As part of the Expansion Project, Trans Mountain is building two new transmission lines. The transmission lines provide additional power to pump stations, which help move our product through the pipelines.

Transmission lines are large, high voltage lines that typically deliver power to smaller distribution lines that go to homes, businesses and other buildings. There are large towers that support the conductor lines – known as conductors -  with poles in between towers to support the tension of the cables. Towers are typically 50 to 100 feet tall.  These transmission lines will use a combination of lattice towers and support poles.

Transporting materials to the tower sites and site preparation

The materials for construction needed for each tower are brought to site and distributed along the right-of-way where the towers will be built. Smaller poles are placed between the towers to support the transmission cables.

After completing site surveys, flagging and placing a call to BC One Call, the crews carefully remove the topsoil, and any necessary tree removal and brushing. Access roads are built so construction vehicles and equipment can travel to the site.

Building the foundations and anchors

Different types of foundations may be used to support the towers, depending on the soil type, depth of bedrock, and structure type. Excavation may be done with a mechanical excavator, hydrovac, auger, or hand digging.

Assembling the towers

Towers are generally built from the ground up. Line workers assemble the towers on the ground near the tower location – much like a giant, complicated 3D puzzle. This includes the use of heavy machinery. In areas that have soft ground composition, access mats (sometimes called rig mats) may be used to provide passage over the sensitive ground. Access mats provide structural support for equipment by dispersing weight and providing a solid base. 

Raising the towers and poles

Tower sections are either assembled all in one piece, or in multiple pieces that are connected after they are raised. Telescopic cranes or helicopters are used to raise the tower sections from the ground, and bolt them together to complete assembly.

Poles are used to support cables between transmission towers and to maintain the tension of the cable. Framing and hardwire installation will be completed before the poles are installed, then lifted and set into place.

Unreeling and installing the conductors

The conductors, which are the lines that transport the power, are unreeled and strung from tower to tower using a cable drum. On one end, there is a reel and tensioner, and at the other there is a puller and take-up reel. The conductors are pulled with the puller machine between each of the towers and poles. The puller and tensioner work in conjunction to ensure the conductor maintains a safe ground clearance so it is not damaged. Multiple wire pulling stations are located along the span of the transmission line. Once the conductor is pulled through the entire length of the line, the tensioner is used to achieve the proper sag. Having the right sag in the line keeps the line from sagging too low as the lines expand and contract with temperature changes.

Site restoration

After the transmission line is strung and grounded, cleanup and restoration of the site begins. This includes:

  • Removing all waste and debris
  • Levelling the ground
  • Dismantling any temporary access points
  • Repairing infrastructure
  • Seeding and planting as necessary 

Throughout the project, site supervisors ensure all environmental, health and safety, and quality standards are being met.