HVDC Kingsnorth
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The high voltage direct current transmission (HVDC)system Kingsnorth in Kent was at one time the only application of the technology of high voltage direct current transmission for the supply of transformer stations in a city.
It was designed in the first half of the 1970's and went into service in 1975. It ran from the power station at Kingsnorth as a 59 kilometers long bipolar underground cable, operating at a voltage of 266 kV to the static inverter station in Beddington. The cable continued to run a further 26 kilometers as single-pole line to Willesden.
There was also the possibility, if the static inverter station in Kingsnorth was out of service, to run the system as monopolar HVDC between the stations Beddington and Willesden. The HVDC Kingsnorth was the last HVDC equipped with mercury vapor rectifiers, whereby each static inverter for 266kV consisted of two six-pulse valve bridges for 132kV switched in series, which were each fed via a star-star and a star-delta switched transformer.
All later-built HVDC systems used thyristor valves. The HVDC Kingsnorth could transfer a maximum power of 640 megawatts (320 megawatts per pole).
Because the facility did not correspond to today's operating requirements, it was subsequently shut down and replaced by three-phase alternating current cables.