New Approach for Upgrading an Existing 115 kV Transmission Line

This paper introduces pioneering solution for upgrading 45 km, 115 kV double circuit line, built in 1922, in Ontario. To double the circuits' power transfer, the existing 605 kcmil ACSR was replaced with 997.2 kcmil ACSR/WT conductor and the thermal rating was increased from 85 degrees C to 150 degrees C. Visual inspection and probabilistic corrosion model were used to determine the severity of corrosion and to incorporate corrosion damages into analysis of the steel towers. Relocating the bottom phases to modified middle arms did not provide sufficient ground clearance and using conventional vertical extensions on existing grillage footings were impractical because it require large crane to lift the fully dressed tower, which was impossible in populated areas. Innovative solution using lighter shaft extension inserted above the tower's bend line was designed allowing the use of smaller crane thus considerably lowered material and construction costs. Further, galloping performance was improved by installing inter-phase spacers.