Mechanisms of streamer leading to breakdown in synthetic ester liquid in uniform field

Abstract

Synthetic ester liquids are increasingly considered as alternatives to conventional mineral oils, due to their biodegradability, high flash/fire points and superior moisture tolerance. This high interest has led to growing research attention on streamer and breakdown performance of synthetic ester liquids. Large effort has been made to characterise streamer phenomena of synthetic ester liquids in non-uniform electric fields. However, streamer phenomena of synthetic ester in uniform electric fields are not well studied. In this paper, streamer phenomena in a synthetic ester liquid under both positive and negative standard lightning impulse voltages were studied using a 2 mm plane-plane gap. A mineral oil was also tested as the benchmark. Results showed that during a complete breakdown process, multiple streamers could initiate near the cathode region, but only one streamer propagates to anode leading to breakdown. Streamers could be initiated either on the electrode surface or in the bulk oil, where most streamers are initiated near the cathode region.