AC FLASHOVER PERFORMANCE OF INSULATORS COVERED WITH ARTIFICIAL ICE

A field observation of ice accretion on Hydro-Quebec H.V. insulators w as carried out, as well as a laboratory investigation of the ac flasho ver 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 conduct ed in a 4.8 x 2.8 m x 3.8 m climate room using a H.V. transformer of 1 20 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 w ithstand voltage (V-ws) of ice-covered insulators. Various factors wer e investigated, including the effects on the insulator V-ws Of such pa rticulars as type, thickness, and uniformity of the ice, as well as th e arcing distance of the insulators and the conductivity of freezing w ater. The effects of uniform ice, 2 cm thick, on 5 IEEE insulator unit s was thus considered to be equivalent to the effect of an ESDD of abo ut 0.13 mg/cm(2) on the same insulators.