Dynamic response of arcs in various gases

THE ELECTRICAL characteristics of an arc drawn upon separating the contacts of a circuit interrupter can be classified as the static, or steady-state, and the dynamic characteristic. Both are involved in the circuit interrupting process, but of the two the dynamic characteristic is generally most important. The latter is essentially involved in the transition of the arc from a conductor to an insulator which must precede the recovery of high dielectric strength between the switch contacts. This transition, which depends on changes in energy content associated with the arc conductance, can most conveniently be described and analyzed in terms of differential equations which serve as approximate mathematical “models” of the arc. By means of such models, the arc can be treated as an element in the connected circuit. Usefully simple mathematical models have been devised by several authors by this method, all of which include a characteristic “time constant” which will be designated as θ. This quantity is a measure of the time required for the arc conductance to reach a new steady state when its original state is disturbed.