The Nelson River DC Transmission System, also known as the Manitoba Bipole, is an electric power transmission system of three high voltage, direct current lines in Manitoba, Canada, operated by Manitoba Hydro as part of the Nelson River Hydroelectric Project. It is now recorded on the list of IEEE Milestones in electrical engineering. Several records have been broken by successive phases of the project, including the largest (and last) mercury-arc valves, the highest DC transmission voltage and the first use of water-cooled thyristor valves in HVDC. The system transfers electric power generated by several hydroelectric power stations along the Nelson River in Northern Manitoba across the wilderness to the populated areas in the south. It includes two rectifier stations, Radisson Converter Station near Gillam at and Henday Converter Station near Sundance at , one inverter station, Dorsey Converter Station at Rosser located north west of Winnipeg at ), and two sets of high-voltage direct current transmission lines. Each HVDC transmission line has two parallel overhead conductors to carry the positive and negative feeds. A third line, Bipole 3, was completed in 2018, running from the new Keewatinoow Converter Station along the west side of Lake Manitoba to the new Riel Converter station on the east side of Winnipeg. There are no intermediate switching stations or taps. All three bipolar systems have extensive ground return electrodes to allow use in monopolar mode. History Construction in 1966 of the 1,272 MW Kettle Rapids generating station required a long transmission line to connect it to load centers in the southern part of Manitoba. The Government of Canada agreed to finance installation of an HVDC line to be repaid by Manitoba Hydro when the load growth permitted the utility to assume the debt due to the line. Delivery of direct current electric power began on June 17, 1972. One unit of the Kettle generating station was completed before the direct current converters were completed. For the winter of 1970 the bipole lines were energized with alternating current, contributing a useful amount of energy to the Manitoba system; a shunt reactor was installed to prevent excess voltage rise due to the Ferranti effect. At that time, Bipole I used the world's highest operating voltage to deliver the largest amount of power from a remote site to a city, and employed the largest mercury arc valves ever developed for such an application. The line required construction