ACS INDOOR SWITCHGEAR

Transcription

2 C O P Y R I G H T 2013 T R A N S P O W E R N E W Z E A L A N D L I M I T E D. A L L R I G H T S R E S E R V E D This document is protected by copyright vested in Transpower New Zealand Limited ( Transpower ). No part of the document may be reproduced or transmitted in any form by any means including, without limitation, electronic, photocopying, recording or otherwise, without the prior written permission of Transpower. No information embodied in the documents which is not already in the public domain shall be communicated in any manner whatsoever to any third party without the prior written consent of Transpower. Any breach of the above obligations may be restrained by legal proceedings seeking remedies including injunctions, damages and costs. Transpower New Zealand Limited All rights reserved. Page 2 of 63

3 Table of Contents EXECUTIVE SUMMARY... 1 SUMMARY OF STRATEGIES INTRODUCTION Purpose Scope Stakeholders Strategic Alignment Document Structure ASSET FLEET Asset Statistics Asset Characteristics Asset Performance OBJECTIVES Safety Service Performance Cost Performance New Zealand Communities Asset Management Capability STRATEGIES Planning Delivery Operation Maintenance Disposal and Divestment Asset Management Capability Summary of RCP2 Fleet Strategies APPENDICES A PHOTOS OF TYPICAL INDOOR SWITCHGEAR INSTALLATIONS B SCHEDULE OF MAJOR FAILURES C ILLUSTRATION OF MAJOR FAILURES Transpower New Zealand Limited All rights reserved.

4 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. Arcflash 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. Transpower New Zealand Limited All rights reserved. Page 1 of 53

5 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 nonrecurring 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. Transpower New Zealand Limited All rights reserved. Page 2 of 53

6 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/ /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. Transpower New Zealand Limited All rights reserved. Page 3 of 53

7 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. Transpower New Zealand Limited All rights reserved. Page 4 of 53

8 1 INTRODUCTION Chapter 1 introduces the purpose, scope, stakeholders, and strategic alignment of the indoor switchgear fleet strategy. 1.1 Purpose 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: Scope 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. Transpower New Zealand Limited All rights reserved. Page 5 of 53

9 1.3 Stakeholders 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. 1.4 Strategic Alignment A good asset management system shows clear hierarchical connectivity or line of sight between the high-level organisation policy and strategic plan, and the daily activities of managing the assets. This document forms part of that hierarchical connectivity by setting out our strategy for managing 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. Corporate Objectives & Strategy Asset Management Policy Asset Management Strategy Lifecycle Strategies Planning Delivery Operations Maintenance Disposal Indoor Switchgear Strategy Indoor Switchgear Plan Figure 1: The Indoor Switchgear Strategy within our Asset Management Hierarchy Transpower New Zealand Limited All rights reserved. Page 6 of 53

10 1.5 Document Structure 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. Transpower New Zealand Limited All rights reserved. Page 7 of 53

11 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. 2.1 Asset Statistics This section describes the indoor switchgear asset fleet population, along with their diversity and age profiles Asset Population 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 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. Transpower New Zealand Limited All rights reserved. Page 8 of 53

12 Type 11 kv 22 kv 33 kv Total Vacuum SF Bulk Oil Air Blast Minimum Oil TOTAL HV indoor circuit breakers Table 1: MV Indoor Switchgear Circuit Breaker Population 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 Rangipo Merlin Gerin 34 2 Bream Bay Mitsubishi 32 8 Wilton Mitsubishi 32 7 Tiwai Mitsubishi Motunui Mitsubishi 30 9 Clyde BBC 27 9 Otahuhu Areva 5 12 Wairau Road Alstom 0 6 Hobson Street Alstom 0 6 Table 2: Indoor HV Switchgear Asset Fleet Population Fleet Diversity 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 Age as at The Rangipo GIS installation is shared with Genesis. The Clyde GIS switchgear installation is shared with Contact Energy. These sites are currently being built in Auckland and will be commissioned in Transpower New Zealand Limited All rights reserved. Page 9 of 53

