Humidity effects on dielectric strength of air-gaps for indoor HV installations

For indoor HV installations, the electrode configurations of air-gaps are different from outdoor HV apparatus and the fields are usually optimized. The humidity can be lower and the temperature is often higher than the outdoor atmosphere. In order to study the effect of humidity on the breakdown voltage of the indoor air-gaps, laboratory tests were performed on the typical indoor air gaps-toroid/plane as well as reference gaps-rod/plane and sphere/plane under typical indoor atmosphere conditions. The test results indicate that for the reference air-gaps, the correction procedure recommended by IEC 60060-1 is valid, while there is an over-correction of 6-9% for the toroid/plane air gaps, which is caused by humidity correction.