Conjunct influence of temperature and humidity on discharge voltage of air gap

External insulation is severely influenced by atmospheric environment, such as temperature, humidity and density of air. Based on a large amount of discharge voltages monitored by outdoor auto discharge device and tested in artificial climate chamber, the effects of temperature and humidity on discharge voltage of air gap are studied respectively and jointly in this thesis. It is shown that discharge voltage decrease with the increase of air temperature. It is taken positive correlation between discharge voltage and humidity when relative humidity is less than 80%; while it is negative correlation when relative humidity is above 80%. The outdoor discharge tests show that some discharge voltage is significantly declined, especially under high humidity and low temperature.