13 SF 6 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. MV indoor circuit breakers 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 SF 6 gas types (with either air or SF 6 insulated busbar systems). The diversity is shown in Figure 2. MV INDOOR CB - DIVERSITY BULK OIL (16%) MIN OIL (1%) SF6 (19%) VACUUM (62%) AIR BLAST (2%) HV switchboards Figure 2: MV Circuit Breakers Diversity 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 SF 6 insulated. HV indoor circuit breakers 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 SF Table 3: HV indoor circuit breakers by type and voltage Age Profile 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. Transpower New Zealand Limited All rights reserved. Page 10 of 53

14 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. MV INDOOR CB - AGE PROFILE 120 BULK OIL MIN OIL SF6 VACUUM AIR BLAST AGE (YEARS) 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 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 SF 6 Life Expectancy HV switchboards Table 4: Typical MV Indoor Switchgear Life Expectancy 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 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 Transpower New Zealand Limited All rights reserved. Page 11 of 53

15 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. 2.2 Asset Characteristics 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 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 SF 6 emissions oil spills. These issues are described below. Transpower New Zealand Limited All rights reserved. Page 12 of 53

16 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 hazards 6 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 relivening 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 SF 6 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 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, In the case of older generation switchboards, the failure can be particularly catastrophic, resulting in oilfilled or compound-filled compartments rupturing and ejecting shrapnel and burning oil and gas. There are records in Australia of complete switchroom buildings burning down. 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. Transpower New Zealand Limited All rights reserved. Page 13 of 53

17 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 standard 9 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 SF 6 SF 6 (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 SF 6 is a potent greenhouse gas, with a global warming potential vastly greater than that of CO 2. There are particularly large quantities of SF 6 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 SF 6 contained within our gas compartments. Poor design, ageing of seals and gaskets is a contributing factor in SF 6 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 Power installations exceeding 1 kv a.c. Part 1: Common rules. Transpower New Zealand Limited All rights reserved. Page 14 of 53

18 2.2.2 Asset Criticality 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. MV INDOOR CB - CRITICALITY HV INDOOR CB - CRITICALITY LOW (47%) MEDIUM (35%) HIGH (18%) LOW (23%) MEDIUM (46%) HIGH (31%) Figure 4: Indoor Circuit Breaker Criticality Asset Condition 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. Transpower New Zealand Limited All rights reserved. Page 15 of 53

19 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 heatshrink 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 The GIS installation is shared with Genesis Energy. There have been persistent problems with SF 6 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 SF 6 seals. The repairs carried out to date have been successful. This maintenance has cost approximately $50,000 $100,000 each year. An online SF 6 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 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 SF 6 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. Transpower New Zealand Limited All rights reserved. Page 16 of 53

20 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 SF 6 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 SF 6 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 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 Transpower New Zealand Limited All rights reserved. Page 17 of 53

21 the age of the asset (relative to expected life) the typical degradation path of that model ACS Indoor Switchgear Fleet Strategy 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. MV indoor circuit breakers Figure 5 shows that approximately 5% of MV indoor circuit breakers are now due for replacement. MV INDOOR CB - ASSET HEALTH 12+ YRS (82%) 7-12 YRS (6%) 2-7 YRS (7%) 0-2 YRS (0%) NOW DUE (5%) Figure 5: MV Indoor Circuit Breakers Asset Health as at June 2013 HV indoor circuit breakers 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 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. Transpower New Zealand Limited All rights reserved. Page 18 of 53

22 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 SF 6 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. Transpower New Zealand Limited All rights reserved. Page 19 of 53

23 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 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 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 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. Transpower New Zealand Limited All rights reserved. Page 20 of 53

24 Major failures 10 ACS Indoor Switchgear Fleet Strategy 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. Transpower New Zealand Limited All rights reserved. Page 21 of 53

25 Forced and fault outage performance MV switchgear ACS Indoor Switchgear Fleet Strategy The forced and fault outage rate of indoor MV switchgear circuit breakers is shown in Figure 6. MV INDOOR CB - FORCED AND FAULT OUTAGES EQUIPMENT FAILURE OTHER 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 Subsection 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 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. Transpower New Zealand Limited All rights reserved. Page 22 of 53