy Regulation Board (ERB)
Engineering Institution of Zambia (EIZ)
Kansanshi Mining Company Plc (KMP)
Konkola Copper Mines Plc (KCM)
Lunsemfwa Hydro Power Company Plc (LHPC)
Department of Energy, Ministry of Mines, Energy and Water Development Rural Electrification Authority (REA)
University of Zambia (UNZA)
Zambia Bureau of Standards (ZABS)
ZESCO Limited
Zambia Bureau of Standards
Lechwe House
Freedom Way South End
P.O. Box 50259, Lusaka
Email: zabs@zamnet.zm /infozabs@zamnet.zm
website: www.zabs.org.zm
i
DZS 907-1:2015
CONTENTS
FOREWORD ...............................................................................................................................................v
INTRODUCTION .......................................................................................................................................1
1.
SCOPE ...............................................................................................................................................2
2.
NORMATIVE REFERENCES .......................................................................................................2
3.
DEFINITIONS AND ABBREVIATIONS ......................................................................................3
4.
5.
3.1
Definitions ................................................................................................................................3
3.2
Abbreviations and Acronyms ...................................................................................................5
NETWORK PLANNING AND DESIGN .......................................................................................6
4.1
General......................................................................................................................................6
4.2
Substation Equipment and Component Sizing .........................................................................8
SUBSTATIONS.................................................................................................................................9
5.1
Transformers .............................................................................................................................9
5.2
Switchgear ..............................................................................................................................15
5.3
Busbars ...................................................................................................................................43
5.4
Controlgear .............................................................................................................................46
Equipment .......................................................................................................................................67
5.5
6.
7.
Auxiliary Equipment ..............................................................................................................67
CABLES AND CONDUCTORS....................................................................................................68
6.1.
General....................................................................................................................................68
6.2.
Fault currents and short-circuit ratings of cables ....................................................................68
OVERHEAD DISTRIBUTION LINES ........................................................................................72
7.1
General....................................................................................................................................72
7.2
System Voltages .....................................................................................................................72
7.3
Conductors ..............................................................................................................................72
7.4
Support Structures ..................................................................................................................74
7.5
Insulators.................................................................................................................................77
7.6
Aerial Guard Earth Wire .........................................................................................................80
7.7
Anti-climbs .............................................................................................................................80
ii
DZS 907-1:2015
7.8
Cradle Catch nets ....................................................................................................................80
7.9
Red Balls.................................................................................................................................80
7.10 Goal posts ...............................................................................................................................81
7.11 Pole Mounted Equipment .......................................................................................................81
8.
9.
10.
UNDERGROUND DISTRIBUTION SYSTEMS.........................................................................85
8.1.
Components ............................................................................................................................85
8.2.
All joints shall comply with IEEE 404, IEC 60840 and SANS 10198-9 to 11. Trenches: ...85
8.3.
Cable Trays/Racks ..................................................................................................................86
8.4.
Cable Route Markers ..............................................................................................................86
EARTHING AND LIGHTNING PROTECTION REQUIREMENTS .....................................87
9.1.
General....................................................................................................................................87
9.2.
Earthing of Equipment ............................................................................................................87
9.3.
Lightning protection ...............................................................................................................94
9.4.
Insulation Co-ordination .........................................................................................................94
VOLTAGE REGULATORS ..........................................................................................................95
10.1. General....................................................................................................................................95
10.2. Secondary Transformer Voltage Regulation ..........................................................................95
11.
CAPACITORS ................................................................................................................................96
11.1. Power Capacitors ....................................................................................................................96
11.2. Shunt Capacitors .....................................................................................................................96
11.3. Capacitor Banks ......................................................................................................................96
12.
FEEDER PILLAR ........................................................................................................................102
12.1. General..................................................................................................................................102
12.2. Specification for Feeder Pillars.............................................................................................102
13.
SUBSTATION CONCRETE WORKS .......................................................................................104
13.1 General..................................................................................................................................104
13.2 Substation equipment plinths ................................................................................................104
13.3 Oil containment tanks ...........................................................................................................105
14.
WAYLEAVE .................................................................................................................................106
14.1. General Requirements...........................................................................................................106
iii
DZS 907-1:2015
14.2. Specific requirements ...........................................................................................................106
14.3. Prevention against Animal diseases ......................................................................................108
15.
LONG-TERM PRESERVATION OF SUPPORT STRUCTURES FOR DISTRIBUTION
INFRASTRUCTURE ...................................................................................................................109
15.1 Painting .................................................................................................................................109
15.2 Concrete Poles ......................................................................................................................109
15.3 Steel Poles.............................................................................................................................109
15.4 Steel Structures for Outdoor Substations ..............................................................................109
APPENDICES .........................................................................................................................................110
APPENDIX 1:
ORDER
INFORMATION REQUIRED WITH TRANSFORMER ENQUIRY AND
110
iv
DZS 907-1:2015
FOREWORD
The Zambia Bureau of Standards (ZABS) is the Statutory Organization established by an Act of
Parliament. ZABS is responsible for the preparation of national standards through its various technical
committees composed of representation from government departments, the industry, academia,
regulators, consumer associations and non- governmental organizations.
This National standard has been prepared in accordance with the procedures of the ZABS. All users
should ensure that they have the latest edition of this publication as standards are revised from time to
time.
No liability shall attach to ZABS or its Director, employees, servants or agents including individual
experts and members of its technical committees for any personal injury, property damage or other
damages of any nature whatsoever, whether direct or indirect, or for costs (Including legal fees) and
expenses arising out of the publication, use of, or reliance upon this ZABS publication or any other ZABS
publication.
Compliance with a Zambian standard does not of itself confer immunity from legal obligations.
DZS 907: 2015 was prepared by the TC 5/7 on Electricity Supply
v
ZAMBIAN STANDARD
ELECTRICITY DISTRIBUTION INFRASTRUCTURE – Application Guide
Part 1:
Construction (Design, Selection, Installation and Commissioning)
INTRODUCTION
This standard provides a set of guidelines for the design, construction and installation and
commissioning of electricity distribution infrastructure within Zambia. These guidelines are to
be applied to all publicly and privately owned electricity distribution infrastructure, so as to
ensure safety and quality electricity distribution within Zambia.
Electricity distribution infrastructure needs to be planned, designed, constructed, maintained and
operated in accordance with the requirements, standards and guidelines provided in the
approved standards document to achieve the set objectives of equipment reliability, safety,
providing quality service to the consumer and meeting the environmental protection
requirements.
The quality and reliability of the installed infrastructure is of paramount importance and
compliance to set standards will help achieve the objective of reliability and security of supply,
safe operation and safety of the consumer and the general public.
Therefore, the focus of this standard will be on quality of electrical components and other
accessories and requirements for installations of these components in the distribution system.
The standards are intended to ensure that: components are able to be interchanged without any
deviation; there is minimum interruption on the service delivery to the consumer and that the
utilities‟ expenditure on electrical components replacements is reduced due to increased life of
the components.
This standard is expected to achieve the following:
i).
ii).
iii).
iv).
v).
vi).
vii).
viii).
ix).
Electrical equipment design and construction in accordance with good engineering
practices;
High operational reliability owing to good quality material and installation;
Reduction on maintenance costs;
Improvement of the quality of service delivery to consumer;
Promote product upgrade and technological innovation in the electricity supply industry
in Zambia;
Control on the quality of electrical products on the market;
Operational safety;
Electrical equipment designed for use within certain voltage limits that is safe to use;
and,
Environmental protection.
1
1.
SCOPE
This part of DZS 907 covers the planning, design, construction, installation, and commissioning
of ac distribution networks ranging from three phase 33,000 volts to 220 volts a.c. single phase.
It is a general guide to good technical practice for economical overhead and underground
distribution networks in Zambia.
This standard excludes power supply to mining underground power distribution and other zoned
and categorized areas e.g. explosive environments, solvent extraction plants, military
installations and flammable environments.
2.
NORMATIVE REFERENCES
The following standards contain provisions which, through reference in this text, constitute
provisions of this part of DZS 907. All standards are subject to revision and since any reference
to a standard is deemed to be a reference to the latest edition of that standard party to
agreements based on this part of DZS 907 are encouraged to take steps to ensure the use of the
most recent editions of the standards indicated below.
Information on currently valid national and international standards can be obtained from Zambia
Bureau of Standards.
IEV 441-18-09
IEV 441-18-081
IEV 441-18-111
IEV 441-18-131
IEC 60
IEC60812
IEC 60865
IEC 60909
IEC 60050-195, 195-06-05
IEC 61024
IEC 62262 – IK Code
IEC 62305
IP Code - IEC 60529
IEC 61643
IEC 60071,
IEC60085,
IEC 60283,
IEC 60296,
IEC 60815,
IEC 61211,
IEC61467
IEC 60801- EMI & RFI,
EMC-IEC 61000
IEC 60947,
IEC 61363
IEC 61892
IEC 61439
2
IEC 62271
IEC 62357,
IEC 61850
ZS387
IEEE C57.12.00 - Standard General Requirements for Liquid-Immersed Distribution, Power,
and Regulating Transformers
ZS791- Wiring of Premises
ZS 746-1
ZS 746-2
3.
DEFINITIONS AND ABBREVIATIONS
3.1
Definitions
3.1.1
Bund wall: A wall/barrier of sufficient height constructed around fluid filled
equipment to contain spillage of liquids.)
3.1.2
Busbar: a low-impedance conductor to which several electric circuits can be separately
connected.
3.1.3
Controlgear: general term covering switching devices and their combination with
measuring, protective and regulating equipment, also assemblies of associated control,
such devices and equipment with associated interconnections, accessories, enclosures
and supporting structures, intended in principle for the control of electric energy
consuming equipment
3.1.4
Cross-arm: a pole that is used in a horizontal or near- horizontal position in a structure
for the support of power distribution lines, but that is not intended to be used in contact
with the ground
3.1.5
Cut-out base: The fixed part of a cut-out provided with the contacts and terminals.
3.1.6
Degree of protection: The extent of protection provided by an enclosure against
access to hazardous parts, against. ingress of solid foreign objects and/or against
ingress of water and verified by standardized test methods
3.1.7
Direct contact: Contact of persons or livestock with live parts.
NOTE: This IEV definition is given for information. In this standard "direct contact" is replaced
by "access to hazardous parts ".
3.1.8
Drop-out fuse-link assembly [cut-out]: An assembly that comprises all components
that form a complete device intended to protect equipment or parts of a reticulation
system (or both), in which the fuse-carrier automatically drops into a position that
provides an isolating distance after the fuse has operated.
NOTE: In this specification the term “cut-out” is often used in place of “drop-out fuse-link”
assembly.
3.1.9
Enclosure: A part providing protection of equipment against certain external
influences and, in any direction, protection against direct contact.
3
NOTE: This definition taken from the existing International Electro-technical Vocabulary (IEV)
needs the following explanations under the scope of this standard:
1) Enclosures provide protection of persons or livestock against access to hazardous parts.
2) Barriers, shapes of openings or any other means - whether attached to the enclosure or formed
by the enclosed equipment - suitable to prevent or limit the penetration of the specified test probes
are considered as a part of the enclosure, except when they can be removed without the use of a
key or tool.
3.1.10
Expulsion fuse: A fuse in which operation is accomplished by the expulsion of gases
produced by the arc. [IEV 441-18-111]
3.1.11
Fuse element: That part of the fuse-link which is designed to melt under the action of
a current that exceeds some definite value for a definite period of time. [IEV 441-18081]
3.1.12
Fuse-carrier: The movable part of a fuse-link assembly designed to carry a fuse-link.
[IEV 441-18-131]
3.1.13
Fuse-link: The part of a fuse including the fuse element(s) intended to be replaced
after the fuse has operated. [IEV 441-18-09]
3.1.14
Hazardous live part: A live part which, under certain conditions of external
influences, can give an electric shock (see IEC 60050-195, 195-06-05).
3.1.15
Hazardous mechanical part :A moving part, other than a smooth rotating shaft, that is
hazardous to touch
3.1.16
Hazardous part: A part that is hazardous to approach or touch
3.1.17
Insulator: That component of a cut-out base, which is intended to insulate the loadside and the source-side from each other and from earth and which is fitted with an
insulator-fixing stem.
3.1.18
Insulator-fixing stem: A component for attaching the insulator to the mounting Lbracket.
3.1.19
IP Code: A coding system to indicate the degrees of protection provided by an
enclosure against access to hazardous parts, ingress of solid foreign objects, ingress of
water and to give additional information in connection with such protection
3.1.20
Lower contact: The load-side contact of a cut-out base, which also allows a
removable fuse-carrier or solid-link to pivot.
3.1.21
Mounting L-bracket: A device used to facilitate the mounting of a cut-out on either
a wooden cross-arm or a steel cross-arm.
3.1.22
Outdoor distribution cut-out: A drop-out vented expulsion fuse-link assembly or
solid-link assembly, together with the associated components.
3.1.23
Rated fibre stress: stress in the wood from the applied load just before breaking
4
3.1.24
Solid-link assembly: An assembly that comprises all components that form a
complete device intended to isolate equipment or parts of a reticulation system, or both,
from the source of supply.
3.1.25
Solid-link: A component for use in place of a fuse-carrier, to effect a manual
disconnection.
3.1.26
Spacer block: a piece of timber that is used as a spacer between poles and cross-arms
in five- pole structures but that is not intended to be used in contact with the ground
3.1.27
Substation- An enclosed assemblage of equipment, e.g., switches, circuit breakers,
buses, and transformers, under the control of qualified persons, through which electric
energy is passed for the purpose of switching or modifying its characteristics to
increase or decrease voltage or control frequency or other characteristics.
3.1.28
Switchgear: the combination of electrical disconnects switches, fuses or circuit
breakers used to control, protect and isolate electrical equipment. It is used both to deenergize equipment to allow work to be done and to clear faults downstream.
3.1.29
Treated/treatment: impregnated/impregnation with an acceptable preservative
3.1.30
Upper contact: The source-side spring-loaded contact of a cut-out base.
3.2
Abbreviations and Acronyms
3.2.1
ACSR:
Aluminium Conductor Steel Reinforced
3.2.2
ONAN:
Oil Natural Air Natural
3.2.3
ONAF:
Oil Natural Air Forced
3.2.4
OFAF:
Oil Forced Air Forced
3.2.5
OFWF:
Oil Forced Water Forced
5
4.
NETWORK PLANNING AND DESIGN
4.1
General
The primary purpose of an electricity distribution network system is to meet the customer‟s
demands for energy. Depending on the geographical location, the distribution network can be in
the form of overhead lines or underground cables.
The objective of planning for the distribution network is to ensure that the required power
demand by the customers is met. However, to achieve this objective the designer of the network
should take into account the technical performance of the network being designed and its
associated costs so that the electricity distribution network is technically sound and cost
effective.
The factors influencing network design that need to be considered fall into the following three
categories;
a).
Fixed parameters within which the electrical designer might have to work, include:
i).
Statutory requirements:















ii).
Existing services:







iii).
Environmental Impact Assessment with ZEMA, Environmental Protection and
Pollution Act
Land Acquisition Act
Local Government Act
Town and Country Planning Act
Occupational Health and Safety Act 36 of 2010
Factories Act Cap 441
Electricity Act
Energy Regulation Act
Petroleum Act
Mines and Minerals Act
Water Resource Management Authority Act
Zambezi River Authority Act
Forestry Act
Civil Aviation Act
Zambia Wildlife Act
Electricity Utilities
Water Utilities and sewerage
Information and Communication Technology service providers
Road Development agency
Local Authorities
Oil pipeline
Rail line
Existing area layout:
6




iv).
Nature of the terrain:



v).
Topographic
Soil conductivity for earthing
Soil bearing capacity for civil works
Geographic location:




vi).
Local Authority
Geological Survey
Planning and Buildings Department
ZAWA
Proximity to sensitive infrastructures i.e. fuel storage tanks, storage magazines
or other explosive materials
Seismic Zones
Lightening prone areas
Existing infrastructures i.e. tall buildings, airport area
Factors over which the designer has limited or no control, including:


Consumer loads;
Diversity;
vii). Factors over which the designer should exercise control, including:





b).
Initial capital costs and life cycle costs;
New area layout;
Number and positioning of metering points;
Cable and conductor sizes and types of cable and conductor; and,
Number, sizes, locations and types of substation;
The designer shall obtain supply characteristics at the supply points from the service
provider i.e. Voltage drop and unbalance, within limits of design load, and all other
parameters as prescribed in the Zambian Power Quality Standard ZS 387
NOTE: No design should be considered in isolation. The planner should take into account the
relationship between the area to be supplied and adjacent supply areas, proposed future
developments and environmental considerations. When applying the guidelines to individual
schemes, it is necessary to take into account all local conditions and total life cycle cost (for
example, capital outlay and the upgrading of operational and maintenance requirements).
c).
Climatic Conditions
Some examples of the effects of climatic conditions on overhead lines are:
i).
ii).
iii).
iv).
Ambient temperature and wind affect the sag of overhead conductors and their
current-carrying capacity;
Wind affects pole supports, stays and clearances;
Lightning causes surge voltages to be induced into the network; and
In cases where overhead lines are situated close to the coast, the combined effects
7
of pollution and high relative humidity on insulators have an adverse effect on
the system. Salt fog can be corrosive on conductors with steel reinforcing if not
adequately greased.
4.2
Substation Equipment and Component Sizing
A substation is a part of an electrical generation, transmission and distribution system. Its
primary purpose is to transform voltages from high to low, or the reverse, or perform any of
several other important functions. All substation equipment and associated components shall be
designed, constructed, installed and commissioned to meet the requirements as set out in this
standard.
The expected thermal, chemical, mechanical and environmental conditions shall be considered
in the design of the equipment. Further, all equipment shall be designed to withstand the effects
of normal, emergency and fault conditions expected during operation. The substation equipment
specified in this standard include; transformers, switchgear (circuit breakers, busbars,
fuses), control gear and substation auxiliary equipment (substation lighting, fire
suppression systems and telemetry).
The following safety considerations shall be taken into account in the planning, designing,
construction, installation and commissioning of substations in accordance with the provisions of
ZS 418 Parts 1 and 2:
i).
ii).
iii).
iv).
v).
Safety clearance
Signage
Fencing
Personal Protective Equipment ( PPE)
Substation Perimeter
For other safety considerations refer to IEC 61558 on Safety of installations and IEC 61557
8
5.
SUBSTATIONS
5.1
Transformers
5.1.1 General
All distribution transformers shall comply with IEC 60076- Power Transformers – All Parts.
In this standard, a transformer is an electrical device that transfers energy between two or more
circuits through electromagnetic induction.
The standard applies to three-phase and single- phase power transformers (including autotransformers) with the exception of certain categories of small and special transformers such as;
a).
b).
c).
d).
e).
f).
g).
single-phase transformers with rated power less than 1 kVA and three-phase
transformers less than 5 kVA;
instrument transformers;
transformers for static convertors;
traction transformers mounted on rolling stock;
starting transformers;
testing transformers; and
welding transformers.
It‟s recommended that an agreement shall be reached concerning alternative or additional
technical solutions or procedures. Such agreement is to be made between the manufacturer and
the purchaser, the matters should preferably be raised at an early stage and the agreements
included in the contract specification.
5.1.2 General Design and Construction
This part of the standard prescribes the specific technical requirements applicable to
transformers.
NOTE 1:
For the exact limit and acceptable tolerance of a particular parameter, this specification is to be
used in conjunction with the descriptions and the specifications of IEC 60076 Part 1, 2 and 3.
5.1.2.1 Service Conditions
The service conditions for transformer shall be as specified in Table 5-1 below:
Table 5-1:
Service Conditions for Transformers
S/N Service Condition
1.
2.
3.
4.
5.
6.
7.
8.
9.
Altitude above mean sea level
Maximum ambient temperature for design purpose
Average ambient temperature for design purposes
Minimum ambient temperature for design purposes
Relative humidity maximum at 35oC
Maximum wind speed
Mean annual rain fall
Maximum solar radiation
Isokeraunic Level average
9
Specification
1400m
40oC
30oC
-1oC
95%
40m/s
1065mm
1200 W/m2
130 days/year
5.1.2.2 Installation
Power transformers shall be so installed that all energized parts are enclosed or guarded so as to
limit the likelihood of inadvertent contact, or the energized parts shall be physically isolated.
The case shall be effectively grounded or guarded.
Oil-immersed transformers are to be hermetically sealed with integral filling. Oil in
transformers is used as insulation and also serves as a cooling medium.
The installation of liquid-filled transformers shall utilise one or more of methods highlighted
below to minimise fire hazards. The method to be applied shall be according to the degree of the
fire hazard. Recognised methods are the use of less flammable liquids, space separation, fire
resistant barriers, automatic extinguishing systems, absorption beds, and enclosures. The
amount and characteristics of liquid contained should be considered in the selection of space
separation, fire-resistant barriers, automatic extinguishing systems, absorption beds, and
enclosures that confine the liquid of a ruptured transformer tank, all of which are recognized as
safeguards.
i).
Transformers and regulators 75 kVA and above containing an appreciable amount of
flammable liquid and located indoors shall be installed in ventilated rooms or vaults
separated from the balance of the building by fire walls. Doorways to the interior of the
building shall be equipped with fire doors and shall have means of containing the liquid.
ii).
Transformers or regulators of the dry type or containing a nonflammable liquid or gas
may be installed in a building without a fireproof enclosure. When installed in a building
used for other than station purposes, the case or the enclosure shall be so designed that
all energised parts are enclosed in the case that is effectively grounded. As an alternate,
the entire unit may be enclosed so as to limit the likelihood of inadvertent contact by
persons with any part of the case or wiring. When installed, the pressure-relief vent of a
unit containing a non-biodegradable liquid shall be furnished with a means for absorbing
toxic gases.
iii).
Transformers containing less flammable liquid may be installed in a supply station
building in such a way as to minimize fire hazards. The amount of liquid contained, the
type of electrical protection, and tank venting shall be considered in the selection of
space separation from combustible materials or structures, liquid confinement, fireresistant barriers or enclosures, or extinguishing systems.
5.1.2.3 External Clearances
External clearances shall be such that there will be no visible corona up to 1.1 pu system
voltage. In addition, the minimum external clearances between live parts and live parts to
ground shall not be less than that specified in ZS 418.
5.1.2.4 Identification
The transformer must contain a nameplate reverted on the tank and clearly visible. The
nameplate shall indicate:
10
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

















The year of Manufacture
The standard to which the unit is made
Name of manufacturer
Serial number
Cooling type
Vector Symbol
Vector group diagram
Winding configuration diagram
Tap changer type (Onload/Offload)
Number of Taps and nominal Tap
Specific tap voltages
Inscribed Tested Voltage percent impedance
KVA rating
Frequency
Primary and Secondary Voltage at Nominal
Maximum Secondary and primary currents at Nominal
Weight of the oil
Weight of core and tank
Gross weight
5.1.2.5 Manufacturers’ Drawings
The following drawings approved by the purchaser shall be availed by the manufacturer:






Wiring and schematic drawing of the tap changer and transformer
Complete assembly drawing of the transformer and accessories
Foundation Drawings
Outline drawing
Instruction Manuals
An instruction manual shall be availed by the manufacturer composed of the
following sections:











Introduction
General Transformer features
Parking, Transportation and Handling
Assembling and Installation
Pre-commissioning checks
Commissioning
Maintenance
Troubleshooting
End of life disposal
Drawings and catalogue
Loss evaluation and Payment
11
Both No Load and Full Load losses shall be specified to the potential supplier of the
Transformer. The calculated and actual losses shall be compared during factory
acceptance test and payment may be calculated.
In the event of actual loss being higher than agreed, parties may agree on a price
discount or rejection of the unit.
5.1.3 Rating Characteristics
5.1.3.1 Transformer Rating
The transformer shall have an assigned rated power for each winding which shall be marked on
the rating plate. The rated power refers to continuous loading. This is a reference value for
guarantees and tests concerning load losses and temperature rises.
If different values of apparent power are assigned under different circumstances, for example,
with different methods of cooling, the highest of these values is the rated power.
A two-winding transformer has only one value of rated power, identical for both windings.
When the transformer has rated voltage applied to a primary winding, and rated current flows
through the terminals of a secondary winding, the transformer receives the relevant rated power
for that pair of windings.
The transformer shall be capable of carrying, in continuous service, the rated power [for a multiwinding transformer: the specified combination(s) of winding rated powers] under conditions
listed in Clause 5.1.2.1 and without exceeding the temperature-rise limitations specified in IEC
60076-2.
5.1.3.2 Transformer Loading
The maximum loading of the transformer shall be specified at all cooling levels i.e. ONAN,
ONAF, OFAF and OFWF. The transformer will be loaded to not more than 1.5 times maximum
nameplate rating. All transformer parts shall be sized to allow full use of the winding's loading
capability for the following loading types (These loading capabilities shall apply to all
transformers for the following conditions):
i).
Preload of 90 % of nameplate MVA rating;,
ii).
The hottest spot temperature not to exceed 140º C, a top oil temperature not to exceed
110ºC; and,
iii).
Loss of life not to exceed 1.0% per incident. Short Time Minimum Acceptable Loading
Capability p.u. of nameplate MVA rating.
The loadings are depicted in the Table 5-2 below:
Table 5-2:
Transformer Loading
Ambient Temperature (oC)
Load In Per Unit of Nameplate Rating
12
10
40
5.1.3.3 Short Circuit Capability
(Load Duration in Hours)
0.5
1.0
2.0
1.50
1.45
1.39
1.26
1.23
119
4.0
1.34
1.15
8.0
1.31
1.13
The transformer and its current-carrying parts including tap changers and bushings shall have
short circuit capability in accordance with IEC 60076-5. Tertiary Windings, when specified,
shall be self-protecting. System fault power may be supplied from either one or both unfaulted
terminals. The maximum short circuit current at the tertiary bushings shall not exceed either, 25
times the rated tertiary winding capacity or 32 kA whichever is lower.
5.1.3.4 Earthquake Strength
The completely assembled transformer shall meet the High Seismic Qualification Level with
2% which is the highest seismic reading in Zambia.
5.1.3.5 Wind Loading Strength
The transformer shall be designed to withstand winds up 40m/sec in its service configuration
(i.e., with bushings, arresters, radiator/coolers, conservator, etc. installed). The earthquake and
wind forces need not be considered as occurring simultaneously. Documentation in the form of
test data or calculations shall be provided to confirm the transformer‟s wind and mechanical
shock withstand capabilities.
5.1.3.6 Sound Level
The sound level shall not exceed 75db at full load
5.1.3.7 Vibration
The transformer accessories shall be protected from damage by vibration during operation,
transportation or short circuits
5.1.4 Transformer Auxiliary Equipment
The size, type and location of the transformer dictate the amount of auxiliary equipment
associated with it. All auxiliary equipment should be checked for proper operation to assure
they are not defective.
The following accessories shall be included on all oil filled substation transformers:
i).
ii).
iii).
iv).
v).
vi).
vii).
Pad lockable tap changer for de-energized operation ( for transformers greater than 1000
kVA rating)
Upper filling plug and filter press connection
Drain valve with a sampler (two-inch drain valve for transformers above 2500 kVA
rating)
Dial type thermometer
Pressure/vacuum gauge [with] [without] bleeder connection
Magnetic liquid level gauge
Pressure Relief Valve/Device,
13
viii).
ix).
x).
Alarm contacts on [all gauges] [dial thermometer] [liquid level gauge] [pressure vacuum
gauge]
Pressure relief diaphragm
Buchholz relay( for transformers greater than and including 1200 kVA rating)
14
5.2
Switchgear
Switchgear shall comply with IEC 62271-SER ed1.0 (2015-02) High-voltage switchgear and
control gear - ALL PARTS.
5.2.1. Normal Service Conditions
5.2.1.1 Indoor switchgear and controlgear
a).
The ambient air temperature does not exceed 40 °C and its average value, measured over a
period of 24 h, does not exceed 35 °C.
The preferred values of minimum ambient air temperature are –5 °C, –15 °C and –25 °C.
b).
c).
d).
e).
The influence of solar radiation may be neglected.
The altitude does not exceed 1 000 m.
The ambient air is not significantly polluted by dust, smoke, corrosive and/or flammable
gases, vapours or salt. The manufacturer will assume that, in the absence of specific
requirements from the user, there are none.
The conditions of humidity are as follows:




