Partial vacuum breakdown characteristics of helium at 20 kHz for inhomogeneous field gap

In general, power devices and systems operating in vacuum or space environment are more susceptible to partial discharges, corona, or volume discharges due to the partial vacuum conditions. Additionally, high frequency operation of a power system is a contributing factor in lowering the breakdown voltage of insulation. In this paper we present our studies on the breakdown characteristics of helium operating in DC and 20 kHz AC field in partial vacuum, for a point-to-point and point-to-plane electrode configurations. Breakdown voltage as a function of pressure in the range of 27 to 400 Pa (0.2 to 3 torr) for both the DC and 20 kHz AC cases is presented. Voltage and current waveforms along with the optical emission waveform of the breakdown events are also presented. A variable DC power supply for DC and an in-house built variable DC-offset-AC power supply for the high frequency breakdown experiments are used. A high voltage probe and a Pearson current sensor are used for the voltage and current detection, and a photo-multiplier-tube with a digital pico-ammeter and a video camera are used for the optical signal detection of this set-up. The breakdown voltage as a function of pressure for both the AC and DC experiments, along with voltage breakdown waveforms for both electrodes are presented.