Post arc currents in medium voltage interrupting devices

Current zero measurements in modern circuit breakers are discussed. It is shown that vacuum interrupters always exhibit a postarc current when breaking at high current. On the other hand, it is shown that, due to the very short time constant of SF/sub 6/ circuit breakers, no measurable postarc current is driven in these devices. A description of the current zero phenomena in SF/sub 6/ is proposed, which includes the interaction with the circuit. It is noted that O. Mayr's (1943) and A. M. Cassie's (1939) models are not sufficient for describing the current zero phase.>