Performance of Vacuum Circuit Breaker in Frequently Capacitor Bank Switching

Reactive power compensation in power systems is crucial for improving the grid's power factor, reducing line losses, and enhancing the quality of electric energy. Shunt capacitor compensation is widely used in medium-voltage power systems. Typically, the rated current of capacitor compensation devices does not exceed 1000A. Due to daily switching, the opening and closing operations of the compensation circuit are frequent. Medium-voltage power systems commonly use vacuum circuit breakers to switch capacitor banks. During capacitive current switching, the closing inrush current can cause the vacuum interrupter contacts to melt and weld, increasing the likelihood of re-strike. The performance verification process for circuit breakers handling capacitive current switching is outlined in IEC 62271–100, which requires a C2 level of 104 operations. However, vacuum circuit breakers in capacitor bank compensation circuits often exceed this number. The new “K-type” vacuum interrupter was developed for frequent switching of capacitor banks. These interrupter contacts have higher resistance to fusion welding, and the closing inrush current has less impact on the contact surface. Vacuum circuit breakers with “K-type” interrupters have successfully passed three rounds of back-to-back capacitor bank switching tests of class C2 (40.5kV, 1250A), totaling 264 operations, in accordance with IEC 62271–100. This paper details the cumulative frequency of the pre-ignition electric field strength and the form and energy distribution of the inrush current during testing. After 264 tests, the insulation performance of the “K-type” vacuum interrupter meets the relevant GB/IEC standards, and the surface roughness and micro-welding of the contacts are significantly improved.