the average value of the relative humidity, measured over a period of 24 h, does not
exceed 95 %;
the average value of the water vapour pressure, over a period of 24 h, does not
exceed 2.2 kPa;
the average value of the relative humidity, over a period of one month, does not
exceed 90 %;
the average value of the water vapour pressure, over a period of one month, does not
exceed 1.8 kPa.
For these conditions, condensation may occasionally occur.
f).
NOTE 1:
Condensation can be expected where sudden temperature changes occur in periods of
high humidity.
NOTE 2:
To withstand the effects of high humidity and condensation, such as breakdown of
insulation or corrosion of metallic parts, switchgear designed for such conditions should
be used.
NOTE 3:
Condensation may be prevented by special design of the building or housing, by suitable
ventilation and heating of the station or by the use of dehumidifying equipment.
Vibrations due to causes external to the switchgear and controlgear or earth tremors are
insignificant relative to the normal operating duties of the equipment. The manufacturer
will assume that, in absence of specific requirements from the user, there are none.
NOTE 4:
The interpretation of the term “insignificant” is the responsibility of the user or specifier
of the equipment. Either the user is not concerned with seismic events, or his analysis
shows that the risk is “insignificant”.
Outdoor switchgear and controlgear
a).
The ambient air temperature does not exceed 40 °C and its average value, measured over a
period of 24 h, does not exceed 35 °C.
The preferred values of minimum ambient air temperature are -10 °C, -25 °C, -30 °C and 40 °C.
15
Rapid temperature changes should be taken into account.
b).
Solar radiation up to a level of 1 000 W/m2 (on a clear day at noon) should be considered.
NOTE 1:
NOTE 2:
Under certain levels of solar radiation, appropriate measures, for example roofing, forced
ventilation, test simulating solar gain, etc., may be necessary, or derating may be used, in
order not to exceed the specified temperature rises and design pressure limits.
Details of global solar radiation are given in IEC 60721-2-4.
c).
The altitude does not exceed 1 000 m.
d).
The ambient air may be polluted by dust, smoke, corrosive gas, vapours or salt.
e).
The ice coating shall be considered in the range from 1 mm up to, but not exceeding, 20
mm.
f).
The wind speed does not exceed 34 m/s (corresponding to 700 Pa on cylindrical surfaces).
NOTE 3:
g).
Consideration should be given to condensation or precipitations that may occur.
NOTE 4:
h).
Characteristics of wind are described in IEC 60721-2-2.
Characteristics of precipitation are defined in IEC 60721-2-2.
Vibrations due to causes external to the switchgear and controlgear or earth tremors are
insignificant relative to the normal operating duties of the equipment. The manufacturer
will assume that, in the absence of specific requirements from the user, there are none.
NOTE 5:
The interpretation of the term “insignificant” is the responsibility of the user or specifier
of the equipment. Either the user is not concerned with seismic events, or his analysis
shows that the risk is “insignificant”.
5.2.2. General Design and Construction
Switchgear can be of indoor and outdoor types.
Metal-enclosed switchgear and control gear shall be designed so that normal service, inspection
and maintenance operations, determination of the energized or de-energized state of the main
circuit, including the usual checking of phase sequence, earthing of connected cables, locating
of cable faults, voltage connected cables or other apparatus and the elimination of dangerous
electrostatic charges, can be carried out safely. An earthing conductor shall be provided
extending the whole length of the metal-enclosed switchgear and control gear. The current
density in the earthing conductor, if of copper, shall under the specified earth fault conditions
not exceed 200 A/mm2 for a rated duration of short circuit of 1 s and 125 A/mm2 for a rated
duration of short-circuit of 3 s. However, its cross section shall be not less than 30mm2. It shall
be terminated by an adequate terminal intended for connection to the earth system of the
installation.
The metallic parts of a withdrawable part which are normally earthed shall also remain earthconnected in the test and disconnected positions under the prescribed conditions for the isolating
distance and also in any intermediate position. The metallic parts of a removable part which are
normally earthed shall remain earth-connected until the removable part is separated from the
switchgear.
16
5.2.1.1. Shutters
Means shall be provided to ensure the reliable operation of the shutters, e.g. by a mechanical
drive, where the movement of the shutters is positively driven by the Movement of the
removable part. If, for maintenance or test purposes, there is a requirement that one set of
fixed contacts shall be accessible through opened shutters, all the shutters shall be provided
with means of locking them independently in the closed position or it shall be possible to
insert a screen to prevent the live set of fixed contacts being exposed.
When, for maintenance or test purposes, the automatic closing of shutters is made inoperative in
order to retain them in the open position, it shall not be possible to return the switching device
to the service position until the automatic operation of the shutters is restored.
This restoration may be achieved by the action of returning the switching device to the service
position. The shutters of the three types of metal-enclosed switchgear and control gear may be
either metallic or non-metallic. If shutters are of insulating material, they shall not become
part of the enclosure, If they are metallic, they shall be earthed, and if they become part of the
enclosure, they shall provide the degree of protection specified for the enclosure.
5.2.1.2. Interlocks
It shall not be possible to close the circuit-breaker, switch or contactor in the service position
unless any auxiliary circuits associated with the automatic opening of these Devices are
connected. Conversely, it shall not be possible to disconnect the auxiliary Circuits with the
circuit-breaker closed in the service position. Interlocks shall be provided to prevent operation
of disconnections under conditions other than those they are intended for.
The operation of a disconnector shall not be possible unless the associated circuit-breaker,
switch or contactor is in the open position. If earthing of a circuit is provided by a circuitbreaker in series with an earthing switch, the earthing switch shall be interlocked with the
circuit-breaker and the circuit-breaker shall be secured against unintentional opening.
5.2.1.3. Earthing of Switchgear and Controlgear
5.2.1.3.1. Earthing of the main circuit
To ensure safety during maintenance work, all parts of the main circuit to which access is
required or provided shall be capable of being earthed prior to becoming accessible. This does
not apply to withdrawable and removable parts which become accessible after being separated
from the switchgear.
5.2.1.3.2. Earthing of the enclosure
Switchgear and controlgear shall be provided with a reliable earthing terminal having a
clamping screw or bolt for connection of an earthing conductor suitable for specified fault
conditions. The connecting point shall be marked with the "protective earth" symbol, as
indicated by symbol 5019 of IEC 60417. Parts of metallic enclosures connected to the
earthing system may be considered as an earthing conductor.
17
All metallic components and enclosures that may be touched during normal operating
conditions and are intended to be earthed shall be connected to an earthing terminal.
An earthing conductor shall be provided extending the whole length of the metal-enclosed
switchgear and control gear. The current density in the earthing conductor, if of copper,
shall not exceed 200 A/mm2 under the specified earth fault conditions; however, its crosssection area shall be not less than 30 mm2. It shall be terminated by an adequate terminal
intended for connection to the earth system of the installation.
NOTE - If the earthing conductor is not made of copper, equivalent thermal and mechanical requirements should be met. In general,
the continuity of the earth system shall be ensured taking into account the thermal and mechanical stresses caused by the current it may
have to carry. The maximum value of earth fault currents depends upon the type of system neutral earthing employed and shall be
indicated by the user. Where earthing connections have to carry the full three-phase short-circuit current (as in the case of the shortcircuiting connections used for earthing devices) these connections shall be dimensioned accordingly.
5.2.1.4. Requirements for liquids in switchgear and control gear
The manufacturer shall specify the type and the required quantity and quality of the liquid to be
used in switchgear and controlgear and provide the user with necessary instructions for
renewing the liquid and maintaining its required quantity and except for sealed pressure
systems.
NOTE:
Attention is drawn to the need to comply with local regulation relevant to pressure vessels.
5.2.1.4.1. Liquid level
A device for checking the liquid level, preferably during service, with indication of minimum
and maximum limits permissible for correct operation, shall be provided.
NOTE:
This is not applicable to dash-pots.
5.2.1.4.2. Liquid quality
Liquids for use in switchgear and controlgear shall comply with the instructions of the
manufacturer.
For oil-filled switchgear and controlgear, new insulating oil shall comply with IEC 60296.
NOTE:
For sealed pressure systems, instructions for maintaining the liquid quality are not applicable.
5.2.1.5. Requirements for gases in switchgear and control gear
The manufacturer shall specify the type and the required quantity, quality and density of the gas
to be used in switchgear and controlgear and provide the user with necessary instructions for
renewing the gas and maintaining its required quantity and quality except for sealed pressure
systems.
For sulphur hexafluoride (SF6) filled switchgear and controlgear, SF6 in accordance with
either IEC 60376 or IEC 60480 can be used. In order to prevent condensation, the maximum
allowable moisture content within gas-filled switchgear and controlgear filled with gas at the
rated filling density for insulation ρre shall be such that the dew-point is not higher than −5 °C
for a measurement at 20 °C. Adequate correction shall be made for measurement made at other
18
temperatures. For the measurement and determination of the dew-point, refer to IEC
60376 and IEC 60480.
Parts of high-voltage switchgear and controlgear housing compressed gas shall comply with the
requirements laid down in the relevant IEC standards.
NOTE - For checking of sulphur hexafluoride in service, refer to IEC 60480.
5.2.1.6. Auxiliary and control equipment
Auxiliary and control equipment is considered to be of conventional or non-conventional
(electronic) design components. For non-conventional design components refer to IEC
62063.
For electronic devices, electro-magnetic (EM) susceptibility shall be considered.
5.2.1.6.1 Enclosures
5.2.1.6.1.1
General
The enclosures for low-voltage control and auxiliary circuits shall be constructed of materials
capable of withstanding the mechanical, electrical and thermal stresses, as well as the effects of
humidity which are likely to be encountered in normal service.
5.2.1.6.1.2
Protection against corrosion
Protection against corrosion shall be ensured by the use of suitable materials or by the
application of suitable protective coatings to the exposed surfaces, taking into account the
intended conditions of use in accordance with the service conditions stated in Clause 5.2.1.
5.2.1.6.1.3
Degrees of protection
The degree of protection provided by an enclosure for low-voltage auxiliary and control
circuits shall be in accordance with 5.13.
Openings in cable entries, cover plates, etc. shall be so designed that, when the cables are
properly installed, the stated degree of protection of an enclosure for low-voltage auxiliary and
control circuits, as defined in 5.13, shall be obtained. A means of entry, suitable for the
application stated by the manufacturer, should be selected.
Any ventilation openings shall be shielded or arranged so that the same degree of protection as
that specified for the enclosure is obtained.
5.2.1.6.1.4
Protection against electric shock
5.2.1.6.1.4.1 Protection by segregation of auxiliary and control circuits from the main
circuit
Auxiliary and control equipment which is installed on the frame of switching devices shall be
suitably protected against disruptive discharge from the main circuit.
19
The wiring of auxiliary and control circuits, with the exception of short lengths of wire at
terminals of instrument transformers, tripping coils, auxiliary contacts, etc. shall be either
segregated from the main circuit by earthed metallic partitions (for example, tubes) or
separated by partitions (for example, tubes) made of insulating material.
5.2.1.6.1.4.2 Accessibility
Auxiliary and control equipment to which access is required during service shall be accessible
without the need to compromise clearances to hazardous parts.
Where clearances may be compromised by environmental related changes in the service access
level (for example accumulation of snow, sand, etc.) the use of increased clearances should be
considered.
5.2.1.6.1.5
Fire hazard
5.2.1.6.1.5.1 General
As the risk of fire is present in auxiliary and control circuits, the likelihood of fire shall be
reduced under conditions of normal use and even in the event of malfunction or failure.
The first objective is to prevent ignition due to an electrically energized part of auxiliary and
control circuits. The second objective is to limit the fire impact, if fire or ignition occurs inside
the enclosure.
5.2.1.6.1.5.2 Components and circuit design
In normal operation, heat dissipation of components is generally small. However, a
component may, when faulty or in an overload condition resulting from an external fault,
generate excess heat such that fire may be initiated.
The manufacturer should design or choose components taking into account normal conditions
and self-ignition characteristics due to the effects of the maximum fault power. Special
attention should be given to resistors.
Consideration should be given to the assembly of components and the relative arrangement of
those that may dissipate excessive heat by providing around them sufficient space and/or
ventilation.
5.2.1.6.1.5.3 Managing fire impact
Provisions should be taken in order to manage fire impact. Enclosures should be constructed,
insulated, made watertight, etc. with materials sufficiently resistant to probable ignition and heat
sources situated within. The manufacturer should consider that, if it ignites, a component may
emit melted flaming material and/or glowing particles.
5.2.1.6.1.6
Components installed in enclosures
5.2.1.6.1.6.1 Selection of components
20
Components installed in enclosures shall comply with the requirements of the relevant
IEC standards where applicable. Where an IEC standard does not exist the component should be
qualified with reference to another standard (issued by a country or another organization).
All components used in the auxiliary and control circuits shall be designed or selected to be
operational with their rated characteristics over the whole actual service conditions inside
auxiliary and control circuits enclosures. These internal conditions can differ from the external
service conditions specified in Clause 5.2.1.
Suitable precautions (insulation, heating, ventilation, etc) should be taken to ensure that those
service conditions essential for proper functioning are maintained, for example, heaters to
maintain the required minimum temperature for the correct operation of relays, contactors, lowvoltage switches, meters, operation counters, push-buttons, etc. according to the relevant
specifications.
The loss of those precaution means should not cause failures of the components nor
untimely operation of switchgear and controlgear. The operation of switchgear and
controlgear shall be possible during 2 h after the loss of those means. After this period, nonoperation of the switchgear and controlgear with its associated auxiliary and control circuit is
acceptable provided that the functionality resets to its original characteristics when
environmental conditions inside the enclosure for auxiliary and control circuits are back to the
specified service conditions.
Where heating is essential for correct functioning of the equipment, monitoring of the heating
circuit shall be provided.
In the case of switchgear and controlgear designed for outdoor installation, suitable
arrangements (ventilation and/or internal heating, etc.) shall be made to prevent harmful
condensation in low-voltage control and auxiliary circuits enclosures.
Polarity reversal at the interfacing point shall not damage auxiliary and control circuits.
5.2.1.6.1.6.2 Installation of components
Components shall be installed in accordance with the instructions of their manufacturer.
5.2.1.6.1.6.3 Accessibility
Closing and opening actuators and emergency shut-down system actuators should be located
between 0.4 m and 2 m above servicing level. Other actuators should be located at such a height
that they can be easily operated, and indicating devices should be located at such a height that
they can be easily readable.
Structure-mounted or floor-mounted enclosures for low-voltage auxiliary and control circuits
should be installed at such a height, with respect to the servicing level, that the above
requirements for accessibility, operating and reading heights are met.
21
Components in enclosures should be so arranged as to be accessible for mounting, wiring,
maintenance and replacement. W here a component may need adjustment during its service life;
easy access should be considered without danger of electrical shock.
5.2.1.6.1.6.4 Identification
Identification of components installed in enclosures is the responsibility of the manufacturer and
it shall be in agreement with the indication on the wiring diagrams and drawings. If a
component is of the plug-in type, an identifying mark should be placed on the component and
on the fixed part where the component plugs in.
W here mixing of components or voltages could cause confusion, consideration should be
given to more explicit marking.
5.2.1.6.1.6.5
Requirements for auxiliary and control circuit components
The auxiliary and control circuit components shall comply with applicable IEC standards if one
exists. Annex D is provided as a quick reference to many of the component standards.
5.2.1.6.1.6.5.1 Cables and wiring
The specification of cables to connect auxiliary and control circuits of the switchgear and
controlgear is the responsibility of the manufacturer. The choice is governed by the current that
must be carried, by the voltage drop and the current transformer burden, by the
mechanical stresses to which the cable is subjected and by the type of insulation. The choice of
conductors in enclosures is also the responsibility of the manufacturer.
Where a facility for external wiring is required, an appropriate connecting device shall be
provided for example terminal blocks, plug-in terminations, etc.
Cables between two terminal blocks shall have no intermediate splices or soldered joints.
Connections shall be made at fixed terminals.
Insulated conductors shall be adequately supported and shall not rest against sharp edges. W ire
routing should take into account the proximity of heating elements.
The available wiring space shall permit spreading of the cores of multi-core cables and the
proper termination of the conductors. The conductors shall not be subjected to stresses that
reduce their normal life.
Conductors connected to apparatus and indicating devices in covers or doors shall be so
installed that no mechanical damage can occur to the conductors as a result of movement of
these covers or doors.
The number of connections made to a terminal shall not exceed its designed maximum.
The method and extent of identification of conductors, for example by numbers, colours or
symbols, is the responsibility of the manufacturer. Identification of conductors shall be in
agreement with the wiring diagrams and drawings, and the specification of the user, if
22
applicable. This identification may be limited to the ends of the conductors. W here
appropriate, identification of wiring according to IEC 60445 may be applied.
5.2.1.6.1.6.5.2 Terminals
Terminals shall maintain the necessary contact pressure, corresponding to the current rating and
the short-circuit current of circuits.
Terminal blocks for wiring components inside the enclosure shall be chosen according to the
cross-section of the conductors used.
If facilities are provided for connecting incoming and outgoing neutral, protective and PEN
conductors, they shall be situated in the vicinity of the associated phase conductor terminal.
5.2.1.6.1.6.5.3 Auxiliary switches
Auxiliary switches shall be suitable for the number of electrical and mechanical operating
cycles specified for the switching device.
Auxiliary switches, which are operated in conjunction with the main contacts, shall be
positively driven in both directions. However, a set of two one-way positively driven auxiliary
contacts (one for each direction) can be used.
5.2.1.6.1.6.5.4 Auxiliary and control contacts
Auxiliary and control contacts shall be suitable for their intended duty in terms of
environmental conditions (refer to 5.4.3.1), making and breaking capacity and timing of the
operation of the auxiliary and control contacts in relation to the operation of the main
equipment.
Auxiliary and control contacts shall be suitable for the number of electrical and mechanical
operating cycles specified for the switching device.
Where an auxiliary contact is made available to the user, the technical documents provided by
the manufacturer should contain information regarding the class of this contact.
The operational characteristics of the auxiliary contacts should comply with one of the classes
shown in Table 5-3.
23
Table 5-3:
Auxiliary contact classes
D.c.
Class
Rated
continuous
current
Rated shorttime withstand
current
1
10 A
100 A/30 ms
2
2A
100 A/30 ms
3
200 mA
1 A/30 ms
Breaking capacity
110 V ≤ U a ≤ 250 V
≤48
440 W
22 W
50 mA
NOTE 1 This table refers to auxiliary contacts [IEV 441-15-10] which are included in an auxiliary circuit and
mechanically operated by the switching device. Control contacts [IEV 441-15-09] which are included in a control
circuit of a mechanical switching device may be covered by this table.
NOTE 2 If insufficient current is flowing through the contact, oxidation may increase the resistance.
Therefore, a minimum value of current may be required for class 1 contact.
NOTE 3 In the case of the application of static contacts, the rated short-time withstand current may be reduced if
current-limiting equipment, other than fuses, is employed.
NOTE 4 For all classes, breaking capacity is based on a circuit time constant of not less than 20 ms with a relative
tolerance of ±20%.
0
NOTE 5 An auxiliary contact which complies with class 1, 2 or 3 for d.c is normally able to handle
corresponding a.c. current and voltage.
NOTE 6 Class 3 contacts are not intended to be subjected to full substation auxiliary-supply short-circuit current.
Class 1 and 2 contacts are intended to be subjected to full substation auxiliary-supply short- circuit current.
NOTE 7 Breaking current at a defined voltage value between 110 V and 250 V may be deduced from the
indicated power value for class 1 and class 2 contacts (for example, 2 A at 220 V d.c. for a class 1 contact).
5.2.1.6.1.6.5.5 Contacts other than auxiliary and control contacts
A contact other than an auxiliary or control contact is a contact driven by a component (relay,
contactor, low-voltage switch, etc.) used in the auxiliary and control circuits.
Where a contact other than an auxiliary or control contact is made available to the user, the
technical documents provided by the manufacturer should include the rated continuous
current and making and breaking capacity of this contact. The user is responsible for
ensuring that the contact performance is adequate for the task.
The number of contacts provided shall be specified to the manufacturer in accordance with
Clause 9 or the relevant equipment standard.
5.2.1.6.1.6.5.6 Relays
Where a relay is chosen and used at a voltage different from the rated voltage of auxiliary and
control circuits, an appropriate device shall be provided to allow it to operate correctly under the
conditions specified in 4.8 (for example, provision of a series resistor).
5.2.1.6.1.6.5.7 Shunt releases
24
Shunt releases are designed for specific purposes. As no IEC standard exists for shunt releases,
they should satisfy the requirements of the relevant equipment standard.
The electrical power of the shunt releases shall be stated by the manufacturer.
5.2.1.6.1.6.5.8 Heating elements
All heating elements shall be of the non-exposed type. Heaters shall be situated so that they do
not cause any deterioration in the wiring or in the operation of the components.
W here contact with a heater or shield can occur accidentally, the surface temperature shall not
exceed the temperature-rise limits for accessible parts which need not be touched in normal
operation, as specified in Table 3.
5.2.1.6.1.6.5.9 Operation counters
Operation counters shall be suitable for their intended duty in terms of environmental
conditions and for the number of electrical and mechanical operating cycles specified for the
switching devices.
5.2.1.6.1.6.5.10 Illumination
In some enclosures, for example enclosures containing manual operating means (handles, pushbuttons, etc.), lighting should be considered. W here lighting is installed, consideration should
be given to the heat and electromagnetic disturbance produced by the lighting on the auxiliary
and control-circuit components.
5.2.1.6.1.6.5.11 5.4.4.5.11
Coils
Coils not covered by a component standard shall be suitable for their intended duty (for
example, with respect to temperature rise, dielectric withstand, etc.).
5.2.1.7. Dependent power closing
A switching device arranged for dependent power operation with external energy supply shall
be capable of making and/or breaking its rated short-circuit current (if any) when the voltage or
the pressure of the power supply of the operating device is at the lower of the limits
specified under clauses 5.2.2.7 and 5.2.2.10 (the term "operating device" here embraces
intermediate control relays and contactors where provided). If maximum closing and opening
times are stated by the manufacturer, these shall not be exceeded.
Except for slow operation during maintenance, the main contacts shall only move under the
action of the drive mechanism and in the designed manner. The closed or open position of the
main contacts shall not change as a result of loss of the energy supply or the re-application of
the energy supply after a loss of energy, to the closing and/or opening device.
25
5.2.1.8. Stored energy closing
A switching device arranged for stored energy operation shall be capable of making and
breaking all currents up to its rated values when the energy storage device is suitably
charged. If maximum closing and opening times are stated by the manufacturer, these shall not
be exceeded.
Except for slow operation during maintenance, the main contacts shall only move under the
action of the drive mechanism and in the designed manner, and not in the case of reapplication of the energy supply after a loss of energy.
A device indicating when the energy storage device is charged shall be mounted on the
switching device except in the case of an independent unlatched operation.
It shall not be possible for the moving contacts to move from one position to the other, unless
the stored energy is sufficient for satisfactory completion of the opening or closing operation.
Stored energy devices shall be able to be discharged to a safe level prior to access.
5.2.1.8.1 Energy storage in gas receivers or hydraulic accumulators
When the energy storage device is a gas receiver or hydraulic accumulator, the requirements of
5.2.1.8 apply at operating pressures between the limits specified in items a) and b).
a).
External pneumatic or hydraulic supply
Unless otherwise specified by the manufacturer, the limits of the operating pressure are
85 % and 110 % of the rated pressure. These limits do not apply where receivers also
store compressed gas for interruption.
b).
Compressor or pump integral with the switching device or the operating device
The limits of operating pressure shall be stated by the manufacturer.
5.2.1.8.2 Energy storage in springs (or weights)
When the energy storage device is a spring (or weight), the requirements of 5.2.1.8 apply when
the spring is charged (or the weight lifted).
5.2.1.8.3 Manual charging
If a spring (or weight) is charged by hand, the direction of motion of the handle shall be marked.
The manual charging facility shall be designed such that the handle is not driven by the
operation of the switching device.
The maximum actuating force required for manually charging a spring (or weight) shall not
exceed 250 N.
26
5.2.1.8.4 Motor charging
Motors, and their electrically operated auxiliary equipment for charging a spring (or weight) or
for driving a compressor or pump, shall operate satisfactorily between 85 % and 110 % of the
rated supply voltage (refer to 5.2.2.7), the frequency, in the case of a.c., being the rated supply
frequency (refer to 5.2.2.8).
NOTE For electric motors, the limits do not imply the use of non-standard motors but only the selection of
a motor which at these values provides the necessary effort, and the rated voltage of the motor need not
coincide with the rated supply voltage of the closing device.
5.2.1.8.5 Energy storage in capacitors
When the energy store is a charged capacitor, the requirements of 5.2.1.8 apply when
the capacitor is charged.
5.2.1.9. Operating of releases
The operation limits of releases shall be as follows:
5.2.1.9.1 Shunt closing release
A shunt closing release shall operate correctly between 85 % and 110 % of the rated supply
voltage of the closing device (see 5.2.2.7), the frequency, in the case of a.c., being the rated
supply frequency of the closing device (see 5.2.2.8).
5.2.1.9.2 Shunt opening release
A shunt opening release shall operate correctly under all operating conditions of the switching
device up to its rated short-circuit breaking current, and between 70 % in the case of d.c. – or 85
% in the case of a.c. – and 110 % of the rated supply voltage of the opening device (refer to
5.2.2.7), the frequency in the case of a.c being the rated supply frequency of the opening
device (see 5.2.2.8).
5.2.1.9.3 Capacitor operation of shunt releases
When, for stored energy operation of a shunt release, a rectifier-capacitor combination is
provided as an integral part of the switching device, the charge of the capacitors to be derived
from the voltage of the main circuit or the auxiliary supply, the capacitors shall retain a charge
sufficient for satisfactory operation of the release 5 s after the voltage supply has been
disconnected from the terminals of the combination and replaced by a short-circuiting link. The
voltages of the main circuit before disconnection shall be taken as the lowest voltage of the
system associated with the rated voltage of the switching device (refer to IEC 60038 for the
relation between "highest voltage for equipment" and system voltages).
5.2.1.9.4 Under-voltage release
An under-voltage release shall operate to open the switching device when the voltage at the
terminals of the release falls below 35 % of its rated voltage, even if the fall is slow and gradual.
27
On the other hand, it shall not operate the switching device when the voltage at its terminals
exceeds 70 % of its rated supply voltage.
The closing of the switching device shall be possible when the values of the voltage at the
terminals of the release are equal to or higher than 85 % of its rated voltage. Its closing shall be
impossible when the voltage at the terminals is lower than 35 % of its rated supply voltage.
5.2.1.10. Low and high pressure interlocking devices
All vacuum or gas filled switchgear shall be fitted with a pressure gauge. The operating pressure
shall be indicated in both Bars and MPa and clearly Visible. The pressure gauge shall have
contacts for Low pressure alarm, Lockout and spare contacts.
The switchgear shall be fitted with both visible and audible low pressure alarms. In case of a
breaker, the breaker shall be wired in such a way that gas pressure below the low pressure set
point shall render the breaker inoperational or into lockout mode. In such a state, the breaker
will maintain the initial position until the anomaly is corrected. The lockout alarm shall also be
both visible and audible.
The breaker shall also be fitted with both audible and visible alarms for pressure above
manufacturer‟s maximum recommended limits. In case of loss of vacuum the breaker shall be
rendered inoperational or into lockout mode.
Values for pressure points shall be as specified by the manufacturer of the switchgear corrected
to 20ºCelsius and the switchgear shall be filled with gas not exceeding the manufacturer‟s
recommendation. All parts in direct contact with the gas such as pipes, flanges, seals and others
shall be of material that is non-reactive to the gas.
5.2.1.11. Nameplates
Switchgear and controlgear and their operating devices shall be provided with nameplates which
contain the necessary information such as the name or mark of the manufacturer, the year of
manufacture, the manufacturer's type designation, the serial number or equivalent, the rated
characteristics etc. as specified in the relevant IEC standards.
If applicable, the type and mass of insulating fluid shall be noted on the nameplate.
NOTE It should be stated whether pressures (or densities) are absolute or relative values.
For outdoor switchgear and controlgear, the nameplates and their methods of attachment shall
be weather-proof and corrosion-proof.
If the switchgear and controlgear consist of several poles with independent operating
mechanisms, each pole shall be provided with a nameplate.
For an operating device combined with a switching device, it may be sufficient to use only one
combined nameplate.
Technical characteristics on nameplates and/or in documents which are common to several
kinds of high-voltage switchgear and controlgear shall be represented by the same symbols.
28
Such characteristics and their symbols are:
rated voltage
Ur
rated lightning impulse withstand voltage
Up
rated switching impulse withstand voltage
Us
rated power-frequency withstand voltage
Ud
rated normal current
Ir
rated short-time withstand current
Ik
rated peak withstand current
Ip
rated frequency
Fr
rated duration of short circuit
Tk
rated auxiliary voltage
Ua
rated filling pressure (density) for insulation
p re (ρ re)
p rm (ρ rm )
rated filling pressure (density) for operation
p ae (ρ ae)
p am (ρ am )
alarm pressure (density) for insulation
alarm pressure (density) for operation
minimum functional pressure (density) for insulation
minimum functional pressure (density) for operation
p me (ρ me)
p mm (ρ mm )
Metal-enclosed switchgear and control gear, all their components and operating devices shall
be provided with durable and clearly legible nameplates which shall contain the following
information:
a).
Manufacturer‟s name or trade mark;
b).
Type designation or serial number;
c).
Applicable rated values;
d).
Number of the relevant standard.
The nameplates of each functional unit shall be legible during normal service. The removable
parts, if any, shall have a separate nameplate with the data relating to the functional units
they belong to, but this nameplate need only be legible when the removable part is in the
removed position.
5.2.1.12. Protection of persons against approach to live parts
The degree of protection shall be specified separately for the enclosure and for partitions. For
cubicle switchgear and control gear, it is only necessary to specify the degree of protection for
the enclosure. For main circuits of gas-filed compartments, no degree of protection needs to be
specified. The degree of protection against contact of persons with live parts of auxiliary
circuits and with any moving parts (other than smooth rotating shafts and moving linkages) shall
be indicated by means of the designation specified in Table 5-4.
29
The characteristic numeral indicates the degree of protection provided by the enclosure with
respect to persons, also to the equipment inside the enclosure.
Table 5-4 gives details of objects which will be “excluded” from the enclosure for each of the
degrees of protection. The term “excluded” implies that a part of the body or an object held
by a person, either will not enter the enclosure or, if it enters, that adequate clearance will be
maintained and no moving part will be touched. Degree of Protection against approach to live
parts and contact with moving parts protection
Table 5-4:
Degrees of protection against solid foreign objects indicated by the first characteristic
Numeral
Degree of Protection
IP2X
Protection against approach to live parts and contact with moving
parts
By fingers or similar objects of diameter greater than 12mm
IP3X
By tools, wires, etc., of diameter or thickness greater than 2.5mm
IP4X
By wires of diameter or strips of thickness greater than 1.0mm
NOTE – the designation of the degree of protection corresponds to IEC 60529
5.2.1.13. Internal fault
Failure within the enclosure of metal-enclosed switchgear and control gear due either to a defect
or an exceptional service condition or mal-operation may initiate an internal arc. There is little
probability of such an event occurring in constructions which satisfy the requirements of this
standard, but it cannot be completely disregarded. Such an event may lead to the risk of injury,
if persons are present, but with an even lower probability. It is desirable that the highest
possible degree of protection to persons should be provided. The principal objective should be
to avoid such error or to limit their duration and consequences. Experience has shown that faults
are more likely to occur in some locations inside an enclosure than in others, so special attention
should be paid to these.
5.2.1.14. Enclosure
Enclosures shall be metallic. When the metal-enclosed switchgear and control gear is installed,
the enclosure shall provide at least the degree of protection specified in table 1. It shall also
assure protection in accordance with the following conditions: The floor surface, even if not
metallic, may be considered as part of the enclosure. The measures to be taken in order to obtain
the degree of protection provided by floor surfaces shall be subject to an agreement between
manufacturer and user. The walls of a room shall not be considered as parts of the enclosure.
Gas-filled compartments shall be capable of withstanding the normal and transient pressures to
which they are subjected in service. While these compartments are permanently pressurized
in service they are subjected to particular conditions of service which distinguish them from
compressed air receivers and similar storage vessels. These conditions are:
- gas-filled compartments enclose the main circuit not only to prevent hazardous approach to
30
live or moving parts but are so shaped that, when at or above the minimum functional
pressure they ensure that the rated insulation level for the equipment is achieved (electrical
rather than mechanical considerations predominate in determining the shape and materials
employed); gas-filled compartments shall be filled with a non-corrosive gas, thoroughly
dried, stable and inert.
5.2.1.15. Inspection windows
Inspection windows shall provide at least the degree of protection specified for the enclosure.
They shall be covered by a transparent sheet of mechanical-strength comparable to that of the
enclosure. Precautions shall be taken to prevent the formation of dangerous electrostatic
charges, either by clearance or by electrostatic shielding (for example a suitable earthed Wiremesh on the inside of the window). The insulation between live parts of the main circuit and
the inspection windows shall withstand the test voltages specified in Sub-clause 4.2.1 of IEC
62271-1 for voltage tests to earth and between poles.
5.2.1.16. Ventilating openings, vent outlets
Ventilating openings and vent outlets shall be so arranged or shielded that the same degree of
protection as that specified for the enclosure is obtained. Such openings may make use of wire
mesh or the like provided that it is of suitable mechanical strength. Ventilating openings and
vent outlets shall be arranged in such a way that gas or vapour escaping under pressure does not
endanger the operator.
5.2.1.17. Partitions and shutters
Partitions and shutters shall provide at least the degree of protection specified in Partitions and
shutters made of insulating material shall meet the following requirements
a).
b).
c).
The insulation between live parts of the main circuit and the accessible surface of
insulating partitions and shutters shall withstand the test voltages specified in Subclause 4.2.1 of IEC 62271-1 for voltage tests to earth and between poles;
Apart from mechanical strength, the insulating material shall withstand likewise the test
voltages specified in Item a), The appropriate test-methods given in IEC 60243-1
should be applied;
The insulation between live parts of the main circuit and the inner surface of insulating
partitions and shutters facing these shall withstand at least 150 % of the rated
voltage of the equipment;
5.2.1.18. Partitions
Partitions of metal-clad switchgear and control gear shall be metallic and earthed. Partitions of
compartmented and cubicle switchgear and control gear may be non-metallic. If partitions
become part of the enclosure with the removable part in any of these positions, they shall be
metallic, earthed and provide the degree of protection specified for the enclosure. Partitions
between two gas-filled compartments or between a gas-filled compartment and another
compartment may be of insulating material provided they do not become part of the enclosure
but are not intended by themselves to provide electrical safety of personnel, for which other
31
means such as earthing of the equipment may be necessary; they shall, however, provide
mechanical safety against the normal gas pressure still present in the adjacent compartment.
5.2.1.19. Pressure relief of gas-filled compartments
Where pressure relief devices are provided, they shall be arranged so as to minimize the danger
to an operator during the time that he is performing his normal operating duties if gases or
vapours are escaping under pressure. In certain designs pressure relief may be achieved by
allowing the arc to burn through the enclosure at designated points. Where such means are
employed, the resultant hole is deemed to be a pressure relief device.
5.2.1.20. Disconnections and earthing switches
The devices for ensuring the isolating distance between the high-voltage conductors are
considered to be disconnections which shall comply with IEC 60129, except for mechanical
operation tests
The requirement that it shall be possible to know the operating position of the disconnector or
earthing switch is met if one of the following conditions is fulfilled:
i).
ii).
The isolating distance is visible;
The position of the withdrawable part in relation to the fixed part is clearly visible and
the positions corresponding to full connection and full isolation are clearly identified; the
position of the disconnector or earthing switch is indicated by a reliable indicating
device. Any removable part shall be so attached to the 'fixed part that its contacts will
not open inadvertently due to forces which may occur in service, in particular those due
to a short circuit.
5.2.1.21. Interlocks
Interlocks between different components of the equipment are provided for reasons of safety
and for convenience of operation. Visible indication shall be provided to show whether the
mechanism is locked or free. The following provisions are mandatory for main circuits:
5.2.1.21.1. Metal-enclosed switchgear and control gear -with removable parts
The withdrawal or engagement of a circuit-breaker, switch or contactor shall be impossible
unless it is in the open position. The operation of a circuit-breaker, switch or‟ contactor shall be
impossible unless it is in the service, disconnected, removed, test or earthing position.
It shall be impossible to close the circuit-breaker, switch or contactor in the service position
unless it is connected to the auxiliary circuit, unless it is designed to open automatically without
the use of an auxiliary circuit.
32
5.2.1.21.2. Metal-enclosed switchgear and control gear without removable parts and
provided with disconnector
Interlocks shall be provided to prevent operation of disconnector under conditions other than
those they are intended for. The operation of a disconnector shall be impossible unless the
associated circuit-breaker, switch or contactor is in the open position.
NOTE - This rule may be disregarded if it is possible to have a busbar transfer in a double busbar system without current interruption.
The operation of the circuit-breaker, switch or contactor shall be impossible unless the associated disconnector is in the closed, open or
earthing position (if provided). The provision of additional or alternative interlocks shall be subject to agreement between
manufacturer and user. The manufacturer shall give all necessary information on the character and function of interlocks. It is
recommended that earthing switches having a short-circuit making capacity less than the rated peak withstand current of the circuit
should be interlocked with the associated disconnector
5.2.3. Rating Characteristics
The ratings of metal-enclosed switchgear and control gear shall cover the following:
a).
b).
c).
d).
e).
f).
g).
h).
i).
Rated voltage and number of phases;
Rated insulation level;
Rated frequency;
Rated normal current (for main circuits);
Rated short-time withstands current (for main and earthing circuits);
Rated peak withstand current, if applicable (for main and earthing circuits);
Rated duration of short circuit;‟
Rated values of the components forming part of the metal-enclosed switchgear and
Rated filling pressure (of gas-filled compartments).
NOTE: For the co-ordination of rated voltages, rated short-time withstand currents, rated peak withstand currents and rated normal currents of metal enclosed switchgear and control gear.
5.2.2.1. Rated voltage
The rated voltage is equal to the maximum system voltage for which the equipment is designed.
It indicates the maximum value of the "highest system voltage" of networks for which the
equipment may be used. Standard values of rated voltages are given below:
a).
Range I for rated voltages 245 kV and below:
3.6 kV, 7.2 kV, 12 kV, 17.5 kV, 24 kV, 36 kV, 52 kV, 72.5 kV, 100 kV, 123 kV, 145 kV, 170
kV, 245 kV
b).
Range II for rated voltages above 245 kV:
300 kV, 362 kV, 420 kV, 550 kV, 800 kV
NOTE - Components forming part of metal-enclosed switchgear and control gear may have individual values of rated voltage in
accordance with their relevant standards.
5.2.2.2. Rated insulation level
The rated insulation level of switchgear and controlgear shall be selected from the values given
in Tables 6-1. In these tables, the withstand voltage applies at the standardised reference
atmosphere (temperature (20 °C), pressure (101.3 kPa) and humidity (11 g/m3)) specified in
33
IEC 60071-1.
These withstand voltages include the altitude correction to a maximum altitude of 1 000 m
specified for the normal operating conditions. The rated withstand voltage values for lightning
impulse voltage (Up), switching impulse voltage (Us) (when applicable), and power-frequency
voltage (Ud) shall be selected without crossing the horizontal marked lines. The rated insulation
level is specified by the rated lightning impulse withstand voltage phase to earth.
For most of the rated voltages, several rated insulation levels exist to allow for application of
different performance criteria or overvoltage patterns. The choice should be made considering
the degree of exposure to fast-front and slow-front overvoltages, the type of neutral earthing of
the system and the type of overvoltage limiting devices.
The "common values" used in Tables 1a and 1b apply to phase-to-earth, between phases and
across the open switching device, if not otherwise specified in this standard. The withstand
voltage values "across the isolating distance" are valid only for the switching devices where the
clearance between open contacts is designed to meet the functional requirements specified for
disconnectors.
Table 5-5:
Rated Insulation levels for rated voltages of Range I
Rated
voltage
Ur
kV (r.m.s. value)
Rated short-duration powerfrequency withstand voltage
Ud
kV (r.m.s value)
Common value
(1)
(2)
Across the
isolating
distance
(3)
3.6
10
12
7.2
20
23
12
28
32
17.5
38
45
24
50
60
36
70
80
52
72.5
100
95
140
150
185
185
230
110
160
175
210
210
265
123
34
Rated lightning impulse
withstand voltage
Up
kV (peak value)
Common value
(4)
Across the
isolating
distance
(5)
20
40
40
60
60
75
75
95
95
125
145
170
250
325
380
450
450
550
23
46
46
70
70
85
85
110
110
145
165
195
290
375
440
520
520
630
145
170
245
230
275
275
325
360
395
460
265
315
315
375
415
460
530
550
650
650
750
850
950
1
050
630
750
750
860
950
1
050
1
200
5.2.2.3. Rated frequency (fr)
The standard values of the rated frequency are 16 2/3 Hz, 25 Hz, 50 Hz and 60 Hz.
5.2.2.4. Rated normal current and temperature rise
5.2.2.4.1. Rated normal current (Ir)
The rated normal current of switchgear and controlgear is the r.m.s value of the current which
switchgear and controlgear shall be able to carry continuously under specified conditions of use
and behavior.
Some main circuits of metal-enclosed switchgear and control gear (e.g. busbars, feeder circuits,
etc.) may not have the same value of rated normal current.
5.2.2.4.2. Temperature rise
The temperature rise of components contained in metal-enclosed switchgear and control gear
which are subject to individual specifications not covered by the scope of IEC 62271-1 shall not
exceed the temperature-rise limits permitted in the relevant IEC standard for that component.
The maximum permissible temperatures and temperature rises to be taken into account for
busbars are those specified for contacts, connections and' metal parts in contact with
insulation, as the case may be.
5.2.2.5. Rated peak withstand current
The peak current associated with the first major loop of the rated short-time withstand current
which switchgear and controlgear can carry in the closed position under prescribed conditions
of use and behaviour.
The rated peak withstand current shall be defined according to the d.c time constant which is a
system characteristic. A d.c time constant of 45 ms covers the majority of cases and
corresponds to a rated peak withstand current equal to 2.5 times the rated short-time
withstand current for a rated frequency of 50 Hz and below it, and for a rated frequency of 60
Hz it is equal to 2.6 times the rated short-time withstand current.
For some applications, system characteristics are such that the d.c. time constant is higher than
45 ms. Other values generally suitable for special systems are 60 ms, 75 ms and 120 ms
depending on the rated voltage. For those cases, the preferred value is 2.7 times the rated shorttime withstand current.
35
NOTE - In principle, the rated short-time withstand current and the rated peak withstand current of a
main circuit cannot exceed the corresponding rated values of the weakest of its series connected
components. However, for each circuit or compartment, advantage may be taken of apparatus limiting
the short-circuit current, such as current-limiting fuses, reactors, etc.
5.2.2.6. Rated duration of short circuit
The intervals of time for which switchgear and controlgear can carry, in the closed position, a
current equal to its rated short-time withstand current.
The standard value of rated duration of short circuit is 1 s.
If it is necessary, a value lower or higher than 1 s may be chosen. The recommended values are
0.5 s, 2 s and 3 s.
5.2.2.7. Rated supply voltage of closing and opening devices and auxiliary circuits
5.2.2.7.1. General
The supply voltage of closing and opening devices and auxiliary and control circuits shall be
understood to mean the voltage measured at the circuit terminals of the apparatus itself
during its operation, including, if necessary, the auxiliary resistors or accessories supplied or
required by the manufacturer to be installed in series with it, but not including the conductors
for the connection to the electricity supply.
NOTE The supply system should preferably be referenced to earth (i.e. not completely floating) in order to
avoid the accumulation of dangerous static voltages. The location of the earthing point should be defined
according to good practice.
5.2.2.7.2. Rated supply voltage (Ua)
The rated supply voltage should be selected from the standard values given in Tables 5-6
and 5-7. The values marked with an asterisk are preferred values for electronic auxiliary
equipment.
Table 5-6:
Direct current voltage
Ua
[V]
24
48*
60
110* or 125
Table 5-7:
Alternating current voltage
Three-phase, three-wire or
Single-phase, three-wire
36
Single-phase, two-wire
four- wire systems
[V]
–
120/208
(220/380)
230/400*
(240/415)
277/480
347/600
systems
[V]
120/240
–
–
–
–
–
–
systems
[V]
120
120
(220)
230*
(240)
277
347
NOTE 1 The lower values in the first column of this table are voltages to neutral and the higher values are voltages
between phases. The lower value in the second column is the voltage to neutral and the higher value is the voltage
between lines.
NOTE 2 The value 230/400 V indicated in this table should be, in the future, the only IEC standard voltage and
its adoption is recommended in new systems. The voltage variations of existing systems
at 220/380 V and 240/415 V should be brought within the range 230/400 V ± 10 %. The reduction of this
range will be considered at a later stage of standardization.
5.2.2.7.3. Tolerances
The relative tolerance of a.c. and d.c. power supply in normal duty measured at the input of the
auxiliary equipment (electronic controls, supervision, monitoring and communication) is 85 %
to 110 %.
For supply voltages less than the minimum stated for power supply, precautions shall be
taken to prevent any damage to electronic equipment and/or unsafe operation due to its
unpredictable behaviour.
For operation of shunt-opening releases, the relative tolerance shall comply with the
requirements of 5.2.1.9
5.2.2.7.4. Ripple voltage
In the case of d.c supply, the ripple voltage, that is the peak-to-peak value of the a.c.
component of the supply voltage at the rated load, shall be limited to a value not greater than 5
% of the d.c. component. The voltage is measured at the supply terminals of the auxiliary
equipment.
5.2.2.7.5. Voltage drop and supply interruption
IEC 61000-4-29 (d.c supply voltage) and IEC 61000-4-11 (a.c supply voltage) should apply to
electrical and electronic components.
As far as supply interruptions are concerned, the system is considered to perform correctly if:



