Effect of Single Rising Bubble on Impulse Breakdown Characteristics of Mineral Oil

Liquid insulation systems will generate bubbles under the effects of environmental stress and material aging. Studies have shown that bubbles are a typical defect of liquid insulation systems and pose a potential threat to the insulation state. In order to clarify the harmfulness of isolated bubbles to the state of liquid insulation, an experimental platform was established to study the effects of bubbles on the impact discharge characteristics of liquid insulation. The results showed that the isolated nitrogen gas bubbles in the homogeneous field have little effect on the lightning impulse breakdown voltage of the mineral oil gap, and the breakdown voltage is 4% lower when there is a bubble than no bubble. However, the breakdown time delay is significantly longer with bubbles than without bubbles. From the perspective of the initial electron generation mechanism, it is considered that although the field strength in the bubble is much larger than the initial field strength of discharge, the discharge cannot be initiated due to lack of effective initial electrons. Therefore, the influence of isolated microbubbles on the liquid insulation system under impulse voltage is not as serious as expected.