PROPERTIES AND EFFECT OF FREEZING RAIN AND WINTER FOG ON OUTLINE INSULATORS

Firstly, this paper presents the results of a field study which was carried out at a site near the EHV transmission facilities of Ontario Hydro most severly impacted by the March 10, 1986 storm. This storm caused a large number of flashovers resulting in the failure of most of the 500 kV transmission system in southern Ontario. Ontario Hydro's research concentrated on the meterological, microphysical and chemical properties of winter fog and freezing rain storms. Based on the results of this field study, extensive laboratory experiments on fog accretion were carried out at the University of Quebec in Chicoutimi. These experiments were performed in a cold room at temperatures controlled between -1-degrees and-5-degrees-C. Ice was accreted from the supercooled droplets, 15-mu-m in diameter, on a short string of four insulator units, energized at 14 kV per unit. The amount of ice and the length of icicles were measured as a function of liquid water content and icing period. In addition, the leakage current intensity and the conductivity of water dripped from the insulators was determined during the de-icing periods as a function of the rate of increase in ambient temperature. It was found that the conductivity of dripped water as well as the intensity of the leakage current of the insulators was initially high, but decreased as melting progressed.