Jump height of overhead-line conductors after the sudden release of ice loads

A series of tests was performed on a five-span section of 132kV line to determine the jump height of the conductors after the release of simulated ice loads from the centre span. The use of semitension assemblies at the suspension towers reduced the maximum jump height compared with that obtained with standard suspension-insulator strings, but did not prevent the phase conductors from passing dangerously close to each other. The importance of the sag in determining the jump height is stressed, and experimental and theoretical values for sag and jump height are compared. It was shown experimentally that the large sag differences resulting from some arrangements of ice loading brought phase conductors close together, and that the clearance to ground of the bottom conductor of the loaded span was reduced below the safety level for ice loads in excess of 1 lb/ft. It is concluded that, with heavy ice loads, phase-to-phase flashover can only be prevented by ensuring sufficient horizontal separation between phases.