The 250 kV d.c. submarine power-cable interconnection between the North and South Islands of New Zealand

The submarine power cables across Cook Strait are a part of the ±250 kV 600 MW d.c. transmission system from Benmore, in South Island of New Zealand, to Haywards in North Island. Two 24mile single-core gas-filled submarine cables convey the power from Fighting Bay in South Island to Oteranga Bay in North Island, and a third cable serves as a spare. The paper describes the cable route and site conditions and then deals with the cable design, manufacture and proving. Novel features are the use of a bend-restricting construction where the cable is laid on a rocky sea bed, and short-circuiting studs between sheath and armour to limit overvoltages developed across the anticorrosion serving. Because the water depth necessitates an internal gas pressure of 425lbf/in2, the sealing ends are so designed that the pressure porcelain is not in tension. The cable-laying equipment and methods are explained, and the repair of the fault which occurred during the laying of one of the cables is described.