Polarity effects on breakdown strength for high energy storage liquid dielectrics in microsecond regime

Development of high power microwave (HPM) requires high power pulse conditioning system with high output power, small volume and wide application range^1-2. Propylene carbonate (PC), because of its great dielectric constant and high breakdown strength, has attracted extensive attention in high energy storage liquid dielectrics of Pulse Forming Line. In this paper, we investigated the polarity effects on the breakdown voltage of PC by using gaps of 0.5, 1.0 and 2.0 mm for the needle-plate electrode. The equipment used in this study involved a compact capacitive-energy-storage pulsed power source with charging time vary from 5 to 20 microsecond and a test cell with the needle-plate electrode in it. The breakdown voltage and the time to breakdown were recorded on a digital oscilloscope for each gap. The data of these three groups noted that the positive breakdown voltage was higher than the negative one. And the breakdown voltage of PC increases with increasing electrode gap. Moreover, an investigation of the polarity effect of glycerin has been undertaken as a comparison. The results also show that the breakdown voltage for positive polarity was higher than for the negative one. Finally, through the comparison of the polarity effect between PC and glycerin, some pertinent conclusions are drawn. The research results deepen our understanding of the polarity effects in liquid dielectrics and can be used in the further research on the high energy storage liquid dielectrics.