AC Breakdown Characteristics of Mineral Oil with Nitrogen Fine Bubbles under Nitrogen Gas Atmosphere

In recent years, fine bubble technology has attracted attention and its research is advancing in various fields. Because fine bubbles became known to have various specific characteristics different from normal large bubbles. Usually, it is known that bubbles in the insulating oil become a starting point of the breakdown and cause the breakdown voltage decrease. However, fine bubbles may be able to impart new characteristics to the insulating oil without decreasing the breakdown voltage. In this paper, the insulation properties of mineral oil with and without fine bubbles with nitrogen gas were investigated under nitrogen atmosphere. In addition, the bubble diameter of mineral oil with fine bubble added was measured. As a result, it was confirmed that the breakdown voltage of the mineral oil did not decrease significantly. Furthermore, it was found that fine bubbles were present in the mineral oil at a diameter of 200-2000 nm.