A study of the leakage current of H.V. insulators under glaze and rime

Electrical behavior of iced insulators was investigated by measurement of leakage current and observation of growth and melting of icicles during icing periods. A long rod elastomer insulator or a cap-and-pin porcelain insulator was suspended in a cold room and supercooled droplets directed on them. The leakage current was found to be made of four components: basic leakage current I_B, melting current I_M, white arc current I_W and flashover current I_F. I_M and I_W increased with applied voltage. With glaze icing, an equilibrium was found between melting rate and icing rate, and basic leakage current I_B was proportional to the icing rate. At low thickness of ice accumulation there was no white arc occurrence at temperature near 0°C. Elsewhere, white arc threshold current was found to be independent of icing regions and equal to about 18 mA rms. Hard rime icing was the most dangerous icing type for HV insulators due to the high probability of white arc occurrence.