Mathematical modeling of the high frequency behavior of vacuum interrupters and comparison with measured transients in power systems

When the gap length of a vacuum switch at current zero is too short (i.e. contacts open shortly before current zero), high frequency transients, known as multiple reignitions or virtual current chopping, may occur under certain network conditions. In order to estimate the probability of such transients a mathematical vacuum breaker model, based on numerous measured data, has been developed. It is able to simulate the HF-behaviour in single or three phase networks. To verify the abilities of the breaker model, complex measurements of the interruption of a modern 11 kV dry type transformer with a vacuum breaker under no-load conditions have been carried out. A comparison between the measured data and the results of the simulations, which require an equivalent HF-network for all involved devices (especially the transformer), is presented.