There are no false operations;
There are no false alarms or false remote signaling;
Any pending action is correctly completed, even with a short delay.
5.2.2.8. Rated supply frequency of operating devices and auxiliary circuits
The standard values of rated supply frequency are d.c or 50 Hz.
37
5.2.2.9. Rated filling pressure (of gas-filled compartments)
This shall be the pressure in bars (gauge) assigned by the manufacturer referred to atmospheric
air conditions of 20°C at which the gas-filled compartment is filled before being put into
service.
5.2.2.10. Rated pressure of compressed gas supply for controlled pressure systems
The preferred values of rated pressure (relative pressure) are:
0.5 MPa – 1 MPa – 1.6 MPa – 2 MPa – 3 MPa – 4 MPa.
5.2.4. Circuit breakers
5.2.3.1.
General
Circuit-breakers for voltages above 600V shall be either SF6 or vacuum type, whereas moulded
case circuit breakers shall be used for voltages up to 600 V.
Note:
Oil circuit breakers are not recommended.
5.2.3.2.
Connection
The supply end connections to equipment will be at the top end and load end connections at the
bottom.
5.2.3.3.
Operating Mechanisms
The circuit-breaker mechanism shall normally be motor wound spring with hand wound spring
as standby. The circuit-breaker shall be capable of closing fully and latching against its rated
making current.
In the case of designs utilising portable jacking devices, three devices per switchboard are
required subject to a minimum of one for each rating of equipment in the switchboard.
Spring operated mechanisms shall have the following additional measures:a).
If the circuit-breaker is opened and the springs charged the circuit-breaker can be closed
and then tripped without further rewind.
b).
If the circuit-breaker is closed and the springs charged there shall be sufficient energy to
trip, close and then trip the circuit-breaker without further rewind..
c).
Mechanical indication shall be provided to indicate the state of the charging spring and
main contacts.
d).
Motor charged mechanisms shall be provided with means for charging the springs by
hand and also a shrouded push button for releasing the springs. An electrical release coil
shall also be provided.
38
e).
Under normal operation, motor recharging of the operating spring shall commence
immediately and automatically upon completion of each circuit-breaker closing
operation. The time required for spring recharging shall not exceed 3 minutes.
f).
It shall not be possible to close a circuit-breaker, whilst the spring is being charged. It
shall be necessary for the spring to be fully charged and the associated charging
mechanism fully prepared for closing before it can be released to close the circuitbreaker.
g).
For SF6 circuit breakers there shall be a lock-out facility incorporated when the gas
pressure is low.
All circuit-breaker operating mechanisms shall be fitted with an electrical shunt trip release coil
and in addition a mechanical hand tripping devices. The electrical tripping and closing devices
shall be suitable for operation from a power supply as stated in this Specification and shall
operate satisfactorily over the ambient temperature range when the voltage at their terminals is
any value within the voltage range stipulated in 5.2.2.1
All operating coils for use on the d.c supply shall be connected so that failure of insulation to
earth does not cause the coil to become energised. Tripping and closing circuits shall be
provided with a fuse in each pole on each unit and shall be independent of each other and all
other circuits.
Approved positively driven mechanically operated indicating devices shall be provided to
indicate whether a circuit-breaker is in the open or closed service, isolated or earthed position.
Locking facilities with padlocks shall be provided so that the circuit-breaker can be prevented
from being closed when it is open and from being manually tripped when it is closed. These
facilities shall not require the fitting of any loose components prior to the insertion of the single
padlock required. It shall not be possible, without the aid of tools, to gain access to the tripping
toggle or any part of the mechanism which would permit defeat of the locking of the manual
trip. It shall not be possible to lock mechanically the trip mechanism so as to render inoperative
the electrical tripping.
5.2.3.4.
SF6 Circuit-Breakers
Circuit-breakers employing SF6 gas as an interrupting medium shall operate on the principle of
self-generated gas pressure for arc extinction. The rate of gas leakage per annum shall be
guaranteed and shall not be greater than 1% for any compartment. Means of confirming the
existence of adequate gas density in the circuit-breakers shall be available without removing the
unit from service. The system of gas monitoring shall be temperature compensated and shall be
to the approval of the Engineer.
Suitable facilities shall be included for replenishing the volume of SF6 gas should this be
necessary due to leakage. Absorption of moisture and the decomposition products of the gas
shall be achieved by integral filters.
39
5.2.3.5.
Vacuum Circuit-Breakers
Circuit-breakers employing the vacuum interruption principle shall incorporate vacuum bottles
of declared and established manufacture. Each interrupter shall be capable of individual
adjustment for correct operation and easily removed for maintenance or replacement. Full
instructions for monitoring the state of vacuum and contact life shall be provided to the approval
of the Engineer.
Vacuum bottles shall not require the addition of insulation or stress shielding to achieve the
necessary dielectric strength externally and shall not be mechanically braced by components
which may reduce the integrity of the insulation across the open gap.
Further reference is available in IEC 62271 series
5.2.3.6.
Moulded case circuit breakers
This section covers single- or multi-pole moulded case circuit breakers for use in power
distribution systems, suitable for panel mounting, for rating up to 1000A, 600V, 50Hz;
a).
The circuit-breakers shall comply with IEC 60947;
b).
The continuous current rating, trip rating and rupturing capacity shall be as specified;
c).
The contacts shall be silver alloy and shall close with a high pressure wiping action;
d).
Where specified, the circuit breaker shall be capable of accommodating factory fitted
shunt trip or auxiliary contact units or similar equipment;
e).
The operating handle shall provide clear indication of “ON‟”, “OFF” and “TRIP”
positions;
f).
The mechanism shall be of the TRIP-FREE type preventing the unit from being held in
the ON position under overload conditions;
g).
All moulded-case circuit breakers in particular installation as far as practical are to be
supplied by a single manufacturer;
h).
The incoming terminals of single-pole miniature circuit breakers shall be suitable for
connection to a common busbar;
i).
The circuit breaker shall have a rating plate indicating the current rating, voltage rating
and breaking capacity.
For further reference on moulded circuit breakers see IEC 60947 series.
40
5.2.5. Disconnector/Isolator
5.2.4.1. Guide to the selection of disconnector and earthing switches
5.2.4.1.1 Selection Criteria
For the
selection of disconnectors and earthing switches the following conditions and
requirements at site should be considered:
a).
b).
c).
d).
e).
f).
g).
h).
Normal current load and overload conditions;
Existing fault conditions;
Static and dynamic terminal loads resulting from the substation design;
Use of rigid or flexible conductors to be connected to the disconnector or earthing switch
or to which the separated contact is mounted;
Environmental conditions (climate, pollution, etc.);
Altitude of the substation site;
Required operational performance (mechanical endurance);
Switching requirements (bus transfer current switching by disconnectors, induced
current switching by earthing switches; short-circuit making capacity of earthing
switches).
5.2.4.2. Requirements in respect of the isolating distance of disconnector
For reasons of safety, disconnectors shall be designed in such a way that no dangerous
leakage currents can pass from the terminals of one side to any of the terminals of the
other side of the disconnector. This safety requirement is met when any leakage current is led
away to earth by a reliable earth connection or when the insulation involved is effectively
protected against pollution in service.
NOTE: It is usual that the isolating gap of a disconnector is longer than the phase-to-ground insulating
distance since IEC 62271-1 specifies higher withstand test levels across the isolating distance than for the
phase-to-ground insulation.
Where a long creepage distance is required, the phase-to-ground insulation distance should
become longer than the isolating gap. For such cases, to maintain low probability of disruptive
discharge across the isolating gap, the use of protective devices such as surge arresters or rod
gaps may be necessary.
5.2.4.3. Operation of disconnectors and earthing switches - Position of the movable
contact system and its indicating and signalling devices
5.2.4.2.1. Securing of position
Disconnectors and earthing switches, including their operating mechanisms, shall be designed in
such a way that they cannot come out of their open or closed position by gravity, wind pressure,
vibrations, reasonable shocks or accidental touching of the connecting rods of their operating
system.
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Disconnectors and earthing switches shall permit temporary mechanical locking in both the
open and closed position for safety purposes (for example maintenance).
NOTE: This last requirement need not be met in the case of disconnectors or earthing switches that are
operated by means of a hook-stick.
5.2.4.2.2. Additional requirements for power-operated mechanisms
Power operated mechanisms shall also provide a manual operating facility. Connecting a handoperating device (for instance a hand crank) to the power-operated mechanism shall ensure safe
interruption of the control energy to the power-operated mechanism.
5.2.4.2.3. Indication and signalling of position
Indication and signaling of the closed and open position shall not take place unless the movable
contacts have reached their closed or open position, respectively: and the first paragraph of
clause 5.2.4.2.1 (securing of position) is fulfilled.
5.2.4.2.3.1.
Indication of position
It shall be possible to know the operating position of the disconnector or earthing switch. For
the open position this requirement is met if one of the following conditions is fulfilled:


