acs power transformers

96 Pages·2013·2.64 MB·English

ACS POWER TRANSFORMERS
Fleet Strategy
Document TP.FS 20.01
November 2013
ACS POWER TRANSFORMERS FLEET STRATEGY
© Transpower New Zealand Limited 2013. All rights reserved. Page 1 of 96
ACS Power Transformers Fleet Strategy
TP.FS 20.01
Issue 1
November 2013

C O P Y R I G H T © 2 0 1 3 T R A N S P O W E R N E W Z E A L A N D L I M I T E D . A L L R I G H T S
R E S E R V E D
This document is protected by copyright vested in Transpower New Zealand Limited (‘Transpower’). No part of the document may be
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without the prior written permission of Transpower. No information embodied in the documents which is not already in the public
domain shall be communicated in any manner whatsoever to any third party without the prior written consent of Transpower.
Any breach of the above obligations may be restrained by legal proceedings seeking remedies including injunctions, damages and costs.

ACS POWER TRANSFORMERS FLEET STRATEGY
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ACS Power Transformers Fleet Strategy
TP.FS 20.01
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November 2013

Table of Contents
EXECUTIVE SUMMARY ...................................................................................................................... 4
SUMMARY OF STRATEGIES .............................................................................................................. 7
1 INTRODUCTION ....................................................................................................................... 8
1.1 Purpose ................................................................................................................................. 8
1.2 Scope .................................................................................................................................... 8
1.3 Stakeholders ......................................................................................................................... 8
1.4 Strategic Alignment ............................................................................................................... 8
1.5 Document Structure .............................................................................................................. 9
2 ASSET FLEET ........................................................................................................................ 10
2.1 Asset Statistics .................................................................................................................... 10
2.2 Asset Characteristics .......................................................................................................... 14
2.3 Asset Performance .............................................................................................................. 26
3 OBJECTIVES .......................................................................................................................... 39
3.1 Safety .................................................................................................................................. 39
3.2 Service Performance ........................................................................................................... 39
3.3 Cost Performance ............................................................................................................... 40
3.4 New Zealand Communities ................................................................................................. 40
3.5 Asset Management Capability ............................................................................................ 41
4 STRATEGIES.......................................................................................................................... 43
4.1 Planning .............................................................................................................................. 43
4.2 Delivery ............................................................................................................................... 51
4.3 Operation ............................................................................................................................. 57
4.4 Maintenance ........................................................................................................................ 60
4.5 Preventive Maintenance ...................................................................................................... 60
4.6 Disposal and Divestment .................................................................................................... 67
4.7 Asset Management Capability ............................................................................................ 68
4.8 Summary of RCP2 Fleet Strategies .................................................................................... 72
APPENDICES ..................................................................................................................................... 74
A POWER TRANSFORMER IMAGES ....................................................................................... 75
B ADDITIONAL COSTING INFORMATION ............................................................................... 76
C ADDITIONAL BENCHMARKING RESULTS .......................................................................... 77
D TRANSFORMER ASSET STRATEGY ECONOMIC ANALYSIS, 2010 ................................. 80
E POWER TRANSFORMER WINDING FAILURE HISTORY ................................................... 93
F HISTORIC TRANSFORMER ‘MID-LIFE’ OVERHAULS ......................................................... 96
ACS POWER TRANSFORMERS FLEET STRATEGY
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ACS Power Transformers Fleet Strategy
TP.FS 20.01
Issue 1
November 2013
EXECUTIVE SUMMARY
Introduction
Power transformers play an essential role within the transmission network by enabling the
transfer of energy between different voltage levels of the Grid. The performance of power
transformers is critical to maintaining reliability of supply to customers.
Our asset management approach for power transformers seeks to achieve a high level of
reliability for this essential equipment, to mitigate safety hazards and to achieve least whole-
of-life cost.
Asset fleet and condition assessment
1
As at June 2013 we had 352 power transformers in service. The main power transformer
fleet comprises supply transformers and interconnector transformers. The two main
configurations are three - phase transformers, and banks comprising a set of three single -
phase transformer units.
The average age of the 132 banks of single-phase transformers is 51 years. There are 211
three-phase transformers, with an average age of 20 years. We also have 9 traction
transformers, with an average age of 20 years.
Long-term reliable performance of power transformers depends mostly on the quality of the
original design and manufacture, together with competent operation and maintenance.
Many older power transformers on the network are known to be of poor design and
manufacture. In particular, the transformers manufactured in the 1970s and 1980s are
considered to be high risk.
Our transformer fleet as a whole currently suffers from a high rate of forced and fault
outages. This high rate leads to increased risk of interruptions to customers. We would need
to cut this outage rate in half, just to be an average performer among our peers.
The single-phase transformers make a disproportionate contribution to the high rate of
forced and fault outages. The tap changers and bushings of aged single-phase transformers
are a particular cause of unreliability.
Our rate of major failures of power transformers also exceeds that of comparable
international benchmarks. Major failures lead to significant risks to the reliability of service
to customers, high costs of restoration and recovery, and can have potentially severe safety
and environmental consequences.
Most of the causes of the defects, poor performance and major failure risks in the older
transformers are related to their design and manufacture. These risk factors cannot be fully
mitigated through maintenance. However, some specific risks and modes of failures are
being addressed, through programmes of work to improve tap changer performance and
replace high-risk bushings.
Our approach to procuring power transformers changed markedly from around 1992, in
response to the high rate of power transformer failures we had experienced, and the
associated risks and costs. From that point, we applied a much more demanding technical

