Fundamentals of Electrical Discharges

Natural phenomena, such as gamma rays produced by radioactive decay processes in the soil and cosmic radiation originating from solar flares and other galactic objects, can ionize the air molecules. This chapter first discusses ionization and deionization processes in gases. This is followed by a discussion on ionization and attachment coefficients. Two typical breakdown mechanisms occur in gases, each of them operating under specifically favorable conditions: Townsend's mechanism and the streamer mechanism. Corona discharges in air can burn on the overstressed zones of hot electrodes. This kind of discharge occupies a short layer, attached to the energized conductor. When a conductor is in corona, then the electric field on the surface is somehow influenced by the surrounding ion space charge. Kaptzov's hypothesis (KH) relates to the assumption that the space charge emitted into the interelectrode gap is in amounts that hold the surface field at the onset level.