Modelling of Electromagnetic Transients in Multi-Unit High-Voltage Circuit-Breakers

High-voltage (HV) circuit-breakers (CBs) often consist of several making and breaking units (MBUs) in series. A multi-unit circuit-breaker EMTP® model is proposed to analyze the effects of non-simultaneity between MBUs of the same pole. The model allows for simulations of high-frequency voltage and current transients during opening or closing operations. The simulations include the non-simultaneity of MBUs of the same pole or differences in dielectric withstand characteristics for vacuum circuit-breakers (VCBs) and SF6 CBs. According to simulation results, the maximum non-simultaneity of MBUs of the same pole, as permitted per international standards, can lead to multiple re-ignitions during opening or excessive overvoltages during closing operations. These phenomena are rarely simulated with conventional CB models. The simulations also highlight the important challenges facing high-voltage VCB design due to the inherent characteristics of vacuum bottle technology. The proposed models serve as useful tools for understanding and studying the effect of multi-unit CBs in various system studies and advanced diagnostics.