Mercury-arc Valve - Applications

Applications

As solid-state metal rectifiers became available for low-voltage rectification in the 1920s, mercury arc tubes became limited to higher voltage and especially high-power applications.

Mercury-arc valves were widely used until the 1960s for the conversion of alternating current into direct current for large industrial uses. Applications included power supply for streetcars, electric railways, and variable-voltage power supplies for large radio transmitters. Mercury-arc stations were used to provide DC power to legacy Edison-style DC power grids in urban centers until the 1950s. In the 1960s, however, solid-state silicon devices, first diodes and then thyristors, replaced all lower-power and lower voltage rectifier applications of mercury arc tubes.

One of the last major uses of mercury arc valves was in high voltage DC (HVDC) power transmission, where they were used in many projects until the early 1970s, including the HVDC Inter-Island link between the North and South Islands of New Zealand and the HVDC Kingsnorth link from Kingsnorth power station to London. However, starting about 1975, silicon devices have made mercury-arc rectifiers largely obsolete even in HVDC applications. The largest ever mercury-arc rectifiers, built by English Electric, were rated at 150-kilovolt, 1800 amp and were used until 2004 at the Nelson River DC Transmission System high-voltage DC-power-transmission project. The valves for the Inter-Island and Kingsnorth projects used four anode columns in parallel, while those of the Nelson River project used six anode columns in parallel in order to obtain the necessary current rating. The Inter-Island link was the last HVDC transmission scheme in operation using mercury arc valves. It was formally decommissioned on 1 August 2012. A similar mercury arc valve scheme, the HVDC Vancouver Island link between Vancouver Island and the Canadian mainland had been previously removed from service. The mercury arc valve converter stations of the New Zealand scheme were replaced by new thyristor converter stations. The Vancouver Island scheme was replaced by a three-phase AC link.

Mercury arc valves remain in use in some South African mines, Kenya (at Mombasa Polytechnic - Electrical & Electronic department), and on the Manx Electric Railway on the Isle of Man.