Power Transmission

Building a Line


There are seven main steps to build a transmission line and it takes many tradespeople to meet the challenge. At each step, Hydro-Québec adopts strict safety, project quality and environmental protection practices. For example, it is environmentally sound to build in winter since construction on frozen ground considerably reduces certain impacts.

Video: Building a 735-kV line: Quebec has met the challenge

Duration: 1 minute 47 seconds

Building a power transmission line is a major challenge that involves seven major stages and a wide diversity of skilled workers. In this video, you'll witness the stages to building a transmission line carrying 735 kV: the highest level of voltage in Hydro-Québec's network.

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This video shows the construction of a 735-kV line, which is the highest voltage level in Hydro-Québec's grid.

To learn about the construction process, see the photos below from various projects across Québec.


Safety, the environment and quality are top priorities at all times.

Expert advisors ensure compliance with worksite health and safety, quality assurance and environmental conservation laws and regulations.
(315-kV line at Blainville substation)

Types of towers

Conventional towers-also called lattice towers‐are the most common type in Québec.
(315-kV Chénier-Outaouais line)

Guyed V towers are very light and often built in areas that are difficult to access.
(Romaine-1-Romaine-2 and Romaine 2‐Arnaud lines)

Tubular towers are more easily integrated into certain environments and are often installed in urban areas.
(View of downtown Montréal from Verdun)

For more information on the different types of towers, visit the Towers section of this site.

1. Transporting materials to the tower sites

The materials are transported to each tower site.

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The parts are carefully distributed and the construction materials needed for each tower are left directly on the site where the tower will be built.
(315-kV Chénier‐Outaouais line)

2. Building the foundations and anchors

The construction team begins by clearing the project area. The workers carefully set aside the topsoil, which will be reused. During excavation for the foundations that will stabilize the tower, pumping may be required to remove the water and dry the site. The size of the excavation site depends on the type of soil and the type of tower. Anchors depend on the type of tower installed.

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The foundation depends on the types of tower and soil and the depth of the bedrock.

Concrete foundations are poured for self-supporting and tubular towers.

Steel-lattice foundations (in overburden) are used for guyed and self-supporting towers. They are the most common type of foundation.

Pile foundations with ground anchors are built when the soil’s load bearing capacity is too low (clay or silt).

Guy anchoring adapted to V towers
(230-kV Goémon‐Mont-Louis‐Gros-Morne line)

3. Assembling the towers

The project area must be adapted to the type of tower that will be built. Because this step requires the use of heavy machinery, all the necessary precautions are taken. For example, in wetlands, steel plates are sometimes placed on the ground to accommodate the machinery and preserve the environment.

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Line workers assemble the towers on the ground. This step may seem simple enough but a tower is actually a huge 3D puzzle that requires a lot of experience and skill to put together.
(Romaine-4-Montagnais line)

4. Raising the towers

Once the tower is assembled on the ground, it is raised using a telescopic crane.

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The raising of a tower in the Matapédia region.
(Rimouski-Les Boules line)

5. Unreeling and installing the conductors

The conductors are unreeled and strung section by section from tower to tower. There is a cable drum with a reel and tensioner at one end and a puller and take-up reel at the other. In this step, workers make sure that the voltage levels in the conductors are within acceptable limits and that there is adequate clearance between the ground and the cables. Our practices are adapted to account for sensitive and special environments.

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Tension site, equipped with a drum and tensioner, and pull site, equipped with a puller.

Using specialized equipment, we bring cable reels, also called drums, directly to the jobsite. These drums hold 2 to 3 km of cables.
(Romaine-2‐Arnaud line)

Here, electric cables are laid on wooden planks to avoid damaging them during pulling.
(120-kV Beauceville‐Sainte-Marie line)

To reduce inconveniences, including traffic disruptions, cables are sometimes pulled at night in urban settings.
(315-kV line ‐Bélanger substation)

6. Installing the counterpoise wires

Counterpoise wires are installed to ground each tower and protect the line from lightning. A counterpoise wire is actually an underground conductor that ensures the electrical connection between some or all of the line’s towers and the ground.

When minor excavation and filling work is required, mitigation measures are implemented. For example, counterpoise wires are not installed near wetlands to avoid heavy machinery traffic and excavation.

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Counterpoise wires are generally buried 60 cm deep. On agricultural land, they are buried deeper: 90 cm underground.

A bulldozer equipped with a reel at the front and a ripper at the back is used to install the counterpoise wires. It has extra-wide tracks to exert less pressure on the ground.

The ripper is equipped with one to three blades to dig deep into compact soil to place the counterpoise wires.

7. Restoring the site

Once a project is complete, Hydro-Québec always restores the site by:

  • removing all the debris and waste
  • levelling the ground
  • dismantling the temporary accesses (roads, bridges, culverts)
  • repairing any infrastructure that was damaged during the work (roads, fences, etc.)
  • seeding or planting whenever necessary based on the characteristics of the site (shoreline, wetland, etc.)

When the work is carried out on private land, Hydro-Québec meets with the landowners to ensure they are satisfied with the restoration. It takes responsibility for any damages that may have occurred as part of the work and compensates the landowners according to project regulations.

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1. During construction

2. The site restoration after one year

Final state of the site of the 315-kV supply line for Anne-Hébert substation

Final state of the site of the 230-kV Saint-Césaire‐Bedford line on agricultural land

Throughout the project, site supervisors ensure that all the actions undertaken meet environmental, health and safety and quality standards.

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