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Huntly Power Station – 220kV Bushing Replacement

Project Scope

Built during the 1970s and 1980s and comprising six different generating plants, Huntly Power Station can be fi red by coal, gas or both simultaneously.

When urgent maintenance work was required to replace the 220kV pressurised oil-filled termination bushings linking the power station to the national grid, Northpower was identified as one of a handful of electrical contractors in New Zealand with the capability to carry out this delicate task.

The contract included replacing, vacuuming, repressurising and commissioning all terminations. Included in the scope of the project was draining, replacing, vacuuming and refilling a damaged bushing.

Challenges

With safety to staff and equipment being of the highest priority, Northpower began with a comprehensive assessment which deemed that work could not begin while there was any moisture in the air.

Due to its location beside the Waikato River the power station frequently experiences foggy, misty or humid conditions, especially over the winter months, so the Northpower team was forced to wait several weeks for a window of two consecutive fine, dry days.

It was essential that the equipment was given a day to dry out completely before the parts could be replaced and commissioned on the second day.

This had to be balanced against the need to complete the work in order to ensure security of supply to the national grid.

The team faced technical challenges as they worked on a system which was originally installed in the 1970s using Swiss-made equipment for which spare parts are no longer available.

Solutions

While waiting for optimal weather conditions to allow the work to be carried out, the Northpower team took contingency measures to ensure that the power supply was maintained, installing a back-up bushing until repairs could be done.

Working from the original 1970s plans, Northpower had fittings, including gaskets and bolts, designed and custom-made locally. All preparations were made in advance, including the erection of scaffolding and tarpaulins, and a team was put on permanent standby until weather conditions were optimal.

Results

Due to Northpower’s thorough approach and planning, the contract was completed successfully on time without any loss of supply to the national grid.

FACTS AND FIGURES

• 200 litres of cable oil used
• 6 team members on site
• 20 hours continuous working to replace bushing
• 2 full days of testing by 2 technicians

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