Alternating Current Corona in Foul Weather II - Below Freezing Point

The mechanism of ac corona caused by the presence of ice particles is shown. Two kinds of precipitation are distinguished: the snow-like and hail-like forms. Conditions of snowcover formation on transmission-line conductors are analyzed. This cover may result in the highest corona energy losses, caused mainly by steady pulseless corona in the positive, and Trichel impulses in the negative, half-cycle. No streamers are reported from the snowcover by conductor voltage gradients of less than 20 kV rms/cm. Streamer discharges and high radio interference are caused by impinging snowflakes and liquid or frozen waterdrops on the conductor surface. The results of laboratory tests confirmed field investigations on the Hydro-Quebec 315-kV transmission system. The work reported in this paper was supported in part by financial assistance from the National Research Council of Canada in connection with the laboratory investigation.