Guide to Power Transformer
Specification Issues
www.epecentre.ac.nz
Electric Power Engineering Centre – Guide to Power Transformer Specification Issues
Edition 2, January 2009
DISCLAIMER
This document was prepared by the Electric Power Engineering Centre (EPECentre) at the University of Canterbury
in Christchurch, New Zealand. The content included in this document is based on a power transformer specification
workshop held in July 2007. The EPECentre takes no responsibility for damages or other liability whatsoever from the
use of this document. This includes any consequential damages resulting from interpretation of material.
Electric Power Engineering Centre, University of Canterbury
Published by Electric Power Engineering Centre (EPECentre), University of Canterbury
1st Edition 1, August 2007 [revised January 2008]
Reviewed & edited by: Wade G. Enright BE(Hons), PhD, MIPENZ, MCIGRE
Produced & co-edited by: Joseph D. Lawrence BE, MEM, PMP, MPMINZ, MNZIM
Acknowledgements: Sponsors and participants of the EPECentre Power Transformer Conference 2007, Workshop:
Guide to Transformer Technical Specification, 3 July 2007, University of Canterbury, Christchurch, New Zealand
Electric Power Engineering Centre
University of Canterbury
Private Bag 4800
Christchurch
New Zealand
T: +64 3 366 7001
E: info@epecentre.ac.nz
www.epecentre.ac.nz
© 2008 Electric Power Engineering Centre, University of Canterbury, Christchurch, New Zealand. All rights reserved,
no part of this publication may be reproduced or circulated without written permission from the Publisher.
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Electric Power Engineering Centre – Guide to Power Transformer Specification Issues
Edition 2, January 2009
Electric Power Engineering Centre -
GUIDE TO POWER TRANSFORMER
SPECIFICATION ISSUES
CONTENTS
FOREWORD ...................................................................................................................................3
INTRODUCTION .............................................................................................................................4
SETTING THE SCENE....................................................................................................................6
PART 1. FIRE & EXPLOSION PROTECTION ................................................................................7
PART 2.THE DETAILED DESIGN REVIEW ...................................................................................9
PART 3. TECHNICAL SPECIFICATION EXPERIENCES ............................................................11
APPENDIX A. REFURBISHMENT & REPAIR OF POWER TRANSFORMERS*…………………13
APPENDIX B. DRIVEN FACTORS FOR TRANSFORMER LONG LIFE** ………………………..30
APPENDIX C. EPECENTRE ELECTRIC POWER R&D CAPABILITY ......………………………..92
* Courtesy of Transfield Services Limited ©
** Courtesy of Pauwels Trafo Asia Limited ©
2
Electric Power Engineering Centre – Guide to Power Transformer Specification Issues
Edition 2, January 2009
FOREWORD
Tēnᾱ koutou te whᾱnau,
Nga mihi ki koutou mana, koutou korero, koutou whakaaro,
koutou awhina. Kua mutu te wᾱnanga. No reira tēnᾱ koutou,
tēnᾱ koutou, tēnᾱ koutou katoa.
The power transformer technical specification workshop is
completed. Thank you to all that attended, for your
presence, discussions, thoughts and support.
Australasia is currently most active in the processes
associated with purchasing power transformers. July 2007
was a good time to peer review some important
components within this process, and some of the present
practices. It was also fantastic to have representatives from
Indonesia, France, Australia and Aotearoa involved in the
workshop.
The
Electric
Power
Engineering
Centre
(EPECentre) has prepared a summary of the workshop for
each of you, enjoy.
Hei kōna,
Dr. Wade Enright and Prof. Pat Bodger (EPECentre
Director) pictured with the 15kVA, single phase, prototype
superconducting transformer, designed and built at the
University of Canterbury in Christchurch, New Zealand.
Wade Enright
Dr. Wade G. Enright
Associate, Electric Power Engineering Centre, University of Canterbury
August 2007
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Electric Power Engineering Centre – Guide to Power Transformer Specification Issues
Edition 2, January 2009
INTRODUCTION
Power Transformer Technical Specification
During 2006 and 2007 to date, an unusually high number of requests have arrived for Technical Specification
reviews, both in New Zealand and Australia.
More than six power transformer Technical Specifications for machines over 200MVA in New Zealand alone.
The challenges of a significantly loaded electrical network reliant on service aged equipment: refurbish and/or
replace.
The challenges of increasing load and “new” generation types e.g. wind turbines.
The commodity price issues (copper, electrical steel, structural steel and oil).
The changes from well established European factories to new South East Asian manufacturing sites.
The need for form relationships with new people (new manufacturer personnel, new employers/clients).
It may be that power transformer Technical Specifications has become cumbersome, out of focus and needs a
“spring clean”.
The peer review process: are our ideas good ones?
Published Documents
Published documents that contain guidelines specific to power transformer Technical Specification:
CIGRE Working Group 12.15., “Guide for Customers Specifications for Transformers 100MVA and 123kV and
above”, Technical Brochure 156, April 2000.
ABB, “Transformer Handbook”, ABB Power Technologies Management Ltd, 2004.
Heathcote, M.J., “The J&P Transformer Book”, Twelfth Edition, Newnes, 1998, ISBN 07506 1158 8.
ABB, “Testing of Power Transformers, Routine Tests, Type Tests and Special Tests”, 1st Edition, ABB Business
Area Power Transformers, 2003, ISBN 3 00 010400 3.
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Electric Power Engineering Centre – Guide to Power Transformer Specification Issues
Edition 2, January 2009
Refocus: Why Have a Technical Specification?
From an Employer (Client) perspective:
To formally and fairly communicate exactly what you want the Contractor to deliver.
From a Contractor perspective:
To be able to accurately offer services and products which provide a satisfactory solution
(technical/commercial) to an Employer (Client); while remaining a long-term profitable
business.
For both Contractors and Employers (Clients):
To avoid relationship mishaps associated with costly Variation work misunderstandings.
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Electric Power Engineering Centre – Guide to Power Transformer Specification Issues
SETTING THE SCENE
Edition 2, January 2009
The repair bill is significant.
What is the Industry going to do about it?
1. The Use of International Standards –
Example: Australian Standards
AS60076.1-2005: “Power Transformers – General.”
AS2374.2-1997: “Power Transformers –
Temperature rise.”
AS2374.3.0 – 1982 “Power Transformers – Insulation
levels and dielectric tests, General Requirements.”
Including Amendment 1 – 1992.
AS2374.3.1 – 1992 “Power Transformers – Insulation
levels and dielectric tests, external clearances in air.”
AS60076.4 – 2006 “Power Transformers – Guide to
the lightning impulse and switching impulse testing –
power transformers and reactors.”
3. Partial Discharge Testing of Refurbished
Power Transformers in New Zealand
This is an expensive and time consuming test.
It could commonly be the case that the original power
transformers were not designed to be subjected to
the Partial Discharge test.
Why are expected Partial Discharge pass levels
being set at 50% of the value specified in the IEC
International Standard for new transformers?
What is the plan if the Partial Discharge fails?
