AC FLASHOVER PERFORMANCE OF INSULATORS COVERED WITH ARTIFICIAL ICE

A field observation of ice accretion on Hydro-Quebec H.V. insulators was carried out, as well as a laboratory investigation of the ac flashover performance of various types of insulators covered with artificial ice. The field observations made it possible to identify the type and physical aspect of naturally occurring ice accretions produced during freezing rain precipitation. The laboratory investigation was conducted in a 4.8 x 2.8 m x 3.8 m climate room using a H.V. transformer of 120 kV, 240 kVA with a short-circuit impedance of 5%. A method based on the standard IEC 507 method was developed for measuring the maximum withstand voltage (V-ws) of ice-covered insulators. Various factors were investigated, including the effects on the insulator V-ws Of such particulars as type, thickness, and uniformity of the ice, as well as the arcing distance of the insulators and the conductivity of freezing water. The effects of uniform ice, 2 cm thick, on 5 IEEE insulator units was thus considered to be equivalent to the effect of an ESDD of about 0.13 mg/cm(2) on the same insulators.