HVDC Inter-Island

The HVDC Inter- Iceland is a high-voltage direct current transmission line ( HVDC) between the South and the North Island in New Zealand. It is the only line which allows an energy transfer between the two island as part of the electrical power supply. The HVDC can carry only electric power from the South Island to the North Island in the more densely populated areas around the capital, Wellington, a load flow in the other direction is not provided.

The line is operated by the network operator Transpower New Zealand Limited, and was taken in 1965 with mercury vapor rectifiers in operation. In 1991 a change was made on thyristors. The facilities were built by Asea Brown Boveri (ABB).

The line starts in the South Island at the Benmore Dam in Canterbury, including a transmission line of 535 km in length, crosses the submarine at 40 km in length, the Cook Strait and ends in Haywards near Wellington on the North Island.

The HVDC is designed as an asymmetric, bipolar HVDC transmission which is operated due to the asymmetry with two separate poles: Pole 1 is operated with a DC voltage of 270 kV and pin 2 wired to -350 kV. The total transmission capacity is 1240 MW.