HVDC Kingsnorth was a

high-voltage direct-current A high-voltage direct current (HVDC) electric power transmission system uses direct current (DC) for electric power transmission, in contrast with the more common alternating current (AC) transmission systems. Most HVDC links use voltages betwe ...

(

HVDC A high-voltage direct current (HVDC) electric power transmission system uses direct current (DC) for electric power transmission, in contrast with the more common alternating current (AC) transmission systems. Most HVDC links use voltages betwe ...

) transmission system connecting Kingsnorth in

Kent Kent is a Ceremonial counties of England, ceremonial county in South East England. It is bordered by Essex across the Thames Estuary to the north, the Strait of Dover to the south-east, East Sussex to the south-west, Surrey to the west, and Gr ...

to two sites in

London London is the Capital city, capital and List of urban areas in the United Kingdom, largest city of both England and the United Kingdom, with a population of in . London metropolitan area, Its wider metropolitan area is the largest in Wester ...

. It 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, and the first HVDC link to be embedded within an AC system, rather than interconnecting two asynchronous systems. It was also the first HVDC scheme to be equipped with self-tuning harmonic filters and to be controlled with a "Phase Locked Oscillator", a principle which subsequently became standard on all HVDC systems. It was designed in the late 1960s and went into service in 1974. It ran from Kingsnorth power station as a 59 kilometers long bipolar (3-wire) underground cable. The positive pole operating at a voltage of +266 kV terminated at the converter station in

Beddington Beddington is a suburban settlement in the London Borough of Sutton on the boundary with the London Borough of Croydon. Beddington is formed from a village of the same name which until early the 20th century still included land which became ...

near

Croydon Croydon is a large town in South London, England, south of Charing Cross. Part of the London Borough of Croydon, a Districts of England, local government district of Greater London; it is one of the largest commercial districts in Greater Lond ...

. The negative pole continued to run a further 26 kilometers at -266 kV line to a similar station at

Willesden Willesden () is an area of north-west London, situated 5 miles (8 km) north-west of Charing Cross. It is historically a parish in the county of Middlesex that was incorporated as the Municipal Borough of Willesden in 1933; it has formed ...

in North London. There was also the possibility, if the converter station in Kingsnorth was out of service, to run the system as monopolar HVDC between the Beddington and Willesden stations. The HVDC Kingsnorth was one of the last HVDC schemes equipped with mercury vapour rectifiers, which were ARAG/4-valves designed by English Electric. Each converter station for 266 kV consisted of two six-pulse valve bridges for 132 kV switched in series, which were each fed via a star-star and a star-delta connected transformer. Apart from the Nelson River Bipole 1 system in

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

, all later-built HVDC systems used

thyristor A thyristor (, from a combination of Greek language ''θύρα'', meaning "door" or "valve", and ''transistor'' ) is a solid-state semiconductor device which can be thought of as being a highly robust and switchable diode, allowing the passage ...

valves. The Kingsnorth HVDC scheme could transfer a maximum power of 640 megawatts (320 megawatts per pole). In 1981, one mercury arc valve at Willesden Static Inverter Plant, was replaced by a H200 thyristor valve, developed by English Electric. The system described was shut down in 1986 or 1987 following system reinforcement on the network it was embedded in. However the capacitor banks located at Kingsorth were used for voltage control on the network. These were later removed from the system completely in the mid 1980s? (1990s?) as they contained PCB.

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{{National Grid, state=expanded Infrastructure in London Electrical interconnectors to and from Great Britain HVDC transmission lines Electric power infrastructure in England Energy infrastructure completed in 1974 1974 establishments in England