The Partial Discharge test initially failed but has now
passed, how does this make you feel?
AS2374.5 - 1982 “Power Transformers – Ability to
withstand short-circuit.”
AS2374.6 - 1994 “Power Transformers –
Determination of transformer and reactor sound
levels.” Including Amendment 1 – 2000.
AS2374.7-1997 “Power Transformers – Loading
guide for oil immersed power transformers.” Including
Amendment 1 – 1998.
AS2374.8 – 2000 “Power Transformers – Application
Guide.”
AS1265 – 1990: “Bushings for alternating voltages
above 1000V.”
AS60214.1 – 2005: “Tap-changers, Performance
requirements and test methods.”
AS60214.2 – 2006 “Tap-changers, Application
guide.”
4. On-Load Tap-Changers on Generator
Step-Up Transformers
More and more tapping ranges.
Lower and lower tap sizes.
Why – the generator has an Automatic Voltage
Regulator?
Has system simulation taken over the importance of
reliable machine design?
What is the impact upon short-circuit with-stand e.g.
multi-start, layer wound tapping windings?
5. Transformer Cooling
ONAN/ONAF/ODAF versus ODW versus ONAN?
2. The Single-Point Earthing of Power
Transformer Cores, Frames and Tanks
The insulation is failing.
Dissolved Gas Analysis tests are being over-run with
alarming gas signatures.
When should we buy straight ONAN machines?
Reliable, not dependent on l.v. systems, and simple.
ONAN/ODAF may be significantly more cost effective
above 65MVA?
Will specifying ODW significantly reduce the number
of Contractors who will tender for the work?
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Electric Power Engineering Centre – Guide to Power Transformer Specification Issues
Edition 2, January 2009
steam and gas plant than hydro. All money and
susceptible to damage.
Nitrogen.
Enclosure.
Fire Wall.
Blast walls in all critical areas.
Design of location.
Fast acting protection.
PART 1. FIRE & EXPLOSION
PROTECTION
What is considered an acceptable level of
fire and explosion protection that should be
specified for power transformers in the c) A generator step-up transformer connected to a
following scenarios?
hydro-turbine unit
Environmental risks - oil contamination of lakes /
rivers, etc.
Containment of full volume of oil.
Buchholz relay.
Pressure relief.
Vented cable box.
Generator circuit breaker.
Bushing monitoring.
Conservator tank isolation.
Choice of oil.
Temperature indicators.
Fire protection (foam).
GSU transformer - generator CB – required.
Water sprinklers and oil interceptor.
Hydro in environment sensitive areas, must
consider heat and oil.
Environmental issues are important, especially oil
containment.
Deluge.
a) A remote outdoor substation
Physical separation (firewalls if duplicate units).
Buchholz relay.
Pressure relief.
Separate cable terminations > 100MVA.
Vented cable box.
Generator circuit breaker.
Bushing plus monitoring.
Conservator tank isolation >100MVA.
Temperature indicators.
Single unit (rural) - let it burn!
Double unit - physical separation / + blast wall.
Sump flame trap - Important substations.
Control consequential damage.
Consider the layout of the surroundings.
Consider building materials.
Consider neighbouring natural environment.
Dependent on size use pressure relief valve and
shut off valve on conservator.
Blast walls for smaller critical areas.
d)
b) A generator step-up transformer connected to a
steam or gas turbine unit
Possible use of Sergi protection, etc.
Positioning transformers away from station.
However, look at the economics.
Buchholz relay.
Pressure relief.
Vented cable box.
Generator circuit breaker.
Bushing monitoring.
Conservator tank isolation.
Choice of oil.
Temperature indicators.
Fire protection (foam).
GSU (Generator Step Up) transformer Generator CB (Circuit Breaker) – preferred.
Blast walls and deflectors.
Water sprinklers on the walls.
More likely to provide fire fighting equipment for
Any power transformer greater than 100MVA
Physical separation (firewalls if duplicate
units).
Possible use of ‘Sergi’ protection, etc.
Positioning transformers away from station.
However, look at the economics.
Environmental risks - oil contamination of
lakes / rivers, etc.
Containment of full volume of oil.
Buchholz relay.
Pressure relief.
Vented cable box.
Generator circuit breaker.
Bushing plus monitoring.
Conservator tank isolation.
Choice of oil.
Temperature indicators.
Fire protection (foam).
Blast walls and sprinklers on wall.
Conservator shut off valves.
Options: foam, water curtain, CO2, FR3™.
Sergi system economical for larger units.
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Electric Power Engineering Centre – Guide to Power Transformer Specification Issues
Edition 2, January 2009
High velocity water spray system.
C02 for sealed enclosures.
Fast acting digital protection.
Sergi transformer protection or gas insulated
transformer.
e) Indoor substation
Buchholz relay.
Pressure relief.
Vented cable box.
Generator Circuit Breaker.
Bushing monitoring.
Conservator tank isolation.
Choice of oil.
Temperature indicators.
Fire protection (foam).
General Notes:
All scenarios require risk assessment.
Consider use of polymer bushing i.e. GSA, etc.
All scenarios depend on transformer size and blast
wall requirements.
Oil containment bunding with fire-traps/ drainage.
Situational considerations – not one answer for all
remote transformers or all hydro, etc.
All situations consider:
ƒ NFPA850 Guidelines – but these are only
guidelines, but you must go through and specify.
ƒ Blast walls for specified separation.
ƒ Bunding w/ drainage to suffocate fire.
ƒ Shutter valves on conservators.
ƒ Differential Protection.
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Electric Power Engineering Centre – Guide to Power Transformer Specification Issues
PART 2.THE DETAILED DESIGN
REVIEW
When the Detailed Design Review process is
specified:
a) Employers
(Clients),
what
Detailed
Edition 2, January 2009
Provide alternatives.
Assurance that the design will work and meet
specifications.
Provides assurance that the employer is getting
what we want.
Facilitates forum for improvements in design that
may impact on overall cost and performance.
Gain understanding of the design so we can gain
understanding of test results.
Find any steps in design/manufacture that you
want to witness to help with maintenance.
Design
Review (DDR) outputs do you require and why?
Using knowledge of supplier to tailor client
requirements.
b) Contractors (suppliers), what are the key matters
that will influence the power transformer detailed
Adding value to project.
design that you need the Employer (Client) to
Specifically reviewing: component mounting,
footprints, weights, shape, oil volumes etc.
clarify?
Ensuring spec following best practice.
Reconfirmation of 'no surprises' / confirmation
that supplier has the ability to deliver.
Possible provision of future on-line monitoring
equipment.
Compatibility with existing spares / stock, intercompatibility with existing network.
What is important to client i.e. on time, cost, etc?
Key scope requirements.
Fit for purpose.
Confirmation of spec / deviations.
QA (Quality Assurance) requirements.
Delivery.
Drawing, documentation, manuals, maintenance
procedures.
Inspection process.
Required specs.
Transport / shipping to site.
Seismic requirements.
Site constraints.
Weight - gross, transport.
Performance criteria.
Dimensions - centre of gravity.
