Electricity Asset Management Plan 2019-2029
108
Vector Limited://
segments of the network have been identified for conductor replacement, based on the asset health in our CBARM model, the same portion of line will undergo general refurbishment and repairs of defects. I.e. crossarms, insulators, connectors will be replaced to extend the asset life. Our intervention programme to control vegetation to improve SAIDI and SAIFI will continue and be extended. As part of the programme to renew HV overhead feeders, we use acoustic technology to find failed or failing insulators that are then replaced. Conductor sampling is also used to assess condition and to build up a profile and database of the network that contains conductor with poor asset health. As part of conductor condition driven rebuilds, poles, crossarms and stays will be replaced as required. In rural areas failures of conductors can have disastrous consequences such as electrocution and bush fires and we are investigating the use of alternative overhead technologies such as 11 kV aerial bundled conductors and the so-called Hendrix spaced covered conductor systems. We have also commenced with a targeted sampling and testing plan with a focus on areas where conductors have failed to increase our understanding of the condition, degradation and failure modes of the conductor fleet. This will be used in statistical analysis for our intervention programme to further assist us to better identify and target conductors for replacement. Because many poles in our network share OH lines of different voltages from subtransmission to low voltage, pole data cannot be separated per voltage; hence this section includes overhead supports for 33 kV subtransmission as well – only 110 kV OH supports are excluded and are described in the section for Subtransmission assets. Overhead supports consist of poles, stays and crossarms. Poles for overhead distribution circuits are predominantly pre-stressed concrete with timber crossarms. About 8% of poles in rural distribution feeders are treated softwood timber poles with only a few hardwood poles in the network. Timber poles are extensively used as support structures for connections to customers. Concrete poles in the Auckland region are about 40% as strong as new prestressed concrete poles. Any upgrade or refurbishment of overhead lines utilises pre-stressed concrete poles unless specific locations call for specialised steel poles. Population and Age The nominal asset life for concrete poles is 60 years while wooden poles are expected to last from 30 to 60 years depending on type, treatment and installation conditions (traditionally crossarms were expected to typically last between 15 and 30 years but our present specification for wooden crossarms requires a life of 40 years). Due to legacy reasons, the age of all poles in the Auckland network is not available and age dates were estimated based on other factors e.g. the date that an area was established. The table below provides statistics for our pole population. Further details of our strategy for renewal is described in Vector’s asset strategy EAA401 Overhead Lines. Details of the replacement and refurbishment programme and details of the vegetation control programme are given in Section 5. 4.4.2 DISTRIBUTION FEEDERS OH SUPPORTS Overview
DESCRIPTION
AUCKLAND
NORTHERN
No of reinforced concrete poles
1758
48848
No of prestressed concrete poles
43108
11742
No of softwood wood poles
2552
1969
No of hardwood wood poles
1822
297
No of steel lattice towers
0
60
No of steel monopoles
4
1
No of U-poles (composite poles)
358
455
Table 4-12 Key statistics for Poles
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