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Nelson River Bipoles 1 and 2 terminate at Dorsey Converter Station near Rosser, Manitoba. The station takes HVDC current and converts it to HVAC current for re-distribution to consumers

Dorsey Converter Station near Rosser, Manitoba - August, 2005

The Nelson River Bipole is a historic electric power transmission system of two high voltage, direct current lines in Manitoba, 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.

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 and Henday Converter Station near Sundance, one inverter station, Dorsey Converter Station at Rosser (26 km from Winnipeg), and two sets of high-voltage direct current transmission lines, each with two parallel overhead conductors to carry the positive and negative feeds. Both bipolar systems have extensive ground return electrodes to allow use in monopolar mode.

A 150 kV mercury arc valve at Manitoba Hydro's Radisson converter station, August 2003

Bipole 1 runs 895 km from Radisson to Dorsey. It is rated to run at a maximum potential difference of +/- 450 kilovolts and a maximum power of 1620 megawatts. When it was built between March 1971 and October 1977, mercury arc valves were used to rectify the alternating current. These were the most powerful mercury arc valves ever built. In 1993 the mercury arc valves of one pole were replaced with thyristors, increasing the maximum power and voltage of the line to its current levels. By the end of 2004 the last of the mercury arc valves had been replaced by thyristors.

Six thyristors in a module, with cooling piping and protective capacitors.

The Bipole 2 transmission line runs 937 km from Henday to Dorsey. Bipole 2 can transfer a maximum power of 1800 MW at a potential of +/- 500 kV. Bipole 2 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. Unlike Radisson station, Henday station has always been equipped with thyristors.

A 2000A 250 kV thyristor valve at Manitoba Hydro's Henday converter station, April 2001

Construction in 1966 of the 1272 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.^[1] 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 of over 3,900 guyed towers and 96 self supporting towers across varied terrain. Permafrost in some areas led to foundation settling of up to 3 feet (1 meter).

The loan by the Government of Canada was discharged when Manitoba Hydro bought the line and outstanding debt in 1992 [1]. In 1997 a tornado damaged 19 towers of the DC lines. During repairs, some major customers were advised to curtail load, but imports over the 500 kV lines from adjacent utilities in the United States prevented serious interruption of power.

• Manitoba Hydro
• http://www.transmission.bpa.gov/cigresc14/Compendium/NELSON1.htm
• http://www.transmission.bpa.gov/cigresc14/Compendium/NELSON2.htm
• http://www.transmission.bpa.gov/cigresc14/Compendium/Nelson2%20Pictures.pdf

• [1] L. A. Bateman, "A History of Electric Power Development in Manitoba", in IEEE Canadian Review, Winter 2005
• IEEE History Center

1. ^ Leonard A. Bateman, An Engineering Career in the Hydroelectric Industry, Engineering Institute of Canada Working Paper 22/2004, July 2004