Cooling plus interlock systems.
Terminations.
Material listing.
Specification does not cover all details. Need
DDR these details, Allows agreement on these
details.
No DDR for standard transformers only one
off/New Designs.
Also discussed customer acceptance
Clarification of:
ƒ Out of date standards included in spec.
ƒ Standard Designs i.e. 6MVA spec but a
7.5MVA standard – cheaper, faster, and
easier.
ƒ Component specification – e.g. bushings,
colour, tap changer type – This may effect
delivery and cost.
ƒ Transport issues.
ƒ Paint colour.
ƒ Factors relating to delivery and cost.
Acceptance tests.
Type tests / compliance.
Special tests.
Material quality.
Review of mechanical design.
Review of loss calculations.
Scope of DDR and timing of review at supplier.
Compare DDR outputs to specification clauses.
Special transformers need proper DDR.
Report on basis of IEC and CIGRE DDR guide
documents.
Result is confidence in the transformer design.
9
Electric Power Engineering Centre – Guide to Power Transformer Specification Issues
ƒ
Need to know in spec if employer wants
influence on design e.g. stress levels or
specific short circuit.
ƒ
Need employer to have expertise or a
contractor to be brought in.
Edition 2, January 2009
General Notes:
Should a detailed spec be required? How about the
customer saying we need a transformer to fill this
space, these are the connections, go to it. However,
still a lot of things need to be known. Different
tolerances are not always required, overbuilding, etc.
It’s about relationship/confidence in supplier. QA
systems, review, etc. should be done before
specifications i.e. due diligence.
Standardisation of one set of designs does not
always work, as component costs may change
meaning the set design is no longer the most
economical.
Where is the innovation coming from? Suppliers or
Clients? Probably a combination of both. Clients
drive adoption of certain items e.g. condition
monitoring. Suppliers drive changes in winding types,
materials, etc.
In general, this is a very important process that is
important for both parties. It aids clarification and
understanding of how to proceed with design
(contractor) and provides a certain level of
optimisation for the employer (client) i.e. relationship
building.
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Electric Power Engineering Centre – Guide to Power Transformer Specification Issues
PART 3. TECHNICAL
SPECIFICATION EXPERIENCES
a) From an Employer (Client) and / or Contractor
(Supplier) perspective, what information must be
given in a 2007 Technical Specification?
Edition 2, January 2009
Refer to AS60076.1 appendix A as a minimum
requirement.
Site requirements – Footprint, Transport etc.,
MVA, Voltage, Losses, Vector group. Bushing
types, taps, terminations, SCADA interfaces,
protection devices, auxiliaries, voltage, and
cooling and seismic requirements.
Finishing – Painting, galvanising, wielded or
bolted.
Refer to standard lists.
Documentation for transfer and timetable.
MVA, voltage, impulse, tap changer, connection,
vector group, and seismic.
As built, maintenance manuals, specs, wiring
specs and code. Standards AS/NZ and IEC.
Intended application.
Relevant standards.
General characteristics / performance criteria
Auxiliary components / systems.
Arrangement
of
transformer;
dimensions;
bushing/terminal layouts; site requirements;
system requirements.
Voltage, vector group, frequency, noise
requirements (sound pressure, sound power,
distance), loss’s, rating, list of standards that it
must comply to, Overload rating, ambient
temperature, earthing, fault level, environment,
seismic requirement, altitude, typical rang of
impedance, tap rang, type of entry.
Rating, MVA, kV.
Vector group.
Cooling, type of oil.
Impedance.
Tap-changer, plus minus percentage.
Load profile.
Regulation.
Standards (manufacturers).
List of accessories.
b) Employers (Clients) and Contracts (Suppliers),
Type of bushing.
what times have you witnessed recently in
Short circuit withstand capability.
Technical
Seismic.
Specifications
that
have
been
unhelpful to the process?
System earthing.
Loss evaluation formula.
Clearances - often specified when standards are
in place (Designer wants a different clearance for
some reason?)
Guaranteed losses.
Too prescriptive specs i.e. 'old school'
Corrosion protection.
Too many standards.
Tank strength.
Insistence on copper winding.
Noise level.
Totally useless offload sufficient.
Specification of duplicate/overlapping test
requirements ( contributes to additional cost/time)
e.g. stating two test methods to gain same result,
such as meggar vs. sweep frequency tests.
Irrelevant/out of date standards.
PD (Partial Discharge) test requirements NZ/AUS
very low – almost impractical.
Radiator specified to be both galvanised and
painted.
Colour of bushing in cable box.
Items that are contradictory.
Items that are out of date.
BIL (Basic Insulation Level).
Phase clearance, spacing.
Creepage distances.
Surge arrestors.
Cable box, open bushings.
CT
(Current
protection.
Transformer)
Remote tap changing.
Station voltage.
requirements,
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Electric Power Engineering Centre – Guide to Power Transformer Specification Issues
Edition 2, January 2009
c) Why are on-load tap changers being fitted to
e) When transformers over 150MVA are specified,
generator step-up transformers and what are the
how should they be livened if the high voltage
implications of increasing tapping ranges and
network
decreasing step sizes?
experiences with such livening?
must
be
used?
What
are
some
Insurance policy.
Point on wave switching.
Guarantees and flexibility?
480MVA back livening, audible complaint from
other transformer for 10– 15 minutes.
Pre-Insertion resistors.
Transformer design.
Old school, conservative.
Asset owner compliance.
More voltage regulation required.
f)
What are the key acceptance criteria that will
Near load centres.
allow
Increase tap range: extreme ends of tap settings
are not used.
(Supplier) to close-out a project?
Totally useless offload sufficient.
More leads and more introduced points of
potential failure.
EGR
(Electricity
Governance
Rules)
requirements impact on generators ability to
support/import reactive power is severe.
Tap changers are not needed on generator
transformers with an AVR (Automatic Voltage
Regulator).
d) Is single-point earthing of core, frames, and tanks
a good approach? What happens when the single
point earthing fails?
an
Employer
(Client)
and
Contractor
Setting of maintenance procedures.
Drawings.
Documentation.
Defects.
Warranty, commercial bonds, etc.
Successful livening.
Handover of drawings, manuals, test certificates,
etc.
Clear communication and well defined procedure
needed.
Define in contract.
Pass site acceptance test.
Good idea! Cost trade-off on insulation maybe.
Agreed acceptance testing completed.
In service for specified period and handed over.
On site install / commissioning completed and
documentation complete.
Fence sitting: cost of coping with circulating
current vs. single point.
Want device that is reliable regardless of design
Choice of single point earthing or not is a trade
off between equipment costs and losses. The
“best” will vary with circumstances.
General Notes:
Single point earthing lives! Need better construction
to withstand transport failures, lamination failures etc,
not necessarily insulation failure. Need better access
for repair, replacement.
On-Load Tap Changer (OLTC) - AVR might be all
good, but if it has a problem, the OLTC provides
good backup. But it may still not be needed as it
won't be in operation if AVR is out.
