Electricity Asset Management Plan 2019-2029
179
Vector Limited://
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: Business as usual – no additional investment
Continue with current level of investment to maintain subtransmission cables and accept the risk that the wear out period as per the bathtub curve might be approached for certain populations of the subtransmission cable fleet. This option will not address the risk of complete loss of supply to a large area should both or more subtransmission cable circuits to a zone substation fail. Under the Symphony load forecast model a 7% demand increase is forecast by 2028. For certain areas the installation of a new network technology installation, e.g. a large scale BESS system, will provide respite for peak demand in the event of loss of one subtransmission supply but this option will not suffice for any of the subtransmission projects in the summary of investment list below This solution will address the risk as per the bathtub curve where cable population of the same age is approaching the end of their design life.
Rejected
Option 2: Use new network technology options to offset the requirement to replace subtransmission circuits
Rejected
Option 3: Undertake a staged and scheduled programme of works to replace subtransmission cables that are approaching the end of design life
$43.19M Selected
PROPOSED INVESTMENT SUMMARY ($MILLION NOMINAL) DESCRIPTION FY20 FY21 FY22 FY23 FY24
FY25
FY26
FY27
FY28
FY29 TOTAL
Glen Innes subtrans replace
10.00
10.00
Ponsonby subtrans replace
3.70
3.70
Takanini subtrans replace
3.18
3.18
Onehunga subtrans replace
0.20
6.00
2.70
8.90
Chevalier subtrans replace
2.00
4.59
6.59
Westfield subtrans replace
1.10
5.72
6.82
Northern subtrans replace
0.50
0.50
1.00
1.00
1.00
4.00
Total CAPEX
17.08
6.00
4.70
5.69
5.72
0.50
0.50
1.00
1.00
1.00
43.19
5.2.2 ZONE SUBSTATIONS Similar to subtransmission feeders, zone substations do not currently have a significant impact on SAIDI due to their N-1 design criteria. Zone substations are subject to regular inspections as set out in Section 4 and use SCADA for real time monitoring. Through this inspection and monitoring regime, several projects have been identified that could impact on SAIDI in the future that is mainly due to the fact that a large population of zone substation assets are of the same age and as for subtransmission cables above, this population will reach end of their design lives at the same time. This means the bathtub risk of curve of ‘wear out failure rate’ comes into play. This risk applies to oil-filled switchgear and zone substation power transformers where there is a substantial population that dates from the 1960s. Age profiles are included in Section 4.
The following sections set out the project proposals for different assets in zone substations:
33 AND 22 KV PRIMARY SWITCHGEAR REPLACEMENT
NEEDS STATEMENT Vector has made inroads with renewing its fleet of 1960s and 1970’s 33 kV and 22 kV oil-filled switchgear but a number of sites with bulk outdoor oil filled switchgear still remain – the population and age profile is shown in Section 4. In RY18
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