Benmore Power Station

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Benmore HVDC Static Inverter Plant is the terminal at Southern end of Inter-Island HVDC link, the high voltage direct current connection between the two main islands of New Zealand, which went into service in 1965. It was built with mercury arc rectifiers in its static inverters. The project was, until it was upgraded in 1993, a bipolar HVDC line with an operating voltage of 400 kV and a maximum transmission capacity of 1200 MW.

The transmission line connecting the static inverter stations at Benmore Dam in the South Island and Haywards in the North Island has a total length of 610 km. The line runs overhead for 570 km. A 40-km undersea cable is laid across Cook Strait. In 1993 the system was upgraded with thyristors in its static rectifiers, which use a transfer voltage of 350 kV. During this upgrade 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.

As of 21 September 2007, Pole 1 of this system which still utilized the original mercury arc rectifiers, was shut down indefinitely. Transpower noted in November 2007 that in december 2007, it would increase the south to north transfer capacity at Pole 2 from 500MW to 700MW by reconfiguring the three operational undersea cables by switching one the two undersea Pole 1 cables to Pole 2