May need OLTC to allow for future system
expansion/change. Lowers system reliability but
increases system flexibility. System planners should
consider this more. OLTC alters voltage seen by
generator, but AVR can withstand plus minus 5%
typically anyway (sometimes!).
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Electric Power Engineering Centre – Guide to Transformer Technical Specification
Edition 1, August 2007
APPENDIX A
REFURBISHMENT & REPAIR OF POWER TRANSFORMERS*
* Courtesy of Transfield Services Limited ©
Page 13 of 94
Refurbishment & Repair of Power TransformersA review of current practices in New Zealand
Conference- Christchurch,2-3 July 2007
Presented by – Ramesh Gopalan
Transfield Services Partners for Change
Overview
ƒ
General Principles of Refurbishment
ƒ
ƒ
What is being done at present
Specific aspects
ƒ
What could be done during refurbishment
ƒ
ƒ
Review of specifications
Repair of Power Transformers
- What could be done – An overview from the contractor
Transfield Services Partners for Change
2
ƒ
Refurbishment of transformers
Transfield Services Partners for Change
3
General Principles of Refurbishment
ƒ
Power Transformers worldwide are ageing
ƒ
ƒ
ƒ
The average age in New Zealand is about 36 years
Grid & Network operators have an ongoing programme of
refurbishment for life extension.
Refurbishment includes
ƒ
ƒ
ƒ
ƒ
ƒ
Testing the average DP of transformer insulation
De-tank & Inspection of core & windings
Minor modifications to blocking arrangement
Changes to insulation structure- paper wound cylinders to solid cylinders
Single point Earthing modifications- not always practical
Transfield Services Partners for Change
4
Refurbishment of Transformers
ƒ
ƒ
ƒ
Dry-out of core & windings using heat and vacuum
Re-tightening and clamping windings.
Replacement of accessories- OTI, WTI, Buchholz Relay etc
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
Replace Explosion Vent to PRV .
Install Flexible Separators in Conservators
OLTC replacements
Corrosion control of tank and enclosures
Oil reclamation to improve physical and dielectric properties.
Routine Low Voltage testing following refurbishment
Transfield Services Partners for Change
5
EPRI Guidelines for residual life estimates
DP Value
% Life Left
1000 to 1400
100%
500
60 to 66%
300
30%
200
0%
Source: Guidelines for the Life Extension of Substations, 2002 Update,
Electric Power Research Institute( EPRI), California, USA
Transfield Services Partners for Change
6
Residual Life Estimates-NZ network transformers
»Remaining life estimates are favourable for up-rating
Mid Year of
No. of
Decade of Samples
Manufacture tested
1.
2.
Average
tested DP
value
% Life Left
# of years
of service
life left
Total
Service
Life
1955
35
520
60%
30
80
1965
110
543
60%
30
70
1975
39
505
60%
30
65
1990*
9
719
80%
40
55
DP Values tested during refurbishment, Residual Life Assessment based on EPRI
Guidelines.
The above figures affirm the assessment of post 1970 transformers will have a
lower life than those manufactured during 50-60’s
Transfield Services Partners for Change
7
What could be done during refurbishment
ƒ
Refurbishment Specifications should
include
ƒ
ƒ
A review of cooling arrangement
Older transformers have different
style of radiators
ƒ
Not necessarily efficient
Could be changed to more efficient
Plate-fin type radiators with
symmetrical arrangement
ƒ ONWF arrangement could be
changed to ONAN instead of OFWF
ƒ
Transfield Services Partners for Change
8
What could be done during refurbishment
ƒ
Up-rate transformers during
refurbishment
ƒ
ƒ
ƒ
ƒ
Generally not called for
Review original Heat-run test
reports
Most of the transformers are
ONAN cooled
Could be changed to
ONAN/ONAF and increase
capacity
Transfield Services Partners for Change
9
Dry-out of windings
ƒ
Dry-out is under-taken using Hot-air heating and vacuum drying
thereafter
ƒ
ƒ
Vapour phase drying is not under-taken as set up cost is prohibitive
The termination of dry-out is generally based
ƒ
ƒ
on volume of water collected per hour and
a certain minimum value of vacuum
ƒ
ƒ
usually less than 1 mbar
Recommend this be changed to standard Moisture-Equilibrium curves
published by IEEE
ƒ
ƒ
Dr.Oommen curves are used by most manufacturers
Eliminates the need for collecting water and monitoring water collection
ƒ
Cumbersome
Transfield Services Partners for Change
10
ƒ
Testing of transformers
Transfield Services Partners for Change
11
Testing of Transformers
ƒ
ƒ
Post refurbishment, testing is done only at low voltage
Emphasis on Insulation resistance test post refurbishment
ƒ
Minimum acceptable value is specified based on TMI-US guidelines
ƒ
ƒ
ƒ
ƒ
IR & PI values are often not achievable due to the transformer capacitance
IEC standards do not specify a minimum value
Minimum value for Insulation Resistance should be specified independent of
kVA Rating
We recommend
ƒ
ƒ
50Hz separate source voltage test at 75% rated value for refurbished
transformers
No-load excitation at 100% voltage for 30 minutes for refurbished transformers
Transfield Services Partners for Change
12
Partial Discharge test
ƒ
ƒ
Post repair, a partial discharge test is specified
IEC 60076 recommends PD test for transformers with
Um>300kV
ƒ
ƒ
ƒ
Some clients insist on this test for lower voltages
Values specified are 50% of IEC recommended values
The transformer is manufactured 25-30 years ago
ƒ
ƒ
ƒ
Only part of the winding is replaced
The transformer was originally not subjected to a PD test
Is it practical to achieve such low levels?
ƒ
The PD test is conducted in an unshielded environment
Transfield Services Partners for Change
13
ƒ
Repair of transformers
Transfield Services Partners for Change
14
Repair of Transformers
While choosing to repair, some
clients
ƒ
ƒ
Based on internal economic models,
prefer the least cost option.
The purchase price of transformers
has doubled in the last three years
ƒ
ƒ
ƒ
ƒ
Transformer Price Variation
Cost of repair likely to be 20-25% of
the cost of new transformer.
Lead times for new transformers
exceeds 12 months
Repair should consider existing risk
Generally recommended to replace
whole windings
ƒ
ƒ
At least the complete winding of the
faulted phase
Minimises risk
Transfield Services Partners for Change
2.400
2.200
2.000
1.800
1.600
P r ic e In d e x
ƒ
1.400
1.200
Pq/Po
1.000
0.800
0.600
0.400
0.200
0.000
Jan-04 Aug-04 Feb-05 Sep-05 Mar-06 Oct-06 Apr-07 Nov-07 Jun-08
Month-Year
15
Repair of Transformers
ƒ
While formulating repair specifications, we recommend
ƒ
Testing of the replacement winding for turns ratio, resistance and inter-strand
tests
ƒ
ƒ
This will involve the windings be put on a transformer core
ƒ
ƒ
prior to shipping the windings to New Zealand
But it is recommended
We have had failures of replacement windings having
ƒ
Centre entry and two halves in parallel
ƒ
ƒ
Recommend the involvement of replacement contractor in inspecting the
winding prior to shipping
ƒ
ƒ
Unequal turns between parallel halves
to avoid surprises / delays upon arrival in New Zealand
Specify PD levels to which transformer will be tested to the replacement
winding manufacturer
Transfield Services Partners for Change
16
Electric Power Engineering Centre – Guide to Transformer Technical Specification
Edition 1, August 2007
APPENDIX B
DRIVEN FACTORS FOR TRANSFORMER LONG LIFE**
* Courtesy of Pauwels Trafo Asia ©
Page 30 of 94
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
ELECTRICAL DEPARTMENT – PAUWELS TRAFO ASIA
Contact person ; Didik Susilo Widianto (+62.21.8230430.ext 230)
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Transformer life time
The Transformer life expectation is measured by
the Rate of Degradation of the Insulation
normally this Insulation is cellulose paper.
