A Reliable Transmission System

Hydro-Québec is a leader in transmission system design, operation and maintenance. Recognized the world over for the reliability of its grid, it spares no effort to stay at the forefront of the industry in this regard.

Its transmission system is the most extensive in North America, comprising 519 substations and 33,915 km of lines at various voltages. In addition, the system includes 17 interconnection points allowing energy interchanges with the Atlantic provinces, Ontario and the U.S. Northeast.

One of Hydro-Québec’s main challenges lies in the fact that its large generating facilities are located in northern Québec while the major load centres are concentrated in the south. To ensure the quality of power transmission over greater and greater distances, the company has had to innovate constantly:

735-kV lines
In 1965, Hydro-Québec inaugurated the world’s first 735-kV line. Today, it operates 11,683 km of lines at 765 and 735-kV. One of the advantages of transmitting power at very high voltages is that it reduces line losses.
Series compensation
From 1989 to 1996, Hydro-Québec reinforced its 735-kV transmission system by adding series compensation to 32 lines (11,000 Mvar). Series compensation offers several benefits, including increased stability and greater transmission capacity, and constitutes a lower-cost alternative to the construction of new lines.

DC transmission
DC power transmission—another area of Hydro-Québec expertise—facilitates the transfer of large quantities of power over long distances at high voltages (e.g., 450 kV). It is also used for energy interchanges between asynchronous AC power systems, because the power flows can be regulated so as to prevent the propagation of disturbances. Nicolet substation, which serves several large urban centres in Québec, is equipped with AC-DC converters that make it a veritable hub for the importing and exporting of power.

High-performance power stabilization and voltage regulation systems
Hydro-Québec was one of the first power companies to equip its generating fleet with high-performance power stabilization and voltage regulation systems as a means of increasing transmission capacity. These systems have been optimized using grid simulations and their behavior has been tested in each generating station.

Defense plan against cascading 735-kV line trips
To improve the reliability of the 735-kV transmission system, Hydro-Québec has developed a highly sophisticated defense plan against system instabilities. This includes special protection systems that constantly monitor the behavior of the entire transmission grid, thus preventing fault propagation.

Service continuity: One of the world’s best track records

Hydro-Québec has a stringent maintenance program to ensure the reliability and efficiency of its facilities and the security of its system control. As a result, its customers enjoy service quality and continuity that are among the best in the world.

In August 2003, a blackout affecting some 50 million people in Ontario and in eight states in the U.S. Northeast caused damage estimated at US$6 billion. The Hydro-Québec power system escaped this catastrophe for two reasons: first, it is not synchronous with adjacent systems; and second, it is connected to other systems via high-voltage direct current (HVDC) lines, and this protects it from the cascading disturbances that can afflict interconnected systems. In fact, the HVDC interconnections linking Québec with the U.S. helped ensure continuity of service in northern New York State and most of New England. Hydro-Québec also facilitated the restoration of service in the rest of New York State and in Ontario.