CORONA AND BREAKDOWN ACROSS INSULATING SURFACES

Abstract

The present work was concerned with an investigation of the effect of atmospheric ions on the impulse voltage flashover and pre-flashover characteristics of an insulator made of cycloaliphtic polyurethane with dolomite filler, occupying the space between the coaxial electrode system. Switching and lightning impulses were used. The practical situation was simulated by deposition of negative ions from separate sources, upon the insulator, prior to application of the impulse voltage. As a reference, a parallel series of measurements has been made, between electrodes of identical dimensions in air, with the insulator removed, so that the effect of the insulator surface on the discharge has been studied. The main results obtained may be summarized as follows.

Pre-flashover characteristics

Corona development across the insulator surface and in air were investigated with and without excess negative ions in the ambient air, using lightning and switching impulses of the forms of (1/50, 9/3160 and 17/3160) sec.

1- Effeet_of excess negative ions

i- Corona inception

The excess negative ions have no significant effect on the initiation of the first corona pulse under application of both lightning and switching impulses across the