Unison, NZ has become the first distribution company in the world to trial a unique condition assessment device on 11kV lines.

The ‘Cormon’ unit, one of only three world-wide, was used to perform condition assessments on one of the main types of conductor on Unison’s network, providing information that will help to determine the remaining life of the assets.

“Working alongside service provider LineTech, we have been using the unit to test 11kV and 33kV lines,” said Unison General Manager Networks & Operations, Jaun Park.

“The results from this trial will determine if the technology would be a suitable addition to our Asset Condition and Health Assessment programme, which aims to extend the lifecycle of assets, and defer capital expenditure for the benefit of our customers.”

The unit is mainly used on transmission lines, with limited testing to date on 33kV lines.  Unison will be the first distribution company globally to test both 33kV and 11kV lines.

“The unit assesses the condition of the line millimetre by millimetre, using a high frequency signal to induce small currents in the conductor as it works its way along the full length of the live lines, detecting areas where corrosion could occur.”

Unison used the unit on ‘ACSR’ conductors, which stands for ‘Aluminium Conductor, Steel Reinforced’.  ACSR cable consists of aluminium – a good conductor of electricity but of relatively low mechanical strength – strengthened with steel strands.

“Inside ACSR conductor there is a layer of zinc, which acts as a protective galvanised coating on the steel. The zinc prevents a chemical reaction between the steel and aluminium, but over time the zinc erodes away, and eventually the aluminium starts to react with the bare steel and corrode.

“The Cormon unit detects how much of that protective layer of zinc coating is left inside the conductor, enabling us to have a much better insight into how much useful remaining life the asset has, rather than replacing the asset on a life-expectancy basis.  This will defer capital expenditure as well as help us to conduct maintenance before the asset fails, causing disruption to our customers.”

Unison has now started analysing the results of the tests to determine if the tool will be incorporated into Unison’s Asset Condition and Health Assessment work.

Conditionassessment 

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