The expectation of transformer end life can be
indicated by the degree polymerization of paper
approximate 200 (and other indications).
Tuesday, August 21, 2007
Introduction Power Transformer
2
Two important design driven factors
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Transformer temperature behavior ;
IEC 60076 – part 2 and IEC 600354 indicate the limits based on
temperature of this life time expectation. The normal life
time/temperature rise & emergency capabilities at particular ambient
temperatures have to be considered.
Partial discharge levels ;
IEC 60076 – part 3 indicates the standard limits of partial
discharges for 130% Um (300 pC) and 150% Um (500 pC). These
levels seem to be are very high and we would not manufacture to
them. One must have low PD as with increasing moisture content,
the PD rises quite dramatically at 20 ppm, 20oC moisture content
mineral oil (see diagram for moisture content) while the transformer
is normally tested at very good oil condition.
Tuesday, August 21, 2007
Introduction Power Transformer
3
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Why is temperature important for
transformer life time ???
Tuesday, August 21, 2007
Introduction Power Transformer
4
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Cellulose Conductor Insulation Ageing
Tuesday, August 21, 2007
Introduction Power Transformer
5
TRANSFORMER LIFE TIME – CELLULOSE DESIGN
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
IEC 354 – Loading Guide
• Section 1.2; The hottest part of the winding is used
for evaluation of a relative value for rate of thermal
ageing. Conductor insulation ageing
• Section 2.6.2; Relative thermal ageing based on
20oC ambient + 78oC hot spot rise = 98oC.
Tuesday, August 21, 2007
Introduction Power Transformer
6
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
TRANSFORMER LIFE TIME – CELLULOSE
DESIGN
yearly average hot spot 98oC
Tuesday, August 21, 2007
Introduction Power Transformer
7
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
TRANSFORMER LIFE TIME – CELLULOSE
DESIGN
V=2
(θh-98)/6
yearly average hot spot 98oC
Tuesday, August 21, 2007
Θh
Relative ageing rate
92oC
98oC
104oC
110oC
134oC
0.5
1.0
2.0
4.0
64
Introduction Power Transformer
8
Temperature Rise and Driven Factors
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Temperature Rise for Class A (IEC 60076-2/ ANSI C57);
Top oil rise ; = 60K / 55 K or 65 K.
Average oil rise ; = 65 K / 55 K or 65 K (By resistance method)
Hot spot rise ; = 78 K / 65K or 80K.
Site elevation height;
The standard elevation height is 1000 m above sea level.
Climatic temperature behaviors;
Yearly average ambient temperature (IEC std = 20oC) Î transformer life time.
Hot monthly average ambient temperature (IEC std = 30oC)
Maximum ambient temperature (IEC std = 40oC) Î transformer loading capability
Temperature class;
Insulation class
Operating temperature
Tuesday, August 21, 2007
A
E
B
F
H
105oC
120oC
125oC
145oC
220oC
Introduction Power Transformer
9
Temperature Identification
Hf x gradient
cooler
gradient
Hot spot factor is normally presented between
1.1 to 1.5 depending on winding design.
Tuesday, August 21, 2007
Introduction Power Transformer
Hot spot
Average winding
Top oil
Mean oil
winding
Bottom oil
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
core
10
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Cooling Medium
INTERNAL COOLING MEDIUM
Besides the thermal absorption, the internal cooling medium
also functions as the insulation medium.
Class A;
9Mineral oil (Inhibited or Un-inhibited oil).
Class K;
9Silicon oil
9Synthetic ester
9Hi-Temp natural liquid (seeds).
EXTERNAL COOLING MEDIUM
9Air
9Water
Tuesday, August 21, 2007
Introduction Power Transformer
11
Terminology Of Cooling System
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Directed Cooling ;
Indicates that the oil is flowing in the winding by zig-zag
paths. This Directed Cooling is using Oil Barriers in several
sections of winding to guide the oil flow.
Non Directed Cooling ;
Indicates that the oil is flowing in the winding axially.
Normally, clack bands are used to improve the cooling
performance.
Pumped unit – Fully Directed Cooling ;
Indicates that the principal part of the pumped oil from heat
exchangers or radiators is forced to flow through the
windings arrangement.
Tuesday, August 21, 2007
Introduction Power Transformer
12
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Winding Cooling System
Directed Cooling
Tuesday, August 21, 2007
Non-directed Cooling
Introduction Power Transformer
13
Pumped - Fully Directed Flow
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
In order to avoid > 60% of cold oil leakage, the Fully Directed
Cooling is the only recommended cooling for Pumped unit.
Windings ; 80% oil flow
core
cooler
Core & leakage ;
20% oil flow
winding
Oil Chamber for oil
flow distribution
Pump
Tuesday, August 21, 2007
Introduction Power Transformer
14
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Class A Standard Temperature Limits
*) suitable for
thermally up graded
paper insulation
Maximum temperature design limit [oC]
Oil
Winding
Metal part
Consequences
Annual average
80
98 / 110 *
110
Life time
Long Emergency
105
140
140
Gas generation
Short emergency
115
160
160
Gas generation
1.Copper
115
250
160
Conductor
softening
2.Aluminum
115
200
160
Thermal short circuit
Tuesday, August 21, 2007
Introduction Power Transformer
15
Conservative Temperature Limits
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Temperature limits for mineral oil filled transformer with conservative safety
margin to avoid any insulation degradation;
1. 125oC for maximum winding hotspot temperature during short
emergency at max. 30 minutes.
2. 115oC for maximum winding hotspot temperature during
continuous emergency (above time constant).
Pumped - Fully Directed oil flow cooling is the most effective solution
to fulfill those conservative temperature limit requirements for medium
& large power transformer.
The 50/100% for ONAN/ODAF cooling is the optimum combination
in the case of pumped, finned radiator & fan combination (external
cooling).
Tuesday, August 21, 2007
Introduction Power Transformer
16
Recommended Cooling Method
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Directed cooling;
For pumped unit (OD), the Fully Directed windings with oil
Directed to the windings and through the windings is the most
optimum for medium & large transformer with conservative
temperature limits & severe overloading requirements.
