11kV Overhead Electrical Conductor

Overview

Wellington Electricity (WE) engaged Modla to analyse their 11kV Overhead (OH) conductor fleet. This involved developing and running various analyses on a Reliability Centred Maintenance & Decisions (RCMD) asset class model.

Objectives

The objective of the project was to produce a prioritised list of conductors that should be replaced in the coming year(s). The analysis prioritised conductors based on their current likelihood of failure due to age related failure modes. By calculating the likelihood of failure for each conductor section, WE can target replacements to minimise their risk exposure due to conductors failing unexpectedly. As an aside, the project also evaluated the merit of performing visual inspections at alternate frequencies. The optimum interval to schedule visual inspections at was identified by running a cost minimisation optimisation.

“This has been a useful experience for us and we are incorporating the results of this project into our future asset management activities.  ” - Agnes Canita & Graham Clark, Asset Engineer & Graduate Engineer @ WE

Results

• The project developed an asset class model for 11kV OH conductors which codified the current understanding of conductor asset performance.
• The analyses identified 28 connectors with a likelihood of 10% or higher of failing in the next year.
• The analyses produced a rank ordered list of conductors to replace based on their likelihood of failure. The likelihood of annealing, fretting fatigue, clashing, corrosion, connector failure, and third-party impacts were considered.
• The analyses determined that less than 50% of conductor sections are cost beneficial to visually inspect.

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Summary

This project modelled 7,418 of WEs 11kV OH conductors, comparing run to fail and five year optimised maintenance scenarios. The run to fail scenario identified sections of conductor that should be replaced as a priority. Most of the failures experienced by WE are driven by events outside of their control such as vehicle or third party impacts. In general conductors seldom fail from unassisted modes like corrosion due to their comparably long-life span. However, the analysis does identify conductors that bring the most benefit to WE if replaced and informs their programs of work.

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