the isolating distance or gap is visible;
the position of each movable contact ensuring the isolating distance or gap is indicated
by a reliable visual position indicating device.
5.2.4.4. Electrical position signalling by auxiliary contacts
A common signal for all poles of a disconnector or earthing switch shall be given only if all
poles of the disconnector or earthing switch have a position in accordance with 5.2.4.2.3.
Where all poles of a disconnector or earthing switch are mechanically coupled so as to be
operable as a single unit, it is permissible to use a common position-indicating device.
5.2.4.5. Maximum force required for manual operation
The values given below also apply to maintenance and operation of normally motor-operated
disconnector and earthing switches.
NOTE: These values include ice-breaking, if applicable.
The operating height above servicing level should be agreed between manufacturer and user.
5.2.4.6. Operation requiring up to one revolution
The force needed to operate a disconnector or earthing switch requiring up to one revolution
(swing lever for example) should not exceed 250. A peak value of 450 N is accepted during a
rotation of 15° maximum.
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5.2.4.7. Dimensional tolerances
For the mounting dimensions and the dimensions of high-voltage connections as well as the
earthing connections of disconnector and earthing switches, the tolerances given in ISO 2768-1
shall apply for linear and angular dimensions.
5.2.4.8. Mechanical operating tests
Operating tests are made to ensure that the disconnector or earthing switches show the
specified operating behaviour within the specified voltage and supply pressure limits of their
operating mechanisms.
During these tests, which are performed without voltage on, or current flowing through the
main circuit, it shall be verified that the disconnector or earthing switches open and close
correctly when their operating mechanisms are energized.
The tests shall be performed according to IEC 62771-102. The mentioned test programme shall
be performed only once.
During these tests no adjustment shall be made and the operation shall be faultless. The closed
and open position shall be reached with the specified indication and signaling during each
operating cycle.
After these tests, no parts of the disconnector or earthing switch shall be damaged.
For disconnector and earthing switches with a rated voltage of 52 kV and above, the
mechanical operating routine tests may be performed on sub-assemblies.
Where mechanical routine tests are performed on separate components, they shall be
repeated at site on a complete assembled disconnector during the commissioning tests. The
same total number of operations as specified in IEC 62771-102 shall be performed.
NOTE: The mechanical operating test will not be representative for the operating conditions in the
substation when complicated linkages are used between the point of operation and the switchgear
and when the bearings are mounted to weak supports.
5.2.6. Fuses
Fuses for use in distribution systems shall be as per ZS 746 -1 and ZS 746-2.
5.3
Busbars
5.3.1. General
A busbar is a low-impedance conductor to which several electric circuits can be separately
connected.
NOTE: The term busbar does not presuppose the geometrical shape, size or dimensions of the conductor. A main busbar is a busbar
to which one or several distribution busbars and/or incoming and outgoing units can be connected. A distribution busbar is a busbar
within one section which is connected to a main busbar and from which outgoing units are supplied (see IEC 60439-1)
Three phase busbars and one neutral busbar shall be provided in accordance with SANS
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10198. At the lower end of the compartment an earth bar shall be provided to which all metal
parts of the substation are to be bonded. The neutral of the substation shall be connected to the
earth bar at one point only by means of a removable link. Provision shall be made to connect
the substation earth to the earth bar.
5.3.2. Busbars Indoor Type
5.3.2.1. Current rating
a) The maximum allowable temperature of busbars (including joints) carrying full load
current in an ambient temperature as specified shall not exceed 80°C taking into
consideration a maximum ambient temperature of 40°C in Zambia. ;
5.3.2.2.
Mounting
The rating and fixing of busbars shall be designed to withstand mechanical and temperature
stresses during fault conditions.
5.3.2.3. Neutral busbar
The current density in the neutral busbar shall under the specified earth fault conditions not
exceed 200A/mm2 for a rated duration of short circuit of 1s and 125A/mm2 for a rated duration
of short circuit of 3s.
The neutral shall be terminated by an adequate terminal intended for the connection to the earth
system of the installation, refer to IEC 60298.
5.3.2.4. Street lighting busbars
The street lighting busbar shall have a cross-sectional area equal to that of a phase busbar. The
busbar shall be of standard mounting and insulated.
5.3.2.5. Busbar connections
Conductor ends will be terminated in accordance with SANS 1213.
5.3.2.6. Screws, bolts and nuts
a) All bolts and screws shall be cadmium plated yellow passivated stainless steel grade
304 to BSS standards;
b) All nuts and washers shall be electro-plated;
c) Coach screws shall be electro-plated galvanized;
d) All bolts, nuts, screws shall have ISO threads;
e) The largest possible size bolt that will fit into holes in lugs and fixing holes of equipment
shall be used;
f) Bolts shall be of sufficient length so that at least two but not more than five threads
44
protrude beyond the nut.
For voltages less than 1000 V, the guidelines in the following table must be used.
5.3.3. Busbars Outdoor Type
The busbars shall consist of either stranded conductors or tubes. Stranded conductors having
hollow cores shall not be used.
Material used for busbars, busbar connections and their supports, whether insulated or
otherwise, shall not be stressed beyond two fifths of its elastic limit or its 0.1% proof stress
whichever is applicable. Satisfactory provision shall be made for expansion and contraction of
busbars connections with variation in temperature.
The maximum permissible temperature of unprotected bare busbars or busbar connections when
carrying rated current shall be 85 oC.
All busbar connections shall be kept as short and as straight as possible. The design of
connections to busbars and other equipment shall be such as to permit easy dismantling for
maintenance purposes. The busbars shall be so arranged that they may be extended in length
without difficulty.
All clamps and fittings necessary for attaching the busbars and busbar connections to either
insulated supports, together with all connectors, terminals and accessories required for attaching
the connections to the busbars, switchgear, transmission lines and power transformer bushings
shall be provided. Where dissimilar metals are connected approved bi-metal clamps shall be
provided to prevent electrochemical action or corrosion. Stranded copper connections shall be
tinned at clamping points. The open ends of all tubes shall be fitted with end caps.
Busbar supports shall be designed and constructed so that resonant vibrations are eliminated or
reduced to negligible proportions.
Overhead conductors carried by substation structures shall be erected with such sags and
tensions that the maximum loading of structures is not exceeded when the conductors, at
minimum temperature, are subjected to maximum transverse wind pressure and of fault currents
on the whole projected area. Copies of the conductor sag charts and calculations relating to the
design of tubular busbar systems shall be submitted to the Engineer for approval.
Where bolted connections are used for current carrying joints torque spanners shall be used for
tightening bolts and nuts. Also where necessary washers shall be provided under bolt heads and
nuts to spread the load and reduce the effect of compressive creep under pressure. Torque value
must be quoted on drawings.
Where current carrying surfaces of alloy connections are bolted together such surfaces shall
have the oxide film removed and shall be cleaned and de-greased. A coating of approved
jointing compound shall be applied to contact surfaces and voids before bolting. Copperconnectors shall be tinned
45
5.4
Controlgear
5.4.1 Equipment Cubicles and Ancillary Apparatus
5.4.1.1 General
All cubicles shall be manufactured from enameled sheet and protection classification at least
IP3X.
Each item of equipment mounted on each cubicle shall be positioned to allow full and easy
access to the item and to all equipment adjacent of it. All equipment shall be mounted not more
than 2 metres and not less than 500 mm from the floor.
Subject to the approval of the Engineer one cubicle may accommodate equipment associated
with two primary circuits. In this case a vertical barrier must be provided inside the cubicle to
segregate the wiring and equipment associated with each primary circuit.
If 400V connections are taken through a cubicle they shall be adequately screened or insulated
and a “400 Volts DANGER” notice shall be fixed on the outside of the cubicle.
Cubicle doors shall be hinged to lie back flat to avoid restricting access. Hinges shall be of the
lift-off type. Doors shall be secured by means of handles and locking facilities shall be
provided to the approval of the Engineer.
Each cubicle shall have an interior light fitted to illuminate all apparatus inside the cubicle
without dazzle. The interior lights in each suite of cubicles shall be controlled by a switch
complete with indicating lamp which shall be mounted prominently at one end of the suite.
All cubicles shall be complete with all necessary labels fitted to the front & back to describe the
function of the equipment which shall be approved by the Engineer.
5.4.1.2 Control switches
Control switches for electrically operated circuit-breakers shall be of the pistol grip or
discrepancy type and shall be arranged to operate clockwise when closing the circuit-breakers
and anti-clockwise when opening them. The control switches shall be so designed as to prevent
them from being operated inadvertently and where switches of the discrepancy type are used
they shall require two independent movements to effect operation. The control switch shall be
so designed that when released by the operator it shall return automatically to the “neutral”
position after having been turned to the “closed” position and shall at the same time interrupt the
supply of current to the operating mechanism of the circuit-breaker.
Switches for other apparatus shall be operated by shrouded push buttons or have handles of the
spade type, the pistol-grip type shall be reserved for circuit-breaker operation only.
Control, reversing, selector and test switches shall be so mounted, constructed and wired as to
facilitate the maintenance of contacts without the necessity for disconnecting wiring.
46
5.4.1.3 Instruments
All instruments shall be of the flush mounting type, dust and moisture proof, 96mm DIN square
cases complying with IEC 60051, and shall be fitted with non-reflecting glass.
All instruments and apparatus shall be capable of carrying their full load currents without undue
heating. They shall not be damaged by the passage of fault currents within the rating of the
associated switchgear through the primaries of their corresponding instrument transformers. All
instruments and apparatus shall be back connected and all cases shall be earthed. Means shall
be provided for zero adjustment of instruments without dismantling..
All voltage circuits to instruments shall be protected by a fuse in each unearthed phase of the
circuit placed as close as practicable to the instrument transformer terminals or, where
instruments are direct-connected, as close as practicable to the main connection. All power
factor indicators shall have the star point of their current coils brought out to a separate terminal
which shall be connected to the star point of the instrument current transformer secondary
windings.
Electrical energy meters where specified shall be of static type, class 0.5s, complying with ZS
644 (ZS IEC 62053-22). They shall be 3-phase instruments with two measuring elements and
equipped with operation monitoring indicators. Where maximum demand indicator has been
specified the measuring period shall be capable being selected either 30min or 60min.
All indicating instrument scales shall be long, clearly divided and indelibly marked and the
pointers shall be of clean outline. The marking on the dials shall be restricted to the scale
marking.
In general, instrument dials should be white with black markings. Scales shall be of such
material that no peeling or discolouration will take place with age under humid tropical
conditions.
Instrument scales shall be submitted for the approval of the Engineer.
Kilowatt-hour integrating meters shall comply with the requirements of ZS 643 (ZS IEC 6205321) unless otherwise approved by the Engineers. Cyclometer type registers including a
minimum of five drums reading whole kWh shall be provided.
5.4.1.4 Indications and Alarms
Indicators shall operate reliably at voltages down to 80 per cent of nominal.
A trip circuit supervision scheme shall be provided for each circuit and shall be arranged to
monitor the continuity of the circuit-breaker or fault throwing switch trip coil and as much of
the associated tripping wires as possible. The scheme shall be to approval.
Annunciated alarms and indications shall be by lamps illuminating a legend and shall operate
from the battery specified. The annunciation shall be grouped, each group containing the alarms
and indications associated with the particular switchgear concerned. There shall be two push
buttons for each group of annunciation, one for “Accept” and the other for “Reset”. When an
47
alarm is originated the lamp shall flash, an audible alarm shall sound and a flashing amber
beacon mounted on the substation roof shall be activated. On operation of the “Accept” key the
lamp shall cease to flash and shall give a steady illumination and the audible and visible alarms
shall cease unless already cancelled by the common cut off key.
A distinction shall be made between functions by the use of the following colours:
Red
....
Amber ....
White ....
Trip
Alarm
Indication
The lettering should show white on a dark background or black on an illuminated background.
In the former case the amber or red shall show as a bar of approximately 3 mm below the
inscription. Where it is desired to include fire alarms in an annunciator group, the facias
surround should be coloured red.
The duration of the flash shall be such that the legend may be easily read and the speed of
flashing shall not exceed three times per second.
An alarm whose initiating device does not reset until the abnormality is remedied shall remain
illuminated until the initiating device is reset, when it shall be extinguished without the use of
the reset key.
Annunciations which arise from signals of short duration (fleeting alarms) shall not restore
when the initiating contact restores. It shall be necessary to operate the reset key to clear these.
The reset key shall not be effective until after the alarm has been accepted. If a fleeting alarm is
re-operated after acceptance but before resetting, the annunciation shall return to the flashing
condition.
The annunciation circuit shall be readily adaptable for use with a fleeting or persistent initiating
signal.
Facilities shall be provided for lamp test. The lamp test shall include a test for all spare
windows, which shall be identifiable as such under test conditions.
At each 33/11 kV substation, facilities shall also be provided to extend a common substation
alarm into a remote supervisory system.
As a minimum requirement the following signals shall initiate the audible and visible alarms at
the 33/11 kV substations.
a).
b).
c).
d).
e).
f).
g).
Circuit-breaker tripped
Trip circuit failed
Battery charger failed
Low battery volts
Transformer gas relay operated
Transformer high winding temperature
Transformer overpressure
48
h).
i).
Tap-changer relay operated
Transformer automatic voltage control panel VT supply failed.
5.4.1.5 Indicating lamps
Indicators shall be of the LED or type and all colours shall be to approval by the Engineer.
Filament types may be considered but not encouraged.
LED indicators shall operate at not less than 20mA and red LED indicators shall be of the high
brightness type.
The rated lamp voltage should be ten percent in excess of the auxiliary supply voltage, whether
AC or DC.
The lamp glasses shall be in standard colours (IEC 60073): red, green, blue, white and amber.
The colour is to be in the glass and not applied coating and the different coloured glasses are not
be interchangeable. Transparent synthetic materials may be used instead of glass, provided such
materials have fast colours and are completely suitable for use in tropical climates.
Normally energized indicating lamps, if employed, shall in general be energized from the
station LV AC supply. In addition, facilities shall be provided for manual changeover from the
AC supply to the station DC supply via an automatically resetting switch arranged to reset after
a time interval of approximately five minutes.
Lamps and relays incorporated in alarm facia equipment may be arranged for normal operation
from the station battery, subject to the approval of the Engineer.
Lamp test facilities shall be provided so that all lamps on one panel can be tested simultaneously
by operation of a common key. Where alarm facias are specified, all alarm and monitoring
indications, apart from CB and disconnector position indications, shall be incorporated in the
facia.
All indicating lamps and lamp holder assemblies shall be suitable for continuous operation at
the maximum site ambient temperature.
Indicating lamps and lamp holders shall be arranged so that replacement of lamps and the
cleaning of glasses and reflectors can be readily effected.
To reduce heating and fouling of the panels, lamps which are continuously alight shall have the
minimum consumption consistent with the good visibility of indications in a brightly-lit room.
Indicating lamp glasses on control and relay panels shall conform to the following standard
colour code:Red
....
Circuit-breaker closed
Green ....
Circuit-breaker open
White ....
Indications normally alight
49
Amber ....
Alarm indications (on which an action is necessary)
5.4.1.6 Relays, fuses, links and ancillary apparatus
All relays for front of panel mounting shall be flush pattern. Where practicable the clearances
between relay stems or connecting studs shall not be less than 30 mm and in no case less than
25 mm.
Relays associated with the three phases shall be marked with the appropriate phase
identification and the fuses and links shall also be suitably labelled.
Isolating links and fuses shall be provided on each panel to facilitate the isolation of all sources
of electrical potential, to allow testing or other work to be carried out on the panel without
danger to personnel or interference with similar circuits on other panels.
All fuses and links shall be accommodated within the cubicle. Fuses and links shall be grouped
and spaced according to their function in order to facilitate identification. As an alternative to
fuses and links miniature circuit-breakers will be accepted.
Links in current transformer circuits shall be of the bolted type.
All incoming circuits in which the voltage exceeds 125 volts shall be fed through insulated fuses
and/or links, the supply being connected to the lower terminal. The contacts of the fixed portion
of the fuse or link shall be shrouded so that accidental contact with live metal cannot be made
when the moving portion is withdrawn.
Resistance boxes shall be so mounted inside the cubicle that their adjustment screws are on a
vertical and accessible face. Resistances shall be provided with stud terminals. Set screws shall
not be used.
5.4.1.7 Earthing arrangements
All control and relay panels shall have a continuous earth bar of a sectional area of not less than
75 mm2 run along the bottom of the panels, each end being connected to the main earthing
system. All metal cases of equipment on the panels shall be connected to this bar by conductors
having a sectional area not less than 2.5 mm2.
Current transformer and voltage transformer secondary circuits shall be complete in themselves
and shall be earthed at one point only through links situated in an accessible position. Each
separate link shall be suitably labelled. The links shall be of the bolted type with provision for
attaching test leads.
5.4.1.8 Auxiliary Switches
Where appropriate, each item of plant is to be equipped with all necessary auxiliary switches,
contactors and mechanisms for indication, protection, metering, control, interlocking,
supervisory and other services. All auxiliary switches are to be wired up to a terminal board on
the fixed portion of the plant, whether they are in use or not in the first instance.
50
The number of switches to be provided shall be determined to cater initial installation and allow
for all anticipated future extensions.
5.4.1.9 Cable terminations
5.4.1.9.1 General
All junction boxes, terminal boxes and marshalling kiosks shall be constructed of steel. All main
equipment shall be arranged so that it is accessible from the front of the box or kiosk.
5.4.1.9.2 Outdoor Boxes and Kiosks
Outdoor boxes and kiosks shall have domed or sloping roofs and the enclosure shall be of IP54
protection classification with adequate ventilation and draining facilities. They shall be so
designed that condensation does not affect the insulation of the apparatus, the terminal boards or
the cables. Where necessary, heaters shall be provided. Where these exceed 40 watts, they
shall be controlled by means of a switch mounted on the outside of the box or kiosk.
Any divisions between compartments inside the boxes or kiosks shall be perforated to assist the
natural air circulation.
If the width of the box necessitates the provision of two hinged front covers they shall close on
to a centre post which shall be removable to facilitate cable termination. The depth of the outer
case shall be not less than 200 mm unless otherwise approved.
The outer cases shall be treated before painting to prevent corrosion and shall be finished in
glossy enamel to colour approved by the Engineer.
Access shall be provided at both the front and back of kiosks and junction boxes except for
small terminal boxes of the type normally employed for wall mounting.
Doors and access covers shall be easily opened and shall not be secured by nuts and bolts.
Doors and covers under 14 kg in weight may be of the slide-on pattern; above this weight they
shall preferably be hinged.
Kiosk doors shall be fastened with integral handles. Nuts, bolts or carriage keys shall not be
used. Provision shall be made for padlocking each door.
5.4.1.10 Terminal boards
All terminals boards shall be mounted in accessible position and, when in enclosed cubicles, are
preferably to be inclined towards the door. Spacing of adjacent terminal boards shall be not less
than 100 mm and the bottom of each board shall be not less than 200 mm above the incoming
cable gland plate.
Separate terminations shall be provided on terminal boards for the cores of incoming and
outgoing cables including all spare cores. Not more than two cores may be connected to any one
terminal. Where bridging connections are necessary, these shall be incorporated in the terminal
boards.
51
For terminations modular terminals, Weidmueller type (or approved equivalent) SAK 2.5/35 or
SAK 4/35 (the latter for CT circuits) shall be provided. Current transformers shall be connected
in two parallel terminations in the way that test instrument can be connected in the CT circuit
without a need to short circuit that particular CT.
10 percent spare terminals shall be provided
400/230 V circuit terminals shall be segregated from other terminals and shall be fitted with
non-flammable plastic covers to prevent contact with any live parts. They shall have warning
labels, with red lettering, mounted thereon in a conspicuous position.
5.4.1.11 Cable Entry
All cables shall enter boxes and kiosks at the base via removable gland plates.
Conduits shall not be run at or below ground level but shall wherever practicable enter boxes or
kiosks near the base.
Plates for supporting cable glands shall be at least 450 mm above ground level. Means shall be
provided to drain water off the surface of the gland plate. The back, sides and front of the box
or kiosk shall project at least 50 mm below the gland plate to prevent moisture draining on to
the plate and cable glands.
5.4.1.12 Small Wiring
All control and relay panel wiring, secondary control wiring in CBs, motor starters, controlgear
and the like shall be carried out in a neat and systematic manner with cable supported clear of
the panels and other surfaces at all points to obtain free circulation of air.
In all cases, the sequence of the wiring terminals shall be such that the junction between multicore cables and the terminals is accomplished without crossover.
For wiring inside cabinets PVC-insulated single core non-sheathed cable with single-wire
copper conductor, cross section 1.5 or 2.5 mm2, type H07V-U (GENELEC standard HD 21.S2
and IEC 227-3) shall be used. Multi-stranded flexible conductor cable shall be employed where
connections are subject to movement or vibration during shipment, operation or maintenance.
All wires shall be fitted with numbered ferules of approved type at each termination. At points
of inter-connection between wiring, where a change of numbering cannot be avoided, double
markers shall be provided. Such points shall be clearly indicated on the wiring diagram.
The markers on all wiring directly connected to circuit breaker trip coils, tripping switches, etc.,
shall be of a colour, preferably red, different from that of the remainder and marked "trip".
No wires may be teed or jointed between terminal points.
Bus wiring between control panels, etc., shall be fully insulated and completely segregated from
the main panel wiring.
52
All metallic cases of instruments, control switches, relays, etc., mounted on control panels or in
cubicles shall be connected by means of copper conductors of not less than 2.5 mm2 section to
the nearest earth bar. These conductors shall have yellow/green coloured insulation.
5.4.2 Protective Relays and Associated Apparatus
5.4.2.1.
General
Protective equipment shall be designed to disconnect faulty circuit with speed and certainty
without interference with healthy circuits. They shall also be so designed that when properly
applied incorrect operation of the circuit-breakers does not occur as a result of transient
phenomena not arising from a faulty condition of the section of line or plant associated with
each set of relays but which may occur during fault periods due to disturbances on the system.
The equipment owner shall be responsible for ensuring the correct operation of the protective
equipment and shall submit for approval recommended relay settings supported by design
calculations for all protective equipment being supplied.
5.4.2.2.
Protective Relays
5.4.2.2.1. General
All d.c relays used for tripping shall operate when the supply voltage is reduced to not less than
60% or raised up to 120% of rated voltage.
All relays shall be capable of withstanding voltages up to 120% of rated voltage.
In order to minimise the effect of electrolytic corrosion, indicator coils and d.c. relay operating
coils shall be so placed in the circuit that they are not connected to the positive pole of the
battery except through contacts which are normally open.
5.4.2.2.2. Protection Settings
Unless otherwise specified the equipment owner shall calculate maximum and minimum short
circuit currents in faults at all substation buses. Based on the results of these calculations the
Equipment owner shall prepare a table of all settings for relays in those substations which
belong to the scope of the particular Contract. This table of settings shall be submitted to the
Engineer and Employer for approval prior to commissioning of any plant.
The Equipment owners shall co-operate closely in determining relay settings.
5.4.2.2.3. Form of Relays
All relays shall be contained in dustproof cases. Relays shall be of solid state type and shall be
drawout pattern, modular construction for flush mounting in standard racks. All metal bases and
frames of relays shall be earthed except where the latter must be insulated for special
requirements.
This specification applies particularly to stand alone relays, but relays forming part of a
comprehensive measurement/protection/ interlocking system may be proposed where overall
advantages can be offered. .
53
The relays shall be so arranged that replacements can be effected quickly and with the minimum
amount of labour. Relay equipment incorporating electronic devices shall be arranged to plug
in and shall have positive means for retaining them in the service position. Equipment
incorporating telephone type relays shall have similar facilities.
All relays shall be arranged so that provided reasonable care is taken any dust which may have
collected in or upon the case shall not fall on the relay mechanism when opening the case.
Where relays are required to operate with a time delay the delaying apparatus shall not be of the
dashpot type.
5.4.2.2.4. Performance Requirements
Relays shall provide the electrical characteristics, repeatability, immunity to harmonics,
transients and interference, and environmental protection needed to ensure that system
performance can be achieved. The system performance requirements will be defined in
procurement schedules, and the relays and other components shall be designed to provide the
degree of discrimination, back-up and supply integrity required.
5.4.2.2.5. Reliability
The Tenderers shall quote the reliability for each device offered, in terms of designed mean time
to failures. This figure shall be used in evaluating the reliability of the overall system, the
requirement for which shall be defined in specifications covering system design.
5.4.2.2.6. Maintainability
Relays shall be designed to facilitate first line on-site maintenance, by provision of diagnostic
features and the facility to replace modular elements. As far as practicable any relay fault shall
be indicated by an alarm, which shall give a local indication and facility to transmit a signal on
the SCADA system. Maintenance should be possible without disturbing any wiring connections
or requiring other items of plant to be disconnected. Equipment owners shall provide details of
any special test equipment required for site or workshop maintenance and give recommended
maintenance procedures.
5.4.2.2.7. Setting
The relays shall be capable of being set to cover a range of main circuit parameters, and should
generally be selected such that setting ranges give scope for adjustment either side of the design
setting. Settings shall be effected at the relay and by a remote link if provided. Any such link
shall include a facility to give remote readings of settings. Settings shall be effected by switches
or by input of digital data; conventional potentiometers shall not be used for settings. The
settings shall be clearly indicated at the relay, either by the position of switches or by a digital
display. It shall be possible to alter settings with the relay in service. Loss of electrical supplies
to the relay shall not result in loss of settings for a period of 30 days.
5.4.2.2.8. Relay Contacts
The contacts of all relays shall be capable of making the maximum current which can occur in
the circuit which they have to control. They shall also be capable of breaking such currents
54
unless provision is made for breaking the current on contacts elsewhere in the circuits. Relays
shall not be affected by mechanical shock or vibration or by external magnetic fields consistent
with the place or method of mounting. The contacts shall be capable of repeated operation
without deterioration.
Unless otherwise agreed all protective relays which initiate tripping shall have not less than two
independent pairs of contacts of which one shall operate the tripping relay or circuit-breaker trip
coil without the interposition of auxiliary contactors and without the use of reinforcing
contactors.
5.4.2.2.9. Tripping and Lock-out
Relay operations shall cause trips or lock-out of main circuits, as required by the equipment
schedules. Once initiated the trip signal shall persist until the trip circuit is interrupted by
opening of a normally open auxiliary contact on the circuit-breaker or device being tripped.
5.4.2.2.10. Indication of Operation
All relays which are connected to complete either the tripping circuit of circuit-breaker or the
coil circuit of an auxiliary tripping relay shall be provided with operation indicators.
Indication of operation of each element shall be given at the relay, and via the SCADA system.
The local indication shall be maintained for a period of 30 days if the electrical supplies to the
relay are lost. The remote indication shall be maintained for at least 500 ms, to ensure detection
by the SCADA system, and shall reset after no longer than 5 seconds.
Indicators shall also be provided on such additional relay elements as will enable the type or
phase of the fault condition to be identified. Each indicator shall be capable of being reset by
hand without opening the relay case and it shall not be possible to operate the relay when
resetting the operation indicator. Each indicator shall be designed so that it will not move
before the relay has completed its operation. Indicators shall be clearly visible from the front
when operated and concealed at all other times.
5.4.2.2.11. Indication of Protective Relay Failure
Internal relay faults shall be diagnosed and shall be indicated by a non-volatile device on the
relay. Failure shall also operate a pair of normally open contacts, which may be used either for
remote indication or for tripping, as required by the equipment schedules. Failure of any
auxiliary supply to the relay shall also be indicated on the relay and shall cause the normally
open contacts to operate. Such contacts shall be commoned to provide a single remote alarm of
protection equipment failure for each switchboard.
5.4.2.2.12. Facility for Resetting
Alarm and trip contacts shall reset automatically on removal of the signal causing the operation.
Lock-outs shall have facility for manual resetting at the relay, and for resetting via the SCADA
system when called for in the equipment schedules. Local indications of operation shall be reset
at the relay. Remote indications of operation shall reset as required in 4.7 above.
55
All relays which are of the hand reset type shall be capable of being reset without the necessity
of opening the case. It shall not be possible to operate any relay by hand without opening the
case.
5.4.2.2.13. Location of Relays
Where practicable relays shall be mounted on the door of a control compartment above the
circuit to which they apply. Where this is not practicable, relays may be fitted to separate
cubicles. The arrangement of such cubicles will be specified according to site arrangements;
they may be free standing, in which case relays should be fitted to fixed front panels with
maintenance access via rear doors, or they may be wall mounted, in which case relays shall be
fitted on hinged door panels.
5.4.2.2.14. Relay Cases
Relay cases shall be of standard height of 177 mm, complying with IEC 297, size 4U, and for
mounting on standard 483 mm racks. Covers shall be fitted and shall have provision for sealing
to prevent unauthorised access. Manual resetting and inspection of indications and settings shall
be possible with the covers in place, but any adjustment shall require removal of covers. With
covers in place the degree of enclosure of the relay shall be IP52 to BS 5490.
5.4.2.2.15. Terminals
Relay terminals shall accept ring type terminals with an M4 or larger screw fixing. Barriers
shall be provided between terminals, and voltage withstand and current rating shall be in
accordance with the circuit ratings and test values.
5.4.2.2.16. Test Blocks
Test blocks associated with each circuit breaker relay panel shall be provided to permit testing
of all functions, and shall be accessible from the front of the equipment. Test blocks shall
accept a multi-outlet test plug, which shall accept 4 mm plugs for interconnection and external
connection.
5.4.2.2.17. Tripping Arrangements
Trip circuits shall be of series seal-in type, and shall be operated from the substation batteries, at
voltages as defined in equipment schedules.
5.4.2.2.18. CT Circuits
Relay cases shall be fitted with devices to short out CT windings automatically on withdrawal
of relays, so that at no time is the CT secondary winding left open circuited.
5.4.2.2.19. Labelling and marking
All relays shall either be suitably marked or shall have a label nearby with the following
information:
a).
b).
Function of relay
Phase identification of the current supply
56
c).
d).
e).
Characteristic curve where appropriate
Rated current and voltage of the relay coils
Rated making capacity of tripping contacts.
Items (a) and (b) above shall be visible from the front without removing the cover.
5.4.2.2.20. Overcurrent & Earth Fault relays
Where specified inverse definite minimum time (IDMT) overcurrent relays shall be provided for
overcurrent and earth fault protection. They shall be of static type.
Overcurrent relays shall be of the three pole type and shall be of the inverse definite minimum
time limit (IDMTL) pattern with separate adjustable time and current settings. The time/current
characteristic of all IDMTL relays shall be to BS 142 normal inverse curve.
The directional overcurrent relays shall have the appropriate technical capability to ensure
correct operation during a close three-phase fault.
Relay directional elements which are designed to be energised normally by voltage and current
when carrying any current between zero and 15 times rated current shall take up such a position
that the contacts are open when the voltage coil is not energised.
Relays should have adjustable settings for both operating current and time. The range of current
settings for phase faults shall be 50-200 per cent of rated current and the time setting adjustment
shall be 0.3 to 3 s at ten times the setting current.
Inverse time earth fault relays, where specified, shall have a range of settings from 10 to 40 %
of rated current.
5.4.2.2.21. Balanced Earth fault relays
Balanced earth-fault relays shall be instantaneous in action unless otherwise specified. The
arrangement however shall be such that the relay is stable under „transient‟ conditions.
5.4.2.2.22. Automatic Reclosing of 11& 33 kV Lines
Where specified the relay protection for 11&33kV overhead lines shall be equipped with autoreclose relay which shall perform high speed and delayed auto-reclose. The dead time for high
speed stage shall be adjustable from 0.1 s to 5.0 s and that for delayed stages from 5 s to 180 s.
Reclaim time shall be at least 5 s. Reclosure shall be initiated only by the earth fault relay.
5.4.2.2.23. Feeder protection with pilots
Pilot wire supervision equipment to the Engineer‟s approval shall be included at all substations
where pilot wire feeder protection is installed. The equipment shall include a supply fail relay,
an approved test feature for the pilot monitoring relay and adequate spare contacts for remote
indication.
5.4.2.2.24. Feeder protection without pilots
Feeder protective equipment without pilots shall be of a discriminative type.
57
5.4.2.3.
Transformer protection
5.4.2.3.1. General
Current transformers which are used for transformer earth fault protection shall not be used for
any other purpose unless agreed by the Engineer.
5.4.2.3.2. Earth Fault Protection
Where earth fault protection having three line and one neutral current transformers is employed
on the winding of a power transformers it shall be so arranged that it does not operate with any
type of fault external to the transformer winding. To ensure compliance with this requirement
the equipment shall be so designed that the current flowing in the relay operating coil with any
type of fault having a magnitude up to the maximum figure specified shall preferably be not
more than a quarter and in no case more than one-half of the current required to operate the
relay when adjusted to the prescribed setting. The setting of the relay shall be such that it will
operate reliably with current of the following magnitudes in the primary winding of the neutral
current transformer alone:a).
b).
Power transformer neutral directly earthed - system voltage 72.5 kV and below - not
more than 20% of the rated current.
Power transformer neutral earthed through resistor or reactor - all voltages - not more
than 25% of the rated current of the resistor or reactor where this rating does not differ
greatly from the primary current rating of the current transformers. Where the prescribed
settings cannot be obtained special approval of the performance shall be obtained.
Where earth fault protection is employed for the winding of a transformer which is earthed
either directly or through an earthing device the Equipment owner shall provide and fix current
transformers in the neutral earthing connection of the winding of the power transformer. One
such current transformer in the neutral connection shall be used for the balanced earth fault
protection and wherever the neutral point of the transformer winding is not directly connected to
earth standby earth fault protection shall be obtained from a second current transformer having a
primary current rating of the standard value nearest to the rated current of the winding of the
power transformer with which the standby earth fault current transformer is associated.
5.4.2.3.3. Differential protection
Where specified Differential protection shall be of the instantaneous three winding biased
differential type capable of detecting phase and earth faults.
Separate facilities shall be provided to enable bias settings to be adjusted. The minimum
operating setting shall not be greater than 20 % of the rated full load current of the transformer.
The blocking based on the ratio of the fifth and the second harmonics shall be included in the
transformer differential relay to prevent unwanted operations. No interposing transformers shall
be needed. Numerical vector group matching shall be included.
58
The protection shall be designed to ensure stability on any transformer tap position under
maximum through fault conditions with maximum DC offset. An infinite source is to be
assumed and through fault current calculated using the transformer impedance only.
The trip coils of the circuit-breakers on the primary and secondary sides of the transformer shall
be so connected to the relays that the circuit-breakers shall operate together when the protective
gear functions. Facilities shall be retained for independent tripping by hand of either circuitbreaker.
5.4.2.3.4. Restricted Earth Fault Protection
Where specified transformer windings and connections shall be protected by REF relay of high
impedance type with necessary protection against overvoltages.
Relays shall be stable for faults outside the protected zone and on magnetising inrush surges.
Sensitivity for solidly earthed windings shall not be greater than 60% of the winding rating, for
resistance earthed windings not greater than 20% of the resistor rating.
The rated stability limit shall not be less than the maximum current available for an external
fault. This shall be taken as 12 times the rated current of the protected winding of the power
transformer.
5.4.2.3.5. Standby earth fault
Where specified standby earth fault (SBEF) shall be provided for all earthing resistors fed from
a current transformer in the resistor earth connection.
The operating current of SBEF-relay shall be adjustable between 20 and 100 per cent of the
resistor rated current. The time delay shall be adjustable between 1 and 10 s.
5.4.2.4.
Distribution Line Protection
5.4.2.4.1. Overcurrent and Earth fault protection
Where specified inverse definite minimum time (IDMT) overcurrent relays shall be provided for
overcurrent and earth fault protection.
Overcurrent relays shall be of the three pole type and shall be of the inverse definite minimum
time limit (IDMTL) pattern with separate adjustable time and current settings. The time/current
characteristic of all IDMTL relays shall be to BS 142 normal inverse curve.
The directional overcurrent relays shall have the appropriate technical capability to ensure
correct operation during a three-phase fault.
Relay directional elements which are designed to be energised normally by voltage and current
when carrying any current between zero and 15 times rated current shall take up such a position
that the contacts are open when the voltage coil is not energised.
Relays should have adjustable settings for both operating current and time. The range of current
settings for phase faults shall be 50-200 per cent of rated current and the time setting adjustment
shall be 0.3 to 3 s at ten times the setting current.
59
Inverse time earth fault relays, where specified, shall have a range of settings from 10 to 40 %
of rated current.
5.4.2.5.
Fault event recorders
When specified fault event recorder or module to an existing protection (without a printer) shall
be provided. This shall store all pertinent data for the analysis of the fault by a separate
computer and printer. The module shall be equipped with a low speed data interface for the
remote data communication to be installed later.
Where a fault locator specified shall be provided which uses the inputs available from the
distance relay. The locator shall operate on the impedance to fault measuring principle.
Preference will be given to schemes with following features:
•
Digital processing of fault and pre-fault data to calculate distance to fault.
•
Printed display identifying faulted line, fault type and distance to fault.
5.4.2.6.
Integrated Microprocessor Based Schemes
5.4.2.6.1. Measurement-Protection-Control
Microprocessor based protection relays may be offered as part of overall schemes to provide
protection, control functions and monitoring. The following items are a guide to the capabilities
required:•
•
•
•
•
•
•
All protective functions for safety tripping and discrimination,
Logic for interlocking and sequence operation of substation equipment and, where
applicable, for reconfiguring of circuits after protective tripping,
Facility for interfacing to SCADA system for remote indication of circuit loading, voltage
etc.,
Facility for remote setting and for remote indication of setting values,
Ability to retain historical data on circuit conditions and to transmit information,
Facility to record exact timing of events, including all protective and alarm operations,
Ability to use historical data to amend tripping levels.
No failure of the remote link shall affect protective functions. The particular requirements and
the details of interfaces to the SCADA system will be subject to agreement with Utility.
5.4.2.7.
Tripping and Control Power Supplies
5.4.2.7.1. Supply Voltage
Tripping and protective circuits shall be supplied from substation batteries and shall be at a
nominal or 110 V d.c.
5.4.2.7.2. Supply Arrangements
Two incoming supplies for tripping and protective equipment will normally be provided from
the substation battery, and provision shall be made for connection of one supply at each of the
end circuits on the switchboard, via links in each pole of the supply. A tripping supply buswire
60
shall be provided, and isolating links shall be inserted in the buswire at each bus-section switch
position on the switchboard. The protective equipment on each circuit shall be connected to the
supply via fuse links in each pole. The trip coil circuits and each protective relay shall be
separately fused. No other circuits (i.e. auxiliary closing) shall be supplied from the tripping
and protective equipment buswire.
5.4.2.7.3. Trip Circuit Supervision
Trip circuit supervision shall be provided for all the 11 and 33kV circuits Depending on the
extent of integrity required the schedules may call for any of the following types as specified in
the Bill of Quantities:•
Trip circuit monitoring for the 11 and 33kV indoor type breakers
•
Full trip circuit supervision for outdoor 33kV breakers.
The indications to the SCADA system shall be from changeover contacts, to maintain a positive
indication at all times.
5.4.3 Batteries & Battery Chargers
5.4.3.1.
General
DC auxiliary power supply voltage shall be 110 V for protection tripping and closing supplies.
DC battery system shall comprise one 100% duty battery composed of independent cells. The
supply for the battery charger may be either three phase 400 V a.c or single phase 230 V a.c.
5.4.3.2.
General Design Principals
5.4.3.2.1. Performance Criteria
Battery and battery charger systems must be designed for the purpose intended and to meet the
requirements of all applicable National standards. The primary role of the substation battery
system is to provide a source of energy that is independent of the primary ac supply, so that in
the event of the loss of the primary supply the substation control systems that require energy to
operate can still do so safely. The battery is required to supply the DC electrical requirements of
the substation, including SCADA, control, protection indication, communications and circuit
breaker switching operations when there is no output from the battery charger.
This may be due to a loss of AC supply to the substation or a fault in the battery charger. Under
these conditions the battery shall supply the DC loads for a minimum period of 5 hours after
which time the battery should then be able to supply trip-close-trip operations of an HV circuit
breaker which would typically restore supply to the battery charger. The 5 hour capacity allows
for ageing and a given minimum cell voltage under load at the end of discharge. There will be
nominally no remaining capacity on the battery at the end of the 5 hour period if subjected to the
given duty cycle at the end of its service life.
The absolute minimum requirement is that the battery has sufficient energy to allow the
substation to be made safe on loss of ac supply. A secondary requirement is to provide high
capacity support to the battery charger for operating high current transient loads that are beyond
61
the charger‟s capability. A substation shall comprise two battery chargers each capable of
providing 100% duty.
5.4.3.2.2. Design Criteria
The number of batteries provided, and the physical & electrical separation of these, shall be in
accordance with Section 17.2.5 (Number of Batteries). Where a 50 V DC supply is required for
substation communications systems, this shall be supplied from the 110V DC battery via a 50V
DC-DC converter or an independent 50V battery.
5.4.3.2.3. Battery Configuration
The battery cells shall be suitable for mounting on their bases. The battery cells shall not sit
directly on the ground instead shall be mounted on the none corrosive earth bonded rack. The
configuration and nominal capacity of the batteries shall be derived as follows: from a fully
charged state the batteries must be capable of meeting both Duty A and Duty B as shown in the
table below:
Battery Type
Solenoid Operated Circuit
Breakers
Duty A
*200 Ah
20 A
5 hr
Spring Operated Circuit
Breakers
Duty A
*200 Ah
25 A
5 hr
Discharge Current
Discharge Time
End terminal voltage not less
than:
Battery ageing factor
50V supply via:
150 A
10 sec
100 V
35 A
10 sec
100 V
20%
dc-dc converter/independent
charger unit
Temperature operating range
-1OC to 40 OC
20%
dc-dc
converter/independent
charger unit
-1OC to 40 OC
Accommodation
Cabinet / Rack in separate
room
Cabinet / Rack in separate
room
Chemistry
VRLA\Lead Acid\Nickel
Cadmium\ Lithium
54
124.9 V (2.23 V / cell
typical)
135.0 V (2.41 V / cell
typical)
VRLA\Lead Acid\Nickel
Cadmium\ Lithium
54
124.9 V (2.23 V / cell
typical)
135.0 V (2.41 V / cell
typical)
Load Duty
Nominal capacity
Discharge Current
Discharge Time
Followed immediately by:
Cells in series
Float voltage (manufacturer
specific)
Boost voltage (max)
(manufacture specific)
62
*
These are nominal capacities only - actual battery capacities are dependent on discharge
rates, final battery voltages and the type of loads to be supplied.
5.4.3.2.4. Number of Batteries
Substations with duplicated protection systems shall have dual (2) battery systems – one for
each protection system. Substations that do not have remote back-up protection systems shall
also have dual battery systems. Substations without duplicated protection systems, and which
have remote back-up protection, shall have a single (1) battery system. Where dual battery
systems are provided the batteries and associated chargers, including all associated wiring, shall
be kept physically and electrically isolated to ensure that potential problems with one system do
not affect the other. Each battery shall have a separate dedicated charger. „A‟ and „B‟ protection
systems shall be supplied by different batteries and the overall substation DC load shall be
distributed as evenly as possible between the two batteries, for example „A‟ protection and
SCADA supplied by battery 1, „B‟ protection, local control, protection, indication and
communications, etc supplied by battery 2.
5.4.3.2.5. Cell Casing
Cell casings shall be clear or translucent material fitted with safety (anti-explosion) vents.
5.4.3.2.6. Connections
All bolts, nuts, fasteners and electrical connections shall be of material that is resistant to
corrosion.
5.4.3.2.7. Cell Numbering
Battery cells shall be numbered starting from the positive terminal i.e. cell “1” for the first cell.
5.4.3.2.8. Battery Charging
Battery charging is to be strictly to the manufacturer‟s specification with no unapproved
changes to the regime.
5.4.3.2.9. Accommodation
5.4.3.2.9.1.
a).
b).
c).
d).
Battery Cabinets
Batteries are to be accommodated in a separate ventilated room fitted with extractor fans
and fire protection systems;
Cabinet to be designed to facilitate front access to the batteries, with sufficient space in
front of the cabinet for lifting and carrying gear for handling individual cells;
Cabinet to be treated against electrolyte spill (electrolyte is gel and limited quantity, so
spread under cell rupture is limited);
Where multiple battery groups are provided, the batteries shall be located with sufficient
separation to enable maintenance or similar activities on one battery to not adversely
affect operation of the other;
63
5.4.3.2.9.2.
a).
b).
c).
d).
e).
f).
g).
h).
i).
j).
Safety
Battery rooms shall provide easy access for batteries and battery stands. In addition,
battery rooms shall be dry, well lit, well ventilated and protected against the ingress of
dust and foreign matter.
Battery room shall have eye wash facilities.
Battery rooms shall provide for possible future expansion / refurbishment, therefore it
shall be located at the end of the building. Battery rooms shall be situated as near to the
associated loads and rectifier equipment as possible.
Every endeavor shall be made to ensure that the battery room is situated on the coolest
side of the building.
Separate battery rooms shall be provided for batteries with different types of electrolyte,
i.e. nickel cadmium and lead-acid batteries shall not be installed in the same room. Two
or more batteries with the same type of electrolyte may be installed in the same room but
on separate battery stands.
An access passage at least one metre wide to all battery rows and a minimum of one
metre between rows of battery stands shall be provided.
Only single row or stepped double row single tier battery stands may be positioned
against a wall. The step shall be such that the top of the cell plates of the back row is
exposed.
The minimum distance between any battery terminal and the nearest water supply point
shall be two metres.
Rows of battery stands shall be positioned such that they do not jeopardize or obstruct
the doorway.
Wherever possible the stands shall be positioned perpendicular to the entrance wall. The
battery arrangements shall comply with the layout drawing, showing the positioning of
the different batteries.
5.4.3.3.
Battery Chargers
5.4.3.3.1. Type
Battery chargers shall be low ripple, UPS style switch mode charger with temperature
compensation facility.
Battery chargers shall be suitable for providing supply to a load with or without a battery
connected in parallel and are to be a suitable for wall and floor mounting. Battery chargers are
to be single-phase connected to facilitate connection of portable generator sets in situations of
loss of ac supply (such as under “black start” conditions or other loss of ac supply).
5.4.3.3.2. Location
Battery charger units shall be located within the Substation Control Room, as close as
practicable to the relevant battery.
64
5.4.3.3.3. AC Supply
For substations where two battery systems are provided, AC supply to each battery charger shall
be taken from a different auxiliary AC distribution switchboard.
5.4.3.3.4. Features
Battery chargers are to have an AC input circuit breaker, battery monitor relay, DC output fuses
or circuit breakers and output voltage indicator. The charger is to be operated in accordance
with the battery manufacturer‟s recommendations.
5.4.3.3.5. DC Supply Circuits
The positive and negative shall be in separate conduits and fused as shown in the figure.
Figure 5-1: Schematic representation of a battery charger
5.4.3.4.
Battery Disposal
Disposal of all batteries shall be in accordance with the Environmental Management Act No.12
of 2011
65
5.4.4 Metering
5.4.4.1. General
The metering shall be for the purpose of measuring kVA/kVAr-hours/kWh for tariff purposes.
The metering equipment shall be static and comply with the following Zambia Standards:
a).
ZS IEC 62053 61: Electricity metering equipment (a.c.) Particular requirements - Part
61: Power consumption and voltage requirements
b).
ZS IEC62053 31: Electricity metering equipment (a.c.) Particular requirements - Part
31: Pulse output devices for electromechanical and electronic meters (two wires only)
c).
ZS IEC 62053 23: Electricity metering equipment (a.c.) Particular requirements - Part
23: Static meters for reactive energy (classes 2 and 3)
d).
ZS IEC 62053 22:2003 Electricity metering equipment (a.c.) Particular requirements Part 22: Static meters for active energy (classes 0.2 S and 0.5 S)
e).
ZS IEC 62053 21: Electricity metering equipment (a.c.) Particular requirements Part
21: Static meters for active energy (classes 1 and 2)
f).
ZS IEC 62053 11: Electricity metering equipment (a. c.) – Particular requirements - Part
11: Electromechanical meters for active energy (classes 0.5, 1 and 2)
5.4.4.2. Design
All integrating meters shall be static and shall be suitable for operating in the following
manner:a).
Single Element Meters (2-wire).
These may be of either whole current or current transformer operated type. In either case
the voltage coil shall be suitable for a nominal voltage of 230 volt connected phase to
neutral. Such meters will be used to measure a single phase input or three single phase
meters will be combined to measure a three phase input where the load may be balanced
or otherwise.
b).
Three Element Meters (4-wire).
These shall be of either the whole current or current transformer operated type and shall
be used for balanced and unbalanced three phase loads at a nominal voltage of 400/230
volt.
c).
Two and Half Element Meters (4 wire)
These shall be designed to operate from current transformers in each of the three phases
and potential transformers connected between two of the phases and neutral
d).
Three Element Meters (3-wire)
These shall be of either the whole current or current transformer operated type and shall
66
be used for balanced and unbalanced three phase loads at a nominal voltage of 400/231
volt
5.4.4.3. Meter Accuracy
The accuracy class or equivalent, is based on the MVA capacity of the connection and for new
installations shall as a minimum be as follows, subject to operating within the combined limits
of error set out in Table 5-8 below: Table 5-8:
Meter accuracy
Equipment
Equipment Accuracy Class
For connections
Equipment Type
Meters
> 100 MVA
>20-100 MVA
1 – 20 MVA
< 1MVA
0.2S
0.5S
1.0
2
5.4.4.4. Meter Enclosure
Meter enclosure shall be IP 51 in accordance with IEC 60529
5.4.4.5. Labels
All meters shall be clearly and permanently labelled.
5.5
Auxiliary Equipment
Substation lighting
Recommended minimum levels of substation lighting shall be maintained at all times for the
safety and security of personnel and the facility. The substation lighting requirements can be
referred to ZS 418.
5.5.1. Fire suppression systems
The design and operation of a new or existing substation shall take recognition of the fire
hazards associated with the installations, the risks involved and the responsible person shall
provide appropriate fire-protection mitigation measures. The requirements can be referred to ZS
IEEE 979.
67
6.
CABLES AND CONDUCTORS
6.1.
General
When cables and conductors are being selected, some of the main points to be considered are:
a).
b).
c).
d).
e).
f).
g).
h).
i).
j).
Maximum operating current;
Cyclic pattern of the current;
Voltage drop;
Short-circuit requirement;
Exposure to mechanical damage;
Lifetime costs, including the cost of losses;
Earthing requirement;
Current ratings, including de-rating factors;
Possibility of theft of cable and energy, and
Ability to withstand ultraviolet radiation.
For the preferred type of cable or conductor available within the ranges covered by the relevant
Zambian cable standards. The permissible short-circuit current for a cable or conductor is
determined by the maximum permissible conductor temperature and the duration of the shortcircuit current, in other words, the time from the start of the short-circuit until it is broken by
protective devices. The relevant formulas or tables and charts that list the maximum
permissible short-circuit currents for different time intervals can be obtained from the cable
manufacturers.
6.2.
Fault currents and short-circuit ratings of cables
6.2.1. Fault current on the MV network
If the fault level in megavolt amperes is known, the fault current on the MV network is given
by:
If 
Pf
Vs  3
(7.1)
Where
If
is the fault current, in kilo amperes;
Pf
is the MV fault level, in megavolt amperes;
Vs
is the MV system voltage, in kilovolts.
The size of the cable can then be checked against the manufacturer‟s tables of short-circuit
ratings for the expected fault clearance time.
Example:
For an MV fault level of 250 MVA, and an 11 kV three-phase system, the fault current is:
68
250
 13.12 kA
3 11
If 
(7.2)
6.2.2. Fault level at the LV terminals of the transformer
The MV fault level should be taken into account in the calculation of the LV fault current at the
transformer bushings. To allow for MV growth, use the maximum planned fault level at the
step- down MV substation or the rating of that substation‟s switchgear.
The formula for the fault level at the LV terminals is:
If 
1000
 1 Z p 10 
 
