Partial discharge inception characteristics in artificial air-filled voids at room and liquid nitrogen temperatures

A part of gas substances in a void in solid insulators becomes liquid or solid at cryogenic temperature and the reduction in gas pressure in it may cause a decrease in partial discharge (PD) inception voltage. In this study, PD inception voltage and PD characteristics around the PD inception in artificial air-filled voids are investigated experimentally at room and liquid nitrogen temperatures. The results show that PD inception voltage decreases with decrease in ambient temperature due to the liquefaction of oxygen. PD characteristics just after the PD inception at liquid nitrogen temperature are affected by arrangement of test sample. Based on the simultaneous measurement of the current pulses and light images, PD characteristic dependence on the sample arrangement is discussed, taking account of the phase change of oxygen in the void.