On the mechanism of partial discharges in gaseous cavities in contact with solid or liquid insulators

A study of partial discharges (PDs) in gaseous cavities subjected to an AC voltage between dielectric surfaces, or between a metal and a dielectric, is presented. The authors present and analyze the characteristic features of discharges under AC and compare them to those obtained by J.C. Devins (1984). The present study was undertaken with a view to obtaining a better understanding of the fundamental mechanisms involved in the gassing of liquids (i.e. their ability to generate or to absorb gases under the effect of PDs). From transient current measurements and light pattern recordings, different discharge types have been analyzed. Two of the types are shown to reflect very fast and localized events, comparable to the streamer discharge regime. A third type reflects a process uniformly distributed in the cavity, attributed to the Townsend avalanche mechanism