Abstract
An analytical formula of a transient recovery voltage and its dv/dt across a circuit breaker has been derived for the case of a transformer secondary fault. A comparison of the calculated results with field test and EMTP simulation results has proved its satisfactory accuracy. Applying the formula, the effect of various circuit parameters on the transient recovery voltage and its dv/dt have been made clear. The dv/dt, defined conventionally as the ratio of the crest value and the time to the crest, is found to be about 2/3 of the maximum value of the dv/dt given as a function of the time. Also, a formula has been developed to give critical circuit parameters by which the dv/dt across a vacumn circuit breaker reaches the critical condition i.e. the circuit breaker fails to interrupt a fault current.
