ACS INDOOR SWITCHGEAR Fleet Strategy

ACS INDOOR SWITCHGEAR 2015–2020 Fleet Strategy © Transpower New Zealand Limited 2013. All rights reserved. Page 1 of 63

ACS INDOOR SWITCHGEAR

Fleet Strategy

Document TP.FL 17.01

October 2013

ACS Indoor Switchgear Fleet Strategy TP.FL 17.01 Issue 1 October 2013

ACS INDOOR SWITCHGEAR FLEET STRATEGY © Transpower New Zealand Limited 2013. All rights reserved. Page 2 of 63

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ACS Indoor Switchgear Fleet Strategy TP.FL 17.01

Issue 1 October 2013

ACS INDOOR SWITCHGEAR FLEET STRATEGY © Transpower New Zealand Limited 2013. All rights reserved.

Table of Contents

EXECUTIVE SUMMARY ...................................................................................................................... 1

SUMMARY OF STRATEGIES .............................................................................................................. 3

1 INTRODUCTION ....................................................................................................................... 5

Purpose ................................................................................................................................. 5 1.1

Scope .................................................................................................................................... 5 1.2

Stakeholders ......................................................................................................................... 6 1.3

Strategic Alignment ............................................................................................................... 6 1.4

Document Structure .............................................................................................................. 7 1.5

2 ASSET FLEET .......................................................................................................................... 8

Asset Statistics ...................................................................................................................... 8 2.1

Asset Characteristics .......................................................................................................... 12 2.2

Asset Performance .............................................................................................................. 20 2.3

3 OBJECTIVES .......................................................................................................................... 27

Safety .................................................................................................................................. 27 3.1

Service Performance ........................................................................................................... 28 3.2

Cost Performance ............................................................................................................... 28 3.3

New Zealand Communities ................................................................................................. 28 3.4

Asset Management Capability ............................................................................................ 29 3.5

4 STRATEGIES.......................................................................................................................... 31

Planning .............................................................................................................................. 31 4.1

Delivery ............................................................................................................................... 39 4.2

Operation ............................................................................................................................. 43 4.3

Maintenance ........................................................................................................................ 43 4.4

Disposal and Divestment .................................................................................................... 48 4.5

Asset Management Capability ............................................................................................ 50 4.6

Summary of RCP2 Fleet Strategies .................................................................................... 52 4.7

APPENDICES ..................................................................................................................................... 54

A PHOTOS OF TYPICAL INDOOR SWITCHGEAR INSTALLATIONS ..................................... 55

B SCHEDULE OF MAJOR FAILURES ...................................................................................... 57

C ILLUSTRATION OF MAJOR FAILURES ................................................................................ 58



EXECUTIVE SUMMARY

Introduction

Our fleet of indoor switchgear is divided into two main classes:

high-voltage gas-insulated switchgear

medium-voltage indoor switchgear.

High-voltage (HV) gas-insulated indoor switchgear provides critically important control, protection and safety functions at some of our most important substation sites. The fleet of medium-voltage (MV) indoor switchgear provides these same functions in lower-voltage network branches, and serves as the point of interface for a large proportion of our customer connections. The performance of our indoor switchgear is essential to ensuring public safety and maintaining reliability of supply to customers.

Our asset management approach for indoor switchgear seeks to achieve an appropriately high level of reliability for this essential equipment, to mitigate safety hazards and to avoid major failures.

Asset fleet and condition assessment

We have nine installations of HV gas insulated indoor switchgear operating at 220 kV and 110 kV, including a total of 73 circuit breakers. These installations serve some of the most important loads on our network. The gas insulated switchgear (GIS) is of robust design, achieves very high levels of reliability and is in good condition. However, recovery from any major failure would be difficult and protracted, because of the specialist nature of the equipment. Asset management of this equipment takes account of the network criticality and the potential consequences of failure.

Our fleet of MV switchgear includes 77 installations operating at 33 kV, 22 kV and 11 kV. There are a total of approximately 750 circuit breakers. There is a wide range of makes and models of switchgear in service, although a significant proportion of the 11 kV indoor switchgear originates from a locally based manufacturer. Most of our indoor MV switchgear fleet is in good condition, and achieves high levels of reliability.

However, there are some older installations, particularly those with withdrawable bulk oil circuit breakers that pose significant risks to safety and reliability. Safety standards in the design of indoor MV switchgear have changed significantly over the past 30 years. The use of oil circuit breakers in new equipment was phased out in the 1980s. Older designs were usually based on withdrawable circuit breakers, but fixed pattern switchgear is now available. Modern indoor switchgear is designed to safely withstand internal arc faults, and is often physically segregated to eliminate the risk of widespread damage to an entire installation in the event of a major failure.

At some of our existing indoor switchgear sites, particularly those with older generation equipment, our studies indicate the potential for hazardous arc flash incidents to occur. Arc-flash protection has already been retrofitted at eight sites, to minimise the risk of harm and limit damage to equipment, by providing fast clearance times for any arcing fault. Further installations of arc-flash protection will be completed at another eight sites during RCP1.



It is not practical to eliminate all potential root causes of major failures in older generation MV switchgear and, despite the retrofitting of arc-flash protection, there could still be serious consequences from such failures.

We have recently completely replaced three indoor MV switchboards employing oil circuit breakers, and a further three switchboards will be replaced during RCP1.

One site that requires special risk management consideration is the large installation at Kinleith, where there are forty-two 11 kV bulk oil circuit breakers and five 33 kV circuit breakers in one switchgear room. This equipment is now due for replacement.

Indoor switchgear strategies

To maintain the asset health of our indoor MV switchgear fleet we plan to replace four MV indoor switchboards at a further three sites during the RCP2 period, including the large installation at Kinleith.

Other safety improvements planned for indoor MV switchgear during RCP2 include installing arc-flash protection at a further 9 sites, and retrofitting design improvements to improve arc fault containment at 10 sites.

To ensure the continued long-term reliable performance of the HV, gas insulated indoor switchgear located at Clyde Power Station, we will undertake a major programme of non-recurring maintenance. This will involve replacing a wide range of components of this switchgear that have deteriorated or require an upgrade.

Improvements

In our planning for the RCP2 period we have made a number of improvements to the asset management of indoor switchgear, including:

developing an asset health indicator system to provide a more systematic approach to long-term forecasting

ensuring replacement prioritisation now takes into account asset criticality

improving the scope and cost estimation process.

Further improvements will include:

refining condition assessment techniques and the asset health model

refining the asset criticality framework.



SUMMARY OF STRATEGIES

This section provides a high-level summary of the main asset management strategies for the indoor switchgear fleet.

Main strategies

The following summaries include the main strategies and their respective costs during the RCP2 period (2015/16–2019/20).

Capital expenditure (Capex)

Replace Legacy and Poor Condition Indoor MV Switchgear

RCP2 Cost $23.7m

A small number of older MV switchboards in service no longer meet our expectations for safety and reliability. These switchboards mostly employ bulk oil circuit breakers. Experience in New Zealand and overseas has shown that this type of equipment is vulnerable to major failure, with significant risks to safety and reliability. Most of these older switchboards do not meet current international safety standards for the physical space around equipment that is required to enable safe access and egress in an emergency.

Our strategy is to continue our existing programme of replacing high-risk MV switchgear with modern indoor switchgear, to reduce safety and reliability risks, and to avoid major failures.

The plan for the RCP2 period involves replacing four MV switchboards at three sites in total, including ones containing oil circuit breakers that were originally manufactured in the 1960s, 1970s and early 1980s.

The scope includes replacing a particularly large installation at Kinleith, where there are forty-two 11 kV circuit breakers and five 33 kV circuit breakers in one switchgear room.

Retrofit Safety Improvements to Existing Indoor MV Switchboards where practicable

RCP2 Cost $3.8m

A number of our MV switchboards do not currently meet our expectations for a safe working environment. For some of these switchboards, it is possible to retrofit significant design changes to improve arc fault containment.

The strategy is to undertake arc fault containment safety improvement works on MV switchboards where practicable, and so defer the need for replacement.

The plan will involve undertaking safety improvements on 10 existing switchboards at an estimated cost of $3.8m.



Arc-Flash Protection Installation for Existing Indoor Switchgear

RCP2 Cost $2.6m

It is standard practice to install arc flash protection on all new indoor switchboards as a safety measure to clear bus faults quickly. The strategy is to retrofit arc flash protection equipment on existing indoor switchboards where it is currently not installed.

The plan will involve installing new arc-flash protection equipment on nine existing indoor switchboards with a forecast cost of $2.6m in RCP2.

Operational expenditure (Opex)

Repair or Replace Components on Clyde GIS switchgear

RCP2 Cost $5.1m

The hydraulic drives, pressure relief devices, moisture filters and other components of the Clyde 220 kV GIS indoor switchgear are either in poor condition or require major upgrades to address failure modes identified from our own experience, or based on advice from the original equipment manufacturer .

Our strategy is to repair or replace these components to ensure continued high reliability. These works will be undertaken as maintenance projects and the forecast expenditure is expected to be $5.1m in total over the RCP2 period.

Chapter 4 has further details on these strategies and a discussion of the remaining strategies.



1 INTRODUCTION

Chapter 1 introduces the purpose, scope, stakeholders, and strategic alignment of the indoor switchgear fleet strategy.

Purpose 1.1

We plan, build, maintain and operate New Zealand’s high-voltage (HV) electricity transmission network (‘Grid’) which includes the indoor switchgear assets.

The purpose of this strategy is to describe our approach to lifecycle management of our medium and HV indoor switchgear fleets. 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 asset management activities across the lifecycle of the asset fleet. These activities include Planning, Delivery, Operations, Maintenance, Disposal and Divestment.

This document has been developed based on good practice guidance from internationally recognised sources, including BSI PAS 55:2008.

Scope 1.2

The scope of the strategy includes our indoor switchgear at both medium-voltage (MV) and HV levels:

MV refers to equipment operating in the voltage range 1 kV to 72.5 kV inclusive;

HV refers to 72.5 kV to 230 kV. Our HV switchgear is often referred to as Gas Insulated Switchgear (GIS).

The indoor switchgear fleet is essential for protecting our power transmission equipment. A large proportion of our indoor switchgear is installed close to the interface point with our customers, and provides control, protection and safety functions for customer feeder and generator connections.

Indoor switchgear generally includes the following components:

metal enclosure

enclosed busbar system

circuit breakers

disconnecting and earthing arrangements

Current Transformers (CTs) and Voltage Transformers (VTs)

local controls, instruments and protection relays

cable boxes

internal arc-flash detection equipment

arc venting system.



Stakeholders 1.3

The indoor switchgear asset fleet forms an important part of our transmission system. Correct operation and maintenance of the indoor switchgear asset fleet is essential for protecting power transmission and distribution equipment, as well as ensuring the safety of our employees and service providers and members of the public in the case of a fault.

Key stakeholders include:

relevant Transpower Groups: Grid Development, Performance and Projects

regulatory bodies: Commerce Commission and Electricity Authority

service providers

customers, including generators and distribution network businesses

landowners.

Strategic Alignment 1.4

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 the indoor switchgear asset fleet to deliver our overall Asset Management Strategy in support of our asset management policy. This fleet strategy directly informs the indoor switchgear Asset Management Plan.

This hierarchical connectivity is represented graphically in Figure 1. It indicates where this fleet strategy fits within our asset management system.

Figure 1: The Indoor Switchgear Strategy within our Asset Management Hierarchy

Indoor Switchgear Plan

Indoor Switchgear Strategy

Corporate Objectives & Strategy

Asset Management Policy

Asset Management Strategy

Lifecycle Strategies

DeliveryPlanning Operations DisposalMaintenance



Document Structure 1.5

The rest of this document is structured as follows.

Chapter 2 provides an overview of the indoor switchgear fleet including fleet statistics, characteristics and their performance.

Chapter 3 sets out asset management related objectives for the indoor switchgear 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 indoor switchgear fleet. These strategies provide medium-term to long-term guidance and direction for asset management decisions and will support the achievement of the objectives in chapter 3.

Additional appendices are included that provide further detailed information to supplement the fleet strategy.



2 ASSET FLEET

Chapter 2 provides a high-level description of the indoor switchgear asset fleet, including:

Asset statistics: including population, diversity, age profile, and spares

Asset characteristics: including safety considerations, asset criticality, asset condition, maintenance requirements and interaction with other assets

Asset performance: including reliability, safety, and risks and issues.

Switchgear generally refers to the combination of circuit breakers, disconnectors and earth switches used to control, protect and isolate electrical equipment on electric power systems. It is used to de-energise equipment to allow maintenance to be carried out and to clear faults. Appropriate asset management of this equipment is important because it is directly linked to the reliability and safety of the Grid.

Our indoor switchgear asset fleet includes switchgear at varying voltages. There are some significant differences between the asset management issues and approach for MV and HV indoor switchgear, because of their different characteristics and costs. These differences are discussed throughout the strategy. Appendix A shows photos of typical MV and HV indoor switchgear installations.

Asset Statistics 2.1

This section describes the indoor switchgear asset fleet population, along with their diversity and age profiles.

