Influence of RC snubbers on the Steepness of Switching Transients caused by Vacuum Circuit Breakers

Vacuum circuit breakers are known to cause steep-fronted traveling waves in electrical systems as a result of pre-and restrike processes. Especially when very steep wave fronts encountering transformers or electrical machines, they will lead to inhomogeneous voltage distributions inside the windings. Therefore, this paper presents high resolution measurements of prestrikes stressing a transformer and analyses the influence of a RC snubber on the steepness of the occurring traveling waves. The results show that the oscillations caused by prestrikes are damped expectedly by the RC snubber. But it also shows, that RC snubbers do not affect the steepness of the initial wave front at all, as well as its initial height. Thus, it can be concluded that a snubber is not reducing all effects of the prestrike phenomenon. This leads to the conclusion that prestrikes may excite overvoltages inside windings independent of the snubber, possibly causing interturn faults.