AC Breakdown through Narrow Chink between Two Insulating Walls.

Abstract

AC breakdown and ac partial discharge through narrow chink between two insulating walls were investigated, using a (knife edge)/(plane) electrode configuration. The chink was formed by two plane walls of PE insulator blocks. The maximum electrode distance studied was 70mm. The experiments were performed in air controlled at 20-25°C and 40-50‰RH.
AC breakdown characteristics depend on width(s) of the chink: In a range of the width(s) about 1mm _??_ s _??_ 20mm, the breakdown voltage decreases with the decrease in the width(s); In the range between about 100μm _??_ s _??_ 1mm, the voltages are higher than that at 2mm of the width(s); In the range between about 15μm _??_ s _??_ 100μm, the voltage decreases with the decrease in the width(s). It was found that these breakdown characteristics are corresponding to the dependence of ac partial discharge characteristics on the width of the chink: AC breakdown voltage is decreased with increases in the number and the maximum strength of positive pulse in ac partial discharges generated near the positive peak of ac applied voltage. The discussion was focused on the dependence of the number and the strength of the positive pulse on the width of the chink.