Asset Population1 2.1.1

MV indoor circuit breakers

We have over 750 MV indoor circuit breakers operating at varying voltages, housed in 77 indoor switchboards. The number of MV switchboards is expected to increase by about 3 each year between now and 2025 as outdoor 33 kV switchyards are replaced with indoor switchgear.

Table 1 shows the breakdown of the fleet of MV Indoor circuit breakers (by interrupter type and voltage) as at June 2013.

1 Each indoor switchgear panel consists of a circuit breaker, disconnectors, instrument transformers and

buswork. However, in terms of expressing the condition, population and diversity, only circuit breakers are used here as the replacement/refurbishment criteria take the entire indoor switchgear panel into account and each panel is assumed to have one circuit breaker.



Type 11 kV 22 kV 33 kV Total

Vacuum 260 14 194 468

SF6 5 26 115 146

Bulk Oil 105 0 12 117

Air Blast 12 0 0 12

Minimum Oil 9 0 0 9

TOTAL 391 40 321 752

Table 1: MV Indoor Switchgear Circuit Breaker Population

HV indoor circuit breakers

There are 73 HV indoor circuit breakers in the fleet of GIS equipment, including 12 from the two new HV installations commissioned in Auckland in 2013 at Wairau Road and Hobson Street.

Table 2 lists all HV GIS installations, showing year of manufacture and volume of associated switchgear.

Site Voltage (kV) Year of

manufacture Manufacturer Age

2

Circuit breakers

Rangipo3 220 1979 Merlin Gerin 34 2

Bream Bay 220 1981 Mitsubishi 32 8

Wilton 220 1981 Mitsubishi 32 7

Tiwai 220 1982 Mitsubishi 31 14

Motunui 110 1983 Mitsubishi 30 9

Clyde4 220 1986 BBC 27 9

Otahuhu 220 2008 Areva 5 12

Wairau Road5 220 2012 Alstom 0 6

Hobson Street5 220 2012 Alstom 0 6

Table 2: Indoor HV Switchgear Asset Fleet Population

Fleet Diversity 2.1.2

MV switchboards

As at June 2013, our indoor MV switchgear panels are located at 64 different sites across the country. The three main switchboard busbar systems are:

compound insulated busbar – this technology is used in older installations (up to the 1970s)

air insulated busbar – this technology has been used for most metal-clad switchgear purchased since the early-1980s and is still being purchased at 11 kV

2 Age as at 2013.

3 The Rangipo GIS installation is shared with Genesis.

4 The Clyde GIS switchgear installation is shared with Contact Energy.

5 These sites are currently being built in Auckland and will be commissioned in 2013.



SF6 insulated busbar – this technology has been used since 2000 and is still current technology for 33 kV switchboards.

In terms of manufacturer diversity, we have approximately 10 different switchgear panel manufacturers, but panel components (such as the circuit breakers, disconnectors, and VTs) may have different manufacturers from the panel manufacturers (for example, a circuit breaker panel by Merlin Gerin and panel work by A & G Price). Currently, there are over 30 different manufacturers and over 300 models for all switchgear panel components.


There are approximately 750 metal-clad indoor circuit breakers in the network operating between 11 kV and 33 kV. Prior to 1980, oil was the main interrupting medium for indoor circuit breakers. Since then, the interrupters in switchboards have been primarily vacuum or SF6 gas types (with either air or SF6 insulated busbar systems). The diversity is shown in Figure 2.

Figure 2: MV Circuit Breakers – Diversity

HV switchboards

As at June 2013, we have indoor HV GIS installations at nine locations, supplied from five manufacturers. The main busbar systems for indoor HV circuit breakers are all SF6 insulated.


As at June 2013, there are 73 HV indoor circuit breakers in the fleet, operating at 220 kV and 110 kV. Table 3 shows the breakdown of these circuit breakers by voltage.

Type 220 kV 110 kV Total

SF6 64 9 73

Table 3: HV indoor circuit breakers by type and voltage

Age Profile 2.1.3

MV switchboards

Most of the MV switchgear has been installed since 1990, although some indoor switchgear installations date back as far as the 1950s to 1960s. There is currently a programme in place to replace outdoor 33 kV switchyards with indoor switchgear, resulting in about 3–4 new indoor switchboards each year.

BULK OIL (16%)

MIN OIL (1%)

SF6 (19%)

VACUUM (62%)

AIR BLAST (2%)

MV INDOOR CB - DIVERSITY



Age profile – MV indoor circuit breakers

The average age of MV circuit breakers is approximately 16 years, with the age profile shown by interrupter type in Figure 3.

Figure 3: MV Indoor Circuit Breaker Age Profile

The 11 kV switchboard population is expected to remain static, but the 33 kV switchboard population will increase due to the continuing conversion of outdoor switchyards. These numbers will be influenced by any additional customer driven investments required, or potential divestment of assets (subsection 4.5.2 covers potential divestment of assets).

MV switchgear – life expectancy

Based on our experience, the life expectancies for the main switchgear types are set out in Table 4. Life expectancy is the nominal life established for fixed asset accounting purposes. It represents the typical average life that is expected from a type of equipment before it is no longer fit to remain in service.

Vacuum Bulk oil Minimum oil SF6

Life Expectancy 35 50 35 35

Table 4: Typical MV Indoor Switchgear Life Expectancy

HV switchboards

The average age of HV indoor circuit breakers is approximately 26 years (excluding the new Hobson Street and Wairau Road installations).

Based on our experience, overseas experience, and advice from the manufacturers, the life expectancy for these circuit breakers is more than 40 years.

Spares 2.1.4

MV switchboards

Only minimal spares are held for most types of MV switchgear. For older switchboards, some spare parts are recovered from the decommissioning of similar types of equipment elsewhere. Original manufacturer support for MV equipment cannot be relied upon over extended periods of time. As an example, for one model of switchboard installed in 1998, it

0

20

40

60

80

100

120

0 5 10 15 20 25 30 35 40 45 50 55 60

AGE (YEARS)

BULK OIL MIN OIL SF6 VACUUM AIR BLAST

MV INDOOR CB - AGE PROFILE



is no longer possible to obtain any replacement parts or compatible equipment to retrofit into the switchboard cubicles.

We have recently built a 12-panel portable switchboard to enable us to respond to a major MV switchboard failure. The containerised switchboard can operate at 33 kV, 22 kV or 11 kV.

We have also recently built a mobile substation that is split onto two separate trailers. One trailer consists of a 4-panel switchboard that can operate at 33 kV, 22 kV or 11 kV. This mobile substation could also be used to enable us to respond to a MV switchboard failure.

The manufacturer of one of our predominant MV switchboard types is based in New Zealand. In the event of a failure on equipment manufactured by them, we can get replacement parts made relatively quickly. They are also able to manufacture some parts for other manufacturers’ equipment and this close working relationship has enabled us to repair a number of switchboard defects.

HV switchboards

We have a small number of spares for the older HV types of GIS switchgear. A significant number of spare parts have been ordered for the three new HV GIS switchboards recently commissioned in the Otahuhu, Hobson Street and Wairau Road Substations in the Auckland region.

Asset Characteristics 2.2

The indoor switchgear asset fleet can be characterised according to:

safety and environmental considerations

asset criticality

asset condition

asset health

maintenance requirements

interaction with other assets.

These characteristics and the associated risks are discussed in the following subsections.

Safety and Environmental Considerations 2.2.1

We are committed to ensuring that safety and environmental risks are minimised at all times. These risks are considered early in our asset management planning process. The most significant safety and environmental considerations for the indoor switchgear fleet are:

the potential for explosive failures and internal arc flashes

physical clearances around switchgear for safe access and escape

SF6 emissions

oil spills.

These issues are described below.



Safety considerations

Circuit breakers provide an essential safety function

Circuit breakers are important safety components of the transmission system. They are expected to remove items of plant from service quickly after a fault is detected and minimise any potential equipment damage or safety risk to personnel and the public. Although the power system usually has some form of backup protection in the event that a circuit breaker fails to trip when required, any such failure significantly increases safety risk to personnel and the public.

A large proportion of our fleet of MV indoor switchgear is located at the interface with our customers’ networks. The circuit breakers in this switchgear provide essential control, protection and safety functions for our customers.

Explosive failures and internal arc flashes

We have undertaken an analysis of switchboard arc-flash hazards6 and found that there is a possibility of significant arc-flash hazard at many of our indoor MV switchboards. The probability is very low, but the consequences are very serious. An arc-flash is a type of electrical ‘explosion’ that can occur at any time, but more so during maintenance and operation of switchgear. It can release a large amount of energy that can cause fatalities and serious permanent injury to personnel in the vicinity of the explosion. It can also cause widespread damage to equipment, leaving systems out of service for long periods of time.

Catastrophic failures can occur in switchgear as a result of electrical breakdown in circuit breakers or busbar insulation. When combined with oil, bituminous and other flammable materials, these electrical breakdowns can cause a substantial explosion and ongoing fire hazard. The risk is most significant in older, withdrawable switchgear where mechanical faults that can lead to an arc fault are more likely to occur and where a cabinet door is often open during switching or maintenance.7

The aftermath and clean-up following major failure incidents in New Zealand has exposed personnel to the potentially toxic products of combustion of electrical insulation materials. Further, the need to restore supply following these events has often led to the urgent re-livening of equipment contaminated by smoke damage, greatly increasing the safety risk exposure from a further failure.8

HV indoor switchgear equipment has a proven record of reliability, and failures are rare. The equipment poses a lower risk of arc-flash hazards than MV switchgear through the use of robust SF6 insulated busbar systems and non-withdrawable circuit breakers. In addition, maintenance is far less frequent, and switching procedures for HV equipment are carried out remotely, meaning personnel are less likely to be nearby if an arc flash was to occur.

6 Calculation and Mitigation of Arc Flash Hazards in Indoor Metalclad Switchgear by Ross Bridson and

Marshall Clark, paper to the 2006 Electricity Engineers’ Association (EEA) Annual Conference, 2006. 7 In the case of older generation switchboards, the failure can be particularly catastrophic, resulting in oil-

filled or compound-filled compartments rupturing and ejecting shrapnel and burning oil and gas. There are records in Australia of complete switchroom buildings burning down.

8 Risk to personnel in these circumstances has been mitigated by the use of portable instruments that

measure partial discharge, and by restricting access, but some increased safety risk has remained until the contaminated equipment has been completely cleaned or replaced.



Physical clearances around switchgear

Adequate physical clearances around switchgear are required to allow safe access for operations and maintenance, and to enable escape in the event of an emergency. The international standard9 requires that 500 mm shall always be available for evacuation, even when removable parts or open doors intrude into the escape routes. It requires that aisles shall be at least 800 mm wide.

The physical clearances around many of the legacy 33 and 11 kV MV switchboards are inadequate and do not meet these safety requirements. In some cases, MV switchgear is installed immediately adjacent to transmission level control and protection equipment.

The lack of segregation in the design of almost all installations built before 2008 significantly increases the risk of widespread damage and extended loss of supply in the event of a fault in switchgear or cable terminations.

An extreme case is Kinleith, where there are forty-two 11 kV circuit breakers and five 33 kV circuit breakers in one switchgear room. The control/relay room immediately adjoins the switchgear room, and the door between the two is not fire rated. The 11 kV switchgear consists of bulk oil withdrawable circuit breakers, and many of the cable connections are made in pitch-filled termination boxes. There is a high fault duty, and inadequate physical clearances around the switchgear. The potential exists for a catastrophic failure to cause a major safety incident, and widespread damage to equipment.

Environmental considerations

SF6

SF6 (sulphur hexafluoride) gas is a dielectric medium commonly used in indoor switchgear. It replaces oil as an insulation medium, and makes it possible to significantly reduce the size of the switchgear. Indoor switchgear is also more reliable and requires less maintenance than outdoor switchyards because of its controlled operating environment. Despite its many benefits SF6 is a potent greenhouse gas, with a global warming potential vastly greater than that of CO2.

There are particularly large quantities of SF6 gas in GIS switchgear. The Clyde 220 kV GIS installation is our largest GIS installation. It is a shared installation with Contact Energy. There is approximately 5,638 kg of SF6 contained within our gas compartments.

Poor design, ageing of seals and gaskets is a contributing factor in SF6 leaks from indoor HV switchgear.

Oil leaks and spills

Circuit breaker insulating oil is classed as an environmental hazard. Any significant spills into the environment are to be reported to the local authority and we may face fines under the Resource Management Act. We employ several methods to prevent oil entering the environment, including bunds, oil separators and spill response kits. In the case of indoor switchgear, oil volumes are relatively low so these risks are reduced; yet the risk of explosive fire remains.

9 IEC 61936-1 ‘Power installations exceeding 1 kV a.c. – Part 1: Common rules’.



Asset Criticality 2.2.2

We have derived a methodology that assesses the impact that the failure of busbars and circuits has on the reliability of each customer’s point of service (POS). Circuits in this context include indoor switchgear. All busbars and circuits are assigned a criticality of high, medium or low impact depending on how they affect customers when taken out of service.

