An Approach for Minimum Percussion Welding in Closing Operation of a 126-kV Vacuum Circuit Breaker

SF₆ circuit breakers are widely used, to safely and reliably protect the high-voltage (72.5-1000 kV) power system. However, SF₆ is a greenhouse gas. It is necessary to develop high-voltage vacuum circuit breakers (VCBs) instead of SF₆ circuit breakers above 110-kV power systems. To obtain the optimum performance from a high-voltage VCB design, the mechanism design must be perfectly matched to it. For a closing operation of a 126-kV VCB, most of the arc energy for performing percussion welding is from the prestrike arc and the bounce arcs if contacts close in vacuum when a high current passes through the contacts. An approach for minimum percussion welding in the closing operation of a 126-kV VCB is investigated by reducing both the prestrike arc duration and the bounce open duration. The breakdown phenomena in 126-kV vacuum interrupters are investigated to obtain a prestrike gap of 4 mm. The bouncing-open time of a prototype of a 126-kV VCB is measured in the prestrike closing velocity range of 0.7 to 2.0 m/s. The results show that the total arcing duration (including the prestrike arc and bouncing arc duration) is a function of the prestrike closing velocity (an average closing velocity in the prestrike gap (d) before the contacts touched each other). According to the function, the optimized prestrike closing velocity is 1.15 m/s, which can minimize the total arcing duration to 4.91 ms in the 126-kV VCB. The prototype of the 126-kV VCB passes the full-voltage synthetic making test successfully by applying the closing characteristic.