Wet tests on naturally polluted glass and composite insulators

The study examines what type of bird excrement contamination will lead to insulator's flashovers on the Estonian 110 kV overhead power lines. Wet tests made in laboratory with naturally contaminated glass and composite insulators show that traditional (insulator's surface) contamination will not lead to flashovers and therefore most likely the flashovers are caused by highly conductive bird excrement streamers. The tests also show that using corona rings at composite insulator's line end fittings, affects the occurring probability of partial discharge extent on wetted insulator.