Creeping discharges in transformer oil under lightning impulse voltages over 100 kV peak value

This paper describes the experimental results on the creeping streamer progressing the surface of a bakelite board immersed in transformer oil under the application of a standard lightning impulse voltage with peak values of plusmn100~350 kV. The growth of streamers is significantly affected by the thickness of bakelite board and the streamers are extended longer exponentially for the applied voltage more than ~plusmn200 kV. These streamers leave the remarkable discharge scars on the bakelite surface. The discharge scars are different by the voltage polarity which influences strongly to the streamer growth. The mean streamer velocities in both polarities have also been examined.