Transmission & distribution
Self-supporting suspension towers (above) are commonly used for our high voltage transmission lines across cultivated land, because the base occupies a space of only 6.5 by 7 metres, making it less intrusive for those working the land.
Manitoba Hydro's transmission system transports electricity from generating stations around the province in a range from 24 kV to 500 kV.
Our major high voltage transmission lines operate at 115 kV, 138 kV, 230 kV and 500 kV. At the terminal stations located near major use centres, large transformers reduce the voltages to 66 kV, 33 kV or 24 kV.
The distribution system is a network of power lines with overhead or underground conductor cables, transformer stations, transformers, voltage regulators, and oil circuit reclosers.
We deliver electricity to our customers using over 13,000 km of transmission lines and 76,000 km of distribution lines.
The distribution system transforms the higher voltages to useable levels for delivery to customers. It maintains a constant supply of power and steady voltage levels despite continuously changing demands for electricity from homes, industrial sites, and commercial establishments. Energy consumption varies throughout the day and can increase by as much as 65 per cent in Manitoba from summer to winter.
AC and DC electricity
We operate alternating current (AC) and direct current (DC) transmission systems:
- AC is an electric current that reverses direction at regular intervals, or alternates from positive to negative, approximately 60 times a second. Most of the electricity used in the world is AC.
- DC is an electric current that flows in one direction. For long-distance transmission, power losses are considerably less with DC than with AC. The cost of a long-distance DC transmission line system uses 2 conductor cables, where an AC system uses 3, making the DC lines approximately 1/3 less expensive. However, DC transmission requires expensive conversion equipment
AC & DC conversions
- At a generating station, the turbine generators produce AC electricity.
- AC that will be travelling a long distance is converted to DC electricity through the rectification process at a converter station.
- DC is converted back to AC through the inversion process at another converter station.
- AC electricity is then transmitted through the AC network to supply customers.
The development of high voltage direct current (HVDC) technology was a key factor in plans for the development of generating stations on the Nelson River.