HVDC Inter-Island

HVDC Inter-Island
Route of the HVDC Inter-Island
Location
Country	New Zealand
General direction	South-North
From	Benmore Hydroelectric Power Station, near Otematata, Canterbury
To	Haywards transmission substation, Lower Hutt
Ownership information
Owner	Transpower New Zealand
Operator	Transpower New Zealand
Construction information
Manufacturer of substations	ABB / Siemens
Construction started	1961
Commissioned	April 1965
Technical information
Type	Bipole HVDC powerline with overhead transmission line and submarine power cables underneath the Cook Strait
Type of current	HVDC
Total length	610 km (380 mi)
Power rating	1200 MW
AC voltage	220 kV
DC voltage	±350 kV
No. of poles	Two

The HVDC Inter-Island link is a 610 km (380 mi) long, 1200 MW high-voltage direct current (HVDC) transmission system connecting the electricity networks of the North Island and South Island of New Zealand together. It is commonly referred to as the Cook Strait cable in the media and in press releases,^[1] although the link is much longer than its Cook Strait section. The link is owned and operated by state-owned transmission company Transpower New Zealand.

The HVDC link starts in the South Island at the Benmore Hydroelectric Power Station, on the Waitaki River in Canterbury and then it travels 534 kilometres (332 mi) on an overhead transmission line through inland Canterbury and Marlborough to Fighting Bay in the Marlborough Sounds. From Fighting Bay, the link travels 40 km via submarine power cables underneath Cook Strait to Oteranga Bay, near Wellington, before travelling the final 37 km on overhead lines to Haywards transmission substation in Lower Hutt.

The HVDC link first became operational in April 1965 to primarily transport electricity from the generation-rich South Island to the more populous North Island. The link originally was a bipolar 600 MW link with mercury arc valves, until the original equipment was paralleled onto a single pole (Pole 1) in 1992, and a new thyristor-based pole (Pole 2) was constructed alongside it, increasing the link's capacity to 1040 MW. The ageing Pole 1 was fully decommissioned effective 1 August 2012, and a replacement thyristor-based pole, Pole 3, was commissioned on 29 May 2013,^[2] restoring the DC link to a bipolar 1200 MW configuration.