Influence of Rain on the Support Insulation Electrical Strength

Abstract

The article presents the results of studying the influence of artificial rain on the electrical strength of an extra high voltage support insulation column containing insulators of different heights when subjected to positive polarity switching impulses. It has been found that, in general, rain has an adverse effect on the support insulation discharge characteristics, which is associated with the occurrence of cascading overlaps from the screen fittings along the insulation structure components. The adverse effect caused by rain tends to aggravate with increasing the column upper element structural height, the switching impulse front time, and rainwater conductivity. As a result, the support insulation electrical strength may drop by as much as 40%. The reason for such a significant effect is the external electric field redistribution along the columns. On the one hand, the presence of a relatively high conductivity water film on the insulator surface when subjected to impulses with a front time of several milliseconds leads to an almost uniform distribution of voltage across insulation structural elements. On the other hand, sharp field strength spikes of the opposite polarity arise on the water droplets and trickles formed at the edges of neighboring sheds, which facilitates the occurrence of spark overlaps across a number of shed spacing distances, weakening of air insulation, and a decrease of structural discharge voltage. Measures to increase the support insulation electrical strength under rain conditions are proposed.