Electricity Asset Management Plan 2019-2029
189
Vector Limited://
DESCRIPTION
DISCUSSION OF OPTION
ESTIMATED COST (NPV IF APPLICABLE)
STATUS
Option 1: Do nothing – do not invest in the installation of NERs
Taking a do-nothing approach means that where ageing 11kV cables with low earth fault ratings exist, parallel operation to ensure uninterrupted N-1 supply to commercial and industrial will not be possible. A BESS system will provide respite of peak demand but will not provide security of supply, and thus not provide uninterrupted supply, in the event of failure of a power transformer or 11kV bus section at a zone substation. Most large customers and building facilities have emergency generation that will provide electrical energy to essential services but there are large commercial and industrial enterprises that have N-1 supplies that require continued uninterrupted supply for failure of one leg of a supply. This option will not provide this function This option will allow continued supply without the risk of extensive damage to 11 kV cables with low earth fault rated screens during cable earth faults or if a 3rd party construction crew accidentally damages an 11 kV cable
Rejected
Option 2: Use new network technology options such as a BESS system to provide the required security of supply or let the customer make provision for security of supply
Rejected
Option 3: Undertake a programme of works to install neutral earthing resistors in zone substations as and where required
$3.86M Selected
PROPOSED INVESTMENT SUMMARY ($MILLION NOMINAL)
DESCRIPTION
FY20
FY21
FY22
FY23
FY24
FY25
FY26
FY27
FY28
FY29 TOTAL
Auckland neutral earthing resistors
0.10
0.18
0.20
0.20
0.20
0.20
0.20
0.25
0.25
0.20
1.98
Northern neutral earthing resistors
0.12
0.16
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.20
1.88
Total CAPEX
0.22
0.34
0.40
0.40
0.40
0.40
0.40
0.45
0.45
0.40
3.86
5.2.3 DISTRIBUTION FEEDERS (HV & LV) The following sections set out the project proposals for HV and LV distribution feeders, with a particular focus on overhead conductors. In addition to these specific projects and programmes, there will be some further expenditure on distribution feeders as part of the general Network Maintenance programme.
OVERHEAD CONDUCTOR RENEWAL
NEEDS STATEMENT Vector’s 11 kV overhead network for the combined Auckland and Northern networks is 3,776 km in route length of which over 600 km consists of small diameter conductors. A substantial portion of the network is in excess of 60 years old 18 and there is increasing failure in older and ageing small conductors in the 11kV network most notably the population of 16mm² Copper conductors but we are also starting to see failures of older 21mm² ACSR conductors. The increasing rate of failure of small diameter 11 kV conductors has impacted reliability (see Section 2) and its poor health is also starting to pose a risk to operational staff and the public. Many portions of the network with small diameter conductors exist in high density urban areas with a high congregation of people and the risk of conductor failure and then, falling to ground presents a hazard to the public. Furthermore, according to a National Institute of Water and Atmospheric Research study in 2017 extreme rainfall, severe droughts, wildfires and wind with increased speeds could hit Auckland in years to come and conductors in poor condition and little resilience will result in further outages and thus an increase in SAIFI unless investment to renew conductors is undertaken. Our CBARM model shows that to meet our service level standards and to reduce the health and safety impact of conductors we will need to replace most of the 600 km of small diameter 11 kV conductor in the AMP period.
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18 Due to legacy issues there are gaps in the data for the age of overhead conductors and assumptions had to be made based on other statistical data, e.g. the date that subdivisions were developed, the dates imprinted on poles, etc.
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