page_title: Hydro-Québec's electricity transmission system
section_title: Electricity pylons
hierarchical_section_title: Hydro-Québec's electricity transmission system / Electricity transmission system features / Electricity pylons
caption_attribution_description: Français&#160;: La centrale thermique de Tracy d'Hydro-Québec, prise du long de la route 138 entre Lanoraie et Berthierville. English: Hydro-Québec's Tracy thermal generating station. Picture taken from route 138, between Lanoraie and Berthierville.
context_page_description: Hydro-Québec's electricity transmission system is an international power transmission system centred in Quebec, Canada. The system pioneered the use of very high voltage 735 kV alternating current power lines that link the population centres of Montreal and Quebec City to distant hydroelectric power stations like the Daniel-Johnson Dam and the James Bay Project in northwestern Quebec and the Churchill Falls Generating Station in Labrador.
  The system contains more than 34,187 kilometres of lines and 530 electrical substations. It is managed by Hydro-Québec TransÉnergie, a division of the crown corporation Hydro-Québec and is part of the Northeast Power Coordinating Council. It has 17 interconnections with the systems in Ontario, Newfoundland and Labrador, New Brunswick, and the Northeastern United States and 6,025 MW of interconnection import capacity and 7,974 MW of interconnection export capacity.
  Major expansion of the network began with the commissioning of the 735 kV AC power line in November 1965, as there was a need for electricity transmission over vast distances from the north to southern Quebec.
  Much of Quebec's population is served by a few 735 kV power lines.
context_section_description: Quebec's transmission system contains a variety of electrical pylons depending on era and voltage level. Older pylon designs tend to consume more material than the newer pylons and the higher the voltage level, the larger the tower.
  735 kV pylons
  Hydro-Québec TransÉnergie uses several different types of electricity pylons to support their 735 kV power lines. All of them are single-circuit, meaning that each pylon carries one power line with three bundles of four electrical subconductors separated by spacers, with each bundle transmitting one phase of current.
  The earliest type of tower used was a massive self-supporting delta pylon, or waist pylon, which consumed 21 tonnes of steel per kilometre of line. This type of pylon was used for the first 735 kV power line from the Manic-Outardes power stations to the load centre of Montreal. There are two significant variations of the delta pylon; one has longer side crossbars such that all three bundles of conductors are suspended on V-shaped insulators. The other has shorter side crossbars, such that the two outside bundles are hung on a vertical insulator string and only the middle bundle is hung with a V-shaped insulator.
  Over the years, Hydro-Québec researchers engineered a new type of pylon, the V-guyed tower, which reduced materials consumption to 11.8 tonnes of steel per kilometre of power line. This type of tower also includes a variation with longer side crossbars, where all conductors are hung with a V-shaped insulator and one with shorter side crossbar, where only the middle bundle hangs from the insulator and the side bundles are strung on vertical insulator strings.
  During the construction of the James Bay transmission system, the cross-rope suspension tower was invented. This type of tower features two guyed-tower legs similar to the V-guyed tower, but the two legs don't converge at the tower base. In the case of the cross-rope suspension tower, the tower legs are spread apart on two different foundations. In addition, the crossbar is replaced by a series of suspension cables with three vertical insulator strings to support the three bundles, which allows this design to consume only 6.3 tonnes of steel per kilometre of line. The design is also known as the Chainette (little necklace).
  TransÉnergie uses two-level pylons for angle towers or structures on 735 kV power lines to change the direction of the line or switch the position of the conductor bundles. Delta pylons and three-leg guyed towers are also used as angle towers; they are referred to as "penguins" by Hydro-Québec linemen.
  Pylons for other voltage levels
  Hydro-Québec TransÉnergie uses a combination of double-circuit three-level pylons and single-circuit delta pylons to suspend electrical conductors of other voltages, such as 315 kV. The ±450 kV high-voltage direct current line in Hydro-Québec's power grid uses a T-shaped tower, lattice or pole, to support two bundles of three conductors on each side. The direct current power line sometimes uses two poles or a wider, pyramidal, self-supporting lattice structure for angle towers.
  Other pylons
  Hydro-Québec usually uses tall, large pylons to cross large bodies of water, like lakes and rivers. These towers are said to be prominent and the tallest pylon in Hydro-Québec's power grid is of this function. The tallest of these is located near the Tracy power station on the shore of the Saint Lawrence River, carrying a 735kV circuit between Lanoraie and Tracy. The pylon, the largest of its kind in Canada, is 174.6 metres (572.8 ft) tall, the same height as the Montreal Olympic Stadium, and slightly larger than the Washington Monument in the United States (555 feet (169.2 m)).
  Pylon strength
  The pylons and conductors are designed to handle 45 millimetres (1.8 inches) of ice accumulation without failure, since Hydro-Québec raised the standards in response to ice storms in Ottawa in December 1986 and Montreal in February 1961, which left 30 to 40 millimetres (1.2 to 1.6 inches) of ice. This has led to the belief that Hydro-Québec TransÉnergie's electrical pylons are "i
caption: 174.6 metre pylon adjacent to Hydro-Québec's now-decommissioned Tracy power plant.
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