valves of Pole 2 were replaced later by Siemens. By the end of 2004 the last of the mercury arc valves in Pole 2 had been replaced by thyristor valves. At both Radisson and Dorsey, the thyristor valves are situated in the same hall where the mercury arc valves originally stood. At both locations, the hall has a height of , a width of and a length of . Bipole 2 The Bipole 2 transmission line runs from Henday to Dorsey. Bipole 2 can transfer a maximum power of 1800 MW at a potential of ±500 kV. Bipole 2 consists of four 12-pulse converter groups at each end (two in series per pole) and was put into service in two stages. After the first stage in 1978 the maximum power was 900 MW at 250 kV, which increased to its present figure when it was completed in 1985. Bipole 2 crosses Nelson River at 56.459811 N 94.143273 W. There is a backup crossing of Nelson River at 56.441383 N 94.176114 W. It is not possible to switch directly the line to the backup crossing. Unlike Bipole 1, Bipole 2 has always been equipped with thyristors. The thyristor valves, supplied by the German HVDC consortium (Siemens, AEG and Brown Boveri) used water cooling for the first time in an HVDC project. Until that time, the relatively few HVDC schemes using thyristors had used either air cooling or, as on the Cahora Bassa project supplied by the same consortium, oil-cooling. The thyristor valves were arranged in floor-mounted vertical stacks of four valves each (quadrivalves). Each valve contained 96 thyristor levels in series, with two in parallel. These were arranged in 16 thyristor modules connected in series with 8 reactor modules. Bipole 3 In 1996 an extreme wind effect damaged both Bipoles 1 and 2 and threatened to black out Winnipeg. Power was maintained by importing from Minnesota while the two existing Bipoles were repaired. To avoid a repetition of this event, and further improve the reliability of the power supply, Manitoba Hydro examined routes further to the west for their Bipole 3 line. The plans also include an additional converter station and feeder lines around the city. Bipole 3 construction started in 2012. The line was completed and entered service in July 2018. The main elements of the Bipole III system are: Keewatinoow Converter Station, located on the Nelson River near the