Study on Characteristics of Partial Discharge Caused by Micro-bubble in Insulating Oil

In the last few decades, Bubbling phenomenon grows to be a major concern for its insulation threats in oil-immersed facilities during dynamic rating or overloading. Formed bubbles with radius from tens to hundreds um could lead to partial discharge or even serious insulation failure. However, previous studies on bubble-induced discharge in insulating oil usually focused on millimeter size bubbles. The research to date has not been able to determine the real threat of micro-bubbles of tens to hundreds um of in oil. In this paper, the characteristics of partial discharge induced by micro-bubbles were investigated. The finding is unexpected and suggests that partial discharge inception electric field strength is significantly higher than the theoretical value, which shows tiny change with variation of bubbles radius. Besides, bubble radius is a significant factor on the number of partial discharge current pulses and the apparent charge. The number of current pulses induced by a single bubble could help to reveal the interaction mechanism between bubbles and discharges. Finally, the equation associating the apparent charge and bubble radius was fitted.