These network criticalities have been considered in conjunction with asset health indicators to provide a risk assessment framework for our indoor switchgear. However, the criticality framework is at an early stage of development and does not presently take into consideration factors such as contingency arrangements, spares availability and site access issues, all of which play a role in identifying the best investment option for the indoor switchgear fleet.

Indoor circuit breaker criticality

Figure 4 sets out the proportion of MV and HV indoor circuit breakers in each criticality category.

Figure 4: Indoor Circuit Breaker Criticality

Asset Condition 2.2.3

The condition of indoor switchgear is assessed during regular inspections and testing. The observation of asset condition is a key tool for our asset management programme. It is the main input into the assessment of asset health – described in the next subsection – which is the main driver of asset management decisions, such as timing of replacement.

The condition assessments provide a score on a scale of 1 to 10, with 1 representing assets in poor condition (with a relatively high likelihood of failure), and 10 representing assets that are in as-new condition.

The following outlines the condition of HV and MV indoor switchgear assets. It is worth noting that indoor switchboards contain a number of separate asset types that may have varying condition.

MV switchgear condition

The 11 kV switchgear supplied before the 1980s generally incorporates heavy oil-insulated CT chambers and cable boxes. This generation of switchgear is becoming unreliable because of ageing insulation, compound and oil leakage. Some of this switchgear is showing signs of partial discharge, which indicates an increasing failure risk. This switchgear is monitored to locate the source and identify the need for repair or potential replacement.

LOW (47%)

MEDIUM (35%)

HIGH (18%)

MV INDOOR CB - CRITICALITY

LOW (23%)

MEDIUM (46%)

HIGH (31%)

HV INDOOR CB - CRITICALITY



Almost all of these existing switchboards use withdrawable circuit breakers that can suffer from mechanical problems such as failure to latch in the closed state, mal-alignment of the racking mechanism, and deterioration of secondary contacts.

Cable termination failures, whether in compound-filled cable boxes or more recent heat-shrink terminations, have been significant causes of faults and failures in metal-clad switchgear.

HV switchgear condition

The HV indoor switchgear installations are in good overall condition. Yet there are some significant issues of concern with the GIS installations at Rangipo and Clyde as detailed below.

Rangipo

The 220 kV indoor switchgear was installed at Rangipo Power Station in 1979. The GIS installation is shared with Genesis Energy.

There have been persistent problems with SF6 leaks from flange seals, and repairs have been made progressively since 1991, during annual power station shutdowns. The early leaks were a result of poor installation, while the later and current leaks are due to aging of the SF6 seals. The repairs carried out to date have been successful. This maintenance has cost approximately $50,000–$100,000 each year.

An online SF6 pressure monitoring system is being installed to enable us to improve our ability to monitor the leak performance of this switchgear and prioritise repairs.

Clyde

The Clyde 220 kV indoor switchgear was installed at Clyde Power Station in 1989. The GIS installation is shared with Contact Energy. The switchgear has generally performed well, but there are a number of issues of concern as set out below. These all have the potential to lead to extended outages of sections of the GIS equipment.

Hydraulic mechanism leaks

The switchgear is SF6 insulated, and the circuit breakers have hydraulic mechanisms that operate at 350 bar (5000 PSI).

Hydraulic leaks from circuit breaker mechanisms have occurred in the equipment and we own and that Contact own. The high operating pressure means that even small hydraulic leaks can cause major problems. The prime cause of the leaks is deterioration of seals and O-rings. When the seals break down, the hydraulic oil can become contaminated with traces of the O-ring material, which can cause alarms due to sticky flow switches, and increase the risk of mal-operation of the hydraulic mechanism. As a temporary measure, regular changes of oil and filters have alleviated the situation.

The hydraulic mechanisms on four of our nine 220 kV GIS circuit breakers at Clyde had major overhauls carried out in 2011 to repair oil leaks. This work required upgraded components to be installed, and specialist tooling and labour was required from ABB in Switzerland.

Pressure relief device deterioration

The original equipment manufacturer (now ABB), has advised us of a number of potential failure modes that have been observed worldwide on this type of GIS.



The most significant potential mode of failure is premature rupture of overpressure relief devices (PRDs). The PRDs are intended to provide a controlled relief of gas overpressure that can occur during an internal electrical arc fault. The original devices have replaceable discs made of graphite. ABB has recommended that all PRDs be changed to a modern stainless steel disc, as the graphite types are prone to ageing which can lead to SF6 gas leaks, moisture ingress into the GIS, and unexpected failure of the discs.

Moisture filters

It is critical for the operation of the GIS, that the SF6 gas content contains a very low level of moisture. Each gas compartment contains moisture filters that absorb any moisture within the GIS. The existing moisture filters are made of aluminium oxide. In the event of an internal arc fault within the GIS, there is a possibility of exothermic reaction of the aluminium oxide that could result in enclosure melt-through and possible danger to personnel. ABB has recommended that these filters be replaced with modern molecular sieve filters.

Contact Energy has already carried out both of these recommended upgrades on their sections of the GIS installation. The filters would need to be changed anyway when the gas compartments are opened to replace the PRDs.

Disconnector and earth switch drive motor protection

The existing design does not include any motor protection to switch off the drive motor in the event of a fault in the mechanism or control circuits. We have already experienced one instance of a drive motor burning out. Fortunately, personnel were on site and they detected the motor burning out and were able to isolate it. This mode of failure has been observed in similar installations worldwide.

ABB has recommended an upgrade of the disconnector and earth switch drives.

The modification includes an upgraded motor assembly and a clutch. Contact Energy has already carried out this recommended upgrade on their sections of the GIS installation.

Asset Health 2.2.4

Asset Health Indices (AHI) is an asset management tool used to provide a systematic approach to prioritisation, based on a range of factors including asset condition. In our model, the health of an asset is expressed as a forecast of remaining useful life. We use the asset health model to make a prediction of the year when the asset will no longer be considered fit to remain in service. The AHI forecast of remaining useful life is based on modelling deterioration or risk that cannot be addressed by normal maintenance (where maintenance to address the deterioration or risk is not possible, practical, or is uneconomic). At this point major intervention is required, such as total replacement of the asset or refurbishment that significantly extends the original design life.

Asset health indicators provide a proxy for the probability of failure in asset risk management analysis.

Asset health indicators are also used in conjunction with asset criticality to assign priority within asset management planning processes.

The AHI is calculated using factors including:

the current condition of the asset

the operating environment



the age of the asset (relative to expected life)

the typical degradation path of that model

any model/type or usage factors that affect the risk or rate of degradation, such as known defects or failure modes, together with positive adjustments for particularly good performers.

We are still at a relatively early stage in the development and application of asset health indicators. More details on our asset health methodology are set out in the document ‘Asset Risk Management – Asset Health Framework.

The distribution of asset health for the indoor switchgear fleet is set out in Figure 5.


Figure 5 shows that approximately 5% of MV indoor circuit breakers are now due for replacement.

Figure 5: MV Indoor Circuit Breakers Asset Health as at June 2013


The HV indoor circuit breaker fleet’s asset health shows that all circuit breakers in this category have a forecast remaining life in excess of 15 years.

Maintenance Requirements 2.2.5

This subsection describes the maintenance activities undertaken on the indoor switchgear fleet which have informed the maintenance strategies discussed in section 4.4. The most common types of maintenance carried out on these assets are:

preventive maintenance, including:

- condition assessments

- servicing

corrective maintenance, including:

- fault response

- repairs

maintenance projects.

Maintenance projects are programmes of works (essentially made up of small projects) used to address repetitive issues identified through preventive and corrective maintenance.

12+ YRS (82%)

7-12 YRS (6%)

2-7 YRS (7%)

0-2 YRS (0%)

NOW DUE (5%)

MV INDOOR CB - ASSET HEALTH



The Maintenance Lifecycle Strategy provides further details on our approach to the above maintenance works, and the specific maintenance requirements are included in the relevant service specification documents.

Maintaining MV switchgear

The maintenance requirements of different types of switchgear vary widely.

The older 11 kV and 33 kV switchboards incorporate withdrawable bulk oil circuit breakers. This type of equipment is relatively maintenance intensive. Major servicing of contact assemblies and oil is required after the circuit breaker has operated to clear heavy faults. This requires handling of contaminated oil.

There are increasing maintenance difficulties with some of this equipment and a lack of spares because these models are no longer manufactured.

Maintenance requirements for modern switchgear are minimal by comparison, particularly for non-withdrawable switchgear. Thorough inspections are carried out to look for signs of abnormal wear, fatigue or overheating. As more vacuum switchgear and SF6 switchgear replace older oil switchgear, the fleet maintenance requirements are decreasing.

Maintaining HV switchgear

Very little maintenance is normally required on HV switchgear. Visual and thermographic inspections are carried out annually. Certificates of inspection must be issued yearly for the external inspection of hydraulic accumulators, and circuit breaker air receivers. Certificates for internal inspections of circuit breaker air receivers are required every four years. The main diagnostic service and inspection for the GIS switchgear group is scheduled each 8 years, but does not require invasive work inside gas compartments or on internal components of circuit breakers.

Historic spend – maintenance

We currently spend approximately $1m each year on indoor switchgear maintenance. On average, over the last 5 years we have spent approximately $200,000 each year on preventive maintenance and approximately $800,000 on corrective maintenance.

The corrective maintenance expenditure is much higher than the preventive maintenance expenditure because there have been a number of major failures in the last five years. A major indoor switchboard failure is costly and these failures have skewed the average annual corrective maintenance expenditure.

Maintenance projects

Maintenance projects typically consist of relatively high-value planned repairs or replacements of components of larger assets. Maintenance projects would not be expected to increase the original design life of the larger assets. Maintenance jobs are typically run as a project where there are operational and financial efficiencies from doing so.

Maintenance projects are usually planned at least 12 months in advance, and are often part of a long-term strategy for a particular fleet of assets. Maintenance projects are included in the integrated works planning process and are supported by individual business cases.

Chapter 4 describes future maintenance projects, including those planned for the RCP2 period.



Historic spend – maintenance projects

We have spent approximately $500,000 each a year over the last five years on indoor switchgear maintenance projects. For additional details, see the Maintenance Lifecycle Strategy.

Interaction with Other Assets 2.2.6

This indoor switchgear strategy is closely related to the following five associated asset strategies.

33 kV Outdoor Switchyard Fleet Strategy: closely related due to the ongoing conversion of outdoor switchyards to indoor switchgear. This programme of conversions is primarily driven by safety considerations.

Buildings and Grounds Fleet Strategy: closely related because in most cases the installation of new indoor switchgear will require additional building space or upgrades. As discussed in subsection 4.2.1, it is preferred that new indoor switchgear be installed in its own building, separate from HV protection, communications and infrastructure equipment.

Power Cables Fleet Strategy: closely related because of the use of cables in connecting indoor switchgear installations.

Power Transformers Fleet Strategy: closely related because, in some circumstances, the replacement of an aged indoor switchboard may be coordinated with the planned replacement or upgrade of existing power transformers.

Secondary Assets Fleet Strategy: closely related because, in some circumstances, the replacement of an aged indoor switchboard or arc-flash protection upgrades may be coordinated with the planned replacement or upgrade of secondary, protection, communications, and revenue metering equipment.

Our Integrated Works Planning (IWP) process allows for coordination to minimise disruption and reduce costs.

Asset Performance 2.3

This section describes the reliability, safety and environmental performance of the indoor switchgear fleet, together with a summary of major risks and issues.

Reliability Performance 2.3.1

Achieving an appropriate level of reliability for our asset fleets is a key objective, as it directly affects the services received by our customers. Reliability is measured primarily by the frequency and length of outages.

A high level of reliability is required for indoor switchgear given the critical safety functions of circuit breakers, and the potential for major failure to result in widespread damage to other equipment and significant interruptions to supply.



Major failures10

There have been 10 major failures of indoor switchgear over the past 25 years. These are listed in Appendix B. While the root causes of these major failures vary widely, there are many similarities in the consequences and in the conclusions arising from the investigation of the failures.

In most of these major failures, there was extensive damage caused by the arc blast and smoke. The lack of pressure relief or arc venting led to significant physical damage to equipment and building structures. In several cases, the contamination of adjacent equipment caused by the fault led to the need for accelerated replacement of the complete switchgear installation because of the corrosive effects of arc products and smoke.

In several cases, the lack of segregation in these installations compromised the reliability of supply from the complete switchboard, and there were several instances of extended periods of loss of supply.

In most cases, the switchgear adjacent to the damaged equipment was re-energised after some interim cleaning, to restore supply. However, this raised significant safety concerns for the personnel involved. Restricted access provisions were implemented in many of these cases because of the increased safety risk, and these remained until the contaminated equipment was fully replaced.

The main conclusion that is common to the major failures is that the design of indoor switchgear must incorporate arc fault containment and venting. Further, where significant loads are at risk, indoor switchgear installations must be segregated so that a major failure incident cannot cause damage to the entire busbar that could lead to a complete loss of service.