For in case natural oil flow unit, we also produce Directed in the
windings only. Some time ago (up to 2000), we had built Non
Directed/Axial cooling with Clack band cooling systems.
Value for money in any system, Fully Directed Oil flow gives the
most effective commercial result and provides significant design
benefits in fully fitting the severe overloading requirements.
Tuesday, August 21, 2007
Introduction Power Transformer
17
Recommended Cooling Method
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Directed cooling;
1. As there is an oil gap in the middle of the winding due to
clack band which is required for additional cooling, the
buckling withstand is more difficult to control. There are
difficulties controlling alignment of the clack band due to
the fixed distance between the clacks.
2. The usage of clack band for the axial cooling duct of Non
Directed cooling reduces the series capacitance of the
winding. Due to this reduction in series capacitance, more
insulation is required to strengthen the insulation
coordination against impulse switching surges and high
frequency voltage spikes inherent in the system.
Tuesday, August 21, 2007
Introduction Power Transformer
18
Recommended Cooling Method
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Directed cooling;
3. Under OD, we are more able to accurately predict and control
our low gradients. A low gradient allows one to more easily
control the temperature behavior and cater for severe
overloading conditions.
The value of the gradient is that as the current increases, the
gradient rises by the power of 1.6 for Non-Directed cooling,
1.2 for natural flow Directed cooling and 2.0 for Fully
Directed pumped oil flow.
The gradient of a competitive unit of Non Directed cooling is
typically almost double the Fully Directed (OD) unit and ,if
one overloads, the gradient temperature increase can be quite
dramatic and limits overload capacity.
Tuesday, August 21, 2007
Introduction Power Transformer
19
Recommended Cooling Method
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Directed cooling;
4. Fully Directed flow units can be made electrically stronger
than Non Directed flow units as the duct size on either side
of the winding can be significantly reduced (increased
strength per mm). In naturally cooled units ie ONAN and
ONAF, the duct normally need to be increased for cooling
considerations due to very low thermosyphonic oil flow.
5. It is the fact that the pumped – fully Directed flow unit will
eliminate the local overheated oil around the hot spot area.
This system is suitable for Hybrid design technology in
mobile transformer application or other compact transformer.
Tuesday, August 21, 2007
Introduction Power Transformer
20
Recommended Cooling Method
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Directed cooling;
6. Due to it’s high cooling effectiveness, the Fully Directed flow
pumped units in combination with low RPM big fans is mostly
able to minimize the cooling noise fitting with extremely low
noise requirements. This solution is the most preferred
solution rather than reducing the induction and increasing the
active material (core & copper) as consequences. ODAN
cooling gives practically lower noise increase at approx. 20%
rating above ONAN in comparison with ONAF solution.
Note :
- we build all types of units, ONAN, ONAF and ODAF
Tuesday, August 21, 2007
Introduction Power Transformer
21
Winding Gradient
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Grad. = Function (q, 1/ψ , 1/ρ , 1/c ,η)
“Grad.” Liquid to conductor gradient temperature [K]
“q”
Distributed losses density [W/mm2]
“ψ”
Distributed liquid mass flow rate [mm/s]
”ρ”
Liquid mass density [kg/mm3]
“c”
Specific heat capacity [J/kg.K]
“η”
Coefficient of convective heat transfer [W/mm2]
Tuesday, August 21, 2007
Introduction Power Transformer
22
Surface Heat Transfer Coefficient
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
η (surface heat transferred coefficient) is a
function of duct size, oil flow length & velocity.
For directed (zig-zag) cooling ;
The axial and radial surface of the winding conductor
are considered as the surfaces for heat transfer. This can
be quite accurately calculated to determine the winding
gradient of the winding.
For non-directed (axial) cooling ;
The axial surface of the winding conductor section is
predominantly considered as the main heat transfer surface.
Tuesday, August 21, 2007
Introduction Power Transformer
23
Mass Flow Rate
ON Cooling
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
1. Determined by thermosyphonic principle of Buoyancy effect.
2. Driven by winding heat due to losses (I2R + eddy losses) and
cooling medium properties (mass density, viscosity).
OD Cooling
1. Determined by thermo-hydrodynamic calculation at
equilibrium hydraulic pressure.
2. Driven by winding heat due to losses (I2R + eddy losses),
designed oil speed, pump capacity and cooling medium
properties (mass density, viscosity, specific heat capacity).
Tuesday, August 21, 2007
Introduction Power Transformer
24
Typical OD Mass Flow Rate Distribution
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
270 mm/s
180 mm/s
110 mm/s
OD design
Tuesday, August 21, 2007
Introduction Power Transformer
25
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Flow Barrier in Directed Cooled Winding
Outside Flapped type barrier
Inside Flapped type barrier
Tuesday, August 21, 2007
Introduction Power Transformer
26
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Partition Ring to Control Thermal
Balance Between Windings
Tuesday, August 21, 2007
Introduction Power Transformer
27
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Fully Oil Directed Cooled All Windings
Oil Directed
Twin Boosters
Tuesday, August 21, 2007
Introduction Power Transformer
28
Gradient Comparison Of Directed vs
Non-directed Cooling In Natural Flow
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
60/90 MVA, 132/33 kV
ONAN/ONAF + 150% CMR
two hours emergency
LV
HV
Directed
Calc.
Meas.
Non-directed
Calc. A Calc. B
AN 0.67 pu
12.6 oC
11.0 oC
19.5 oC
7.9 oC
AF 1.00 pu
15.6 oC
14.2 oC
29.4 oC
15.0 oC
AF 1.50 pu
24.3 oC
23.4 oC
43.8 oC
28.7 oC
CU net weight
2092 kgs
2092 kgs
2550 kgs
# Clack band
NA
NA
3 pcs
AN 0.67 pu
10.7 oC
10.3 oC
22.3 oC
7.9 oC
AF 1.00 pu
16.7 oC
15.0 oC
33.7 oC
15.1 oC
AF 1.50 pu
26.6 oC
25.0 oC
55.5 oC
28.9 oC
CU net weight
2816 kgs
2816 kgs
3450 kgs
# Clack band
NA
NA
2 pcs
Tuesday, August 21, 2007
Introduction Power Transformer
29
Comparison Of Experienced Cooling System
Factory Test Results
ONAN/ONAF
ONAN/ODAF
150 MVA 230/115 kV
250 MVA 220/114 kV
Double Wound
Auto Transformer
Top Oil Rise
42.65 oC
46.8 oC
Winding Gradient
19.2 oC
12.6 oC
Hot Spot Rise
67.6 oC
63.2 oC
Non-Directed
Fully Directed
# Clack band
5 x 5.4 mm thick.
NA
Top Oil Rise
42.65 oC
46.8 oC
Winding Gradient
22.5 oC
18.9 oC
Hot Spot Rise
71.9 oC
71.4 oC
Non-Directed
Fully Directed
4 x 5.9 mm thick.
