Capacitive making of double-break vacuum circuit breaker: Transverse magnetic field contacts are superior to axial magnetic field contacts

Previous studies mainly focused on the behaviours of single-break vacuum circuit breakers (VCBs) in switching capacitor banks. The prestrike characteristics of double-break VCBs subjected to axial magnetic fields (AMFs) and transverse magnetic fields (TMFs) in capacitive making operations, to find a proper structure of double-break VCBs for capacitive switching are experimentally investigated here. Special attention is given to the prestrike gap, inrush current interruption, prestrike voltage, prestrike electric field strength and erosion on contact surfaces of double-break VCBs. The results show that the 50% prestrike gap d(50) and the scatter in prestrike gaps are significantly reduced by nearly 50% by the TMF double-break VCB compared with the AMF double-break VCB. The 50% prestrike arcing time t(a)(50) of the TMF double-break VCB can be reduced by 37.0% compared with the AMF double-break VCB. The voltage distribution ratio between two vacuum interrupters (VIs) is more balanced in the TMF double-break VCB (6:4) than in the AMF double-break VCB (7:3) when prestrike occurs. The TMF double-break VCB can reduce the erosion caused by inrush currents on contact surfaces compared with the AMF double-break VCB. In switching capacitor banks, the TMF double-break VCB is superior to the AMF double-break VCB.