1
For the purposes of this population count, we classify a three-phase set of single-phase transformers as one
transformer bank.
ACS POWER TRANSFORMERS FLEET STRATEGY
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ACS Power Transformers Fleet Strategy
TP.FS 20.01
Issue 1
November 2013
specification, and took a range of steps to ensure greatly improved quality in design and
manufacture. Our current population of power transformers may now be divided into two
main categories – those manufactured after 1992 that are of high-quality design and
manufacture (about 40% at present), and those from earlier periods.
The performance to date of the 125 transformers we have purchased since 1992 has been
good, with only one of these transformers suffering a major failure in service. This
performance is significantly better than relevant international benchmarks, and a marked
improvement on the performance of the legacy fleet.
We have developed an initial model of asset health for the transformer fleet. This model
makes use of an economic analysis of optimum age for transformer replacement, and
incorporates learnings from our operating experience over the past 20 years. The model
shows that 11% of the fleet are now due for replacement.
Power transformer strategies
Our strategy for improving power transformer reliability is to progressively replace the
population of transformers that have the worst asset health, are the worst performers, and
are the most likely to suffer major failures.
Increasing customer demand at Grid Exit Points (GXPs) has often led to the replacement of
older power transformers, as part of providing increased capacity. However, in 2009 we
commenced a specific programme to identify and replace ageing power transformers, based
on their condition and risk factors. Since 2005, we have replaced approximately 30 older
power transformers, either for capacity enhancement or on the basis of condition and risk.
This replacement programme is continuing through the RCP1 period.
We have also purchased a range of strategic spare three-phase power transformers to
improve our ability to restore security in a timely manner, following the major failure of an
in-service unit. Several of these strategic spares have already been deployed following the
failure of an in-service unit, and allowed us to promptly restore security and minimise the
risk of interruptions to customers. We now also have a mobile substation that can be used at
small N security sites to enable extended outages for maintenance, and to facilitate the
restoration of supply after a major failure.
The benefits of our transformer replacement and strategic spares programme to date
include reductions in risk of interruptions to customers, reduced maintenance costs, and
reduced environmental impact of acoustic noise and oil leaks. The replacement transformers
also have significantly lower energy losses, compared with the original units.
Our long-term strategy is to replace the entire population of single-phase power
transformers. We expect that this will take approximately 20 years to complete.
During the RCP2 period, we propose to replace 30 aged and high-risk power transformers at
a total estimated cost of $106m. This replacement programme has been established after
applying resource constraints.
As a consequence of the replacements planned in RCP1 and RCP2, the overall health of the
transformer fleet is forecast to improve significantly over the period. Based on the current
asset health model, it is forecast that the percentage of the fleet that is due for replacement
will reduce from the current 11% to 4% by 2020. This improvement in forecast asset health
will lead to a significant reduction in the risk to customers resulting from transformer forced
and fault outages and major failures.
ACS POWER TRANSFORMERS FLEET STRATEGY
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ACS Power Transformers Fleet Strategy
TP.FS 20.01
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November 2013
Improvements
In our planning for the RCP2 period we have made a number of improvements to the asset
management of power transformers, including:
 developing a prototype asset health forecasting model
 using a customised estimate process to improve the scope and cost estimates
 using network criticality to improve the prioritisation of works.
Further improvements will include:
 refining the asset health model
 refining the criticality framework.
ACS POWER TRANSFORMERS FLEET STRATEGY
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ACS Power Transformers Fleet Strategy
TP.FS 20.01
Issue 1
November 2013
SUMMARY OF STRATEGIES
The following summary lists the main strategy and its respective costs during the RCP2
period (2015–2020).
Capital expenditure (Capex)
Replace Unreliable Power Transformers RCP2 Cost $106.2m
Our strategy is to replace 30 unreliable transformers with modern equivalents over the
RCP2 period. This includes the replacement of five transformers at Kinleith Substation as
part of a large-scale project at that site. The replacement programme for the
30 transformers has been prioritised taking into account asset health, criticality, the
coverage provided by national spare s and the mobile substation, and integrated works
planning considerations .
The cost estimates for these transformer replacements have been developed using a
customised estimating process. The total forecast cost of the replacement programme
during RCP2 is $106.2m.
Chapter 4 has further detail on this strategy and a discussion of the remaining strategies.