Other important conclusions from these major failures are:

MV switchboards with air insulated buswork are inherently vulnerable to insulation failure caused by moisture ingress, degradation of materials, and flashovers caused by rodents

arc protection in indoor MV switchgear is essential as a safety measure, and to minimise damage and the risks of extended interruption to supply in the event of a major fault.

10

Major failures are defined as failures that have caused collateral damage (such as explosion or switchroom fires), extended periods of loss of supply and the potential to cause injury or harm to personnel.



Forced and fault outage performance – MV switchgear

The forced and fault outage rate of indoor MV switchgear circuit breakers is shown in Figure 6.

Figure 6: MV Indoor Circuit Breakers – Forced and Fault Outages

In 2009, there were six forced outages on one of the Brydone substation 11 kV capacitor bank circuit breaker. There was an issue with the spring charge mechanism, which meant that the circuit breaker failed to close on multiple occasions. The issue was only identified after an expert from Reyrolle Pacific was brought in to investigate and the spring charge mechanism was replaced. There was no interruption to customer supplies.

Forced and fault outage performance – HV switchgear

Our HV indoor switchgear has a proven record of reliability and performance. Failures are extremely rare, but any failure could require a costly and time-consuming repair.

Safety and Environmental Performance 2.3.2

Subsection 2.2.1 described the characteristics of the indoor switchgear fleets that impact safety and environmental performance. This subsection reports on the actual safety and environmental performance of the assets.

Safety

There have been two major safety incidents involving indoor MV switchgear over the last 10 years. In these incidents, two maintenance personnel suffered arc-flash burns and one person was fatally injured. These incidents both resulted from unsafe acts and failure to follow our safety practices and procedures.

These tragic events form part of the background to our major drive to improve safety performance that commenced in 2005.

There have been no recorded incidents of major failures of our indoor switchgear directly leading to injury to personnel over the past 20 years. Yet, as outlined in subsection 2.2.1, the potential clearly exists.

0

2

4

6

8

10

12

2005 2006 2007 2008 2009 2010 2011 2012 2013

EQUIPMENT FAILURE OTHER

MV INDOOR CB - FORCED AND FAULT OUTAGES



Appendix C includes photos that illustrate the consequences of arc faults in indoor switchgear in some major failure incidents.

Indoor switchgear has been an area of focus in our overall safety improvements programme, and safety-related risks and initiatives for indoor switchgear are described further in subsection 2.3.3 and in the strategies in section 4.

Environmental

There have been persistent problems with SF6 leaks from flange seals on the 220 kV GIS switchgear at Rangipo, and repairs have been made progressively since 1991, during annual power station shutdowns. The early leaks were a result of poor installation, while the later and current leaks are due to ageing SF6 seals.

Our total inventory of SF6 gas as at 30 June 2013 was approximately 43 tonnes.11 Around 55% of this is contained in eight major GIS installations. For the year from 30 June 2012 to 1 July 2013, SF6 emissions from GIS equipment caused by leaks and losses in handling and repairs and so on represented approximately 12% of our total SF6 emissions.12

The hydraulic mechanisms on four of our nine 220 kV GIS circuit breakers at Clyde had major overhauls carried out in 2011 to repair oil leaks. These oil leaks were fully contained.

Risks and Issues 2.3.3

This subsection briefly discusses the most significant asset risks and issues relating to the indoor switchgear fleets. Strategies to address these risks and issues are set out in chapter 4.

Safety

The key safety considerations associated with our indoor switchgear fleet are set out in subsection 2.2.1. The most significant of these safety concerns are the potential for explosive failures and arc flashes, and inadequate segregation and physical clearances. Details of the safety risks and issues are set out below.

Potential for explosive failures and arc flashes

Electrical arcs and explosive failures in indoor MV switchgear have previously caused serious injury to electrical workers in New Zealand and overseas. Recent studies on the potential for serious harm resulting from arc-flash incidents at our indoor MV switchboards shows that, at some sites, the combination of high fault current and relatively long fault clearance times gives rise to the possibility of significant arc fault hazards.

Indoor switchgear is installed in an enclosure to control environmental factors and reduce the probability of faults. However, the consequences of a bus fault in indoor switchgear are severe and may include considerable damage to other equipment and to any people working on the equipment. Typical damage scenarios are illustrated in Appendix C. To mitigate these risks, reliable protection is essential.

Arc-flash protection is a form of bus protection that detects the arc-flash light within the switchgear during a fault and trips the bus; thereby significantly reducing the arcing time, and significantly reducing the hazard and consequences of failure. Dedicated arc-flash

11

The GIS switchgear at Hobson Street was not yet filled with gas as at 30 June 2013. 12

The balance of our emissions of SF6 was associated with outdoor circuit breakers.



protective relays are used, and the arc-flash light signal is combined with overcurrent detection before tripping the bus, to avoid false trippings.

We have an ongoing programme of work to mitigate arc-flash risks. Arc-flash protection has already been retrofitted at eight legacy sites with high arc-fault potential, to provide fast acting detection and ensure arc fault exposure is minimised. There have already been incidents where the operation of an arc-flash protection system has significantly reduced equipment damage when a fault occurred. Further installations of arc-flash protection will be completed at another eight sites during RCP1.

New requirements for personal protective equipment have also been issued for work at all sites where there is potential for a significant arc fault hazard.

Inadequate segregation

Most of the legacy MV switchboards were installed as a single switchboard in one physical compartment. There is no physical segregation that would help limit collateral damage in the event of a major failure. Lack of physical segregation leads to significantly increased safety risks for employees and service providers in dealing with the consequences of major failure, while also attempting to restore service as quickly as possible.

New designs incorporate physical segregation, as outlined in subsection 4.2.1.

Inadequate physical clearances

IEC61936-1 specifies that the space required for safe escape routes in front of switchgear panels is a minimum of 500 mm, in addition to any space required for removable parts or open doors that may intrude into the escape routes. When taking into account withdrawable circuit breakers or open doors, this may require up to 2000 mm of space in front of the panel. Many of our indoor switchgear installations do not comply with this requirement, and escape in an emergency may be impeded.

The standard also specifies that a minimum of 800 mm space is required for rear and side access to the switchboard. In some cases, physical clearances between the rear of the switchboard and walls (or protrusions from walls), are less than 500 mm. This would make the operation of a voltage detector (VD) (for the standard safety practice of ‘test-before-touch’) difficult and hazardous. The investigation ‘Proposed Recommended Distances Required Behind Indoor Metalclad Switchboards up to and including 33 kV with Rear Entry Cable Terminations’, by Ruth English, suggests that the minimum recommended distance behind 11 kV switchboards should be 1200 mm to allow unhindered operation of a VD.

The standard designs for new switchgear installations outlined in subsection 4.2.1 include provision of appropriate physical clearances.

For the legacy fleet where physical clearances are inadequate some risk mitigation is planned, as set out in subsection 4.1.2. For older installations where retrofitting safety improvements is not practical, the main risk mitigation is total replacement.

Cable termination failures

The failure of cable terminations on MV indoor switchgear has been a significant source of fault outages and major failures in indoor switchgear. The cable termination types affected include those in older compound-filled cable boxes and more recent installations using heat-shrink type terminations. Recent failures have been largely attributed to poor workmanship



in installation, with a contributing factor being inadequate physical space within certain types of switchgear cubicle to adequately install multiple cables for each phase.

Initiatives outlined in the ‘Fleet Strategy – Power Cables’ are intended to address the risk associated with cable termination failures.

Limitations of condition assessment

The currently available techniques for non-invasive condition assessment cannot reliably detect all risks of major failure in indoor switchgear. Some of the techniques that are available for assessment of insulation condition have some risk in themselves, and may require planned outages that are difficult to obtain. The results of some condition assessment tests can be difficult to interpret, because of the lack of prior measurements that would enable trending.

Therefore, asset management decision making cannot rely solely on tests and measurements, and a proactive approach is required to effectively manage risks.

Lack of spares

As described in subsection 2.1.4, there is a lack of spares for older MV switchboards and circuit breakers. This makes response to major failures more time-consuming and expensive, with a complete switchboard replacement being required in some situations.

We have a small number of spares held for the older HV type GIS switchgear. However some of these spares may no longer be in serviceable condition because of the age-related deterioration of seals.

HV switchgear reliability

GIS – critical equipment with little or no immediate recovery options

GIS installations are intended for use in critical applications, and are designed to achieve very high levels of reliability. Major failures of GIS equipment are rare.

Six of the nine GIS installations on our network are in critically important network locations. For most of these installations a major failure could lead to serious consequences, possibly of national significance. Further, in many cases, there is no immediately available alternative or contingency plan in the event of a catastrophic failure. Most of the GIS installations are located on small sites where there would be insufficient space to provide conventional air-insulated switchgear as an emergency alternative.

Recovery from major failure of GIS equipment would be protracted, and would probably require specialist personnel from the original manufacturers. There is still original manufacturer support for this type of equipment and we have established a good working relationship with them. However, the lead time for new components may be up to 12 months or longer.

Therefore, conservative management of the GIS equipment is essential, to ensure that the risk of major failures is kept to as low a level as is reasonably practicable.

Our three modern GIS installations in Auckland have been designed with additional internal isolation devices to enable a faulted section to be quickly isolated to enable repairs with minimal impact to other circuits.



GIS – major failure of hydraulic mechanisms

Although this would be a rare event, the potential exists for major failure in the hydraulically operated mechanisms of the GIS switchgear at Clyde and Rangipo. If oil pressure is lost from the circuit breaker, an alarm will be activated. Below a certain limit, low oil pressure triggers a circuit breaker lockout. This requires urgent operating action to de-energise a bus section, so that the faulty circuit breaker can be de-energised. This has system reliability implications and may result in a loss of generation connection.

The strategy for the hydraulic operating mechanisms of the Clyde GIS switchgear is set out in subsection 4.4.3.

GIS – failure of pressure relief devices

The graphite type of pressure relief devices fitted to our older GIS are prone to deterioration leading to SF6 gas leaks, moisture ingress into the GIS, and unexpected failure of the discs. Moisture ingress into the GIS may lead to internal discharge and deterioration of the switchgear, potentially leading to a major failure. Rupture of the discs leads to lockout of the circuit breaker, and again requires urgent operating action to de-energise a bus section.

The graphite discs at Rangipo have all been changed to a stainless steel type. The strategy for Clyde is set out in section 4.4.3.

GIS equipment – inadequate SF6 gas pressure monitoring facilities

One issue on our older GIS installations is the lack of pressure gauges or transducers on the individual gas compartments.

The original GIS installations had density switches fitted to each gas compartment that provide a two stage alarm to SCADA for SF6 low and SF6 lockout pressure levels. There were no pressure gauges installed, so a maintenance operator had to manually connect a pressure gauge onto each gas compartment to check the actual pressure.

This lack of immediate visibility of gas pressure made monitoring the pressure on the GIS costly and time consuming and did not enable trending or early detection of leakage before the low alarm occurred. The process of manually checking the gas pressures also poses a risk of SF6 gas emissions as a result of valves not sealing correctly after the pressure gauge is removed.

A programme of work is underway for the Rangipo GIS installation to provide pressure gauges and transducers, so that trending information is available. A similar programme of work will be undertaken on the Clyde GIS installation in RCP2, as set out in subsection 4.4.3. There are no plans at this stage to install pressure monitoring on our four Mitsubishi GIS installations.

Our three new GIS installations in Auckland were supplied with pressure gauges or an online monitoring system.



3 OBJECTIVES

Chapter 3 sets out asset management related objectives for the indoor switchgear asset fleets. As described in section 1.4, these objectives have been aligned with our corporate management objectives, higher-level asset management objectives and targets as set out in the Asset Management Strategy.

Our overarching vision for our indoor switchgear fleets is to achieve low maintenance together with high reliability and safety that meets our specifications, including arc containment and pressure relief. Further objectives have been defined in the following five areas:

Safety

Service performance

Cost performance

New Zealand communities

Asset management capability.

These objectives are set out below, while the strategies to achieve them are discussed in chapter 4.

Safety 3.1

We are committed to becoming a leader in safety by achieving injury-free workplaces for our employees and to mitigating risks to the general public. Safety is a fundamental organisational value and we consider all incidents to be preventable. We have defined overarching safety objectives for employee and public safety in our Asset Management Strategy.

Safety Objectives for Indoor Switchgear Fleets

- Zero harm/incidents resulting from:

o explosive failure

o arc flashes

o fire.

- Zero instances of indoor circuit breakers failing to trip.

- Zero fatalities and injuries while maintaining, repairing, installing or decommissioning indoor switchgear, including the handling of contaminated oil and SF6.

- Physical clearances for safe egress around indoor switchgear to meet international standards.



Safety in relation to HV faults is fundamentally about preventing incidents involving HV equipment and where incidents occur, minimising exposure time for employees or members of the public. Protection cannot predict where faults will occur, but the use of appropriate design concepts and technology can reduce injury and chance of death.

Service Performance 3.2

Ensuring appropriate levels of network performance is a key underlying objective.