  Vs  3
P

T
r
 f

(7.3)
A simplified formula which does not take the MV fault level into account (i.e. assumes an
infinite MV bus) can be used. It gives an LV fault level around 5 % higher than when equation
7.3 is used. The simplified formula is:
If 
100  Tr
Z p  Vs  3
(7.4)
Where;
If
is the fault current, in kiloamperes;
Pf
is the MV fault level, in megavolt amperes;
Zp
is the transformer impedance, as a percentage;
Tr
is the transformer rating, in kilovolt amperes;
Vs
is the LV system voltage, in volts.
Example:
For an MV fault level of 250 MVA, an LV system voltage of 400 V and a transformer of 500
kVA and 5 % impedance, the fault current is:
If 
1000
 13.88 kA
5  10 
 1


  400  3
 250 500 
(7.5)
Using the simplified formula, the calculated fault current would be 14.43 kA.
69
6.2.3. Maximum fault current at service distribution points (SDPs).
The three-phase fault level should be calculated at each node on the distributor where the cable
size changes to allow checking whether the fault current rating of the cable from the SDP will
be exceeded.
The impedance at the transformer LV terminals is mainly reactive, whereas the LV feeder
impedances have both resistive and reactive components. For reasonable accuracy, the cable
resistance and reactance both have to be taken into account.
The impedance at any point is the vector sum of the impedance up to the transformer LV
terminals plus the sum of all LV feeder impedances. The feeder impedances should be taken at
the same temperatures used for voltage drop calculations, i.e. 30 °C for underground cables and
40 °C for overhead lines and ABC.
The reactance up to the LV terminals, in ohms, referred to the LV side, is given by:
Vs
3  I s 1000
Xs 
(7.6)
Where;
Xs
is the reactance up to the LV terminals, in ohms;
Is
is the three-phase fault current at the LV terminals, in kilo Amperes;
Vs
is the LV system voltage, in volts. If the sum of the LV feeder impedances is Rf + jXf,
then the total impedance, in ohms, is:
Z t  R  X f  X s 
2
f
2


Vs

 R   X f 

3

I

1000
s


2
2
f
(7.7)
Where:
Rf:
is the sum of the feeder resistances
Xf:
is the sum of the feeder reactances
The three-phase fault current, in kilo amperes, is then given by:
If 
Vs

