Partial discharges in free helium bubbles in transformer oil

Abstract

Partial discharges (PD) in a floating bubble in transformer oil were studied experimentally and theoretically. In test cell, the PD inception was very rare event. Sometimes PD occurred after an exposition of more than 10 hours at the voltage that corresponds to the value three times larger than that required in accordance with the Paschen’s law. The problem is in initiating electrons. Analysis showed that, at the conditions of PD occurrence in helium bubbles, the mechanism of breakdown corresponds to the streamer one. Registrations of electrical and optical signals of PD were performed to estimate both apparent charge and the number of radiated photons. As a result of estimation, number of electrons is approximately equal to the number of photons.