The effect of insulating cylinders (guards) in various gaps-the study of AC breakdown voltages

Tests were conducted in order to measure the 60 Hz AC breakdown voltage of various small air gaps (up to 0.2 m) formed by an energized conductor and a grounded electrode with an dielectric cylinder between them. The energized electrode was a section of an actual power line conductor, the grounded electrode was either a rod or sphere, and the insulating cylinder (a 69 kV line guard) was on the conductor. Qualitative and quantitative results of the experiment series show how the breakdown voltage varies with the type of electrodes, the distance between the electrodes, as well as with the relative position of the electrodes and the guard between them. As for the grounded electrodes, a standard rod and a 75 mm sphere were used. The rod represents a tool held by a lineman during live-line work, the sphere models the fist of a lineman. The test results contribute to the understanding and evaluation of tools used for live-line work and the safety conditions associated with them.