Friday, December 1, 2023

Transpower to replace joints on underground cable

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The 10.5km cable is one of two supplying electricity into Auckland and Northland at times of peak demand as part of the high-capacity double circuit Pakuranga-Whakamaru transmission line.

Transpower has announced that it plans to replace 45 joints at 15 locations on an underground electricity cable between its Brownhill (Whitford) and Pakuranga substations in a two-to-three-year $40 million work programme starting in next year.

GM grid delivery Mark Ryall said Transpower is taking a prudent approach, following two faults in cable joints on this circuit in the past three years, by replacing all joints on the cable in a planned way.

“We are committed to continuing to deliver a secure and reliable power supply through the transmission network for Auckland and Northland,” Ryall said.

“Replacing these joints returns this important cable to its intended condition, so it can operate effectively for its expected remaining 30-40-year life. The issue is unforeseen and unexpected and we will work through the impacts with the industry and affected communities.”

The 10.5km underground cable is one of two supplying electricity into Auckland and Northland at times of peak demand as part of the high-capacity double circuit Pakuranga-Whakamaru transmission line.

Ryall said replacing the joints is a two-to-three-year work programme with physical site work expected to start in May or June 2024. There are 15 cable joint bays across around 10km of cable route, each with three joints that need replacing.

“This is a complex civil works project and there will be disruptions that we will need to manage by working closely with local communities and other stakeholders,” he said.

“We will need to excavate an area about the size of a city bus for each cable joint bay and we anticipate it will take around four months to complete the work for each joint bay. It may take longer for some more complex sites.”

Transpower has not finalised the expected cost for the project as it is still in the planning stage and likely costs will become more certain through the procurement phase. At this stage it is estimated to be more than $40m.

These costs will be absorbed into Transpower’s regulated transmission allowances and allocated to Transpower customers through transmission charges over the life of the asset.

Ryall said Transpower assessed a range of other remediation options for the cable, including continuing to repair faults as they arise or bringing forward significant new investment to ensure electricity supply remains stable and reliable.

“We concluded that replacing the joints over a two-year programme will give the best overall outcome for electricity users in the region,” he said.

Ten of the cable joint bays are located within roads or on roadsides, two are in council reserves, two are on private property and one is on Transpower property. Ryall said Transpower will work with local communities, mana whenua and other stakeholders to minimise the impacts as much as possible.

“We want to work collaboratively to understand any impacts to communities and find the best solution to mitigate or avoid these,” he said.

Transpower said the electricity supply into Auckland and Northland is secure and will continue to be secure during the works. This is because there is a companion cable on the circuit between Brownhill and Pakuranga, and a temporary bypass line has recently been constructed in north Waikato to provide additional security and ensure peak demand can be met.

Transpower will provide regular updates as the project progresses. To sign up to the project e-newsletter visit Updates will also be posted to the Brownhill-Pakuranga Cable Project web page.

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