The Saint Lawrence River HVDC Powerline Crossing is the crossing of Hydro-Québec's Quebec-New England

HVDC A high-voltage direct current (HVDC) electric power transmission system (also called a power superhighway or an electrical superhighway) uses direct current (DC) for electric power transmission, in contrast with the more common alternating curre ...

transmission line over (and later, under) the

Saint Lawrence River The St. Lawrence River (french: Fleuve Saint-Laurent, ) is a large river in the middle latitudes of North America. Its headwaters begin flowing from Lake Ontario in a (roughly) northeasterly direction, into the Gulf of St. Lawrence, connectin ...

between

Grondines Deschambault-Grondines is a municipality of about 2100 inhabitants in the Canadian province of Quebec, located in Portneuf Regional County Municipality. The municipality was incorporated in 2002 by the merger of the formerly independent villages ...

and Lotbinière,

Quebec Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirtee ...

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

. The crossing is remarkable, for being first implemented as an overhead crossing, and then later replaced by a cable tunnel. Hydro-Québec wanted to complete the transmission line in time, which was only possible with an overhead crossing of Saint Lawrence River. However, due to the negative visual impact of the large towers of the overhead crossing on the local populations of Grondines and Lotbinière, it was decided to build a cable tunnel under the river, although this made the project more expensive.

Overhead crossing construction

In 1988 construction work for three artificial islands in the Saint Lawrence River, which were connected with

jetties A jetty is a structure that projects from land out into water. A jetty may serve as a breakwater, as a walkway, or both; or, in pairs, as a means of constricting a channel. The term derives from the French word ', "thrown", signifying somet ...

to the mainland as construction for the pylons of the overhead crossing started. Between July 1988 and spring 1989, 20,000 truck loads of were transported. In 1989 the towers of the temporary overhead line crossing were erected. The suspension pylons on each side of the waterway were 140 meters (459 ft) tall to ensure the required clearance. Building these towers required five months construction time and approximately 40 specially trained workers. At the end of 1989 the overhead crossing, which consisted of five towers, was completed. After the tunnel was completed the overhead line and pylons used for it were dismantled. One of the pylons would later be used for the construction of the La Cité de l'Énergie observation tower.

Underground crossing construction

In spring 1989 work on the long cable tunnel started, which took six months of drilling in two 12-hour shifts. The average drilling rate was a day, but achieved in horizontal sections over a day. On March 26, 1990, the

tunnel boring machine A tunnel boring machine (TBM), also known as a "mole", is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They may also be used for microtunneling. They can be designed to bore thro ...

reached the surface away from its target point. Later the tunnel was covered with concrete, and troughs for the cable support were installed. On November 1, 1990, the underground HVDC transmission line went in service with a transmission rate of 1200 MW, which was increased to 2250 MW on July 1, 1991. In 1992 the overhead line over the Saint Lawrence River, including the artificial islands and the jetties were dismantled. Portions of one of these towers would later be used as part of the observation tower at '' La Cité de l'Énergie'' in Shawinigan. The costs for dismantling was .

References

{{DEFAULTSORT:Saint Lawrence River Hvdc Powerline Crossing Tunnels in Canada Electric power transmission systems in Canada Hydro-Québec Powerline river crossings Saint Lawrence River HVDC transmission lines Tunnels completed in 1991 Electric power infrastructure in Canada Buildings and structures in Quebec Energy in Quebec 1991 establishments in Quebec

Overhead crossing construction

Underground crossing construction

See also

References