Corona Discharge Characteristics of a Single Water Droplet under an AC Electric Field

Higher voltages are increasingly being used in power transmission systems to improve capacity. Whilst overhead line conductors are well-designed for mechanical and electrical requirements, surface defects (e.g. damage, insects, raindrops, and pollution) enhance the electric field and may lead to corona discharge. Raindrops are the primary source of such corona discharge and the discharge behaviour is examined using a single waterdrop under the influence of an AC electric field in a sphere to plane configuration. The droplet is set at the centre of the sphere which is the high voltage electrode and MPD test system is employed to record the discharge process. When the applied voltage is increased beyond PD inception voltage, corona discharge occurs and is observed by a UV camera. The discharge process lasts for 119 s and extinguishes when the drop is ejected and become small enough not to discharge in this electric field. According to Pulse Sequence Analysis, the discharge behaviour does not change significantly during the discharge process but the maximum PD magnitude which is 11.46 nC and the maximum PD number happens at the end of discharge with wider phase angle. Furthermore, the time difference of the adjacent two pulses is nearly 0 s and 0.02 s and the voltage difference is around 0 kV, meaning they occur almost simultaneously or one cycle apart at near voltage. Three situations when discharge probably happens were listed in accordance with voltage difference.