Study of streamer propagation and breakdown in varying electrode gaps under semi-uniform field in natural ester, synthetic ester and mineral oil under lightning impulse voltage

Abstract:
In this paper streamer propagation as well as breakdown behavior in semi-uniform fields under lightning impulse voltage were studied. With three different sphere-sphere electrode configurations with asymmetric field distribution and varying gap distance yet similar degree of homogeneity (0:2–0:3), five insulating liquids were investigated. As insulating liquids two natural esters, two synthetic esters and a mineral oil for reference were chosen. It was observed that under positive polarity natural esters had slightly higher breakdown voltages in all electrode configurations. For negative polarity mineral oil showed significantly higher breakdown voltage with increasing gap distance compared with ester liquids. The time to breakdown was several times higher for mineral oil under negative polarity than for the esters.With positive polarity, time to breakdown was similar for all liquids, only at 40mm gap distance average streamer velocity of mineral oil was lower than of the esters. In this study streamer propagation current and light emission recordings were used to characterize streamer propagation. It was seen that natural and synthetic esters showed similar propagation characteristics. From streamer propagation current it might be possible to draw conclusions as to the streamer shape.