Online measurement of the overlapping time for generator circuit breakers (GCBs) in real plant conditions

The overlapping time of double-contact circuit breakers is defined as the time delay elapsing between the opening of the nominal and the arcing contact pairs. 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 switching operations and interrupted current amplitudes, 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 has been used to measure the overlapping time online, i.e. on live GCBs. Our results, based on a system installed on a live GCB, prove the feasibility of the approach, and are in a good agreement with the predicted performance. The results are analysed and a comparison with DRM is done to prove that our online measurement system matches and exceeds state-of-the-art offline ablation measurement systems.