1000  Z t
Vs


Vs

1000  R   X f 
3  I s 1000 

2
2
f
(7.8)
For a fault level at the transformer LV terminals of 13.88 kA (see previous example) and a total
LV feeder impedance of (0.01299 + j 0.0061) Ω, the fault current in kilo amperes would be:
70
If 
400
400


3 1000  0.01299 2   0.0061 

3 13.88 1000 

2
 8.82
(7.9)
6.2.4. Minimum fault level at ends of feeders
To ensure that fault protection devices operate successfully, the single-phase fault current at the
end of each branch and at the consumer‟s point of supply should be calculated. This is
particularly significant in long, lightly loaded LV feeders. Since these feeders are longer than
usual, their impedance Z rather than resistance only, should be used. The fault current should
be larger than 1.6 times the full load current.
6.2.5. Standardized procedure for short-circuit calculations
Methods for the calculation of short-circuit currents are given in IEC 60909-0 and other
standard texts. These methods can be applied to evaluate the maximum and the minimum shortcircuit currents, in order to correctly select and adjust protection device.
71
7.
7.1
OVERHEAD DISTRIBUTION LINES
General
Overhead power lines will be selected based on the suitability for current carrying capacity,
topology of terrain, interaction with users of the area (crossing points, human proximity, mobile
machinery, agricultural machinery, wildlife and livestock), and the economic requirements.
The overhead line basically consists of the overhead lines (conductors), support structures i.e.
poles/tower, stay wires, insulators, aerial guard earth wire(s), cross arms, lightning arrestors, arc
horns, anti-climbs, red ball aviation warnings systems, catch nets, goal posts.
7.2
System Voltages
Distribution systems in Zambia use system voltages of 33kV, 11kV, 3.3kV, 0.55kV and 0.4kV.
The suitability of the system voltage is basically dependent on the choice of supply of the
distributor with respect to the length of the line, operational machinery, segregation of voltage
ranges etc.
Overhead lines may consist of similar components, however special consideration must be taken
into account with respect to the system voltage of the overhead line in line height clearance, line
to line spacing, aerial earth guard wire to line clearance, choice of insulators, fuse links, arc
horns, and lightning surge arrestors.
7.3
Conductors
7.3.1 Insulated Conductors
7.3.1.1
Aerial Bundled Cables (ABC) Voltages up to 600V
Aerial Bundled Cables are used as a preferred economic means to supply power to areas where
the property of insulation is of prominent importance such as national parks, sub-urban areas
with a large density in population and heavily built-up places with no provision for underground
cabling.
As a guide for determining the specifications for cores consisting of stranded that are insulated
with cross-linked polyethylene (XLPE) and that are intended for use in aerial bundled conductor
(ABC) systems for overhead single-phase and three-phase electricity distribution operating up
to 600/1 000 V, please make use of SANS 1418-1 and refer to IEC 60502.
As a guide for determining the requirements for assembled insulated conductor bundles, please
make use of the SANS 1418-2.
As for further standards for aerial bundled conductors, please make reference to SANS 1713
and for testing guidance and fittings, fasteners, line taps, brackets the following standards can be
used:
1. SANS 10198-14: Handling and installation of electrical aerial bundled
conductor (ABC) cables power cables of rating not exceeding 33 000V.
2. SANS 6282-1: Conductor resistance testing of electrical aerial bundled bare
and insulated conductors.
3. SANS 6282-3: Mechanical testing of electrical aerial bundled bare and
insulated conductors.
4. SANS 6101: Testing to dielectric adherence to conductor of supporting cores
of aerial bundled conductors.
72
5. SANS 6100: performance testing of mechanical and thermal stresses of
supporting cores.
7.3.1.2 Aerial Bundled Cables (ABC) voltages above 600V to 33kV
Considering the nature of the aerial bundled conductors for use up to voltages of
33kV, there supporting structure and components are mainly the same. However, for
guidance make reference:
1. SANS 10198-14: Selection, handling and installation of electrical aerial
bundled conductor (ABC) cables power cables of rating not exceeding
33,000V.
2. SANS 6282-1: Conductor resistance testing of electrical aerial bundled bare
and insulated conductors.
3. SANS 6282-3: Mechanical testing of electrical aerial bundled bare and
insulated conductors.
4. SANS 6101: Testing to dielectric adherence to conductor of supporting cores
of aerial bundled conductors.
5. SANS 6100: Performance testing of mechanical and thermal stresses of
supporting cores.
7.3.2 Bare Conductor
7.3.2.1 Aluminum Conductor, Steel Reinforced (ACSR)
Aluminium conductors with steel reinforcement shall be selected based on the standard size
suitability of current loading and mechanical withstand strength of the support structures and the
requirements of IEC 60889.
7.3.2.1.1
Maximum Limits - Reduced limits to avoid fatigue failure due to vibrations for
Aluminium Conductor, Steel Reinforced (ASCR):
If vibration dampers are not used and the lines have relatively short spans, typically under 200
m, the initial tension at -5 °C should not exceed 25 % of the ultimate tensile strength of the
conductor.
When vibration dampers are used, the following limitations are recommended:
a) The initial tension at -5 °C should not exceed 33.3 % of the ultimate tensile strength
of the conductor;
b) The initial tension at 15 °C should not exceed 2 5 % of the ultimate tensile strength
of the conductor; and
c) The final tension at 15 °C should not exceed 20 % of the ultimate tensile strength of
the conductor.
Additional dampers are not required for bundled conductors if the tension is below a
certain value 7,
proportional to the conductor weight:
T = 1 800 Mc
Where;
T is the limiting tension, in newton‟s; and
Mc is the conductor weight per metre, in newton‟s per metre.
In the case of single conductors, it is not economical to use this value to limit initial
73
tensions, and current practice is to limit the final tensions. Initial tensions are limited
by the support structure capacity on short spans.
All Aluminium Alloy Conductors (AAAC)
Aluminium conductors shall be selected based on the standard size suitability of
current loading and mechanical withstand strength of the support structures and the
requirements IEC 61089.
Maximum Limits - Reduced limits to avoid fatigue failure due to vibrations for All
Aluminum Alloy Conductor (AAAC) (Refer to Item on ASCR)
7.3.2.2 Copper Conductor
Copper conductors shall be selected based on the standard size suitability of current loading and
mechanical withstand strength of the support structures and the requirements of BS 7884.
The tension at 15 °C should not exceed 26 % of the ultimate tensile strength of the conductor.
7.3.3 Conductor Joints
All joints shall be such that their current-carrying capacity exceeds that of the conductors that
are being joined. Tension joints shall have a breaking strength of at least 95 % of that of the
conductor. In areas that are conducive to corrosion, it is good practice to coat the joined ends
and fill the fittings with chemically inert corrosion-inhibiting paste.
There shall be no joints made in either the conductors or the earth wires on a road or rail
crossing span.
7.4
Support Structures
7.4.1 Wooden Poles
The wooden poles shall comply with the specifications in the Zambian standard on wood poles
ZS 746 – 6.
7.4.2 Concrete Poles
7.4.2.1 General
Concrete poles shall be one of the following types, as specified by the purchaser and in
accordance with SANS 470:
a).
b).
c).
Reinforced concrete pole,
Partially pre-stressed concrete pole, or
Pre-stressed concrete pole
Poles shall be manufactured in accordance with NRS 038
7.4.2.2 Design
Length, tip and butt dimension:
The overall length of the pole shall be as specified, and shall be one of the following standard
lengths: 4m, 7m, 9m, 10m, 11m, 12m, 15m, 18m, 21m and 24m. The tip and butt dimensions of
the 4m up to 11m poles shall be as per the detailed figures in NRS 038.
74
7.4.2.3 Cover of reinforcement
The minimum thickness of the overall reinforcement in the case of centrifugally spun poles shall
be not less than 15mm over the entire length of the pole. In the case where poles are
manufactured by any other process the cover shall not be less than 20mm. When poles are
required for use in aggressive soils the special additional requirements may include one or more
of the following: Protective coatings; Additional concrete cover to reinforcement; Replacement
of cement with slagment; higher factor of safety (to limit crack widths)
7.4.2.4 Finish
The finished product will have a smooth external surface free from honeycombing. All corners
shall be clean, straight and rounded to a radius of at least 5mm.
7.4.2.5 Holes
Holes shall be provided in the poles during the manufacturing of the poles. These holes shall be
used for the attachment of strain or suspension and other equipment. The holes shall be
positioned as specified in the relevant figures detailed in NRS 038. Drawings indicating the
specified poles with pole holes shall be furnished for approval prior to ordering thereof. On all
transformer poles, the integral earthing facility EW 2900 and EW 8700 shall be replaced with a
PVC conduit embedded in the concrete to protect the earth conductor in order to allow for
separate earthing of the MV and LV earth in accordance with SANS 10292 and SANS 10200
respectively. This separate earthing is necessary when the earth resistivity value of the
transformer structure is above 1 ohm. On all other MV poles the earthing ferrules (EW 2200 and
EW 8000) shall be provided for earthing of the poles.
7.4.2.6 Pole Strength
Pole strengths shall comply with Table 7-1,
Table 7-1:
Standard pole lengths, minimum ultimate loads and torsional capacities
75
7.4.3 Steel Poles/Towers
11.4.3.1 Design
All steel structures shall be manufactured in accordance with industry standards and ISO
certifications in accordance with SANS 121. Steel structures shall be galvanized in order to
protect the structure from corrosion.
11.4.3.2 Paint and Finishing
Painting and finishing shall be in accordance with BS 2569 and SANS 1091. Where the
galvanized coating has been damaged during erection and after all assemblies have been
attached to the structure, zinc metal paint in accordance with BS 2569 shall be applied to the
areas for protection against corrosion.
7.4.4 Stay wires
The stay should be installed in accordance with figure below and carefully backfilled:
Figure 7-1: Stay anchor assembly installation detail
When the stay is installed, the stay wire should be made off in accordance with figure above.
Stayed poles should be so erected that they lean away from the stay position by at least half a
pole diameter at the top. This will ensure correct alignment when the stay is made off correctly.
76
When the stay wire is tensioned using the correct tensioning equipment such as a pull-lift and
come-along clamps, the stay is tensioned until the pole leans towards the stay by at least half a
pole diameter at the top.
No off-cuts of stay wire should be left on site, since these are dangerous to livestock.
7.4.5 Failure Limits of Support Structures:
Type
Supports
Material of elements
All elements, except
guys
Loading mode
Ultimate (breaking)
tensile stress
Yield (elastic) stress
Shear
Compression
(buckling)
90% (elastic) shear stress
Non elastic deformation
from //500 to //100
Tension
Lowest value of:
 yield stress(70% to 75
% UTS)
 deformation
corresponding to 5%
reduction in tower
strength
 need to readjust
tension
Ultimate tensile stress
Moments
1% of non-elastic
deformation at the top, or
elastic deformation that
impairs clearances.
Local buckling in
compression or ultimate
tensile stress in tension.
Compression
(buckling)
Non elastic deformation
from //500 to //100
Shear (breaking) stress
Moments
3% of non-elastic
deformation at the top, or
elastic deformation that
impairs clearances.
Local buckling in
compression or ultimate
tensile stress in tension.
Steel
Poles
Wood
Compression
(buckling)
Concrete
Failure limit
Tension
Lattice towers, selfsupporting or guyed
Steel guys
Damage limit
Permanent or nonpermanent loads
Non elastic deformation
from //500 to //100
Crack opening after
release of loads, or 0.5%
non-elastic deformation.
Shear (breaking) stress
Collapse by instability
Collapse by instability
Collapse of the pole
NOTE 1 The deformation of compression elements is the maximum deflection from the line joining end points. For elements
subjected to moments, it is the displacement of the free end from the vertical
NOTE 2 / is the free length of the element
NOTE 3 The width of crack for concrete poles to be agreed upon.
7.5
Insulators
7.5.1 General
Long rod, Class A insulators shall be used at all cross arms for medium voltage strain, terminal
and pole mounted transformer structures. The cycloaliphatic long rod, polymer type (silicone
rubber) and porcelain insulator shall be puncture proof and of the type as specified in design
Detail Specifications as approved by the user/utility.
The end fitted attachment shall be of the aluminium alloy clevis and tongue twisted type or
made of hot-dip galvanized forged steel or ductile cast iron, are directly attached to the glassfiber-reinforced plastic (FRP) core rod as in the case of silicone rubber insulators. The insulator
77
shed material shall have a high resistance to tracking by surface leakage currents and operate
normally under adverse weather conditions.
Line post type insulators shall be installed on straight line structures and the insulating material
shall be a cycloaliphatic resin, silicone rubber or porcelain complete with 20mm spindle
including nuts and washers. Line post insulators shall furthermore be of the capless, solid-core
type, be puncture proof, radio interference free and shall display superior performance in
polluted environments. They shall have a basic insulation level of either 135kV or 150kV as
specified in the Detail Specification in accordance with referenced standards. All standards
referenced at the end of this section shall be adhered to.
Glass type insulators shall where possible not be used due to vandalism. However glass
insulators can be used if the service feels it necessary and is in accordance with the relevant
international standards. Glass insulators are permitted in coastal regions up to 40 km in land
from the coastal region, due to corrosion and heavy pollution (of which silicone rubber
insulators off a great resistance to pollution effects).
7.5.2 Electrical design
Insulators together with their fittings shall comply with SANS 60305, SANS 60383, BS EN
60305, BS 3288 and IEC 61109 and shall offer a high resistance to damage, caused by
malicious vandalism. Insulator material shall be cycloalipohatic resin or polymer type such as
silicon rubber based. As an alternative high grade porcelain insulators shall be used. The
flashover and puncture voltages shall not be less than the values stated in the table below.
Insulator flashover voltage, wet and dry, shall be less than the puncture voltage. Shackle
insulators shall be used on all low voltage overhead conductors. The shackle insulators suitable
for mounting to the pole with a D-bracket shall be of the type specified in the Standard
Specification in accordance with the requirement.
7.5.3 Mechanical design
The strength of the insulator shall be such that at the maximum working load of 4kN for line
post insulators and 40kN for strain insulators shall be afforded.
7.5.4 Clamps and conductor fittings
Tension conductor clamps shall be of approved type and shall be as light as possible, and shall
be designed to avoid any possibility of deforming the stranded conductor and separating the
individual strands. All fittings shall comply with the stranded coupling dimensions specified in
the reference standards.
Intermediate pole conductor binding shall be carried out by means of wrap lock ties complete
with neoprene cover. Tension fittings shall be the preformed wire type, specially designed for
the ACSR conductor used together with suitable fittings for securing the tension insulators.
Tension insulator sets and fittings shall be of approved standards to give the minimum required
clearances between the jumper conductor and the rim of the live end insulator units. Adequate
bearing area between fittings shall be provided and “point” or “line” contacts shall be avoided.
All split pins for securing the attachment of fittings of insulator sets shall be of stainless steel
type material and shall be backed by washers. D-shackles between insulator and eye shall be
installed at all strain positions in accordance with SANS 10280.
78
7.5.5 Strain insulators
Strain insulators of the twisted clevis tongue type are required for strain and terminal poles. The
insulators shall be cycloaliphatic resin or high grade porcelain material as specified in the
detailed project specification and the approved national standards. Strain insulators shall be
complete with galvanized clevis pin (to SANS 121) c/w washer and stainless steel split pin (304
s/steel), for preformed dead end. Strain insulators shall be installed and connected to cross-arms
and A-frames, with D- shackles, clevis thimble and preformed dead end for conductor as per
design specifications.
Table 7-2:
Mechanical strengths
Nominal voltage:
Impulse withstand (Minimum)
Mechanical strength (Minimum)
11kV
22kV
33kV
120kV
150kV
180kV
70kN
70kN
70kN
7.5.6 Porcelain disc insulator
High grade porcelain, 70kN mechanical strength. Nominal voltage – 11kV, 22kV or 33kV as
specified in this standard.
7.5.7 Long rod insulator:
Cycloaliphatic long rod, min. failing load 70kN, with clevis tongue twisted arrangement with
corrosion resistant end caps, complete with galvanized clevis pin (to SANS 121) c/w washer
and stainless steel split pin (304 s/steel), preformed dead end type for conductor size as
specified – nominal voltage of 11kV, 22kV or 33 kV as specified.
Silicone long rod insulators are designed to meet the highest requirements in distribution power
systems up to 72 kV. They have high lightning impulse and power frequency withstand voltages
and a long creepage class (> 31 mm/kV). Silicone long rod insulators are available with
mechanical ratings up to Specified Mechanical Load (SML) = 70 kN.
7.5.8 Intermediate insulators
Line post insulators are required for the intermediate poles on A-frames and for staggered
vertical delta configurations. Complete installed and connected to A-frame, with spindles or on
poles c/w spindles, curved washer (50 x 50), spring washer and nuts. A-frame mounting: Short
spindle – Type M2 threaded to 44mm complete with washer, nut and locknut, for mounting
bracket, complete with line tie for specified the specified conductor. Pole-mounting: long
spindle – Type M2 with 178mm shank threaded to 100mm, 250mm for mounting through pole,
c/w curved washer (50 x 50), spring washer and nut. Complete with line tie for specified
conductor.
7.5.9 Porcelain line post insulator
High grade porcelain for 11kV, 22kV or 33kV, 4kN lateral mechanical strength. Complete
installed with line ties for specified conductor.
79
7.5.10 Cycloaliphatic line post insulator
For A-frame mounting cycloaliphatic line post insulator – cantilever failing load 4kN, for M20
spindle – for 11kV and 22kV as specified
7.6
Aerial Guard Earth Wire
For high voltage lines, two longitudinal 18 to 27 mm2 galvanized steel earth wires are to be
provided with 6mm diameter galvanized steel cross lacings. The longitudinal earth wires are to
be located at a horizontal distance outside the conductors of not less than two-thirds of the
vertical distance between the lowest adjacent high voltage conductor and the aerial earth wire,
or 200mm, whichever is the greater. The aerial earth guard wire shall be so placed that all
conductors fall within the shielding angle.
7.6.1 Mechanical Strength of the aerial earth guard wire:
In the case of galvanized steel earth wires of minimum breaking strength in the range 700 MPa
to 1100 MPa, the maximum tension at 15 °C should be such that the stress in the earth wire does
not exceed 180 MPa. This criterion permits the use of tensions (at 15 °C) of the following
percentages of minimum breaking strength:
a).
b).
700 MPa wires: 25 %; and
1 100 MPa wires: 15 %.
Earth wires are often strung to match, approximately, the sag of the conductors, and, when the
conductors are strung to the tension limits recommended for vibration, the earth wire tension
limits stated above are usually not exceeded. If the limits are exceeded, satisfactory performance
can usually be obtained by the addition of a damping device to the earth wires. Because the
conductors generally have a higher thermal expansion coefficient than the earth wire, in cold
weather the clearance between the two will reduce if the line is not operational. This could lead
to flashovers when the line is energized. As an additional safety margin and also to improve the
shield angle at mid-span, earth wires should sag to 85 % of the sag of the conductors.
7.7
Anti-climbs
An anti-climb shall serve as a deterrent to unauthorized persons from climbing support
structures. All support structures for overhead lines or pole mounted transformers shall be fitted
with anti-climbs. These shall be of the nature of steel spikes, barbered wire or razor wire and
come at a height of significant safety. The recommended minimum height shall be not less than
3m above ground, but within standard height clearance from the overhead conductor.
7.8
Cradle Catch nets
At points of crossing overhead lines of system voltage of 11kV and 33kV at major commercial
roads, rail lines and other voltage power lines, a catch net shall be provided under the overhead
lines with the highest system voltage at not less than 1.2m without bleaching clearances of the
other voltages.
7.9
Red Balls
80
Where there is extreme aviation proximity with power overhead lines, visible red balls will be
placed on over the conductors in that vicinity as per guidance of relevant standards.
7.10 Goal posts
For 11kV and 33kV overhead lines heavy machinery crossings, goal posts will be erected at the
designated crossing point for that machinery under the overhead lines.
7.11 Pole Mounted Equipment
7.11.1. Switches
7.11.1.1. Line Isolation Switch
Isolators shall comply with the requirements of IEC 60129 and IEC 60265-1. The switch shall
be of the triple pole, gang operated, rocking type, spring assisted manually operated preferably
having hinged blades and front connections and shall be capable of breaking full load current at
a power factor 0.7 leading. The isolators shall be capable of making the system fault current
specified in the Technical Schedules, without damage to the equipment or danger to the
operator.
7.11.1.2. Isolator with Earth Switch
The equipment shall comprise a line isolator integral with an earth switch and shall be suitable
for pole mounted operation.
The line isolation switches shall be fitted with approved type three phase earthing switches to be
located on either the top or the bottom contact terminals of the switch.
The earth switch shall be of three pole construction, spring assisted manually operated and fully
rated for the system fault rating. The earth switch shall form an integral part of the main switch.
Two independent earthing pads with connectors suitable for the specified size of the earth
conductor shall be provided, one at each end of the switch.
The main switch and the earth switch shall be mechanically interlocked such that it will not be
possible to close the earth switch when the main switch is closed. The rated peak short circuit
current and the rated short time current of the earthing switch.
7.11.1.3. Switch Fuses
Switch fuses shall comply with the requirements of IEC 60129 and IEC 60265 and shall meet
the interrupting current requirements of IEC 282-2.
The design and mounting shall be such as to permit easy operation from ground level using an
operating rod i.e. an operating eye shall be provided on the fuse tube designed for use with a
hook stick.
The fuse holder of a switch fuse shall be dimensionally compatible with a universal fuse link of
corresponding rating.
The main assembly may be mounted on a two insulator base arrangement, the top and bottom
contact sub-assemblies and mounting fitting shall be fitted into the porcelain insulators, the
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upper fixed contacts shall positively latch. Insulators shall be of the solid glazed porcelain type
and be bird proof, they shall meet the electrical and mechanical characteristics of IEC 383 and
provide a minimum creepage distance as specified in SP-GGE-001 and in the Technical
Schedules.
The assembly shall be designed such that the tube can be closed without using undue care even
when the closing force is applied at an angle. The angle of the fuse tube or link relative to the
vertical shall be a minimum of 20o.
The fuse tube shall be capable of accepting IEC/BS EN fuse links.
The toggle mechanism shall provide locking action to protect the fuse link from shock. A
spring assisted flipper shall assist arc interruption by withdrawal of the fuse tail.
The fuse tube cap shall preferably be of the non-expendable type and an arc shortening rod, if
provided, shall be attached to the fuse tube cap.
7.11.1.4. Isolator with Switch Fuse and Earth Switch
The equipment shall comprise a combined 33kV line isolator with switch fuse and earth switch
suitable for pole mounted outdoor operation. The fuse switch arrangement shall be mounted on
the same phase below the line isolator and shall comprise three single pole type expulsion fuses
or drop-out fuses as specified.
7.11.1.5. 11 and 33 kV Fuse Links
11 and 33 kV fuse links shall be general purpose, powder filled, fault limiting fuses and shall
comply with their requirements of IEC 60282 Part 1 and 2 and shall be suitable for use with fuse
isolators to be provided and shall be so rated and shall have such fusing characteristics as to be
suitable for selective operations with the fuse links presently in use on the system.
All current carrying parts of the fuse links shall be on non-ferrous materials, the main
requirements being resistance to atmospheric corrosion.
Each fuse link shall be permanently marked with the following information:Vendor or identifying mark, current rating, type designation (e.g. K or T).
The switch fuse mechanical arrangement shall allow for any rating or dimension of the fuse,
within the standard design of the isolator including modifications required, if any.
7.11.1.6. Drop Out Fuses and Line Links
These shall be single phase pole mounted link stick operated. They shall be provided on pole
mounted transformer supplies and on overhead line Tee-Offs at 11kV and 33kV.. The mounting
arrangement shall be as detailed in the attached detail drawing.
Fusible links shall be designed to carry 150% of their rated current without deterioration of the
fusible element or damage to the cut-out unit in which they are installed. Melting of the element
shall cause the cut-out link to be expelled from the line contacts.
All metallic hardware and components of fuses and links shall be hot-dip galvanised. .
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7.11.1.7. Operating Mechanisms
The switches along with their interlocked earth switches shall be complete with gang/manually
operated switch opening and spring assisted push button triggered closing operating
mechanisms. The mechanism drive and linkage of the isolator shall allow the operating handle
to be mounted about 1.25 metres above the ground and shall be designed to minimize wear and
permit some degree of misalignment of the structure. It shall be as simple as possible
comprising a minimum of bearing and wearing parts. Shaft and pin bearings shall be of selflubricating or dry type and shall be such as to permit easy manual operation by one person even
following long periods of non-operation. The operating rod shall have an insulator insert of
wood (e.g. Permalli) or approved equivalent, the insulating medium used to be stated by the
Contractor.
The mechanism shall provide simultaneous isolation of all three phases and arranged for up‟ON‟ operation.
The closing mechanism shall be a spring assisted manual device designed so that the speed of
operation is independent of the operator. The mechanism shall be of robust construction and
shall be carefully fitted to ensure a quick, smooth simple and effective operation. The time of
operation shall be as fast as possible.
The operating mechanism shall be of substantial construction utilising such materials as may be
necessary to prevent sticking due to rust or corrosion. The ganged switching mechanism shall
be provided with sufficient adjustment to allow for final alignment of the switch blades for
simultaneous operation. Adjustable stops shall be provided to prevent over travel in either
direction.
It shall not be possible after final adjustment has been made, for any part of the mechanism to
be displaced at any point in the travel sufficiently to allow improper functioning of the switch
when the switch is opened or closed at any speed.
The overall design of the mechanism shall be such as to reduce mechanical shock to a minimum
and shall prevent its inadvertent operation due to fault current stresses, vibrations or other
causes. The mechanisms shall be self-locking in both the open and closed position and shall be
of a type that shall operate all three phases simultaneously.
The operating mechanism shall be suitable for manual off operation by means of the operating
handle positioned as specified above on the overhead line structure and push button triggered
“ON‟ operation after the spring is charged using the operating handle.
The operating mechanism and operating handle shall be complete with all supporting
accessories, all brackets, angles, guides or guide bearings or other members as may be required
for attaching the operating mechanism and operating handles to the wood pole structures. All
bearings as required shall be weather protected by means of covers. The lubrication
requirements shall be as specified.
The connecting assembly between the mechanism of the switches and their operating down rods
shall be robust and strong with a positive mechanical connection between linkages to provide
adequate gripping force in order to prevent slipping between the mechanisms during the
operating of the switches.
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7.11.1.8. Accessories
7.11.1.8.1. Counter Balance Springs
These shall be provided as may be necessary for counter balancing the switches to prevent
impact at the end of travel both on opening and closing of the switch/earth switch. The springs
shall be of non-rusting alloy.
7.11.1.8.2. Earthing Pads
Each pole of the switch shall be provided with two earthing pads of non-corroding material at
opposite ends, brazed to the supporting base. Flexible copper earth connectors shall be provided
for connecting operating handles of switches/earth switches to the earthing system.
7.11.1.8.3. Position Indicator
A mechanical position indicating device shall be provided for each switch/earth switch.
7.11.1.8.4. Padlocks
The operating mechanism of each switch and the earth switch shall be provided with facilities
for locking the switch in the “OPEN” or “CLOSED” position. The facilities include those for
the spring charging handle and the closing push button.
7.11.1.8.5. Name Plate
A weather proof and corrosion proof name plate shall be provided on the switches, and the
operating devices. The name plates shall conform to IEC standards.
7.11.1.8.6. Live Line/Earthing Clamp Support
In order to carry out live line maintenance, clamp supports to receive a live line clamp and an
earthing clamp shall be provided adjacent to bottom terminal of line isolation switches and,
when equipped, at the bottom terminals of the fuses.
Necessary extension of the terminals shall be provided in order to enable proper support of the
clamps as described above. The extension shall be at least 150 mm long and shall have a 16
mm diameter hole to suit the dimension the cable lug to which connection shall be made.
7.11.2. Fencing off
All substations and pole mounted units shall be fenced off and locked out to avoid unauthorized
access to the structures.
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8.
UNDERGROUND DISTRIBUTION SYSTEMS
8.1.
Components
8.1.1. Cables
Cables shall be selected based on their suitability for the terrain and current carrying capacity
and shall be compliant to ZS 688.
8.1.1.1. Cable accessories such as glands, bolts and fasteners:
8.1.1.1.1. Cable Glands:
A gland is a cable terminating fastener used on armoured cable which may or may not include a
metallic inner sheath or screen, but shall be so constructed that provision is made to ensure
electrical earthing continuity between the armour of the cable and the metallic structure of the
enclosure to which the gland may be attached.
For further reference please make reference to SANS1213 and IEC 60079.
8.1.1.1.2. Bolts and nuts:
All metal parts shall be secured by means of bolts and nuts whose minimum diameter shall be
12mm. All bolts, nuts and screw threads shall comply with SABS 135 (there is no SANS
equivalent) and galvanized in accordance with SANS 121 unless otherwise approved. Bolts and
nuts shall be of steel with hexagonal heads. The nuts of all bolts for attaching to the tower plats,
brackets or angles supporting insulator sets or droppers to earth conductor clamps shall be
locked by approved means. No screwed threads shall form part of the shearing plane between
members. Unless otherwise approved, all bolts and screwed rods shall be galvanized including
the threaded portions; all nuts shall be galvanized with the exception of the threads, which shall
be greased. When in position all bolts or screwed rods shall project through corresponding nuts,
but such projection shall not exceed the diameter of the actual bolt.
Where different grades of steel are used, bolts of any given diameter and length shall conform to
the same grade of steel.
8.1.1.1.3. Junctions/Joints:
8.2.
All joints shall comply with IEEE 404, IEC 60840 and SANS 10198-9 to 11.
Trenches:
Cables of voltages above 600V shall be buried at a minimum depth of 1000mm below ground
level and cables for voltages below and including 600volts shall be buried at a minimum depth
of 800mm..
Trenches shall not be less than 300mm wide for single and multiple LV service connection
cables, and the trench width shall be increased where more than two LV feeder or service
connection cables are laid together so that the cables may be placed at least 150mm apart
throughout the run. Cables installed in earth trenches shall be laid on a bedding of sand or soil
free of stones, and covered with the same material to a depth of at least 100 mm. Special
constructions of cables can be chosen, if necessary, to protect against chemical effects. Cable
routes shall be identified with cable route markers – SANS10142-2;
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Streetlight cables buried in trenches under un-tarred roads shall be buried in a trench with
minimum depth of 600mm and 300mm wide. Trenches under tarred roads shall be buried a
minimum of 500mm deep, and normally in HDPE corrugated sleeving of applicable size,
quantity and required spare quantities. Where the nature of the ground does not permit the
excavation of the cable trenches to the specified depth, the engineer may authorize trenches not
less than 500mm deep. Such authority shall be given in writing. The Contractor must take all the
necessary precautions to prevent trenching work being in any way a hazard to the public, and to
safeguard all structures, roads, railways, sewer works or other property from any risk of
subsidence and damage. Soil type shall be graded.
For further guidance on trenches make reference to IEC 60502, IEC60840, and BS6622.
8.3.
Cable Trays/Racks
This is an assembly of cable supports consisting of cable tray lengths or cable rack lengths and
other system components such as cable tray/rack fittings, support devices, mounting/anchorage
devices and various accessories required to demarcate or segregate the cables, offer cable
retention on the tray/rack and covering devices.
For further guidance on installation, testing and use, please refer to IEC 61537: CABLE TRAY
SYSTEMS AND CABLE LADDER SYSTEMS FOR CABLE MANAGEMENT
8.4.
Cable Route Markers
Cable route markers of approved manufacture shall be provided at each end of an underground
cable route and at all points where such routes deviate from a straight line. Joints in the cable
shall be marked and the maximum distance between route markers shall not exceed 100m.
For underground cabling, above ground route markers shall also be provided at every change of
direction in the routing and at both sides of road or pipeline crossings, except when cable
routing is already indicated by colored concrete pavement.
The cable markers shall be tapered blocks cast from concrete in accordance with approved detail
drawings
Each cable marker shall be buried with its upper face 100mm above the natural ground level.
Marking of cable markers shall also be in accordance with approved detail drawings.
For underground cable marking purposes non‐ corroding strips shall be used, each having
ample length to be wrapped twice around the cable and in which the cable number has been
imprinted by means of letter/cipher punches. For above ground cabling, plastic markers resistant
to the site conditions shall be strapped round the cables.
Tempering with the position of this installed cable markers shall be strictly prohibited and
supported with an inspection and maintenance regime in place for every installation.
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9.
EARTHING AND LIGHTNING PROTECTION REQUIREMENTS
9.1.
General
Every substation shall be provided with an earthing installation designed so that in both normal
and abnormal conditions there is no danger to persons in any place to which they have
legitimate access. The installation must be able to pass the maximum current from any fault
point back to the system neutral without establishing dangerous potential gradients in the
ground or dangerous potential drops between parts of the substation with which a person may be
in a simultaneous contact.
The design shall be such that the passage of fault current through the earthing system does not
result in any thermal or mechanical damage or damage to insulation of connected apparatus and
that protective gear, including surge protection is able to operate correctly. Measures shall be
taken to minimize high “substation potential rise” and “transferred potentials” as necessary.
Such measures are usually necessitated by large earth fault currents, particularly if these occur
in a substation in an area of higher than 250 ohm metres specific soil resistivity.
Substation earthing design shall be based on IEC Recommendations 634-5-54 and IEC 1219 93 The earthing installation shall be designed with earth electrodes as necessary to reduce step,
touch and mesh potentials within the substation to the permissible safe limits. Such potentials at
the substation boundaries and transferred potentials shall also be similarly reduced to safe levels
by approved means.
9.2.
Earthing of Equipment
9.2.1. General
All earth conductors attached to structures shall be fixed by an approved means at
approximately 1 m centres. Bare copper conductors shall not be in direct contact with
galvanised surfaces except at approved electrical joints. Steps shall be taken to ensure
compliance with this requirement which shall be to the approval of the Engineer.
Each item of electrical apparatus shall be connected to the main earth conductor by means of a
separate subsidiary connection. Minor items of plant e.g. small fuse protected motors and field
mounted control equipment etc., may be connected to earth through their associated cable
armour provided that the armouring is connected at each end by copper tape and that the cable
gland is not relied upon for continuity. Any metalwork or chain link fencing around the
substation site shall be adequately earthed in an approved manner.
9.2.2. Earthing system
The earthing system will comprise a network of continuous main copper earthing conductor
installed in and around the substation buildings together with subsidiary and branch copper
conductors to the various items of electrical equipment in the substation. Where the earthing
system is installed outside the substations, it shall be to approval but shall be at a depth not less
than 500 mm.
The main earth conductor shall consist of copper wire or strip of minimum section 95 mm2.
Branch earth conductors shall be 70 mm2 Cu minimum section wire or strip.
87
Cable sheaths may be earthed in groups by a separate branch connection to each item of
equipment in the group with the branch connections being connected by a single subsidiary
connection to the main earth conductor.
9.2.3. Earthing electrodes
Earth electrodes shall consist of round steel-cored copper rods not less than 16 mm diameter.
An earth electrode inspection pit shall be provided at each electrode (or set of electrodes) to
facilitate testing of individual items.
9.2.4. Terminations
The contact faces of earth terminals shall be cleaned before connections are made to the
earthing system.
Earth conductors shall be tinned before being clamped at each earth stud.
When earthing switchgear, connection points shall be positioned not less than 300 mm above
finished floor or ground level and preferably on a vertical plane. Foundation bolts shall not be
used for connections to the earthing system
9.2.5. Guards against mechanical damage
Where earthing conductors are exposed to mechanical damage galvanised sheet steel guards
shall be provided for protection.
9.2.6. Neutral Earthing Resistor
Earthing resistors shall be dry type installed into floor -mounting IP 31 classified hot dip
galvanised steel housing suitable for outdoor service. The resistors shall be complete with lifting
and jacking lugs, access panels, holding down bolts or clamps, high voltage, earth terminals,
connectors and connections as well as with bottom mounting U-bars for erection on the concrete
pad.
Provisions shall also be made for temporary bypassing the resistors with a maintenance earthing
device.. Each resistor shall be equipped with removable link at the earth side for checking the
resistance during bypass.
For connecting the resistors to the neutral, single core XLPE cables (specification see previous
clause) with outdoor terminations shall be used.
9.2.7. Earthing conductor
All grounding (earthing) and bonding conductors shall be insulated stranded copper conductors
unless otherwise specified. The insulation shall be green, green with a yellow stripe or properly
marked with a distinctive green coloring, green tape or stripe or green adhesive label.
9.2.8. Apparatus, Steel Structures and Overhead Shield wires
The frames of all electric apparatus and the bases of all structural steelwork shall be connected
by branches to the earth grid. All disconnector bases, earth terminals, and earthing switches,
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neutral current transformers, lightning arrester bases as well as tower and gantries on which
overhead shield wires are terminated shall be connected to earth grid.
Lightning arresters installed for the protection of transformers shall be connected by direct low
reactance paths both to the transformer tank and to the earth grid.
Capacitor voltage transformers used in connection with the line traps shall be connected by
direct low reactance paths to a single earth rod in addition to the earth grid.
Galvanised steel structures with sufficient area and current carrying capacity may be used as
part of the earth connection to post and strain insulators and to overhead shield wires which
shall be terminated directly on to the steelwork.
9.2.9. Operating Mechanisms and Control Kiosks
Disconnector and earthing switch operating mechanisms and circuit-breaker control kiosks not
integral with the circuit-breakers shall be connected to the earth system by a riser entirely
separate from that employed for earthing the apparatus structures. Such riser shall be connected
to equipotential earth mat which shall be provided beneath the position where an operator will
stand. This mat shall be joined to the earth grid.
9.2.10. Earthing of distribution transformers
The neutral terminals of the transformers shall be connected to earth grid with a bar isolated
from the transformer tank. This busbar shall be tied to the earthing grid via two separate risers.
The transformer tank shall be connected to the earth grid via two separate risers.
The following specifications shall be complimented by the following international and regional
standards, IEEE 80:2000, SANS 10200 and SANS 10292;