Grid performance objectives state that a set of measures are to be met for Grid Exit Points (GXPs) based on the criticality of the connected load. In addition, asset performance objectives linked to system availability have been defined. These high-level objectives are supported by a number of fleet specific objectives, and we will work towards these being formally linked in the future.

Network Performance Objectives for Indoor Switchgear Fleets

- The forced and fault outage rate to be less than 1% each year.

- Restore security of supply within one calendar month of a major failure occurring.

- Zero failures attributable to vermin.

Cost Performance 3.3

Effective asset management requires optimising lifecycle asset costs while managing risks and maintaining performance. We are committed to implementing systems and decision-making processes that allow us to effectively manage the full lifecycle costs of our assets. We have defined cost performance objectives in our Asset Management Strategy, including a commitment to make asset management decisions that minimise whole-of-life costs for the asset fleet and for the transmission system overall.

Cost Performance Objectives for Indoor Switchgear Fleets

- Minimise whole-of-life cost by standardising designs for compact, modular, segregated switchgear.

- Achieve efficiency through divesting non-core transmission and distribution network investment.

New Zealand Communities 3.4

Asset management activities associated with the indoor switchgear fleets have the potential to impact on both the environment and on the day-to-day lives of various stakeholders. Relationships with landowners and communities are of great importance to us and we are committed to using asset management approaches that protect the natural environment.

New Zealand Communities Objectives for Indoor Switchgear Fleets

- Limit SF6 emissions to less than 1% of total inventory each year.

- Minimise the future requirements for SF6 by exploring alternative switchboard



designs (such as CO2 and vacuum).

- No significant oil spills into the environment.

- Minimise damage to third party property resulting from switchboard explosive failures or fires.

- Asset management approach is aligned with customers at the boundary.

- Maintain effective working relationships with customers.

- Consider possible future divestments when selecting the location of new MV switchboard installations.

Asset Management Capability 3.5

We aim to be recognised as a leading asset management company. To achieve this, we have set out a number of maturity and capability related objectives. These objectives have been grouped under a number of processes and disciplines that include:

Risk Management

Asset Knowledge

Training and Competency

Continual Improvement and Innovation.

The rest of this section discusses objectives in these areas relevant to the indoor switchgear fleet.

Risk Management 3.5.1

Understanding and managing asset-related risk is essential to successful asset management. We currently use asset criticality and asset health as a proxy for a fully modelled asset risk approach.

Asset criticality is a key element of many asset management systems. We are currently at an early stage of developing and implementing the models as we work towards formal and consistent integration of asset criticality into the asset management framework. We have commenced this by including criticality as a factor for the prioritisation of the fleet replacement expenditure programmes.

Asset health

We have developed a predictive model for some of our assets based on ‘Asset Health’. Asset Health has not yet been implemented for the indoor switchgear fleets.

Risk Management Objectives for Indoor Switchgear Fleets

- Extend the Asset Health Indices prototype model for indoor switchgear panels

Asset Knowledge 3.5.2

We are committed to ensuring that our asset knowledge standards are well defined to ensure good asset management decisions. Relevant asset knowledge comes from a variety of sources, including experience from assets on the Grid, and information from the



manufacturers. This asset knowledge must be captured and recorded in such a way that it can be conveniently accessed.

Asset Knowledge Objectives for Indoor Switchgear Fleets

- Maintain relationship and liaison with all switchboard suppliers, particularly the HV GIS switchgear suppliers.

- Ongoing sharing of asset condition and performance information with international peers and network operators.

- Improve standard maintenance procedures to obtain more effective condition assessments.

Training and Competency 3.5.3

We are committed to developing and retaining the right mix of talented, competent and motivated staff to improve our asset management capability.

Training and Competency Objectives for Indoor Switchgear Fleets

- All persons operating, installing or performing maintenance on switchgear are adequately trained.

- All persons installing cable terminations into indoor switchgear are certified as competent.

- All persons involved with SF6 handling are adequately trained.

- Retain access to adequate service providers with the appropriate maintenance knowledge of HV GIS switchgear.

Continual Improvement and Innovation 3.5.4

Continual improvement and innovation are important aspects of asset management. A large source of continual improvement initiatives will be ongoing learning from our asset management experience.

Continual Improvement and Innovation Objectives for Indoor Switchgear Fleets

- Awareness of emerging technologies, including CO2, vacuum, and intelligent circuit breakers.

- Develop improved approach to SF6 switchgear leak monitoring and top-ups.



4 STRATEGIES

Chapter 4 sets out the specific strategies for the management of the indoor switchgear fleet. These strategies are designed to support the achievement of the objectives in chapter 3 and reflect the characteristics, issues and risks identified in chapter 2.

The strategies are aligned with our lifecycle strategies below and the chapter has been drafted to be read in conjunction with them.

Planning Lifecycle Strategy

Delivery Lifecycle Strategy

Operations Lifecycle Strategy

Maintenance Lifecycle Strategy

Disposal Lifecycle Strategy.

This chapter also discusses personnel and service provider capability related strategies which cover asset knowledge, training and competence.

Scope of strategies

The strategies focus on expenditure that is to occur over the RCP2 period (2015–2020), but also include expenditure from 1 July 2013 to the start of the RCP2 period and some expenditure after the RCP2 period (where relevant). Capex planned for the RCP2 period is covered by the strategies in Sections 4.1 and 4.2, and operating expenditure is covered by the strategies in sections 4.3 to 4.6. The majority of capex consists of asset replacements, as described in subsection 4.1.3.

Planning 4.1

This subsection describes our strategies for the Planning lifecycle for the indoor switchgear asset fleet and identifies where and how these strategies support the higher-level strategies and objectives for our overall fleet.

Planning activities

The planning lifecycle is primarily concerned with identifying the need to make capital investments in the asset fleet. The main type of investment considered for this fleet is replacement and refurbishment.

We support the planning activities through a number of processes, including:

Integrated Works Planning (IWP)

cost estimation.

The planning lifecycle strategies for these processes are described in the subsections below.

Capital investment drivers

Categories of capital investment generally have specific drivers or triggers that are derived from the state of the overall system or of individual assets. These drivers include demand



growth, compliance with Grid reliability standards and failure risk (indicated by asset criticality and condition).

The most important driver for indoor switchgear investments is the improvement of safety by converting 33 kV outdoor switchyards to indoor switchgear. The conversion programme is detailed in the 33 kV Outdoor Switchyard fleet strategy. Further examples that drive capital investment in the indoor switchgear asset fleet include:

replacement of poor condition or failed indoor switchgear

Connection points for new customers.

The strategies below consider the long-term implications for these drivers as we extend our planning horizon as part of our programme of asset management improvement.

Enhancement and Development 4.1.2

The primary driver of enhancement and development projects stems from requirements for system growth due to changes to the scale and location of electricity supply and demand.

Indoor MV switchgear is preferred over outdoor MV switchyards for new projects because of the superior safety performance of indoor switchgear, together with the reduced maintenance requirements and intervals. In addition, indoor switchgear has a smaller footprint which is particularly beneficial as more substations are being required in urban and suburban areas (where land is difficult to obtain and visual impact is important).

Indoor switchgear is also protected from vandalism, pests and corrosion associated with the external environment.

Install new indoor MV switchgear for upgrade projects

Install new indoor switchgear for approved system growth or enhancement

projects.

A key underlying objective for us is to ensure appropriate levels of system performance and reliability. For equipment to operate reliably, it must be suitably rated and in an appropriate condition. As electricity demand grows, so does the need for system growth, including the replacement and upgrading of indoor switchgear. If these replacements or new installations did not occur, demand would outpace the equipment rating, leading to a drop in reliability.

We publish an Annual Planning Report13 that considers the latest demand forecasts for the next 10 years and summarises planned and possible upgrades of interconnection and connection assets. From this, either Major Capex Projects (for interconnection assets) or New Investment Contracts (for connection assets) can be initiated that can include substations with MV indoor switchgear.

We then assess the capability of the transmission network against the medium-term forecast demand and generation to identify Grid investment required to meet the Grid reliability standards, or which provide a net electricity market benefit.

13

See the Annual Planning Report at https://www.transpower.co.nz/resources/annual-planning-report-2013

https://www.transpower.co.nz/resources/annual-planning-report-2013



Replacement and Refurbishment 4.1.3

Replacement is expenditure to replace substantially all of an asset. Refurbishment is expenditure on an asset that creates a material extension to the end of life of the asset. It does not improve its attributes. This is distinct from maintenance work, which is carried out to ensure that an asset is able to perform its designated function for its normal life expectancy. This subsection describes our replacement strategies for indoor switchgear developed in support of the objectives in chapter 3.

Replace legacy and poor condition MV indoor switchgear

Proactively remove and replace old and poor condition MV switchgear with

modern indoor switchgear that is safer and more reliable.

This strategy focuses on replacing old MV switchgear in our fleet. The equipment concerned is mostly bulk oil circuit breaker type MV switchboards supplied in the 1960s, 1970s and early 1980s. The primary drivers for replacement are to reduce safety and reliability risks, and avoid major failures.

The criteria used to assess the need for replacement of indoor switchgear include:

local or international experience with a particular model of switchgear indicates a high risk of major failure

condition assessment inspection and test and/or service history show insulation or other major component deterioration beyond specified limits (and where reconditioning or component replacement is not a viable option)

maintenance and physical access clearances do not comply with the latest applicable international safety standards

A lack of physical segregation, leading to the potential for widespread damage and significant interruptions of supply in the event of a major failure

the current or fault rating is inadequate for the required service duty, and cannot be economically uprated

an emerging or generic defect has been identified, from Condition Assessment (CA) data or System Faults and Interruption Reports (SFIRs), that has potentially serious consequences and cannot be economically addressed by maintenance

high-criticality spares or replacement components can no longer be purchased, or the cost is excessive

maintenance, reconditioning or repair costs are becoming excessive.

As at 30 June 2013, there are eight sites with indoor switchboards using bulk oil circuit breakers, and two sites with indoor switchboards using minimum oil circuit breakers. At the time of writing, work is proceeding on the replacement of bulk oil switchgear at two of these sites, and we plan to replace minimum oil switchgear at another site by the end of the RCP1 period. A further site with bulk oil switchgear is scheduled for divestment.

One site with vacuum interrupter switchgear is scheduled for replacement by the end of the RCP1 period to mitigate significant safety risks associated with lack of arc fault containment, inadequate maintenance and physical access clearances, and lack of physical segregation.



As a continuation of the existing strategy to mitigate risk, we plan to replace further bulk oil circuit breaker type switchboards during the RCP2 period.

The scope of work for the RCP2 period includes the replacement of a particularly large installation at Kinleith, where there are forty-two 11 kV bulk oil circuit breakers and five 33 kV circuit breakers in one switchgear room.

The plan for these works is set out in the Asset Management Plan. A further site with a bulk oil circuit breaker type indoor switchboard is expected to be divested in the RCP2 period.

The replacement works are planned and estimated individually. Further details on their individual justification can be found in the corresponding customised estimates.

Replacement costs of an indoor switchboard can range from $4m to $7m depending on the size and rating of the switchboard. Cost estimates are produced using the process described in subsection 4.1.5.

We forecast a total expenditure during the RCP2 period of approximately $23.7m to replace four indoor switchboards at three sites.

Avoid refurbishment of aged indoor MV switchgear

Avoid the refurbishment of aged indoor MV switchgear other than in

exceptional circumstances.

Some utilities have refurbished aged metal-clad MV switchgear by retrofitting switchboards with new withdrawable circuit breakers, using modern interrupter technology.

We do not intend to refurbish our small population of aged switchgear because this approach does not mitigate the safety and reliability risks associated with:

main bus insulation

inadequate physical clearances around the switchgear

lack of physical segregation

lack of arc fault venting.

Further, we do not have sufficient volume of identical equipment to obtain economies of scale with developing and implementing retrofit solutions.

Retrofit arc-flash protection for existing MV indoor switchgear

Install arc-flash protection on all existing indoor switchgear that does not

have it, where technically feasible.

It is now standard (TP.PS 17.01) for any new indoor switchgear installations to have arc-flash protection in addition to bus zone protection. This strategy proposes to retrofit arc-flash protection on all existing indoor switchgear that does not yet have it, where technically feasible. The detailed schedule of arc-flash protection planned for installation in existing indoor switchgear until 2019/20 is provided in the Asset Management Plan.

Costs of installing arc-flash protection range from $180,000 to $360,000 for each site.



We forecast a total expenditure during the RCP2 period of approximately $2.6m for the retrofitting of arc-flash protection on nine switchboards.14

Existing indoor switchboards safety improvements

Improve the safety characteristics of our existing indoor switchboards

installed before 2008.

Since 2008, we have installed indoor MV switchgear that has the highest available level of safety to detect, clear, contain and vent any internal arc faults. See subsection 2.3.3 for additional information about arc faults in switchgear.

However, there is a legacy of indoor MV switchboards supplied prior to 2008 that do not feature all of the modern safety features. In the event of an internal arc fault, the arc products would be vented into the switchroom. The consequences could include serious harm injury to personnel in the vicinity of the explosion, and widespread damage to equipment, leaving systems out of service for long periods of time.

