Impulse breakdown of short rod-plane air gaps with a dielectric covered rod

Results are presented concerning breakdown of short rod-plane air gaps with a dielectric-covered rod under positive standard lightning and switching impulse voltages. Breakdown probability distributions were obtained through multiple level tests and the time and voltage to breakdown were measured with the gap length as a parameter. The simple air gaps with a bare rod were considered as reference cases. There is an increase in the dielectric strength of the gap due to the insulating cover, especially under switching impulse voltages. In the presence of the dielectric cover the effect of the impulse waveform on the dielectric strength of the gap is minimal.