Dielectric recovery by an A-C arc in an air blast

SINCE the extinction of the arc drawn upon opening an a-c switch depends upon a rapid transition of the arc near a normal current zero from a conducting to an insulating state, much study has been given by switch designers to this transition, often referred to as dielectric recovery. However, the published experimental data with regard to the mechanism of this dielectric recovery still are meager and there is no generally agreed upon theory, even for the simpler cases. One simple case, of growing importance in this country, is that of the arc in an air-blast circuit breaker. Perhaps the simplest arrangement is found in the nozzle type of air-blast breaker variously described as radial blast or axial blast. Figure 1 is illustrative of such nozzles, somewhat reduced from practical forms.