Our predominant switchgear type at 11 kV is the LMVP product manufactured by RPS (Reyrolle) Switchgear in Petone, Wellington. We have been purchasing this equipment since 1990, and the design has remained largely unchanged. Even so, their latest design includes a number of additional safety features. RPS Switchgear now has solutions available that can be retrofitted onto older LMVP switchboards, to significantly improve operator safety. This includes installing:

arc venting flaps

arc-proof circuit breaker enclosure doors with behind-closed-door racking facility

arc-proof switchboard end cladding

where there is sufficient space behind the switchgear, an external arc venting duct system and arc energy absorbers.15

The detailed scope of work for each site is determined on a case-by-case basis.

We propose to undertake these safety upgrades of LMVP indoor switchgear instead of undertaking complete replacement, as their general condition and asset health have not yet reached replacement criteria.

We will investigate whether similar upgrades may also be possible on some remaining legacy switchboard models from another manufacturer. Yet, in most cases the equipment is no longer supported by the original manufacturer, and upgrades may not be feasible.

Safety improvements for this equipment will be investigated, but feasible options may be limited to installing arcflash protection, restricting normal access around switchboards, and improving situational awareness of the equipment design and safety risks until the switchboard is replaced.

14

A number of existing switchboards have already had arc-flash protection successfully installed. The arc-flash protection equipment can be recovered and used on another switchboard where the system is installed on a switchboard that is subsequently replaced (as occurred recently at Timaru).

15 In some instances this will depend on the model and age of the cable box arrangement.



We forecast a total expenditure during the RCP2 period of approximately $3.8m for the retrofitting of safety improvements on 10 LMVP switchboards.

Integrated Works Planning 4.1.4

Our capital governance process –IWP – includes the creation of business cases that track capital projects through three approval gates, with the scope and cost estimates becoming more accurate as the project becomes more refined.

The IWP process integrates capex across a moving window of up to 10 years in the future. This optimisation approach seeks to ensure that works are deliverable and undertaken in an efficient and timely manner. Planning of our indoor switchgear works takes into consideration relevant site strategies, minimising required outages and resources, and any potential synergies with other projects. In particular, the implementation plan will take into account any transformer replacements due at the site.

In addition, when seeking to schedule indoor switchgear works, customer consultation is crucial to optimise the timing and coordination of investment between ourselves and the customer.

Integrate replacement programme with other works

Align the overall replacement plan with supply point upgrades undertaken by

customers, large replacement works or upgrades, and expected customer

asset acquisitions.

Some indoor switchgear replacements identified as a result of this strategy will be coordinated with risk-based replacements of power transformers. Others may be integrated with ‘customer-led’ supply point upgrades, particularly where supply transformer replacement is required to meet load growth. Customer consultation is crucial, so that a strategy for decommissioning and replacement of the existing equipment can be developed and implemented in a timely manner.

The timeline from conception of project until commissioning typically takes three years. This involves 12–18 months for required customer consultation, project investigation and approval followed by 12–18 months for procurement, construction, installation and commissioning.

Projects to replace indoor switchgear are substantial works, so planning for these projects should be aligned with other works at the same site, including replacements and upgrades, to achieve project efficiencies and minimise outages.

Cost Estimation 4.1.5

Cost estimation is a key stage of the capital investment process and forms a critical input into projects at various stages in the planning process. Historically, cost estimates for indoor switchgear works were developed using proprietary systems. This has now transitioned to a central cost estimation team, which uses the cost estimation tool Transpower Enterprise Estimation System (TEES).

TEES is used to make initial high-level cost estimates using volumetric forecasting. We have established positions of Project Engineer and Project Cost Engineer, to support the feedback



loop of pricing for capital works. We aim to achieve P50 cost estimates.16 Further details on our cost estimation approach can be found in the Planning Lifecycle Strategy.

P50 project cost estimation

Scope and estimate project works to a P50 confidence level (the estimate is

based on a 50% probability that the cost will not be exceeded).

Switchboard installations (whether greenfield or replacement works) will have elements that are unique to that particular project. This reduces the extent to which historic project costs can be relied on to forecast future projects. Indoor switchgear projects involve relatively large investments which, if inaccurately estimated, can lead to large cost overruns and delays. Reflecting this, the cost for each planned replacement has been estimated individually, taking into account the specific context, risks, and requirements of the switchboard and the installation.

A key requirement for an accurate customised estimate is to establish a site-specific scope of work. The main factors influencing the cost of switchboard replacements are the size of the switchboard, building requirements and installation complexity. To determine the scope, we have developed a design layout drawing for each project. The likely location of any new building will be determined from a desktop review of aerial photographs, site layout drawings, underground services drawings, and available cable corridors. These assessments provide reasonably accurate estimates for the variable quantities of materials and work, such as new fencing, power and control cabling, and so on. Other quantities are gathered from the existing single line diagram.

See the Lifecycle Planning Strategy for the rationale behind achieving P50 level of accuracy with volumetric indoor switchgear work.

Assumptions

For indoor MV switchgear replacements and the development of new switchboards17 the main equipment to be considered includes primary plant, buildings, cables and other AC. equipment.

With every new installation, an appropriate switchboard is selected from our standard designs (see discussion in subsection 4.2.1). The hardware cost is estimated based on prices from the current supply panel agreement.

The main assumptions used for preparing cost estimates for new or replacement switchboards are:

standardised ratings for incomers, bus-tie and bus-section circuit breakers and all feeder circuit breakers

incoming cables will be sized to match the full overload rating of the transformer

switchboards will have high impedance bus-zone protection, and arc-flash protection

16

P50 means that there is a 50% probability of the actual project costs being at or below the cost estimate. 17

The Outdoor 33 kV Switchyard Fleet Strategy contains further details on the development of indoor 33 kV switchrooms.



install neutral earthing resistors on the transformers where they are not already installed.

A significant cost driver for indoor switchgear works is the need for us to house the switchboard in a building. The following factors are assessed for each individual project:

new switchroom specifications are based on a desktop review of aerial photographs, site layout drawings, underground services drawings

available cable corridors are used for the new cables

the building is built to the current standard (concrete tilt slab or block construction with a full cable basement)

space is included for installing two future feeders on each end of the bus

demolition costs are included for removing outdoor equipment/old switchroom

costs are included for associated works if the location of the new switchroom requires extending the existing fence and/or creating new access roads.

In addition to the primary equipment and building costs, a number of additional factors have the potential to impact the project cost. These include:

existing underground services (which may require relocation)

consent costs and environmental costs

number of outages expected (may require additional outage planning and switching costs).

The above issues are considered for each individual site to assess whether they need to be included.

Estimation sources

We currently use the TEES US cost estimation tool as a ‘price-book’ for individual costs and unit rates. These component costs are based on historic, specific manufacturer quotes and period supply cost data. Switchgear plant and installation costs have been determined by period supply contracts currently in place and historic installation costs respectively. Historically, both these cost elements have been reasonably accurate. The civil and earthworks costs are currently determined by a unit rate extrapolated from historic costs.

Installation costs have been informed by similar previous projects, identified risks, and updated with current budget prices from installation companies and the specific context of each transformer site. The main assumptions used for defining the scope of the individual projects are set out in the associated customised estimates.

Risk reserves identification

Include additional and indirect cost drivers in the estimate.

A key determinant of accurate cost estimates for capital projects is managing scope risk. As part of our estimation process, we have developed a specific risk estimation approach. This approach is used to determine the need for and magnitude of any risk adjustments to be applied to individual cost items.



The cost items to be assessed will vary from project to project based on specific site conditions and equipment scope. In general, the main cost items that are risk adjusted include:

cable lengths based on building position

civil and geotechnical costs relating to earthworks and ground improvements for the switchgear building.

We have developed three typical scope ranges for each individual line item. Each range has three estimates for the ‘Minimum’, ‘Most Likely’ and ‘Maximum’ value. Using these ranges, we have derived a P50 estimate using a PERT18 distribution. The adjustment is based on likely quantities, as scope has tended to be the most significant variance on this type of work and we are reasonably comfortable with potential unit rate variances.

Further information on our approach to risk estimation is included in the Planning Lifecycle Strategy.

Delivery 4.2

Once the planning activities are completed, capex projects move into the Delivery Lifecycle. Delivery activities are described in detail in the Delivery Lifecycle Strategy. The following discussion focuses on delivery issues that are specific to the indoor switchgear fleet.

Design 4.2.1

When applied to indoor switchgear, the overall design process seeks to deliver our overarching asset management objectives, as discussed in chapter 3. In particular and for our standards to ensure the safety of personnel and the general public, we employ a Safety by Design philosophy throughout the design process.

Design – indoor MV switchgear

A number of key issues must be considered when developing standard designs for indoor switchgear. These include ensuring safety of personnel and the required level of future maintenance. Currently, we have an integrated view of these issues and we have standardised our designs to support our overall asset management objectives. In addition, we procure new equipment from a small number of preferred suppliers to reduce the negative impacts of fleet diversity.

Arc fault detection

For all new enhancement and replacement switchgear projects, provide arc

fault detection, and retrofit this capability where feasible.

Arc fault detection systems are standard in modern switchgear,19 as they significantly reduce the severity of an internal fault and the damage it can cause.

18

Program Evaluation and Review Technique – see the Planning Lifecycle for a discussion on how PERT has been used. 19

The current design being purchased for projects includes the highest possible level of safety from internal arc faults in line with IEC 62271-200 AFCR.



Arc fault detection systems are being retrofitted at sites with high potential for arc fault hazards to help mitigate the risk.

Three of the Alstom type WSA 33 kV SF6 insulated switchboards (Stratford, Silverdale, and Central Park) were supplied in 2003/2004 without arc-flash protection fitted. Subsequent WSA switchboard orders included arc-flash protection. We are investigating whether the panels at Stratford, Silverdale, and Central Park can be modified to include arc-flash protection.20 This work is not likely to be straightforward, as it would require the sealed panels to be de-gassed to enable sensors to be installed into the gas compartments.

Arc fault containment and venting

For all new enhancement and replacement switchgear projects, deploy

switchgear designs that include arc fault containment and venting, and

retrofit this capability where feasible.

As discussed in subsection 2.3.1, one of the main conclusions common to major failures of indoor switchgear equipment is that the design of indoor switchgear must incorporate arc fault containment and venting. Accordingly, all new MV switchgear will be specified to include arc fault containment certified to the latest IEC standards and arc fault venting.

Physical segregation for all new installations serving significant loads

For all new enhancement and replacement MV switchgear projects, provide

physical segregation for all installations serving significant loads.

Physical segregation will be provided between bus sections for switchboards serving large loads or with a large number of feeders, to mitigate the risk that major failures could lead to extensive loss of supply. The segregation is to be implemented by providing firewalls in the switchroom and cable basement. A typical single busbar switchboard installed in two sections, with the sections separated by a firewall, will create four fire cells within the switchroom building.

The design criteria for requiring firewall separation is based on peak load and the number of feeders in the switchboard and illustrated in Figure 7.

The installation of the firewalls eliminates or minimises the risk that a major failure in a component of the switchboard will lead to a total loss of service.21

20

Initial indications are that earlier models of WSA switchboards may not be suitable for retrofitting. 21

We note that cable basements do not require formal ‘Confined Spaces’ designation because of consideration of ratio of SF6 compartment volume versus building volume. Gas cannot create a significant hazard.



Feeders Peak Load (MW)

30 35 40 45 50 55 60

16 12 10 Firewall separation required

8 6 Firewall separation not required 4

Figure 7: Design requirements for firewalls

Indoor switchboards standardisation

For all new enhancement and replacement switchgear projects, deploy

standard switchgear designs.

This strategy aims to reduce the diversity of switchboards within the fleet, resulting in lower costs, risks and increased reliability. New switchboards will be specified based on standard designs wherever practical, and use standard building design and protection systems.

For switchgear rated at 33 kV and above, we have standardised our switchboards to a defined set of designs from a limited set of suppliers. These all include internal arc-fault protection, are fixed pattern switchgear and are suitable for standard building and cabling designs. Cable terminations are standardised on a plug type, to help mitigate the risk associated with the previous use of heat-shrink type terminations.

Our preference is for fixed-pattern switchboards; however at 11 kV the readily available fixed pattern equipment does not currently meet our safety requirements for arc-flash, venting and general protection. In some cases, our seismic requirements may not be fully met. As this technology matures we will move from withdrawable to fixed pattern 11 kV boards.

Some of the main benefits of these design features of fixed pattern switchgear include:

high voltages are fully enclosed from personnel

safety interlocking does not require manual application of earths

virtually no maintenance is required, so the cost and the potential for human element incidents are reduced

reduced requirements for shutdown for maintenance

fixed pattern eliminates unreliability related to withdrawal mechanisms

low forced outage rate.

The implementation of standard switchboard designs reduces cost and improves safety in design. As familiarity with a standard switchgear design increases over time, Safety by Design can be continually improved. In contrast, diversity of the fleet reduces the familiarity of designers with the equipment, so designs are more likely to contain safety issues.

