Switching-impulse flashover of air gaps and insulators in an artificially polluted atmosphere

Rod-rod and rod-plane gaps and a selection of insulators, mostly of dimensions relevant to 110¿132kV systems, have been subjected to switching impulses in artificial pollution. It has been shown that the flashover voltages of the gaps were little affected by the presence of fogs, either of water or of 120g/l salt solution. Substantial reductions, increasing with fog salinity, were found in the flashover voltages of the insulator surfaces. In highly saline fog, the flashover voltages were well under half the values for dry insulators. The preapplication of alternating service voltage to the polluted insulators always led to further reductions in flashover voltage.