The 5L51 and 5L52 Transmission Upgrade Project (TUP) will increase the circuit ratings of 5L51 and 5L52 from 2520 and 2000 Amperes respectively, to 3000 Amperes each. (Ampere is a unit used to measure electric current).
Increasing the current through the circuits will increase the transfer capacity of the circuits. Transfer capacity is the amount of electricity that a transmission facility – such as a transmission line – can transfer from one point to another at any given time. Specifically, the TUP will permit additional south to north electricity transfers.
When additional electricity passes through the conductors, they heat up and sag. To maintain safe clearances between the conductors and ground once the transfer capacity is increased, BCTC will be raising 10 towers along the right-of-way and retensioning (tightening) the conductors in three other locations. Shielding will be added on one span adjacent to the Canada-U.S. border. This work is required in only a few places, as the clearances along the rest of the right-of-way are already sufficient. To support the additional weight of the new steel used to raise the towers, it may be necessary to reinforce the foundations for a few of the towers. No new towers or conductors (lines) are required, and the alignment of the existing circuits will not change.
Raising the towers involves separating the tower at its “waist” – the narrow portion between the top of the tower and the tower legs – and inserting a prefabricated steel extension.
The ten towers that need to be modified range from approximately 18 to 27 metres (59 to 89 feet) high and will be raised approximately 4 to 7 metres (13 to 23 feet), by adding extensions to the mid-section of the towers. The new heights will range from 25 to 34 metres (82 to 112 feet) high.
Tower Raising Diagram (PDF, 89KB)