Hydro-Québec's electricity transmission system

[1] 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.

[2] In 1963 Hydro-Québec purchased the shares of nearly all remaining privately owned electrical utilities then operating in Quebec and undertook construction of the Manicouagan-Outardes hydroelectric complex.

[3] Over the next twenty years from 1965 to 1985, Quebec underwent a massive expansion of its 735 kV power grid and its hydroelectric generating capacity.

[1] The system has transmission lines reaching to power generation facilities located more than 1,000 kilometres (600 mi) away from population centres.

[31] The Ordre des ingénieurs du Québec named the 735 kV power line system as the technological innovation of the 20th century for Quebec.

[27][33] The James Bay hydroelectric dam complex contains several relatively short 735 kV power lines that send electricity to three principal substations, ordered from west to east: Radisson, Chissibi, and Lemoyne.

[34] From these substations, six 735 kV power lines[8] traverse the vast expanses of taiga and boreal forest in clear-cut stretches of land; this shows up clearly in aerial photos.

[37] Starting from the generation station in Newfoundland and Labrador, the power lines span a distance of 1,800 metres (6,000 ft) over the Churchill River gorge and run generally south-southwest for 203 kilometres (126 mi) as three side-by-side power lines in a cleared right-of-way with a width of 216 metres (709 feet).

A lone 735 kV line stems off from the substation, heading to an open pit mine 142 kilometres (88 mi) the northwest.

From there on, the three lines parallel the North Shore as the Gulf narrows to the southwest toward the Saint Lawrence River discharge mouth.

[33] There are two significant variations of the delta tower; one has longer side crossbars such that all three bundles of conductors are suspended on V-shaped insulators.

[35] 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.

[33][39][47] 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.

The tower, 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)).

Leaving the Des Cantons station, the power line crosses the Canada–US border and passes through the hilly Appalachian Mountains in the U.S. state of Vermont, reaching an elevation of about 650 metres (2,130 ft).

At 2:44 am EST on March 13, 1989, a severe geomagnetic storm, due to a coronal mass ejection from the Sun, struck Earth.

The conductors then forwarded this current to sensitive electrical transformers, which require a certain voltage amplitude and frequency to function properly.

The collapsed power grid left six million people and the rest of Quebec without electricity for hours on a very cold night.

Five to six days of freezing rain and precipitation crippled the Hydro-Québec power grid in the Montreal and South Shore regions.

[72] Through successive waves of freezing precipitation, more than 75 millimetres (3.0 inches) of radial ice accumulated on the electrical conductors and the towers themselves.

Even though the electrical wires can withstand this extra weight, when combined with the effects of wind and precipitation, these conductors may break and fall.

[73] The towers, designed to withstand only 45 millimetres (1.8 inches) of ice accretion, buckled and collapsed into twisted heaps of mangled steel.

[B][72] In a region bounded by Montreal between Saint-Hyacinthe, Saint-Jean-sur-Richelieu and Granby, dubbed the "triangle of darkness", half of the overhead power grid was out of service.

[71][73] With over 100 transmission lines paralyzed by the ice, Quebec fell into a massive power outage in the cold Canadian winter.

[77][78] Private companies and other utilities from other parts of Canada and the United States were sent in to help Hydro-Québec undertake this massive restoration task, but these efforts were complicated by the widespread damage of the power grid.

[71] In 2004, shortly before U.S. President George W. Bush's visit to Canada, a tower along the Quebec – New England Transmission HVDC circuit in the Eastern Townships near the Canada–US border was damaged by explosive charges detonated at its base.

[75] Hydro-Québec's large above-ground transmission and distribution system was considered to be exposed to natural disasters, although the cost of undergrounding the grid was prohibitive.

Their Bayesian network analysis suggests that increases in Quebec’s hydroelectric capacity historically correlate more strongly with domestic demand and market price signals, rather than simply the availability of expanded transmission corridors.

These findings can inform discussions of whether newly proposed U.S.–Canada intertie projects should include upstream reservoir development in environmental impact assessments.