AC flashover performance of H.V. insulators under glaze and rime

The influence of the physical aspect of ice accumulation and of water conductivity on the withstand voltage of high-voltage (HV) insulators was determined. Two cap-and-pin insulators and one column type insulator were subjected to flashover testing in a climate room. Artificial ice was accumulated from supercooled droplets at an air temperature of -12°C. The electrical conductivity of the spray water between 5 and 150 μS/cm was adjusted by adding sodium chloride to de-ionized water. The results obtained indicated that, under experimental conditions, the highest probability of flashover resulted from uniform ice accretion. The withstand voltage of the insulators decreased as the conductivity of the spray water increased. In addition, a series of outdoor camera observations made it possible to compare the aspects of ice accretion during actual freezing rain to those obtained in the laboratory