The effect of dielectric cylinders (line guards) on the breakdown voltage of various air gaps

Tests were conducted in order to contribute to the understanding and evaluation of live-line maintenance tools and safety devices. The AC breakdown voltages of various small air gaps (up to 0.2 m) formed by an energized conductor and a grounded electrode with a dielectric cylinder between them were measured. The energized electrode was a section of a power line conductor, the grounded electrode was either a standard rod or a 75 mm diameter sphere, and the insulating cylinder was resting on the conductor. The rod represented a tool held by a worker during live-line work, the sphere modelled the fist of a worker. Results of the test series show how the breakdown voltage varies with the type of electrodes, the distance between them, as well as with the relative position of the electrodes and the line guard between them.