Experimental study of discharge voltage of air gap with high humidity

Discharge Characteristic of external insulation is significantly influenced by Humidity. Most researches concern on low humidity condition. Discharge tests of air gap are carried out in the artificial climatic chamber whose humidity could be adjusted conveniently. The relation between humidity (especially for high humidity) and discharge voltage is studied in this paper. It is shown that the discharge voltage increases with the increase of humidity when relative humidity is less than 80%. Dewdrop on the electrode surface plays an important role. Above 80%RH, discharge voltage decreases slightly with the increase of humidity without dewdrops, while it reduces to half of normal value with a dewdrop. The electric field distribution of the air gap is calculated by Ansys, it is shown that the electric field is distorted seriously by dewdrops, the maximum field strength is doubled and resulting in the serious reduce of discharge voltage, which is consistent with the conclusions of discharge tests in climatic chamber.