A computer simulation of transformer magnetising current interruption by a vacuum circuit breaker

A computer program has been elaborated to calculate the switching overvoltages during transformer interruption of a magnetising current by a vacuum circuit breaker (VCB). This program uses the Monte Carlo simulation technique and takes into account three-phase switching phenomena in an isolated neutral electric circuit. The distinguishing feature of this program is the application of a current chopping model, based on the experimentally determined average arc lifetime vs. current dependency. This model considers both the current´s amplitude and shape. Some generalised dependencies, like maximum overvoltages on the circuit and VCB parameters, are also incorporated. Classification of switching regimes was carried out with respect to different switching behaviour and the VCB´s effect on the reduction of maximum overvoltages