Discrimination of Partial Discharges in Gaseous and Liquid Nitrogen by Using Waveform Characteristics

The cryogenic coolant is important as an electrical insulation in an immersion cooling. One of the dielectric breakdown mechanisms of the cryogenic coolant is via bubbles, caused by partial discharge (PD). The insulation performance has been discussed with PD parameters and breakdown voltage. However, the essential PD mechanism has not been clarified in detail. In this paper, PDs in gaseous and liquid nitrogen were discriminated based on characteristics of the original PD waveform. It was shown that the difference in charge behavior appears significantly in the fall time of the original PD waveform.