Considerations of the suppression of insulator flashover by resistive surface films

It is well known that resistive glazes on porcelain insulators give a ‘voltage-stabilisation’ effect, and improve the performance of such insulators when operated in polluted atmospheres. However, the mechanism of this stabilisation has not been made clear to date, because of the complexity of the problem. A qualitative assessment of some of the mechanisms which may contribute towards the improved performance is made, using a simplified insulator model. It is found that the presence of a stabilising glaze has no effect upon the stress at which a discharge propagates along the insulator surface, and that the effect of the glaze must therefore be to inhibit the formation of discharges.