Minimising fleet diversity supports cost optimisation by reducing the cost of design, installation, maintenance and spares. Maintenance and repair procedures that can be used across a larger proportion of the fleet reduce the breadth of knowledge and expertise required. The interoperability and interchangeability of spare parts allows the inventory to be simplified. This helps to improve the management and deployment of spare parts.



Procurement 4.2.2

For more details of our general approach to procurement, see The Sourcing, Supply & Contracts Approach (2011) and the Delivery Lifecycle Strategy.

The subsection below provides more detail on the specific procurement strategies for indoor switchgear.

Effective supplier relationships

Develop relationships and maintain dialogue with manufacturers to aid asset

management.

Limiting suppliers to an approved list of vendors has been effective in reducing the diversity within the fleet of switchboards, resulting in lower costs, risks and increased reliability.

We will continue to develop relationships and maintain dialogues with manufacturers of MV and HV indoor switchgear. We will seek improvements in information from manufacturers regarding testing and inspections, refurbishment options, life expectancy, replacement drivers, and the availability of spares and expertise. Competition between current and potential new suppliers will be maintained to retain commercial tension. The typical lead time for MV switchgear is 20 to 26 weeks.

Warranty period extensions

Obtain extended warranty periods for indoor switchgear.

We will seek extended warranties on indoor switchgear supply contracts. The typical warranty on equipment is 18 months from delivery, or 12 months from commissioning, covering the supply of replacements for defective parts. As indoor switchgear technology develops with improved reliability (incorporating features that minimise maintenance), we are negotiating longer-term warranty periods with suppliers.

We have recently achieved, at no additional cost to the purchase price, 5-year warranties from commissioning, covering parts and labour, for the latest 11 kV and 33 kV switchgear supply contracts. The objective for future purchases of indoor switchgear is for the warranty period to extend until the first major maintenance is due (8 years). By way of comparison, for other primary equipment, we have recently obtained 8-year warranties and 12-year warranties covering parts and labour, without an increase in purchase price.

Limited number of vendors

Procure indoor switchgear from the minimum possible number of vendors

commensurate with the need to manage supplier risk.

We will work to strengthen relationships with a limited group of vendors to ensure that the indoor switchboards meet our specific quality requirements.

Ideally, at any one time, there will be only one period contract supplier of indoor switchboards for a particular voltage class. Standardising on one vendor for each voltage class enables a wide range of lifecycle cost efficiencies.



Operation 4.3

The Operation Lifecycle phase for asset management relates to planning and real-time functions. Operational activities undertaken are described in detail in the Operations Lifecycle Strategy. The following discussion focuses on operational issues that are specific to the indoor switchgear fleet.

Contingency Planning 4.3.1

The transmission network provides a critical infrastructure service for New Zealand. Failure of the transmission service leads to an immediate impact on end consumers and can result in large costs of disruption to economic and social activity. Some transmission asset failures can present serious safety hazards for employees and members of the public, or result in environmental damage. So it is essential that we have plans in place for responding promptly and effectively to transmission system incidents and emergency situations.

Contingency planning for indoor switchgear focuses on reviewing and maintaining the holdings of spares, provision of a mobile switchboard and ensuring an adequate level of emergency preparedness.

Contingency response capability

Ensure there are sufficient plans, skilled manpower and emergency

equipment in place to enable rapid restoration of transmission service

following failure.

We will retain one spare emergency mobile 33/22/11 kV switchroom that can be deployed anywhere in the country at short notice to enable prompt restoration of supply in the event of a major failure of a MV switchboard.

The transportable switchboard includes 9 feeder circuit breakers, 2 incomers and 1 bus-section circuit breaker. It is fully containerised, and includes protection equipment and auxiliary power supplies.

When this emergency spare switchboard is deployed, there is a significant increase in the risk profile associated with all remaining switchboards that were previously covered by the deployed emergency spare. The risk cover for the remaining indoor switchboards should be restored as soon as is reasonably practicable. This emergency spare will either be recovered within 2 years (via repair or replacement of the original failed indoor switchboard) or, alternatively, a replacement strategic spare will be procured.

For HV GIS, we will maintain contacts with the original equipment manufacturers and review our present holdings of spares, to ensure prompt and effective response in the event of a significant defect or failure.

Maintenance 4.4

We and our service providers carry out ongoing works to maintain assets in an appropriate condition and to ensure that they operate as required. The maintenance undertaken seeks to proactively manage failure risk as well as responding to actual failures as they occur. Our approach to maintenance and the activities we undertake are described in detail in the Maintenance Lifecycle Strategy.



We classify maintenance tasks into the following categories:

preventive maintenance

- condition assessments

- servicing

corrective maintenance

- fault response

- repairs

maintenance projects.

These activities and associated strategies are discussed in the following sections.

Preventive Maintenance 4.4.1

Preventive maintenance is work undertaken on a scheduled basis to ensure the continued safety and integrity of assets and to compile condition information for subsequent analysis and planning. Preventive maintenance is generally our most regular asset intervention, so it is important in terms of providing feedback of information into the overall asset management system. Being the most common physical interaction with assets, it is also a potential source of safety incidents and human error. The main activities undertaken are listed below.

Inspections: non-intrusive checks to confirm safety and integrity of assets, assess fitness for service, and identify follow up work.

Condition Assessments: activities performed to monitor asset condition or predict the remaining life of the asset.

Servicing: routine tasks performed on the asset to ensure asset condition is maintained at an acceptable level.

We intend to implement the following preventive maintenance on our indoor switchgear fleet in support of our objectives stated in chapter 3.

MV switchgear condition assessments

Carry out regular condition assessments on all MV switchgear installations, at

the required frequency as determined by condition and model of switchgear.

This strategy is focused on assessing the condition of our MV switchgear assets to determine asset health. Implementing an appropriate inspection regime will provide information that can be used to prevent faults and failures and extend the life of the switchboard. Proactively addressing identified condition issues will help maximise reliability of the switchboard and reduce the whole-of-life cost of the asset.

Switchgear is characterised by several factors, including age, voltage and interrupting type. The maintenance requirements vary depending on these characteristics. The switchboards, installed since 1990, are generally modern SF6 or vacuum-break types.

There is also a large population of bulk oil type switchgear, mostly manufactured before 1983. Bulk oil type switchgear is particularly prone to oil leakage. Some of this switchgear is



showing signs of partial discharge, which could be a sign of eventual failure. For these reasons, this type of switchgear requires more frequent condition assessments.

Vacuum and SF6 type switchgear is more robust than older, bulk oil switchgear. This means that condition assessments are required less frequently than with bulk oil switchgear.

Indoor HV switchgear condition monitoring

Regularly monitor HV switchgear for condition deterioration.

The indoor HV switchgear that we currently operate has been installed between 1979 and 2013. All indoor HV switchgear uses robust SF6 insulated busbar systems. HV switchgear has a proven record of reliability and failures are rare. However, if failure should occur, it has the potential to be catastrophic. It is therefore important that regular condition assessments are carried out to schedule the necessary maintenance and repairs, and keep the switchgear operating as reliably as possible.

In addition to the regular visual inspections, HV indoor switchgear undergoes comprehensive diagnostic testing and servicing every 8 years.

Corrective Maintenance 4.4.2

Corrective maintenance includes unforeseen activities to restore an asset to service, make it safe or secure, prevent imminent failure and address defects. It includes the required follow-up action, even if this is scheduled some time after the initial need for action is identified. These jobs are identified as a result of a fault or in the course of preventive work such as inspections. Corrective works may be urgent and if not completed for a prolonged period may reduce network reliability.

Corrective maintenance has historically been categorised as repairs and fault (response) activities. Repairs include the correction of defects identified during preventive maintenance and other additional predictive works driven by known model type issues and investigations.22 Timely repairs reduce the risk of failure, improve redundancy and remove system constraints by maximising the availability of assets. Activities include:

Fault restoration: unscheduled work in response to repair a fault in equipment that has safety, environmental or operational implications, including urgent dispatch to collect more information

Repairs: unforeseen tasks necessary to repair damage, prevent failure or rapid degradation of equipment

Reactive inspections: patrols or inspections used to check for public safety risks or conditions not directly related to the fault in the event of failure

Switchgear fault response

All faults will be responded to in a timely manner, as determined by the

criticality of the asset.

22

Where the number of potential repairs is deemed sufficiently high a Maintenance Project will be instigated to undertake the repairs works.



A switchgear fault can occur due to many reasons, such as overloading, operating error, physical degradation of the switchgear or design faults. The main intention of this strategy is to respond to all switchgear faults and carry out repairs to return the equipment to service in a timely manner. The fault response will be adapted depending on the criticality of the asset.

No repairs will compromise the safety or likelihood of repeated failure of the switchboard so it can return to service quickly. This supports our key objectives of reliability, system performance and safety.

Switchboard repairs

Ensure that required repairs on indoor switchgear are carried out promptly.

The main purpose of this strategy is to carry out repairs on all switchgear that require it, so it can return to service, in sound condition and at its rated capacity. This work will be prioritised by criticality of the switchboard. All repairs must sustain or improve the level of safety for operating and maintaining the switchboard.

To repair indoor switchgear in a timely manner, we will maintain the necessary resources and expertise. See subsection 4.6.3 for specific strategies relating to training and competency.

Maintenance Projects 4.4.3

Maintenance projects typically consist of relatively high value planned repairs or replacements of components of larger assets. Maintenance projects would not be expected to increase the original design life of the larger assets. Maintenance jobs are typically run as a project where there are operational and financial efficiencies from doing so. The drivers for maintenance projects include asset condition, mitigating safety and environmental risks, and to improve performance.

Rangipo 220 kV GIS indoor switchgear gas leak repairs

Continue ongoing gas leak repairs at Rangipo Power Station and perform

regular leak detection surveys.

The Rangipo indoor switchgear is 32 years old and is generally in good condition apart from the ongoing need for repairs to leaking gas seals. Allowing the gas leaks to continue indefinitely would increase our SF6 emissions and compromise our environmental objectives. Furthermore, there is potential for the gas leaks to eventually lead to a forced or fault outage of sections of the switchgear. This could result in lengthy outages and interruption to the connection of generation.

HV indoor switchgear can be expected to operate for more than 40 years. Given that the asset is 32 years old and in good condition, we do not believe full replacement (at a cost of approximately $10m and long outage durations) is justified at this point. Ongoing repairs of gas leaks (which have proved to be effective) are considered a more cost-effective solution.

A full leak detection survey will be carried out annually to identify any new leaks, and to monitor the effectiveness of repairs carried out to date.



There are 33 gas compartments in our part of the installation. A programme of work to completely replace all gas seals in the entire installation in one project is not feasible, because it would require planned outages that are not acceptable to the generation customer.

In recent years, considerable progress has been made in progressive identification and repair of leaking seals, with no evidence of leaks from previously repaired equipment.

Repairs are expected to continue at the rate of approximately 1 to 2 operations each year, depending on outage availability.

The forecast cost of ongoing repairs to the Rangipo GIS switchgear is approximately $100,000 each year, which equates to an estimated RCP2 spend of $500,000.

Online SF6 gas pressure monitoring system installation on the Rangipo 220 kV GIS indoor switchgear

Replace gas density switches and provide online gas pressure monitoring on

the Rangipo 220 kV GIS indoor switchgear.

A project is already underway to replace existing gas density switches with new SF6 pressure gauges on all gas compartments of the Rangipo GIS switchgear. The gauges include a transducer that will be connected to an online pressure monitoring system. Half of the gauges have already been installed, and the other half will be installed by the end of 2013. The online monitoring system will be commissioned in 2014. The estimated cost to implement the online monitoring system in 2013/14 is $92,000.

Clyde 220 kV GIS indoor switchgear hydraulic mechanisms repairs

Repair or replace the hydraulic mechanisms on the Clyde 220 kV GIS indoor

switchgear.

Major overhauls have already been completed on the mechanisms of four of our nine 220 kV GIS circuit breakers at Clyde. Similar overhaul work is required on the remaining five circuit breakers.23 An option will be evaluated for replacing the hydraulic mechanisms with spring operated mechanisms, as an alternative to the overhaul, taking into account whole-of-life cost. Pending the cost evaluation for mechanism replacement, we plan to undertake overhauls on the remaining five circuit breakers in the RCP2 period, at a forecast total cost of $1.9m.

Pressure relief devices and SF6 moisture filters replacements

Replace pressure relief devices and SF6 moisture filters on Clyde 220 kV GIS

indoor switchgear.

We plan to change the pressure relief devices (PRDs) in all 141 gas compartments of the Clyde GIS. The existing graphite disc types will be replaced with a stainless steel disc type, to avoid the failure modes that have been observed in this type of equipment worldwide. At

23

Circuit breakers are numbered 488, 498, 508, 542, and 552.



the same time, we plan to change the moisture filters in all of the gas compartments from aluminium oxide to a molecular sieve type.

This work will require extensive outages on the GIS and a significant amount of SF6 gas handling. This work can be combined with the hydraulic mechanism upgrades.

The expected cost to replace all PRDs and moisture filters, including the SF6 gas handling work, is approximately $2.2m over three years during the RCP2 period.