The transformer MV surge diverter earth shall be connected to the transformer tank
earthing stud.
The transformer tank earthing stud shall be connected to the MV three point star earth
electrode arrangement with insulated copper earth lead (size dependent on short circuit
rating -70mm2 minimum)
The transformer LV neutral shall be bonded to the transformer tank earthing stud (MV
earth) via a metal oxide valve (MOV) surge diverter to protect the transformer
The transformer LV phase surge diverter earths shall be connected to transformer neutral
bushing.
The transformer neutral bushing shall be connected to the LV three point star earth
electrode arrangement with 70mm2 insulated copper earth lead. This may be directly
from the transformer, or via the distribution kiosk/board earthing bar.
Bare portions of transformer MV and LV earth electrodes arrangements shall be
separated by at least 5000mm, so that the LV earth is outside the resistance area of the
MV earth.
The transformer MV earth electrodes arrangement and bare parts of consumer‟s ECC
shall be separated by at least 5000mm so that the ECC is outside the resistance area of
the MV earth.
89
Where split earthing and combined earthing issues are raised, the following standards shall be
consulted and applied:


SANS 10200:Neutral Earthing in Medium Voltage Industrial Power Systems;
SANS 10292: Earthing of Low Voltage Distribution Systems.
9.2.11. 33/11/0.4 kV substations
The object of an earthing system in a substation is to provide under and around the substation a
surface which shall be at a uniform potential and near zero or absolute earth potential as
possible. The provision of such a surface of uniform potential under and around the substation
ensures that no human being in the substation is subject to shock or injury on the occurrence of
a short circuit or development of other abnormal conditions in the equipment installed in the
yard.
a).
Mesh earthing
Mesh earthing comprises an earthing mat buried horizontally at a depth of about half-a meter
below the surface of ground and ground rods at suitable points. All non-current carrying parts
contribute little towards lowering the ground resistance. The earth mat is connected to following
in a substation:
i).
ii).
iii).
iv).
The natural point of each system through its own independent earth.
Equipment framework and other non-current carrying parts.
The earth point of lightning arresters, capacitive voltage transformers, voltage
transformers, coupling capacitors and the lightning down conductors in the substation
through their permanent independent earth electrode.
Substation fence.
b).
Solidly grounded systems
Solid grounding refers to the connection of the neutral of the power transformer or grounding
transformer directly to the substation grounding or to the earth. The solidly-grounded system is
the most common system arrangement, and one of the most versatile. The most commonly-used
configuration is the solidly-grounded wye, because it will support single-phase, phase-toneutral loads.
Because of the reactance of the grounded transformer in series with the neutral circuit, a solid
connection does not provide a zero impedance neutral circuit. If the reactance of the system zero
sequence circuit is too great with respect to the positive sequence reactance, the objectives
sought in grounding, principally freedom from transient overvoltages, may not be achieved.
First, the system voltage with respect to ground is fixed by the phase-to-neutral winding voltage.
Because parts of the power system, such as equipment frames, are grounded, and the rest of the
environment essentially is at ground potential also, this has big implications for the system. It
means that the line-to-ground insulation level of equipment need only be as large as the phaseto-neutral voltage, which is 57.7% of the phase-to-phase voltage.
It also means that the system is less susceptible to phase-to-ground voltage transients.
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Second, the system is suitable for supplying line-to-neutral loads. The operation of a singlephase load connected between one phase and neutral will be the same on any phase since the
phase voltage magnitudes are equal. This system arrangement is very common, both at the
utilization level as 480 Y/277 V and 208 Y/120 V, and also on most utility distribution systems.
While the solidly-grounded wye system is by far the most common solidly-grounded system,
the wye arrangement is not the only arrangement that can be configured as a solidly grounded
system. The delta system can also be grounded this has a number of disadvantages. The phaseto-ground voltages are not equal, and therefore the system is not suitable for single-phase loads.
And, without proper identification of the phases there is the risk of shock since one conductor.
A common characteristic of all solidly-grounded systems in general, is that a short-circuit to
ground will cause a large amount of short-circuit current to flow. This condition is known as a
ground fault and the voltage on the faulted phase is depressed and large current flows in the
faulted phase since the phase and fault impedance are small. The voltage and current on the
other two phases are not affected. The fact that a solidly-grounded system will support a large
ground fault current is an important characteristic of this type of system grounding and does
affect the system design.
c).
Resistive grounding
One ground arrangement that has gained in popularity in recent years is the high-resistance
grounding arrangement. For low voltage systems, this arrangement typically consists of a wye
winding arrangement with the neutral connected to ground through a resistor. The resistor is
sized to allow 1-10 A to flow continuously if a ground fault occurs.
The resistor is sized to be less than or equal to the magnitude of the system charging capacitance
to ground. If the resistor is thus sized, the high-resistance grounded system is usually not
susceptible to the large transient overvoltages that an ungrounded system can experience. The
ground resistor is usually provided with taps to allow field adjustment of the resistance during
commissioning.
If no ground fault current is present, the phasor diagram for the system is the same as for a
solidly-grounded wye system However; if a ground fault occurs on one phase the system
response is that the ground fault current is limited by the grounding resistor. The faulted phase
voltage to ground in that case would be zero and the unfaulted phase voltages to ground would
be 173% of their values without a ground fault present. This is the same phenomenon exhibited
by the ungrounded system arrangement, except that the ground fault current is larger and
approximately in-phase with the phase-to-neutral voltage on the faulted phase. The limitation of
the ground fault current to such a low level, along with the absence of a solidly-grounded
system neutral, has the effect of making this system ground arrangement unsuitable for singlephase line-to- neutral loads.
The ground fault current is not large enough to force its removal by taking the system off-line.
Therefore, the high-resistance grounded system has the same operational advantage in this
respect as the ungrounded system. However, in addition to the improved voltage transient
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response as discussed above, the high-resistance grounded system has the advantage of allowing
the location of a ground fault to be tracked.
d).
Impedance grounding
In industrial and commercial facilities, reactance grounding is commonly used in the neutrals of
generators. In most generators, solid grounding may permit the level of ground-fault current
available from the generator to exceed the three-phase value for which its windings are braced.
For these cases, grounding of the generator neutral through an air-core reactance is the standard
solution for lowering the ground fault level. This reactance ideally limits the ground-fault
current to the three-phase available fault current and will allow the system to operate with
phase-to-neutral loads.
9.2.11.1. Ground Mounted Substations (33/0.4kV and 11/0.4kV)
A distribution transformer is normally connected in delta-star with the star winding supplying
the load. The neutral point of the star winding is then earthed either directly or through low
impedance. Where a distribution transformer is so connected that no neutral is available
(normally a transformer connected in star-delta with the delta winding supplying the load), an
artificial neutral point is created.
For a transformer which supplies only high voltage motors, neutral is frequently earthed via low
value impedance usually a resistor. This limits the earth fault currents and the voltage rise above
earth at the fault position. Intermediate switchboards and motor control centres are earthed via
the sheath/armoured wires of supply cables or via a separate earth continuity conductor or both.
It is good practice to provide an additional connection to structural steel work at each high
voltage motor by means of either a copper strip or an insulated lead.
9.2.11.2. Pole mounted substations (33/0.4kV and 11/0.4kV)

