An oscillograph for recording transient recovery voltages

THE importance of the effects of the magnitude and rate of rise of the transient recovery voltage upon the difficulty of arc interruption in circuit breakers has been recognized for a number of years. It is known that differences in the interrupting performance of circuit breakers may be obtained at different locations in power systems, even though the power-frequency voltages and short-circuit currents involved may be similar.¹ In general, the greater the rate at which the transient recovery voltage builds up and the greater the final value that it attains across the arc space as the arc extinction process occurs, the more difficult it is for the circuit breaker to clear the circuit. There is not, however, any simple quantitative relationship between these transient values and the arcing time of a circuit breaker or its interrupting capacity limit. Individual short-circuit interruptions with a given circuit breaker and circuit conditions may show considerable variations in arcing time. For such and other reasons the added complication of transient recovery-voltage rate and magnitude limits has not been added to circuit breaker interrupting capacity ratings or specifications.²