NA
Transformer Rating
Type Of Transformer
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
LV
Winding Cooling
HV
Winding Cooling
# Clack band
External Cooling
Tuesday, August 21, 2007
12 rad. + 30 small fans 1(+1) pumps + 8 rad.+ 4 fans
Introduction Power Transformer
30
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
150 MVA DOUBLE WOUND TRANSFORMER
NON DIRECTED COOLING
End user : CHEVRON Indonesia. (Energized 2000)
90/150 MVA ONAN/ONAF DOUBLE WOUND TRANSFORMER
HV : 230 + 16 x 0.625% kV OLTC.
IV : 115 kV / LV : 13.8 + 2 x 2.5% kV DETC
Tuesday, August 21, 2007
Introduction Power Transformer
31
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
250 MVA AUTOTRAFO – FULLY DIRECTED
End user : TransPower New Zealand. (Energized 2005)
250 MVA ONAN/ODAF AUTOTRANSFORMER
HV : 220 + 8 x 1.25% kV OLTC.
IV : 114 kV / LV : 11 + 2 x 2.5% kV (capacitive load)
Tuesday, August 21, 2007
Introduction Power Transformer
32
Fiber Optic Installation
Purpose :
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
To directly measure the Hot Spot temperature, fibre optics can be used to measure temperatures in
cores and tank walls - not only the windings of the transformer.
Tuesday, August 21, 2007
Introduction Power Transformer
33
Infra Red Thermal Investigation
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Typical Infra Red Thermal Check
To avoid local overheating
Tuesday, August 21, 2007
Introduction Power Transformer
34
Extendable Plate type Water Cooler
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Possibility to extend the cooler capacity at
site to reduce the transformer temperature
Tuesday, August 21, 2007
Introduction Power Transformer
35
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Why is Partial Discharge important for
transformer life time ???
Tuesday, August 21, 2007
Introduction Power Transformer
36
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Partial Discharge
Partial Discharge level will measure the activity of
electron discharging from the conductive materials
thru the dielectric medium. Inside the transformer, the
cellulose insulation and mineral oil are the dielectric
medium and this partial discharge will ionize their
hydrocarbon molecules.
High Partial Discharge Level will destroy the
hydrocarbon chains of the transformer insulation
and cause the electric breakdown ignition. When
there is moisture involved, the insulation
degradation rate will be much faster.
Tuesday, August 21, 2007
Introduction Power Transformer
37
Six Categories Of Partial Discharges
Partial Discharge indicates the defects existence prior to
dielectric breakdown.
breakdown
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
1. Corona discharges occurs due to the sharp edge electrode.
2. Surface discharges (creepage) occurs due to overstress component
parallel to the dielectric medium surface.
3. Internal discharges occurs due to the non-homogenous dielectric
medium.
4. Electric trees due to the particle or cavity in the solid insulation.
5. Floating discharging occurs due to badly grounded component.
6. Contact noise occur in case bad contact terminal.
Tuesday, August 21, 2007
Introduction Power Transformer
38
Optimized Oil Duct Thickness
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
The oil duct thickness has to not only provide reliable cooling
but has to provide electrical insulation. The diagram shows
how a smaller duct provides higher voltage strength per mm.
Tuesday, August 21, 2007
Introduction Power Transformer
39
Moisture Content In Paper [%weight]
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Equilibrium Of Moisture Content In Oil vs. Paper
The transformer is tested normally at less
than 5 ppm moisture content in oil
Moisture Content In Mineral Oil [ppm weight]
Tuesday, August 21, 2007
Introduction Power Transformer
40
Power Freq. Withstand Voltage [%]
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Oil Moisture Content vs Dielectric Strength
Moisture Content In Oil [ppm]
Tuesday, August 21, 2007
Introduction Power Transformer
41
Power Freq. Withstand Voltage [%]
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Paper Moisture Content vs Dielectric Strength
Moisture Content In Oil Impregnated Paper [%]
Tuesday, August 21, 2007
Introduction Power Transformer
42
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Typical Of Low Partial Discharge
Tuesday, August 21, 2007
Introduction Power Transformer
43
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Discharging Circle Prior To Flashover
High Partial
Discharge
Insulation
Ionization
Insulation
weakening
Tuesday, August 21, 2007
Gassing
Introduction Power Transformer
44
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
CONCLUSION FOR MINERAL OIL XMER
Temperature limits;
The temperature limits and the type of overloading at particular ambient
temperature have to be indicated.
New class A cellulose paper covered conductor immersed in new mineral
oil will start gassing at hot spot temperature of 145oC.
Cooling system;
Fully directed cooling with pump is the most suitable for medium & large
transformer. The directed cooling with no pump can be used for cost
effectivenes consideration on small/medium transformer.
Conductor paper ;
The cellulose paper should have Degree Polymerization min. 950.
Low partial discharge product shall be performanced at factory test;
=> 40 pC up to 120% Voltage for 30 minutes.
=> 75 pC up to 150% Voltage for 30 minutes.
=> to monitor the partial discharge at induced level, 1min.
Tuesday, August 21, 2007
Introduction Power Transformer
45
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Doubled Capacity On Existing Foundation
End User : COMALCO ALUMINIUM SMELTER AUSTRALIA
168 MVA ODAF, 220 kV / 2.7 to 40.4 kV in 3 x 52 steps via 2 x OLTCs + DETC.
This was installed on existing foundation of a 110 MVA regulator .
Tuesday, August 21, 2007
Introduction Power Transformer
46
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
FUTURE
FUTURE SOLUTIONS
SOLUTIONS ??
Tuesday, August 21, 2007
Introduction Power Transformer
47
Hybrid Design
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
CALENDERED
KRAFT BOARD
CALENDERED
KRAFT BOARD
Angle Rings
and Caps
Support Washers
NOMEX® T-993
Creped NOMEX®
Static Rings
CALENDERED
KRAFT BOARD
Cylinders
NOMEX® T-410
Conductor
Insulation
NOMEX® T-994
Axial & Radial
Spacers
PRECOMPRESSED
KRAFT BOARD
Tuesday, August 21, 2007
Clamping Rings, Blocks
Introduction Power Transformer
48
Hybrid Design – Engineering Transformer
97oC hot spot rise
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Cellulose pressboard
Capacity
= 12.5 MVA (ONAN)
Voltage
= 115 + 1.4 / 21.5 kV
BIL HV/LV = 550 / 125 kV
Vector group = YNd11
HV winding = Disc / PI 0.8 / ksp. 2.0
LV winding = Disc / PI 0.5 / ksp. 1.5
Cooling
= ONAN in 10 radiators
Top oil rise
= 57 K
Average HV rise = 62.1 K
Cellulose insulated lead outs
Average LV rise = 70.1 K
Measured HV grad. = 25 K
Measured LV grad. = 33 K
Hot spot factor
= 1.2
Tuesday, August 21, 2007
Introduction Power Transformer
49
CASE STUDY – 30 MVA for PG&E
Built by Pauwels for Pacific Gas & Electric
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Power (MVA)
Weight (T)
Cellulose design
with same weight
with same MVA
Cellulose design
with same MVA
45
45
31,5
44,1
57,5
44,1
Hybrid design
IZ (%)
19,1
10,0
10,0
No load losses
(kW)
11,9
10
8
Load losses
(kW)
752
225
110
95
65
65
Temperature
rises (K)
Tuesday, August 21, 2007
Introduction Power Transformer
50
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Hybrid Design In Mobile Transformer
Under Substation Installation
Tuesday, August 21, 2007
Introduction Power Transformer
51
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Hybrid Design In Mobile Transformer
Test Drive
Tuesday, August 21, 2007
Introduction Power Transformer
52
DGA Report – Typical Hybrid design
The gas generation produced by Hybrid transformers
after temperature rise test at PAUWELS factory.