SF6 gas pressure gauge installation on Clyde 220 kV GIS indoor switchgear

Install SF6 gas pressure gauges on the Clyde 220 kV GIS indoor switchgear.

SF6 pressure gauges will be installed on 141 gas compartments of the Clyde GIS. This will enable more effective monitoring of SF6 gas levels, allow early detection of gas leaks and so enable reductions in SF6 gas emissions and the outages required for leak repairs. The pressure gauges will also incorporate pressure transducers to enable an option for future implementation of an online pressure monitoring system. This work can be combined with the PRD and filter upgrades.

The expected costs to install pressure monitoring on all gas compartments is $505,000.

Disconnector and earth switch motor drive upgrades

Upgrade the disconnector and earth switch drives on the Clyde 220 kV GIS

indoor switchgear.

We are planning to upgrade 62 disconnector and earth switch motor drives on the Clyde GIS to mitigate the risk of motor burnout and collateral damage. This work can be combined with other works. The forecast cost to upgrade all disconnector and earth switch drives is $481,000.

Disposal and Divestment 4.5

The disposal and divestment lifecycle phase includes the process from when planning of disposal of an asset begins through to the point where we no longer own the asset.

Asset disposal includes the decommissioning of the asset after which it may be sold as a functioning asset, sold as scrap, disposed of to a waste management facility, or re-used elsewhere as an in-service asset or as a spare. Asset divestment involves the sale of the in-service asset in situ. Divestment often involves the sale of assets to customers, including electricity distribution businesses and large electricity users.

This subsection describes our strategies for disposal of assets within the indoor switchgear fleet.

Asset Disposal 4.5.1

The implementation of asset disposal has many similarities with capital projects, including consideration of cost, safety, environmental impacts, and project management. Aspects specific to successful disposal projects are site restoration and termination of all support activities and planning.



Switchboard asset disposals

Dispose of Indoor switchboard assets in a safe and environmentally

sustainable manner.

Safety and minimisation of environmental impacts are important considerations for us.

Where re-use is not appropriate, we will maintain and follow appropriate decommissioning process as part of projects. Requirements for switchboard demolition, recovery and recycling/disposal work include safe work and site management processes and environmentally appropriate disposal of scrap.

Where possible, the equipment is offered for sale to scrap merchants who salvage and recycle all the metalwork and the oil is recovered by an oil regeneration company. The SF6 gas is recovered and reused.

Reducing the environmental impacts through the recycling of decommissioned assets will avoid landfill fees and will result in the scrap value being credited back to us.

We will be decommissioning bulk oil type indoor switchboards at three sites over the RCP2 period.

Divestment 4.5.2

Implementation of divestment is primarily the change of ownership, although we must also remain aware of any safety and environmental issues and technical impacts on the Grid such as a change in constraints and flexibility of Grid operation.

Indoor switchgear divestment

Divest indoor switchgear as part of substation and transmission line

divestments to customers.

We are continuing with the transfer of a number of assets at the fringes of the existing Grid to electricity distribution businesses. This process and its justification are described fully in the Disposal and Divestment Lifecycle Strategy.

Table 5 shows the number of indoor switchgear likely to be transferred to customers between 2013/14 and 2019/20. This includes all divestments that we believe have a 50% or greater likelihood of occurring during the timeframe.

Period 11 kV 33 kV Total

RCP124

4 1 5

RCP2 3 5 8

Total 7 6 13

Table 5: Indoor Switchgear Divestments

The total number of indoor switchgear to be transferred represents approximately 17% of the total indoor switchgear fleet as at June 2013. However, it is noted that the Outdoor-to-

24

This excludes historical divestments; it includes only those divestments to be carried out in 2013/14 and 2014/15.



indoor conversion programme during RCP2 will increase the population of indoor 33 kV switchgear.

No HV GIS switchgear is considered for divestment during RCP2.

Asset Management Capability 4.6

This section describes the specific strategies for obtaining and maintaining capability in managing and handling the indoor switchgear fleet. These strategies provide medium to long-term guidance and direction to ensure that asset managers and their staff have the required capabilities in regard to fleet management.

We require our Grid assets and equipment to be managed, maintained, tested and operated to high standards of skill, professionalism supported by high-quality asset knowledge and risk management tools. This will ensure satisfactory and safe functioning of the network while minimising whole-of-life costs.

To achieve the required quality standards so as to prevent injury to workers, protect the public and their property from harm and prevent damage to our assets, the work is to be carried out only by individuals with competencies that are appropriate and current. These will include hazard identification, assessment and control of job safety. For further detail, see our Asset Management Competences Framework Project document.

The people planning and implementing the work must also have access to a full and rich set of information, covering the history, condition, performance, and maintenance requirements of assets.

The capability strategies are described under the following headings:

Risk Management

Asset Knowledge

Training and Competence.

Risk Management 4.6.1

Our approach to risk management is central to our asset management decision making as we weigh up the various costs and benefits of options such as replacement timing. We are developing asset health and criticality framework to improve and integrate our risk-based asset management. The strategies below discuss how we plan to progress this as regards the indoor switchgear fleet.

Risk-based options evaluation framework

Develop an improved risk-based framework and associated tools for

evaluation of options for the indoor switchgear fleet.

We will develop an improved risk management framework and tools that can be used across the indoor switchgear fleet to evaluate investment options. The key parts of this will be tools for making quantitative estimates of the likely impacts of indoor switchgear failures on service performance and safety on a case-by-case basis. The risk model will specifically consider uncertainty in the inputs to risk-based decision making.



We will ensure more robust and detailed development of scope for major replacements, to improve the accuracy of cost estimates and the validity of the economic analysis of options. Risk management processes will be made more robust and systematic, and will allow risk assessments to be more readily communicated to internal and external stakeholders.

Asset Knowledge 4.6.2

Robust asset knowledge is critical to good decision making for asset management. Asset knowledge comes from a variety of sources, including overseas experiences, experience from assets on our network, theoretical modelling, and information from the manufacturers. This asset knowledge must be captured and recorded in such a way that it can be conveniently accessed when future asset management decisions are made. A key part of improving our asset knowledge is the commissioning of the new Asset Management Information System (AMIS).

Standard Maintenance Procedures

Complete and implement Standard Maintenance Procedures (SMPs) with

consistent testing and data recording for the fleet of indoor switchgear.

We have begun developing SMPs for indoor switchgear, which will be used by service providers to standardise their interactions with the fleet and the recording of those interactions. In particular, the SMPs will have very clear rules on tests, including detailed instructions on how the tests should be carried out as well as how data should be recorded. This will support more consistent, useful and accessible data on the indoor switchgear that can be analysed to support asset management decisions such as replacement timing.

Training and Competence 4.6.3

Our overarching strategy for maintaining and/or improving worker competence can be summarised as follows:

all persons (our employees, service providers and sub-contractors) working on our assets must be properly trained and competent for the tasks they undertake

all maintenance service providers must comply with the competency criteria set out in the relevant Service Specification

employers must manage the currency of competencies of their workers for the work they undertake to the appropriate requirements of the relevant Service Specification

we must engage cable termination suppliers to provide adequate training and certify competency for our service providers.

We have three service specifications that define the competency requirements for working on primary equipment such as indoor switchgear:

TP.SS 06.23 Minimum competencies for power system equipment operation

TP.SS 06.21 Minimum competencies for substations maintenance and testing

TP.SS 06.25 Minimum requirements for Transpower field work.



Summary of RCP2 Fleet Strategies 4.7

Our asset management plans for the fleet of indoor switchgear is summarised below for each lifecycle stage.

Planning

Enhancement and

Development Install new indoor switchgear for approved system growth or enhancement projects.

Replacement and

Refurbishment

Proactively remove and replace old and poor condition MV switchgear with modern indoor switchgear that

is safer and more reliable.

Avoid the refurbishment of aged indoor MV switchgear other than in exceptional circumstances.

Install arc-flash protection on all existing indoor switchgear that does not have it, where technically

feasible.

Improve the safety characteristics of our existing indoor switchboards installed before 2008.

Integrated Works

Planning

Align the overall replacement plan with supply point upgrades undertaken by customers, large

replacement works or upgrades, and expected customer asset acquisitions.

Cost Estimation

Scope and estimate project works to a P50 confidence level (the estimate is based on a 50% probability

that the cost will not be exceeded).

Include additional and indirect cost drivers in the estimate.

Delivery

Design

For all new enhancement and replacement switchgear projects, provide arc fault detection, and retrofit

this capability where feasible.

For all new enhancement and replacement switchgear projects, deploy switchgear designs that include

arc fault containment and venting, and retrofit this capability where feasible.

For all new enhancement and replacement MV switchgear projects, provide physical segregation for all

installations serving significant loads.

For all new enhancement and replacement switchgear projects, deploy standard switchgear designs.

Procurement

Develop relationships and maintain dialogue with manufacturers to aid asset management.

Obtain extended warranty periods for indoor switchgear.

Procure indoor switchgear from the minimum possible number of vendors commensurate with the need to

manage supplier risk.

Operation

Contingency

Planning

Ensure there are sufficient plans, skilled manpower and emergency equipment in place to enable rapid

restoration of transmission service following failure.

Maintenance

Preventive

Maintenance

Carry out regular condition assessments on all MV switchgear installations, at the required frequency as

determined by condition and model of switchgear.

Regularly monitor HV switchgear for condition deterioration.

Corrective

Maintenance

All faults will be responded to in a timely manner, as determined by the criticality of the asset.

Ensure that required repairs on indoor switchgear are carried out promptly.

Maintenance

Projects

Continue ongoing gas leak repairs at Rangipo Power Station and perform regular leak detection surveys.

Replace gas density switches and provide online gas pressure monitoring on the Rangipo 220 kV GIS

indoor switchgear.

Repair or replace the hydraulic mechanisms on the Clyde 220 kV GIS indoor switchgear.

Replace pressure relief devices and SF6 moisture filters on Clyde 220 kV GIS indoor switchgear.

Install SF6 gas pressure gauges on the Clyde 220 kV GIS indoor switchgear.

Upgrade the disconnector and earth switch drives on the Clyde 220 kV GIS indoor switchgear.



Disposal and Divestment

Asset Disposals Dispose of Indoor switchboard assets in a safe and environmentally sustainable manner.

Divestment Divest indoor switchgear as part of substation and transmission line divestments to customers.

Capability

Risk Management Develop an improved risk-based framework and associated tools for evaluation of options for the indoor switchgear fleet.

Asset Knowledge Complete and implement Standard Maintenance Procedures (SMPs) with consistent testing and data recording for the fleet of indoor switchgear.


ACS INDOOR SWITCHGEAR FLEET STRATEGY © Transpower New Zealand Limited 2013. All rights reserved.

Appendices



ACS INDOOR SWITCHGEAR FLEET STRATEGY © Transpower New Zealand Limited 2013. All rights reserved. Appendices | page 55

A PHOTOS OF TYPICAL INDOOR SWITCHGEAR INSTALLATIONS

The photo in Figure 8 shows the Bream Bay 220 kV GIS (manufactured in 1981). The photo in Figure 9 shows the Clyde 220 kV GIS (manufactured in 1996). The photo in Figure 10 shows the Kinleith 11 kV MV Indoor Switchgear (with oil circuit breaker technology dating from the 1970s). The photo in Figure 11 shows the Paraparaumu 33 kV MV Indoor Switchgear (with vacuum circuit breaker technology dating from 2010).

A1 HV GIS

Figure 8: Bream Bay 220 kV HV GIS (manufactured in 1981)

. Figure 9: Clyde 220 kV HV GIS (manufactured in 1996)




A2 MV Indoor Switchboards

Figure 10: Kinleith 11 kV MV Indoor Switchgear (1970s oil circuit breaker technology)

Figure 11: Paraparaumu 33 kV MV Indoor Switchgear (2010 vacuum circuit breaker technology)




B SCHEDULE OF MAJOR FAILURES

There have been nine major failures of indoor switchgear over the past 25 years:

Central Park 33 kV - 1992

Penrose 22 kV – 16 June 1992

Whirinaki 11 kV – 12 April 2001

Otahuhu 22 kV – 10 July 2007

Westport 11 kV – 7 October 2007

Haywards 11 kV SC2 switchgear – 22 September 2009

Kawerau 11 kV – 11 March 2010

Te Awamutu 11 kV – 27 January 2010

Cambridge 11 kV - 19 April 2013

Owhata 11 kV – 9 June 2013.




C ILLUSTRATION OF MAJOR FAILURES

C1 has before and after photos of the Westport 11 kV switchboard failure on 7 October 2007. The photos in C2 show the Otahuhu 22 kV switchboard failure on 10 July 2007, and the photos in C3 show the Haywards SC2 11 kV switchboard failure on 22 September 2009.

C1 Westport 11 kV Switchboard Failure – 7 October 2007

Before

After




C2 Otahuhu 22 kV Switchboard Failure – 10 July 2007




C3 Haywards SC2 11 kV Switchboard Failure – 22 September 2009

Documents

ACS INDOOR SWITCHGEAR Fleet Strategy