As part of asset inspections last week after Cyclone Gabrielle, Transpower has identified a significant slip near two towers carrying high voltage electricity lines feeding Northland.

110kV tower is closest to the slip, 220kV tower is behind it

The slip is located approximately 10km south-west of Wellsford and impacts one tower on the Henderson to Marsden 220kV line and one tower on the Henderson to Maungatapere 110kV line. The slip, which is near the point where these lines cross, is closest to the tower on the 110kV line.
If it were to move further and bring down the tower on the 110kV line, it could also bring down the 220kV line where they cross, cutting off supply from Warkworth north.

Transpower General Manager Grid Delivery Mark Ryall said geotechnical engineers have inspected the slip and the surrounding area and recommended moving the towers rather than trying to stabilise them in place.

“With more rain forecast, we have removed the 110kV line from service and will lower it to the ground as a precaution,” Mr Ryall said. “This will mitigate the risk of both transmission lines being affected at the same time if there are further slips.

“We will then relocate the 220kV line to bypass the tower in the impacted area. This will be an interim step to improve security while we work on a permanent solution.”

Mr Ryall said that the entire area from Warkworth north is now being supplied exclusively through the double circuit 220kV line, which increases the risk of outages in the region should a fault or another weather event occur.

“We are conscious that the people in these regions have been through a lot in recent weeks,” he said.

“While the risk of a fault or further slip on the 220kV line is small, we wanted to ensure that people are aware of the risk and able to take steps to prepare for any unplanned outages.

“We are working closely with local lines companies Northpower, Top Energy and Vector to manage any local impact in their areas.”

Residents in areas from Warkworth north are advised to consider taking precautionary steps such as having an alternative cooking source such as a BBQ with a full gas bottle and ensuring phones and other electrical appliances are charged frequently, should a fault occur on the 220kV line before a permanent fix can be put in place.

Mr Ryall said that Transpower has identified locations for temporary towers to be erected to complete the bypass of the 220kV line.

“Crews are now on site working forming the required access to the area,” he said. “However, access is challenging, and it will take some time to cut a track to be able to bring in the necessary equipment.

“At this stage we anticipate having the first stage of the bypass complete by the end of next week. We want to assure those in areas impacted that we understand how critical a secure supply of electricity is and we are doing everything that we can to get the bypass in as quickly as possible to mitigate any risk.”

Once the bypass on the 220kV line is in place, the 110kV line will be able to be put back into service, improving security while a permanent solution for the tower on the 110kV line is put in place.

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