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
50 MVA, 161-115/13.8-34.5 kV, Inert air system, Nitro 10XT oil
Gas
Symbol
Temperature rise test (8 hours)
Increment
Cellulose
Before
After
unit
in ppm/hour
Typical
<2
Hydrogen
H2
< 0.8
10.13
ppm
1.27
Oxygen
O2
0.96
0.77
%
-
Nitrogen
N2
2.15
1.61
%
-
Carbon monoxide
CO
7.17
9.40
ppm
0.27
<2
Carbon dioxide
CO2
122.32
205.78
ppm
10.43
< 11
Methane
CH4
1.75
2.01
ppm
0.03
< 0.25
Acetylene
C2H2
0.08
0.11
ppm
-
< 0.25
Ethylene
C2H4
0.11
0.10
ppm
-
< 0.25
Ethane
C2H6
0.12
0.11
ppm
-
< 0.25
Tuesday, August 21, 2007
Introduction Power Transformer
53
Future – Environmental Friendly Liquid
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
• Environmental liquid = Enviro-Temp FR3 by COOPER
• Inhibited oil
= Nitro 10XT by NYNAS
Property – typical values
Inhibited oil
FR3
Antioxidant, phenols
0.08% per Wt
n.a.
500 hours
continuous
Biodegradable in 21 days
25%
100%
Saturated moisture at 25oC
80 ppm
1200 ppm
60/65/78 K
80/110/130 K
Flash point
145oC
330oC
Pour point
-57oC
-18oC
Oxidation stability by 120oC
Temp. rise for unity life time *)
*) Top oil/Average winding/hot spot rise (+ Hybrid design for FR3)
Tuesday, August 21, 2007
Introduction Power Transformer
54
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Water Saturation of Mineral oil vs FR3
Tuesday, August 21, 2007
Introduction Power Transformer
55
Liquid Water Absorption versus Time Exposure
Water Absorption of Dielectric Fluids
Exposed to Ambient Air (2 of 2)
Envirotemp FR3 fluid
conventional transformer oil
80
60
Water Absorption of Dielectric Fluids
Exposed to Ambient Air (1 of 2)
600
40
20
0
0
500
1000
1500
2000
Exposure Time (hrs)
2500
3000
3500
Absolute Water Content (ppm)
R e la tiv e W a te r C o n te n t ( % s a tu ra tio n )
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
100
500
400
300
Envirotemp FR3 fluid
conventional transformer oil
200
100
0
0
100% Saturation =
FR3, 1200 ppm
Mineral Oil, 80 ppm
Tuesday, August 21, 2007
500
Introduction Power Transformer
1000
1500
2000
2500
3000
3500
Exposure Time (hrs)
56
Liquid Dielectric Strength vs. Water Content
Dielectric Strength versus Water Content
D 1816 Dielectric Breakdown (kV)
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
80
70
60
50
40
30
Envirotemp FR3 fluid
conventional transformer oil
20
10
0
0
100
200
300
400
500
600
Water Content (ppm)
Tuesday, August 21, 2007
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57
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Partial Discharge Of FR3 Filled
Transformer
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Introduction Power Transformer
58
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
Prototype transformer filled with FR3
12/17 MVA, 33kV,ONAN/ONAF + provision for future ODAF
Measured PD = 25 pC max. at induced voltage level.
Liquid Main tank = Enviro Temp - FR3
(Hi-Temp natural – ester based 100% biodegradable)
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59
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
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60
Low partial discharge product ;
ÎAssists to increase a units life from overvoltage spikes
and prolongs oil quality
• Typical guaranteed partial discharge ;
ENERGY IS OUR BUSINESS, QUALITY IS OUR MISSION
9 75 pC at 150% Un, IEC 60076 500 pC at 150% Um
9 40 pC at 120% Un, IEC 60076 100 pC at 110% Um
• Typical achievement , by rating voltage = 220 kV (950 kVp BIL);
914 pC at 150% voltage.
927 pC at 200% voltage.
Dirrected cooling path ;
Î Assists life time expectation under overloading
conditions and suitable for Low noise requirement.
Compact design, safety and enviromental friendly;
Î Usage Hybrid design and Vegetable liquid to minimize
the land space required, less flammable risk and
enviromental friendly unit.
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61
Electric Power Engineering Centre – Guide to Transformer Technical Specification
Edition 1, August 2007
APPENDIX C
EPECENTRE ELECTRIC POWER R&D CAPABILITY
Page 92 of 94
New Zealand’s
Centre of
Excellence for
Power
Engineering
Electric Power R&D
Programme
Energy Efficient
Generation &
Distribution
Power
Systems
Reliability
System
Studies
Demand Side
Management
Alternative
Power
Generation
Power
Transformers
HV Testing
Power Quality
Renewable
Energy
Energy Modelling
www.epecentre.ac.nz
Supporting Industry R&D needs for NZ’s Energy Future…
Launched New Zealand’s first
collaborative industry-academia R&D
Programme for power in 2005…
Our Services
Short-term projects in specialist areas (see
overleaf); customised technical workshops &
training; design & testing; technical advise and
support.
About Us
Formed in 2002, the EPECentre is an industry
funded Centre of Excellence for power engineering
in New Zealand, hosted at the University of
Canterbury in Christchurch. It is focused on power
engineering education, research & development,
innovation, and industry interaction.
Our People
The EPECentre has a dedicated team of R&D power
engineers, technical power systems specialists,
research scholars, and in-house project
management and technical support – a combined
team of over 25 power engineers within campus,
combined with a reputation for one of the leading
power engineering programmes in the southern
hemisphere.
Our Facilities
World class facilities and equipment, including a
state-of-the-art electric machines laboratory and a
HV laboratory with an impressive 1.4MV Impulse
Generator - Plus: industry standard test equipment,
including power harmonics analysers, signal
generators, oscilloscopes, and software for harmonic
analysis, power flow, and fault analysis, such as
PSCAD, IPSA, Power Factory, and PSPICE.
Past Clients
Orion, Transpower NZ, Meridian Energy, Vector,
Enermet, ElectraNet SA, Metrix, ACCG, Antarctica
NZ, Canterbury TX, Pearson Innovations, CAE NZ...
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our industry partners:
Electric Power Engineering Centre (EPECentre)
University of Canterbury,
Private Bag 4800, Christchurch, New Zealand
Tel: +64 21 1144 330
Email: joseph.lawrence@epecentre.ac.nz