Client: Rio Tinto Alcan
Location: British Columbia, Canada
POWER designed and installed the world’s second high-voltage transmission line catenary structure in the remote coastal mountains of British Columbia. The catenary stretches approximately 4,000 feet across a valley, 500 feet above ground, and is anchored to the mountains on either side, eliminating the need for structures on the avalanche-prone slopes. The first catenary was installed on the same transmission line in 1955. Initially, POWER performed emergency installation and re-instatement of the 287 kV circuit after an avalanche damaged the conductors and supporting lattice tower for the third time.
The damaged circuit was repaired and placed on a temporary structure mounted on the lost tower’s foundation site. POWER’s permanent design featured galvanized steel cables set in four sets of seven. Each set of cables was bound into a unit with preform wraps. The cable sets were 3,674 feet and 4,372 feet long (1,120 and 1,333 meters) and pinned to four anchorages designed for 476 tons of cable tension. The cable sets were yoked together over the circuits to allow the installation of a 466-foot-long (142 meters) catwalk between the cables and a helipad set near mid-span.
The unique design required custom parts, designed by POWER and fabricated locally, as well as custom installation tools and equipment. The work site, at an elevation of near 6,000 feet (1,829 meters), presented significant challenges. Equipment and personnel had to be transported to the site by helicopter and site work completed within a four-month weather window. The four anchorages were installed during the summer of 2007, and cable installation was accomplished in 2008 during a construction period that saw only 55 workable days due to poor weather. POWER’s role was as the engineer-procure-construction management (EPCM) lead contractor with two primary contractors providing equipment and labor.