DC transmission system

Photo of Nelson River DC Transmission System.

The Nelson River high voltage direct current (HVDC) transmission lines accommodate 2 bipolar transmission systems called Bipole I and Bipole II. The term bipole refers to a positive (+) pole and a negative (−) pole. Each pole is comprised of 2 conductor cables which, in bundles 4 cm in diameter, are supported by the steel transmission towers.

Bipoles I and II deliver approximately 75% of our generating capacity from the Nelson River in northern Manitoba to southern Manitoba via 2 rows of identical steel towers, which follow an 895-km route from Gillam southward through the Interlake region.

One transmission line has its northern terminus at Radisson Converter Station near Gillam. The other extends another 42 km northeast to Henday Converter Station. The southern terminus of both transmission lines is Dorsey Converter Station at Rosser, about 26 km northwest of Winnipeg.

Due to the heavy reliance on one transmission corridor and a single converter station in the south, the system is vulnerable to extensive power outages from severe weather (major ice storm, extreme wind event, tornado), fires, or other events.

Read about the Bipole III Transmission Reliability Project.

The tremendous hydroelectric potential of the Nelson River was untapped in the 1960s when the technology became available for the long-distance transmission of HVDC electricity. Currently, about 80% of our electricity is produced by hydroelectric generating stations on the Nelson River. Manitoba Hydro has since become world-renowned for research and development in this field.

  • Voltage
    • Bipole I: 900 kV (±450,000 nominal, ±463,000 maximum);
    • Bipole II: 1,000 kV (±500,000 maximum).
  • Length of lines
    • Bipole I: 895 km;
    • Bipole II: 937 km;
  • Towers
    • Quantity 4,103;
    • 33.8 metres to 47.2 metres high (average 38 metres);
    • Distance between towers: 427 metres to 488 metres;
    • Right-of-way width 137 metres;
    • Distance between lines I and II: 74.7 metres;
    • Clearing: 10,800 hectares.
  • Conductor: 7,400 km of 4-cm in diameter cable;
  • Thermal carrying capacity - 3,600 amperes;
  • Thyristors: Bipole II 18,432;
  • Converter stations
    • Rectification: Radisson at Gillam, Henday at Sundance;
    • Inversion: Dorsey at Rosser.