ABSTRACT
The subject of electrical breakdown of gases is indispensable for designers and operators of electrical equipment. This chapter briefly discusses the breakdown mechanisms in uniform and nonuniform fields, under direct current (DC), AC, and impulse voltages, of air and SF6 at various pressures and temperatures. Ionization by electron impact is probably the most important process in the breakdown of gases. Two typical gas breakdown mechanisms have been known: the Townsend mechanism and the streamer mechanism. The avalanche process is basic for both mechanisms of breakdown. The electron has a finite chance of ionizing, which depends on its energy. If the density and hence the number of collisions decreases, breakdown can occur only if the chance of ionizing is increased by an increase in voltage, which is shown to the left of the minimum. Empirical relations have been suggested by many workers to express the breakdown voltage of uniform-field air gaps at atmospheric pressure.
