An analysis of let-through I²t variations of a current-limiting circuit breaker by non-simultaneous closing in short-circuit conditions

The let-through I²t characteristics of a current-limiting circuit breaker are provided by a manufacturer and generally determined by a desk study during the design stage and then verified by tests. However, under short-circuit conditions, they can be different from that given when the non-simultaneous closing of the current-limiting circuit breaker occurs; this causes an unintentional operation of the upstream protective device to clear the fault. This article presents the influence of non-simultaneous closing on the let-through I²t variations of the current-limiting circuit breaker in short-circuit conditions by using a simulation study. The simulation results indicate that the let-through I²t values obtained by the non-simultaneous closing of the current-limiting circuit breaker have significantly more variations than that obtained by simultaneous closing.