Contaminated Insulators-Chemical Dependence of Flashover Voltages and Salt Migration

The results of carefully controlled laboratory experiments on contaminated flat plate insulators are presented. Flashover voltages and salt migration effects are shown for the following nine common salts: NaCl, NaNO3, Na2SO4, MgC12, Mg(NO3)2, MgSO4, CaCl2, Ca(NO3)2, and CaSO4. Our results show that the tendency for an insulator to flashover is dependent on the type of contaminant as well as on the equivalent salt density (esd). We also demonstrate the existence of a salt migration effect and conclude that it should be given equal status with dry band formation in attempts to understand flashover and the events leading to flashover.