Overvoltages due to switching off an unloaded transformer with a vacuum circuit breaker

When a vacuuni breaker i s used to disconnect an uiiloaded transforiner, high overvoltages may result on tlic secondary sicle. Iʹlic plieiinmena of current chopping and multiple reigoitions iiftcr coiitact openiiig. sliurtly before current zero, play a significant role in generating these overvoltages. Furthermore, the transient recovery voltage (IʹKV) is also influenced by virtual current chopping wliicli inay lead tu fast interruptions and reignitions. ʹlʹlic paper reports on a vacuuin brealier model implemented in the ATP-EMTP prngrain. Simulations liiive been performed to cletermine overvoltages generated by the vacuum breaker, before and after suppression. Network eleiiients were simulatecl by simplified models of liniitecl complexity.