Each HVDC transmission line has two parallel overhead conductors to carry the positive and negative feeds.

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.

[2] 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.

The loan by the Government of Canada was discharged when Manitoba Hydro bought the line and outstanding debt in 1992.

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.

Bipole 1 consists of six 6-pulse converter groups at each end (three in series per pole), each originally rated at 150 kV DC, 1800 A.

Between 1992 and 1993 the mercury arc valves of Pole 1 were replaced with solid state thyristors from GEC Alsthom, increasing the maximum power and voltage of the line to its current levels.

At both Radisson and Dorsey, the thyristors are situated in the same hall where the mercury arc valves originally stood.

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.

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.

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 system is capable of transmitting 2000 megawatts from the Nelson River stations to loads in the south.

Although normally each of the lines run as bipolar systems, if a pole is shut down for maintenance or a fault, the ground return electrode is used to maintain partial capacity operation.