The Commission’s approval is for the first stage of a two-stage plan to replace and expand the high‑voltage direct current (HVDC) cable capacity and replace the HVDC control system. If approved, the current capacity for electricity transfer between the islands would be protected and the extra cable would deliver an additional 200 MW of transfer capacity.
Associate Commissioner Nathan Strong says the HVDC cables are critical electricity transmission infrastructure and vital for our national security of supply.
“Not only are these cables essential for meeting New Zealanders’ electricity needs, but they also support the country’s development of renewable energy. Installing a fourth cable at the same time unlocks an additional 200 MW of capacity, which can reduce long-term electricity market costs and enable the development of lower cost renewables generation in the South Island. This has been shown to provide a long-term benefit to consumers.”
The current HVDC submarine cables were installed in 1991 and are approaching the end of their operational life. As they age, they become less reliable and failure risks increase. Cable failures would involve lengthy repair times and have a significant impact on electricity market outcomes, ultimately which could increase costs for consumers.
Transpower is seeking an early approval to enable it to secure a timely supply arrangement with the cable manufacturer.
“Getting the installation timing right is as important as the decision to invest in a fourth cable. Delaying the installation of the fourth cable has been shown to reduce the benefits to consumers —even in scenarios where electricity demand grows more slowly than expected” says Associate Commissioner Strong.
Transpower has also demonstrated that the infrastructure supporting the cables needs to be upgraded. Seismic risks at the cable termination stations and loss of the Miramar spare cable storage facility will require additional investment.
Construction is expected to begin after 2028 with the cables being installed in the early 2030s.
The investment would be added to Transpower’s total asset base and recovered gradually over the many decades the equipment is in service. Under the benefits based pricing method, these costs would be shared between electricity consumers and generators who benefit from the HVDC link.
Community and stakeholder feedback will help inform the Commission’s final decision. Submissions close: 4pm, 29 April 2026 Cross submissions close: 4pm, 13 May 2026.
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