Direct and automatic measurement of the overlapping time in GCB applications

The overlapping time of double-contact circuit breakers is defined as the time delay elapsing between the opening of the nominal and the arcing contacts. It is an important criteria for the circuit breaker lifetime. It is usually determined indirectly on live breakers, e.g. derived from the number of breaking operations and the interrupted current amplitude, or directly during the breaker overhaul, using the dynamic resistance measurement (DRM) method. This paper presents a system which is able to perform a direct measurement of the overlapping time of a generator circuit breaker (GCB) with an accuracy better than hundred microseconds, which is up to an order of magnitude better than for DRM. The proposed method can be extended to measure the overlapping time online, i.e. on live GCBs.