Effect of Water on AC Breakdown Properties of Mineral Oil and Vegetable-oil-based Insulating Fluid

Abstract

This paper reports AC breakdown properties of the mineral oil / the vegetable-oil-based insulating fluid containing water and the movement of water-drops under AC electric field in those oils. These results were showed as the following: (i) AC electric strength (Fb) of the mineral oil decreased sharply over several tens ppm of water. Fb of the vegetable-oil-based insulating fluid also decreased with the increase of water amount, but the low degree of inclination that compared with that of the mineral oil was showed. (ii) The water-drops movement in the mineral oil was active, but that in the vegetable-oil-based insulating fluid displayed the gentle movement in contrast.