ACS POWER TRANSFORMERS FLEET STRATEGY
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ACS Power Transformers Fleet Strategy
TP.FS 20.01
Issue 1
November 2013
1 INTRODUCTION
Chapter 1 introduces the purpose, scope, stakeholders, and strategic alignment of the power
transformer asset fleet strategy.
1.1 Purpose
The purpose of this strategy is to describe our approach to lifecycle management of our
power transformer asset fleet. This includes a description of the asset fleet, objectives for
future performance and strategies being adopted to achieve these objectives.
The strategy sets the high-level direction for fleet asset management activities across the
lifecycle of the asset fleet. These activities include Planning, Delivery, Operations, and
Maintenance.
This document has been developed based on good practice guidance from internationally
recognised sources, including BSI PAS 55:2008.
1.2 Scope
The scope of this asset strategy encompasses the fleet of supply and interconnector
transformers including single-phase and three-phase types. It excludes transformers in the
HVDC system, as their management is described in the HVDC Fleet Strategy.
1.3 Stakeholders
Power transformer assets are important components of the transmission system. Correct
operation and maintenance of these assets enables the reliable operation of the power
system. Key stakeholders for these assets include:
 relevant Transpower Groups: Grid Development, Performance and Projects
 regulatory bodies: Commerce Commission, Electricity Authority, and the
Environmental Protection Authority
 customers, including distribution network businesses and industrial plants and
generators that are directly connected
 local residents.
1.4 Strategic Alignment
A good asset management system shows clear hierarchical connectivity or ‘line of sight’
between the high-level organisation policy and strategic plan, and the daily activities of
managing the assets.
This document forms part of that hierarchical connectivity by setting out our strategy for
managing our power transformer assets to deliver our overall Asset Management Strategy.
This fleet strategy directly informs the Power Transformer Asset Management Plan, which
includes more detail on the timing of specific capital and operating works.
This hierarchical connectivity is represented graphically in Figure 1. It indicates where this
fleet strategy and plans fit within our asset management system.
ACS POWER TRANSFORMERS FLEET STRATEGY
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ACS Power Transformers Fleet Strategy
TP.FS 20.01
Issue 1
November 2013

Figure 1: The Power Transformer Asset Strategy within the Asset Management Hierarchy
1.5 Document Structure
The rest of this document is structured as follows.
Chapter 2 provides an overview of the existing power transformer fleet including fleet
statistics, characteristics and their historical performance.
Chapter 3 sets out asset management-related objectives for the power transformer asset
fleet. These objectives have been aligned with the corporate and asset management
policies, and with higher-level asset management objectives and targets.
Chapter 4 sets out the fleet specific strategies for the management of the power
transformer asset fleet. These strategies provide medium-term to long-term guidance and
direction for asset management decisions to support the achievement of the objectives in
chapter 3.
Corporate Objectives & Strategy
Appendices are included that provide further detailed information to supplement the fleet
strategy.
Asset Management Policy
Asset Management Strategy
Lifecycle Strategies
Planning Delivery Operations Maintenance Disposal
Power Transformer Strategy
ACS POWER TRANSFORMERS FLEET STRATEGY
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Power Transformer Plan
ACS Power Transformers Fleet Strategy
TP.FS 20.01
Issue 1
November 2013
2 ASSET FLEET
Chapter 2 provides a high-level description of the power transformer asset fleet, including:
 Asset statistics: including population, diversity, age profile, and spares
 Asset characteristics: including safety and environmental considerations, asset
criticality, asset condition, asset health, maintenance requirements and interaction
with other assets
 Asset performance: including reliability, safety and environmental and risks and
issues.
The two main classes of power transformers considered in this fleet strategy are supply
transformers and interconnecting transformers.
 Supply transformers: These transformers connect between the main
transmission/distribution network (220 kV or 110 kV or 66 kV) and supply networks
(33 kV, 22 kV or 11 kV).
 Interconnecting transformers: These transformers interconnect between the main
transmission network (220 kV) and the regional transmission and sub-transmission
network (110 kV or 66 kV).
Our fleet of power transformers also includes small transformers that provide local service
and earthing functions. These small transformers are not given significant coverage in this
fleet strategy because they typically have only minor impact on overall service, and we have
2
spares that can be deployed promptly in the event of failure.
Traction transformers (dedicated to supply KiwiRail) are not specifically covered in strateg ies
in this document, but are dealt with on a case - by - case basis . There are spares to cover the
traction transformer units in service.
2.1 Asset Statistics
This section describes the power transformer asset fleet population, along with their
diversity and age profiles.
2.1.1 Asset Population
As at June 2013, we have 352 power transformers in service.
Some transformers are sets of three single-phase units grouped to form a bank. These banks
of single-phase units currently make up approximately 40% of the transformer fleet.

2
The replacement of two aged local service transformers of unusual rating at Islington is planned during RCP2 as part of
a major upgrade of the local service supply system, as described in the Fleet Strategy – ACS Other.
ACS POWER TRANSFORMERS FLEET STRATEGY
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