High voltage breakdown and pre-breakdown properties in rape-seed insulating oil

Rape-seed oil is considered for electrical insulation at high voltage. In this work, breakdown and streamer propagation in rape seed oil are studied in point-plane gaps up to 20cm, under impulse voltage of both polarities. In both polarities, two main streamer types are observed: “slow” streamers with a velocity of about 2km/s, and much faster streamers up to 150km/s. Compared to mineral oil in the same conditions, fast streamers in rape-seed oil appear at much lower voltage. They are able to propagate over large distances within a short time at moderate voltage. From these results, it is concluded that the properties of streamers in rape-seed oil are less favorable for high voltage insulation than in mineral oil.