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The HVDC Inter-Island is the high voltage direct current connection between the two islands of New Zealand, which was put into service in 1965. It was built with mercury arc rectifiers in its static inverters and was, until the addition of a modern HVDC system in 1993, a bipolar HVDC line with an operating voltage of 250kV and a maximum transmission capacity of 600 megawatts. The power line connecting the static inverter station at Benmore Dam in the South Island of New Zealand with the static inverter station at Haywards on the North Island has a total length of 610 kilometres, 570 kilometres are built overhead and 40 kilometres are undersea cable across Cook Strait. In 1993 the HVDC Inter-Island was extended by a modern HVDC system with thyristors in its static rectifiers, which uses a transfer voltage of 350kV. During this extension the static inverters of the old scheme, which still use the mercury arc valves from 1965, were modified so that they are now switched in parallel.
Source: http://de.wikipedia.org/wiki/HG%DC_Inter-Island
