Corona between point plane electrodes in air at atmospheric pressure

Several theoretical investigations have been reported in literature on electric field nonuniformity between point plane electrodes. In the present investigations experiments have been performed to determine corona onset voltages in air at atmospheric pressure between point plane electrodes for DC voltage applications of both polarities. The diameter of hemispherical tip of point electrodes used in experiments varied from 1.2 mm to 3.0 mm and gap distances varied from 20 mm to 50 mm (approximately). For these electrode arrangements, calculated variation of electrical field non uniformity factor was from 18 to 48. The measured corona inception voltages were found to increase with increase in diameter of point electrodes and also with increase in gap distance between electrodes. The calculated maximum stresses at tip of point electrode at corona inception are in approximate range of 70kv/cm to 135 kv/cm. The maximum stress, which appears for tip diameter of 1.2 mm for point electrode, does not significantly influence the field variation in these gaps as to disturb Townsend mechanism of ionization growth.