Impulse creepage discharges in rapeseed ester oil [power apparatus insulating oil]

Rapeseed ester oil is considered to be a substitute for the mineral oil that is used in electric power apparatus because of advantages of environmental adaptation and high dielectric strength. This work presents the results obtained on creepage discharges over the pressboard surface in rapeseed ester oil as well as mineral oil and silicone oil under standard lightning impulse voltage conditions. The basic discharge properties such as discharge shape, streamer length, discharge current and charge were measured for the creeping streamer propagating from a needle electrode. It is shown that rapeseed ester oil has a high insulating ability. The barrier effect on the propagation of creeping streamers in rapeseed ester oil was also examined using a high-speed image converter camera (ICC). The streamer propagation velocity appears to be significantly affected by the existence of the barrier.