Where surge arresters are installed:
 The main earth conductor between the surge arrester and the electrode system shall be
as short and straight as possible with no sharp bends.
 Except at locations where it is necessary for an operator to carry out switching
operations, the electrode shall be installed at the base of the pole.
 At locations where it is necessary for an operator to carry out switching operations the
earth electrode shall be installed 5m away from the pole to avoid unacceptable step
potentials close to the operator. Any earth conductor within 5m of the operating
position shall be insulated. The insulated conductor shall be installed inside a PVC duct
to provide additional mechanical protection and insulation. It also serves to maintain
the conductor in a slow bend which improves lightning performance.
 The main earth conductor shall be insulated to a depth of 1m below ground level.
 The earth electrode resistance value shall not exceed 10Ω.
 Aerial Earth Guard Wire
 Arc horns
 Pole leaded Earth wire
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An earth down lead conductor (stranded galvanized steel wire, size ¾.00mm) shall be stapled to
each MV pole in a straight line from 500mm below the lowest conductive part at the top of the
pole to the bottom. The conductor shall not be wrapped around the pole at any point since this
will increase the reactance of the down lead. The interval between staples shall not exceed
500mm
9.2.12. Distribution lines
The permitted earth electrodes are given below.
Note: The use of rod electrodes is preferred but due to practical difficulties, particularly in urban
areas where damage can be caused to other services, cable electrodes are acceptable.
Function
Network
Fault level Electrode
Earth
EPN
Up to 4kA
35mm2 bare Hard drawn stranded copper
cable
SPN
Up to 8kA
70mm2 bare Hard drawn stranded copper
cable
EPN/SPN
All
1m or 1.2m copper clad earth Rods
Electrode
Rod Electrode
o
o
o
The earth rods shall comply with the requirements of SANS 62305-3 with the additions
given below
Earth rods shall comply with the requirements of SANS 1063, and earth electrodes shall be
installed in accordance with the requirements of SANS 10199.
Specific attention is drawn to the requirements for explosive manufacturing and storage
areas (see 12.2).
 Earth mat /and pit
 Refer to IEEE 80 and ECS 06-0023
o
A preformed earth mat (preferred and shown) or an earth mat constructed of bare
conductor shall be:
o
Approximately 1m x 1m in size.
o
Installed directly below where the operator will stand when operating the switchgear.
o
Installed at a depth of 300mm below ground.
o
Connected to the switch handle or control unit.
o
Segregated from all other earthing conductors where possible.
o
Protected above ground by a cable guard.
o
Embedded below ground in earthing compound (two bags below and above) to protect
against theft (preformed mat only).
 Lightning arrestors (line Arrestors) shall refer to IEC 60099 and ECS 06-0023
 Pole mounted lightning spikes shall refer to standard IEC60099-4, SABS171
NOTE: Earthing for premises shall be covered under the Wiring standard
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9.2.13. Fence
Metallic fences shall be connected to earth grid at all supporting posts with 35sq.mm copper
conductor.
The gate shall be connected to an equipotential earth mat
9.2.14. Jointing and bonding
Joints shall have a resistance not exceeding that of an equivalent length of conductor and the
Engineer may require any joint to be tested to prove compliance with this requirement. All
underground connections shall be made by the thermoweld procedure or equivalent. No bolted
clamps shall be used for them.
No drilling of the earth conductor shall be allowed except for jointing or terminating
Joints and connections to the earthing system shall not reduce the current carrying capacity of
the earth conductor and shall be to approval.
Special precautions shall be taken to ensure that the available contact area is fully utilised in all
connections to plant and apparatus.
Connections to plant and equipment shall be carried out by using the earthing terminals
specified.
Stranded earthing conductors shall be terminated with sweated or crimped cable lugs.
9.3.
Lightning protection
Protection against lightning shall be in accordance with IEC 62305
A substation has to be shielded against direct lightning strikes by provision of overhead earth
wires or spikes. This equipment is essential irrespective of the isokeraunic level of the area due
to serious consequences and damage to costly equipment in case substation is hit by a direct
stroke. The choice between these two methods depends upon several factors economy being the
most important consideration. Both the methods have been used sometimes even in the same
station.
Substations shall be provided with overhead earthed screens or spikes in accordance with the
requirements of IEC 62305 to protect against direct lightning stroke to the substation. Down
conductors shall be free of joints and they shall be protected by non-metallic sleeves for a height
of 1.5 m from the ground. Separate down conductors shall be used only when galvanised steel
structure has not sufficient area and current carrying capacity.
Generally an angle of shield of about 45° for the area between ground wires and, 30° for other
areas is considered adequate for the design of lightning protection system.
9.4.
Insulation Co-ordination
Insulation Co-ordination shall be in accordance with IEC 60071-2
94
10.
VOLTAGE REGULATORS
10.1. General
Voltage regulation at the customer metering point shall not exceed:
•
•
+10% for voltages less than 11kV. (Refer to ZS 387-1: 2011)
+5% for voltages greater than or equal to 11kV
Designers of 11 and 33 kV networks shall ensure that under normal feeding arrangements the
11kV design voltage drop shall be less than 5%.
In cases of commercial and industrial customers the overall power factor for loads shall be 0.92
lagging or better, no leading power factor shall be permitted.
10.2. Secondary Transformer Voltage Regulation
10.2.1. Methods of Voltage regulation
10.2.1.1. Line Drop Compensation
Line drop compensation is applied in cases of poor regulation. To some Primary and Grid
Substations, use of this is dependent on the geographical location of the particular substation
and the nature of the circuits it feeds.
During the design of line drop compensations voltage control schemes, system volt drop
calculations for the feeders have to be conducted and the line drop compensation settings
applied accordingly. Distribution substations supplied from the Primary or Grid Substation shall
then have their taps set according to their distance (circuit length) from the source.
NOTE: The presence of embedded generation will affect the operation of Line Drop Compensation
rendering it inappropriate for some 11kV and 33kV networks.
10.2.1.2. Static Balancers
Interconnected Star Balancing Transformers, commonly known as Static Balancers improve
voltage regulation by redistributing some of the neutral current across the phases. They have
proved to be particularly useful on long LV feeders serving small numbers of customers by
improving the load balance.
10.2.1.3.
Voltage Regulators
Where Line Drop Compensation is not appropriate, voltage regulators shall be used.
95
11.
CAPACITORS
11.1. Power Capacitors
The capacitor units or bank are the fundamental part in each power factor correction installation
and/or filter. A thorough study should therefore be performed in order to obtain optimal
capacitor design.
The capacitor current consists of fundamental and harmonic frequency components. As the
magnitude of harmonic components may be very high, especially in a tuned filter, it is necessary
to take them into account when defining rated values of the capacitors.
For filters the voltage increase on the capacitor caused by the series connection of the reactor
should be considered. Refer to IEC61642 (1997).
The capacitor bank is the fundamental part in each filter equipment. A thorough study should
therefore be performed in order to obtain optimum capacitor design.
The filter current consists of fundamental and harmonic frequency components. As the
magnitude of harmonic components may be very high, it is necessary to take them into account
when defining rated data of the capacitors.
The following definitions and designing criteria are specific to filter capacitors:
i).
Rated capacitor voltage, rated capacitor current and tolerances: see the relevant capacitor
standard;
ii).
The ratings of a capacitor should make allowances for element failure or fuse operation
and should co-ordinate with filter protection. During service, if the capacitance change
exceeds the acceptable range for the filter, the filter should be disconnected from the
system. For further reference, refer to IEC61642 (1997).
11.2. Shunt Capacitors
This type of power factor correction installation can be used when it is not necessary to take
measures to avoid resonance problems or to reduce harmonics. This is generally the case when
the resonant frequency given by the network inductance and the capacitance of the power factor
correction installation is relatively high and the harmonic content of the network (i.e. bus
voltage and harmonic currents generated by the loads) is very low.
It should however be understood that the total resulting capacitance of all power factor
correction installations connected to the low voltage side of one distribution transformer
determines the possibility of a harmonic resonance problem. Avoiding such problems when the
power factor correction installation is already in service can be more difficult and costly than at
the original installation time as it is often not possible to re-use existing capacitors, frames, etc.
11.3. Capacitor Banks
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11.3.1 General
This part of the specification covers the design, manufacture, delivery, transportation, and
commissioning of capacitor banks. The capacitors shall be installed indoors or outdoors as
specified along with the related inrush current reactors, switching facilities and protections.
All necessary equipment for the control, protection and supervision of the capacitor banks is
also deemed to be included.
The capacitor bank shall be factory mounted to a maximum possible extent to reduce the work
required at site.
The capacitor banks shall be designed as compactly as possible in order to reduce space
requirements.
The capacitor banks shall be designed for temperature class D (max. 55° C) for outdoor
installation and class B (max. 45° C) for indoor installation.
11.3.2 Capacitor Units
The capacitor banks shall comprise a series of single phase capacitor units suitably designed for
the required total amount of reactive power for the specified frequency and voltage.
The capacitor containers shall be of steel with an adequate corrosion protection. The final coat
shall comply with « light grey ».
The guaranteed minimum values of losses of the capacitor units shall include losses due to
discharge resistors which shall be mounted inside each unit to discharge each unit from peak
voltage to maximum 75 V in less than 10 minutes.
Internal fuses shall be provided in order to limit possible failure to a single capacitor element
only.
The capacitors shall be able to carry continuously 1.3 times the rated current 1.1 times the
maximum system voltage and shall provide continuously 1.35 times the rated output. All the
above requirements shall be fulfilled under maximum ambient temperature.
The dielectric material shall consist of an all film material being suitable to operate the
capacitors on continuous load under the specified ambient conditions. The impregnate shall be
of a hydrocarbon type fluid characterised by high electrical strength and adequate physical and
chemical properties and shall be non-PCB. Oil to conform to IEC 60296-03. Low toxicity is
required and the impregnate shall be a class III B combustible fluid as per IEC 60296-3.
Each capacitor shall have one or two bushings dependent on the mounting arrangement. For
outdoor installation a creepage distance of 50 mm/kV for open rack material or 25 mm/kV for
complete enclosed material and for indoor installation of 25 mm/kV shall be considered.
The arrangement of the fixing and the bushings shall be identical in order to easily exchange
and replace any capacitor element of the total capacitor bank. The terminals for bushings and
fixing elements shall be ISO standard (metric).
97
11.3.3 Capacitor bank
A number of capacitor units shall be combined to capacitor banks in double star arrangement.
The modules shall be arranged as an assembly on suitably designed enclosure and
constructional members of aluminium to avoid any corrosion problem.
The capacitor banks shall include all necessary internal connections and busbars, insulators and
other fittings. The capacitor enclosure structure shall be designed to carry all required unit
capacitors and facilities, and the conductors comprising the incoming and outgoing circuits
under the loadings and factors of safety specified and to give the minimum phase and earth
clearances.
The safe removal and safe replacement of capacitor units shall minimise the dismantling of any
structural member, support, including insulators or main connections.
Where necessary, approved means shall be provided upon the capacitor equipment for the fixing
and bonding of external connections to secure efficient earthing. Steelwork and all items of the
capacitor equipment shall be bonded as necessary with copper straps of adequate cross-section.
In case of outdoor open rack installation tinned copper shall be used.
Approved facilities shall be provided to temporarily earth the connections and apparatus during
maintenance.
11.3.4 Switching Device
11.3.4.1 Source circuit breaker
The …KV Source circuit breaker is excluded from the scope of supply of the multi-stages
capacitor bank equipment. The contractor shall verify with the purchaser that the nominated
source circuit breaker is suitable for capacitor switching duties. Tenderers shall state in their
tender the circuit breaker requirements for the capacitor bank being offered
11.3.4.2 Capacitor switches
Each stage shall be controlled by a suitable SF6 circuit breaker for switching in and out the
respective capacitor stage, according to the capacitive demand required by the system operating
conditions
The tenderer shall provide details of the proposed circuit breaker in his tender, together with
evidence that they are suitable for switching duties and that the circuit breaker and associated
power equipment will not be subject to damaging over-voltages when switching.
11.3.5 Safety Interlocking and Earthing
Interlocking shall be provided to ensure that the access to the capacitor bank enclosure is not
possible until the associated main incoming circuit breaker has been racked and the faulty stage
has been locked out and circuit earth applied.
One earthing switch shall be provided in each capacitor stage and will be placed after the
automatic circuit breaker. For safety raison this earthing switch will be also interlocked with the
main outgoing feeder.
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11.3.6 Reactor and discharge device
11.3.6.1 Current limiting reactor
The transient current that flows on energising shall not exceed the rated making current of the
circuit breaker controlling the capacitor bank stage. If necessary, current limiting reactor shall
be connected in series with each capacitor stage to limit the current to an acceptable value. The
current calculation which flows upon energising shall be declared and shall take into account the
contribution from parallel connected capacitor stages
Current limiting reactors shall be designed for the full system lightning impulse withstand level
The reactor shall be dry air cored, mounted on suitably rated support insulator.
11.3.6.2 Discharge devices
Discharge resistors, suitable to discharge the capacitors from peak rated voltage to less than 75
volt within 10 minutes shall be fitted within the capacitor container. Tenderer shall also propose
suitable fast-discharge devices for consideration that will achieve de-energization in less than 30
seconds
11.3.7 Capacitor Protection
The capacitor banks/units shall be provided completely with its internal and external protection
which is considered as part of the capacitor equipment.. Protection relays shall be of the
numerical type.
11.3.7.1 Fuses
Fuses shall be provided internally for protection of individual capacitor units. The fuses shall
not deteriorate when the capacitor is subjected to discharge testing nor the currents associated
with service operations of the capacitor equipment. Fuses shall only rupture in case the related
unit is subject to failure and shall be capable of breaking the current following a failure of the
capacitor unit without hazard from the fuse or the capacitor. The ruptured fuse of each element
shall withstand indefinitely the voltage imposed across it under all operating conditions.
The remaining capacitor units shall be able to operate within the capacitor bank without undue
disturbance for a present number of unit capacitor failures.
11.3.7.2 Unbalance Protection
Sensitive loss of capacitance and fuse failure detection and alarm facilities shall be provided.
The protection shall comprise two independently adjustable steps with separate alarm and
tripping contacts at each stage. The first stage is set to operate an alarm when a significant
number of capacitor units have failed and the second stage shall initiate tripping after a reset
time delay via a trip relay (block-close function) before the loss of capacitance has resulted in an
unacceptable over-loading of any capacitor. The Tenderer shall submit a table showing the
number of units that can be lost per phase and per series group for a period of 1 month without
derating of the capacitor bank and without reduction in the designed life of the capacitor. The
minimum number of unit capacitors to satisfy these requirements shall not be less than one.
The protection shall be insensitive against inrush and harmonic currents.
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11.3.7.3 Overload and Over-current Protection
For each phase of each capacitor bank an overload and overcurrent protection system shall be
provided to protect the capacitors from excess current (rms), including harmonic currents.
11.3.7.3.1 Overload protection
A first alarm shall be given at a current of approx. 110 to 120 percent of the rated current if
applied for more than approx. 30 min. A second alarm (selectable by links for tripping as well)
shall be initiated at currents of 120 to 140 percent of the rated current suitably time delayed to
avoid spurious alarms (trippings) being situated during short time disturbances.
Each stage of the overload protection shall be independently adjustable.
11.3.7.3.2 Over-current protection
For currents above 140 percent of the rated current a time delayed relay shall be provided to
initiate tripping. An instantaneous element for initiating tripping at currents above 200 percent
of rated current, however properly secured against tripping due to inrush currents shall be added
per phase with separate alarm and trip contacts. Reference is made to the MV over-current
relays specified in Article of these specifications.
11.3.7.4 Over-voltage protection
Suitable over-voltage protection devices shall be provided to control transferred internal and
external over-voltages on the capacitor banks.
11.3.7.5 Loss of Capacitance
Facilities shall be provided to allow for safe, simple and quick identification of defective
capacitor units. Portable test equipment or other means shall be supplied being able to detect
defective units.
11.3.7.5.1 Protection Scheme
The protection scheme shall be designed to isolate the faulted capacitor stage without disruption
to the other stages. Schemes which require tripping the main incoming feeder circuit breaker are
not acceptable.
Over-voltage over-load and unbalance protections may be combined within proprietary relay
designed specifically for protection of capacitor banks.
11.3.8 Capacitor Bank Control
Automatic and manual switching control shall be provided for the different stages. Automatic
control shall be preferably provided by a numerical type of reactive power regulator including
harmonic current supervision and the operating mode of each capacitor bank shall be selectable
via an Auto/ Manual / Off switch. There shall be On / Off push buttons for manual Close/trip.
Manual closing shall only be possible with the selector switch in Manual position. Time delay
facilities shall be provided in the manual control circuit to inhibit any re-closing within a set
delay time. Delay time shall be adjustable over the range of 0-5 minutes.
The automatic control unit will initiate switching f the appropriate number of stages in or out of
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service. The control unit shall select the capacitor stage to be switched in and means shall be
provided to vary the duty cycle to ensure a reasonable distribution of switching operations
between different capacitor stages.
The control system shall provide facility for manual / remote switching out, both locally and
remotely from the control centre. Suitable indications of the status of the capacitor bank shall be
provided locally and made available for signalling to the control centre.
11.3.8.1 Control Panel
A modular panel housing the individual and master controllers is required to be supplied and
will be installed in the control room of the substation. The enclosures shall provide at least IP42
protection to the control equipment.
The capacitor bank will be controlled by a logic control scheme as specified in section below:
11.3.8.2 Controller
The controller shall automatically switch off the Capacitor Banks in the event of loss of the
system supply where applicable. The scheme must be capable of re-starting automatically
following restoration of supplies.
The automatic sequence of switching IN/OUT of the capacitor units in stages shall be controlled
by a programmable logic controller of the power factor controller (PFC).
The switching sequence shall be coordinated with the logic control of the sub-station device and
Voltage Control (VC) device, and these shall be selectable from manual selection facilities. The
switching steps shall be programmable to achieve switching of capacitor sub-banks through
stage controlled circuit breaker.
11.3.9 Power Factor Control
Where applicable, The PFC relay/equipment shall have a range suitable for proper selection of
switching In/Out of the Sub-banks to maintain the Target Power Factor via the PLC.
The relay PF setting range shall be:
The relay shall have as a minimum a digital display of PF, Target PF, Operation Time Delay,
voltage and current.
11.3.10 Testing
Each capacitor unit shall be routine tested to IEC 60871-1&2. Type test certification according
to IE C60871-1&2.
Type test evidence in lieu of tests shall only be accepted on units of identical construction and
similar rating to those proposed for this application.
Other equipment associated with that capacitor banks shall be subject to routine tests to the
relevant IEC standard.
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12.
FEEDER PILLAR
12.1. General
12.2. Specification for Feeder Pillars
12.2.1 General
12.2.1.1 Weatherproof Housing
The weatherproof housing shall be manufactured from sheet steel or other approved material
and designed for ground mounting on a flat base or pier at or slightly above ground level. Fixing
holes shall be provided complete with M16 foundation bolts. It shall be of a totally enclosed
design with cables entering from the bottom. The housing shall be arranged for front access only
by means of side hinged doors which shall be fitted with an internal document holder and a
locking bar to secure them top and bottom. The locking bar shall be operated by a central handle
which shall be lockable by means of a padlock.
The housing shall be dust and vermin proof but adequate ventilation shall be maintained to
permit natural circulation of filtered air.
Provision shall be made for the installation of an electrical heating device to prevent
condensation within the housing. Such heaters shall be of the metalclad convection type and
shall be continuously rated complete with fuses and control switch.
12.2.1.2 Incoming Cables, Links, Busbars and Conductors
Links, busbars and conductors shall be manufactured from hard drawn high conductivity copper
and arranged for access from the front only. The busbars must be fully shrouded.
Phase cables shall be connected to the distribution board busbars by pole operated hinged slow
break links. The neutral connection shall be made by means of a bolted copper link. Links shall
be of the same current rating as the associated busbar.
Busbar support insulators shall be capable of withstanding rated short circuit conditions without
undue stress and be resistant to mechanical shock and vibration however caused.
12.2.1.3 Distribution Circuits
Each distributor board shall be equipped for the number of 3 phase, 4 wire distributor circuits as
specified by the purchaser. Each phase circuit shall be controlled by high rupturing capacity
cartridge type fuse links which conform to IEC 60282 part 1&2;1994. Insulated dividing
barriers shall be provided between phase contact assemblies and phase and neutral contact
assemblies which shall make it impossible to insert a fuse link between contacts of different
phases.
12.2.1.4 Instrument Panel
The accessories to be provided on each distribution board are specified by the purchaser.
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12.2.1.5 Future Requirement
The feeder circuits shall be so designed that additional current transformers can be easily
incorporated so that separate kilowatt hour meters can be installed to record the consumption in
each feeder.
12.2.1.6 Cable Glands
Each item of equipment shall be supplied with a complete set of screw type compression cable
glands suitable for outdoor use with those cables specified in the schedules. Each gland shall be
capable of carrying the short circuit current rating of its associated cable and be provided with
such fittings necessary for fixing in an untapped entry hole.
12.2.1.7 Cable Termination Lugs
Each item of equipment shall be supplied with a complete set of termination lugs and fixing
bolts for the types of cables specified by the purchaser.
12.2.1.8 Fuses and Fuse Carriers
12.2.1.8.1 Fuses for Distributor Circuits
The fuse links shall be in accordance with the requirements 0f IEC 60269 having single tag
contacts for insertion into spring loaded contacts. Each distribution pillar shall be provided with
an insulated fuse removal device.
The nominal rating of the fuses shall be one of the standard values within the range 125 A to
400 A. Within this range the fuses shall be of the same physical dimensions irrespective of the
rating.
12.2.1.8.2 Fuse links
All fuses shall be of appropriate duty, category and conform to IEC 60269. They shall be fully
interchangeable with those of any other make which conform to the dimensions described in
IEC 60269.
The fuse links shall be fitted with striker-pins to actuate the common trip-bar of the fuse switch.
12.2.1.8.3 Fuses for Auxiliary Supply
Fuse carriers for auxiliary circuits shall be of the withdrawable handle insulator type with a
rating of 60 A and shall accommodate cartridge type fuse links of 15 A, 30 A and 60 A ratings.
The fuse links shall conform to IEC 60269.
12.2.1.9 Enclosures
To conform to IEC 60529 (Degrees of Protection for Enclosures)
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13.
SUBSTATION CONCRETE WORKS
13.1
General
This section covers the construction of cast in-situ reinforced concrete slabs and plinths onto
which mechanical/electrical equipment is to be fixed, concrete slabs used for the protection of
cables as well as grouting and screeding.
13.2
Substation equipment plinths
13.2.1
Concreting
All concrete units will be solidly formed using concrete and steel reinforcing as indicated on
drawings which will be submitted to the engineer for approval within 30 days of the contract
having been awarded. Drawings will be submitted in threefold. Each unit will have rectangular
sides.
In general the edges of pockets for holding-down bolts or the centre-lines of holes drilled for
expansion bolts will not be closer than 100 mm to any concrete edge. The concrete unit will
furthermore be designed to be adequate to carry and distribute all live and imposed loads.
For concrete units to be constructed in situ, the excavation will be made 600 mm wider than the
outside dimensions of the unit and to a minimum depth of 200 mm below the lowest point of the
finished ground level (measured along the perimeter of the concrete unit). The bottom of the
excavation will be levelled and compacted to 93% of modified AASHTO density. A 50 mm
thick level concrete blinding layer will be cast covering the entire bottom of the excavation and
will be allowed to set for at least one day, after which the construction of the concrete unit
(fixing of reinforcement, erection of formwork, casting of concrete, etc) will take place. The top
of the concrete unit will protrude for a minimum of 200 mm above the highest point of the
finished ground level (measured along the perimeter of the unit). No concrete will be cast
without the engineer having had the opportunity to inspect and approve the formwork and
reinforcing. The formwork will not be removed before 7 days, and installation of
mechanical/electrical equipment will not commence until 28 days after the concrete have been
cast.
For concrete units constructed on floors which have been constructed by others, adequate
dowelling and bonding of the surfaces of the concrete unit and the existing floor will be
included.
13.2.1.1 Concrete mix
The following concrete mix will be used:



Cement (dry)
Clean dry river sand
Crushed stone (10 mm)
1 part per volume
3 parts per volume
6 parts per volume
The concrete will have 28-day minimum cube strength of 10 MPa.
13.2.2
Reinforcing
Standard brick force as used in 230 mm brick walls will be used as reinforcing and will be
indicated on the drawings.
104
All reinforcing will be inspected by the engineer prior to the concrete being cast.
13.2.3
Grouting
Grout under base plates and machine bases which are subjected only to gravity loading shall
consist of 1:1 sand, cement semi-dry mortar well caulked into the grouting space, unless
otherwise specified by the supplier of the equipment. The relevant concrete surfaces shall be
prepared by scrabbing and cleaning them. The mortar grout shall consist of an approved mixture
of cement, sand, water, and admixture, and shall be so rammed under each base or bedplate (as
applicable) that all voids and pockets are completely filled around the bolt or between the top of
the concrete and the underside of the metalwork, and, in the case of a base or a bedplate, that the
grout projects beyond the base or bedplate. After the void has been completely filled, the edges
of the mortar grout shall be trimmed at an angle of 45 outward from the bottom edges of each
base or bedplate and the trimmed edge wood-floated to a neat finish.
Grout used in bolted fastenings which are subjected to tensile, shear and/or vibration loads shall
be an approved epoxy mortar well caulked into the grouting space, bolt hole pocket or sleeve,
unless otherwise specified by the supplier of the equipment.
13.2.4
Dimensions
The dimensions shall be as indicated on the drawings provided.
13.2.5
Finishing
At all corners that are exposed after backfilling, the concrete will be chamfered 25 mm x 25
mm. The concrete will be well vibrated to eliminate cavities or honeycombing. Unformed
horizontal surfaces (top of concrete) will be floated with a wooden trowel to render a uniform,
skid resistant, horizontal surface.
13.2.6
Testing of Concrete
A sample from each batch of concrete will be taken by the Engineer or his representative for
testing purposes.
13.3
Oil containment tanks
(Definition - Refers to a vessel made from concrete or masonry that is usually wholly or
partially buried, that provides containment of lost oil and can also be an oil/water separator.)
13.3.1
Bund Walls
Bunds shall be designed to contain spillages and leaks of liquids used, stored or processed above
ground and to facilitate clean-up operations. As well as being used to prevent pollution of the
receiving environment, bunds are also used for fire protection, product recovery and process
isolation
105
14.
WAYLEAVE
The requirements for the acquisition, management and operation of wayleaves shall be in
accordance with the Zambian Wayleave Code of Practice.
Notwithstanding the provisions of the Wayleave Code of Practice the following requirements
shall also apply:
14.1. General Requirements
General requirements relating to access to land and premises by a Distribution System Operator
are as follows:
14.1.1
Occupational staff and contractors acting for an electricity utility company will be
briefed on their responsibilities before entering private lands (or premises) or dealing
with owners.
14.1.2
The electricity utility company will take reasonable steps to contact the owner of the
land (or premises) before entering private lands (or premises). The company staff or
contractors will carry identification cards and produce this to the owner of the land (or
premises) when introducing themselves.
14.1.3
The owners of land (or premises) will be dealt with honestly and fairly.
14.1.4
Queries from the owner of the land (or premises) will be dealt with promptly and
courteously.
14.1.5
Company staff or contractors will only enter lands or premises for legitimate purposes
related to its licensed activities including surveying, maintenance, construction and
meter reading.
14.1.6
Company staff and contractors will take due care and attention to minimize land
damage by crews and equipment.
14.1.7
Due care and attention will be taken to minimize the risk of spreading any disease to or
from farmland.
14.1.8
Company staff and contractors will take reasonable steps to ensure that land (or
premises) is left in as good (or better) state than when Company staff or contractors
arrived.
14.1.9
Company staff and contractors will endeavor to ensure that restrictions on the use of
the land (or premises) during construction are minimized.
14.1.10 In the event of queries from the owner of the land (or premises) for further information,
a contact telephone number for the company will be advised to allow for such queries
to be dealt with.
14.2.
14.2.1
Specific requirements
Staff shall take great care to close all gates behind them and not to damage
excessively fences or hedges. Any non-self-restoring damage done to fences or
hedges shall be made good by company staff within one month of agreement and any
damage which requires urgent attention shall be made good or rectified within one
week of notification.
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14.2.2
Trial holes in advance of the main construction programmes, where necessary, shall
be opened only after consultation with the landowner. The method of carrying out this
work, shall be such as to cause the least disturbance. The trial holes shall either be
opened and filled in on the same day or made safe with fencing. The topsoil shall be
stacked to one side separately for reinstatement when refilling the hole. The subsoil
shall be properly compacted and the topsoil spread over it neatly. Rock and other
debris thrown up by the excavation shall be removed off the site by company staff.
Stones thrown up by the excavation shall be removed from the surface.
a). Before any construction work commences, a representative from the electricity
company will discuss the entry routes for construction and as far as possible give
the landowner the proposed programme of work and the date of commencement
of work.
b). Company representatives shall leave with the owner of land or premises, the
name and address of the person to be contacted in the event of any queries arising
out of the company‟s activities on the land or premises.
c). Where construction work is to take place and the entry routes have been agreed,
if the landowner requires, the agreed route shall be outlined by posts placed at
suitable intervals. These marking posts shall not be required in the case of single
entry, such as for wood
d). pole erection but must be provided, in the case of multiple entries such as
concreting operations.
14.2.3
The electricity company will cut up any trees that may be felled into transportable
lengths and bring them to the farmyard or other adjacent storage place. The company
shall dispose of rubbish and all debris from hedge and tree cutting caused by its
activities during line construction and maintenance operations. The landowner or his
representative shall be notified in advance of entry by the company for purposes of
hedge trimming and tree cutting in connection with line construction and
maintenance.
a). Fences shall be provided by the company as necessary for the protection of
persons, animals or crops and to prevent trespass. It must conform to the
reasonable requirements of the landowner. The type of fencing should depend on
its location, purpose and its expected stay in a particular location.
b). If a fenced off area crosses existing farm pathways or roadways, or other access
routes required by the landowner, the company shall provide a means of crossing
them to the reasonable requirements of the landowner, for passage of persons,
machinery and livestock.
c). All permanent pathways and roadways affected by the construction shall be
restored to their original condition before construction started or alternative
arrangements agreed.
d). Before construction work or trial boring operations commence, the landowner
shall notify the company insofar as he knows of the position, type and size of all
underground services, pipelines, drains and wells.
e). All watercourses and water supplies must be protected against pollution arising
107
f).
g).
h).
i).
j).
14.3.
from the work. All proper steps shall be taken to avoid any interference with
water supplies.
Where construction work interferes with drainage or septic tanks, these facilities
shall be maintained by the electricity company with the minimum of interruption
during the course of the work and the landowner shall provide all necessary
access facilities to enable the company to do so. They shall be subsequently
restored to the satisfaction of the landowner or an alternative equivalent service
provided.
All ditches, open drains or watercourses interfered with by the works shall be
maintained in effective condition during construction and finally restored to as
good a condition as before the commencement of works.
In excavation where rock has been removed from the foundations, priority shall
be given to the removal off site of broken rock where it is surplus to back filing
requirements, if required by the landowner.
On completion of works, the company shall remove all temporary buildings,
roadways, surplus soil, stone or gravel and any debris such as trees, brush woods
and any material that does not naturally belong on the site and was brought there
through the operations of the company.
The utility company, after consultation with the landowner, shall take all
necessary precautions to prevent the straying of livestock.
Prevention against Animal diseases
14.3.1 The utility company shall comply with any regulation which may be necessary in
connection with any Disease Eradication Scheme. The company shall ensure that the
local District Veterinary Officer is informed of the entry of company vehicles on farms
with a disease problem and that the Epidemiology Unit of the Department of Agriculture
is made aware of the company activities in a TB affected area.
14.3.2 Where possible the company shall not drive machinery through farmyards or other
places where there is an accumulation of animal manure. If this is necessary, the
company shall take adequate precautions to disinfect vehicles before and after entering
the land, especially on farms with a disease problem (or with neighbouring farms having
a disease problem), or where the company vehicles have recently been in a farm with a
disease problem.
108
15.
LONG-TERM PRESERVATION OF SUPPORT STRUCTURES FOR
DISTRIBUTION INFRASTRUCTURE
15.1
Painting
The following paint and treatment shall apply to the listed types of poles;
Type of Poles
Paint and treatment
Exceptions (aviation
purposes)
Wooden Poles
Creosote
(preservative)
Signal red and white
Concrete poles
Gray
Signal red and white
Steel poles
Admiral gray
Signal red and white
15.2
Concrete Poles
Concrete poles shall maintain the natural colour. Install reflective barrier for concrete poles in
close proximity to roads. Concrete shall be manufactured in line with SANS 470
15.3
Steel Poles
The Steel poles shall be hot dip galvanized in accordance to relevant Standards
Install reflective barrier for steel poles in close proximity to roads
15.4
Steel Structures for Outdoor Substations
Steel structures shall be hot dip galvanized in accordance to a relevant standards e.g. ZS
COMESA 293 AND IEC 61400.
109
APPENDICES
APPENDIX 1:
INFORMATION REQUIRED WITH TRANSFORMER ENQUIRY
AND ORDER
A.1 Rating and general data
A.1.1 Normal information
The following information shall be given in all cases:
a).
b).
c).
d).
e).
f).
g).
h).
i).
j).
k).
l).
m).
n).
o).
p).
q).
r).
s).
t).
Particulars of the specifications to which the transformer shall comply;
Kind of transformer, for example, separate winding transformer, auto-transformer
or booster transformer;
Single or three-phase unit;
Number of phases in system;
Frequency;
Dry-type or oil-immersed type. If oil-immersed type, whether mineral oil or synthetic
insulating liquid. If dry-type, degree of protection (see IEC 60529).
Indoor or outdoor type.
Type of cooling.
Rated power for each winding and, for tapping range exceeding ± 5%, the
specified maximum current tapping, if applicable.
If the transformer is specified with alternative methods of cooling, the respective lower
power values are to be stated together with the rated power (which refers to the most
efficient cooling).
Rated voltage for each winding
For a transformer with tappings:
–
which winding is tapped, the number of tappings, and the tapping range or tapping
step;
–
whether 'off-circuit' or 'on-load' tap-changing is required;
–
if the tapping range is more than ±5 %, the type of voltage variation, and the
location of the maximum current tapping, if applicable.
Highest voltage for equipment (Um) for each winding (with respect to insulation,
see IEC 60076-3).
Method of system earthing (for each winding).
Insulation level (see IEC 60076-3), for each winding.
Connection symbol and neutral terminals, if required for any winding.
Any peculiarities of installation, assembly, transport and handling. Restrictions on
dimensions and mass.
Details of auxiliary supply voltage (for fans and pumps, tap-changer, alarms, etc.).
Fittings required and an indication of the side from which meters, rating plates, oil-level
indicators, etc., shall be legible.
Type of oil preservation system.
For multi-winding transformers, required power-loading combinations, stating, when
necessary, the active and reactive outputs separately, especially in the case of multiwinding auto-transformers.
110
A.1.2 Special information
The following additional information may need to be given:
a).
b).
c).
d).
e).
f).
g).
h).
i).
j).
k).
l).
m).
n).
o).
p).
q).
r).
s).
If a lightning impulse voltage test is required, whether or not the test is to include
chopped waves (see IEC 60076-3).
Whether a stabilizing winding is required and, if so, the method of earthing.
Short-circuit impedance, or impedance range (see annex C). For multiwinding transformers, any impedances that are specified for particular pairs of
windings (together with relevant reference ratings if percentage values are given).
Tolerances on voltage ratios and short-circuit impedances as left to agreement in table
1, or deviating from values given in the table.
Whether a generator transformer is to be connected to the generator directly or
through switchgear, and whether it will be subjected to load rejection conditions.
Whether a transformer is to be connected directly or by a short length of overhead line
to gas-insulated switchgear (GIS).
Altitude above sea-level, if in excess of 1 000 m (3 300 ft).
Special ambient temperature conditions or restrictions to circulation of cooling air.
Expected seismic activity at the installation site which requires special consideration.
Special installation space restrictions which may influence the insulation clearances
and terminal locations on the transformer.
Whether load current wave shape will be heavily distorted. Whether unbalanced threephase loading is anticipated. In both cases, details to be given.
Whether transformers will be subjected to frequent overcurrents, for example,
furnace transformers and traction feeding transformers.
Details of intended regular cyclic overloading other than covered by 4.2 (to enable the
rating of the transformer auxiliary equipment to be established).
Any other exceptional service conditions.
If a transformer has alternative winding connections, how they should be changed,
and which connection is required ex works.
Short-circuit characteristics of the connected systems (expressed as short-circuit
power or current, or system impedance data) and possible limitations affecting
the transformer design (see IEC 60076-5).
Whether sound-level measurement is to be carried out (see IEC 60551).
Vacuum withstand of the transformer tank and, possibly, the conservator, if a specific
value is required.
Any special tests not referred to above which may be required.
A.2 Parallel operation
If parallel operation with existing transformers is required, this shall be stated and the
following information on the existing transformers given:
a) Rated power.
b) Rated voltage ratio.
c) Voltage ratios corresponding to tappings other than the principal tapping.
d) Load loss at rated current on the principal tapping, corrected to the appropriate reference
temperature.
e) Short-circuit impedance on the principal tapping and at least on the extreme tappings, if
the tapping range of the tapped winding exceeds ±5 %.
f) Diagram of connections, or connection symbol, or both.
NOTE
On multi-winding transformers, supplementary information will generally be
required.