The Determination of Circuit Recovery Rates

Actual interruption of an a-c circuit depends upon the ability of the circuit breaker to prevent the re-estabishment of the arc after the current goes through zero and the arc goes out. In some circuits full voltage appears across the contacts as quickly as 40 to 80 microseconds following the current zero. This recovery rate in volts per micro-second depends upon the triple product of: the current interrupted., the normal frequency of the system, and the recovery impedance in ohms of the external circuit. The calculation of circuit recovery rates is given in this paper by presenting in curve and table form the ohmic recovery impedance, and its components, for all the practical circuits found in the field.