Electricity Asset Management Plan 2019-2029
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with adjacent protections. This means that if an outgoing feeder CB fails to clear a fault, all 22 kV incomers will trip to clear the fault, resulting in the loss of Quay Street 22 kV, Quay Street 11 kV and Parnell 22 kV. This would result in widespread critical failure for a vital region for Auckland (and New Zealand’s) economy with the potential to compromise national productivity with the loss of supply to the country’s largest CBD. The current standard for new substations is to install circuit breaker fail (CBF) protection. However, Quay Street 22 kV predates CBF being applied as standard and does not have it installed.
TARGETED OUTCOMES
CUSTOMER EXPERIENCE
SAFETY
RELIABILITY
RESILIENCE
OPERATIONAL EFFICIENCY
CYBER SECURITY AND PRIVACY
OPTIONS CONSIDERED Options to address the need identified above have been assessed and are summarised in the following table.
DESCRIPTION
DISCUSSION OF OPTION
ESTIMATED COST (NPV IF APPLICABLE)
STATUS
Option 1: Do nothing
A do-nothing approach means that the subtransmission protection schemes will continue to rely on ageing and failing copper pilot cables. The existing electromechanical fleet of protection relays for which there is no product support or spares will continue to age. Getting qualified technical staff to maintain the ~60 year old protection schemes is becoming a bigger and bigger challenge as time goes one. Selecting this option will increase the chances of spurious and undue tripping or protection with reduced sensitivity that could result in backup protection trips for faults and thus larger outages and increased SAIFI and SAIDI. This option is not viable and is not recommended. A staged and scheduled programme of works is necessary to establish a protection fleet for the future that provides the reporting and analysing functionality to quickly and accurately analyse faults to plan remedial actions. Retaining a fleet of electromechanical relays some of which are 60 years plus old with no vendor support, unsupervised for failure and for which recruitment of field staff with the necessary experience to maintain this is becoming more of a challenge is simply not viable. The subtransmission protection replacements will go hand in hand with a replacement programme of the ageing copper pilot cable fleet (described in a separate Needs Statement).
Rejected
Option 2: Undertake a staged and scheduled programme of works to replace subtransmission and zone substation protection schemes
$30.86M Selected
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