Switching of capacitive current with vacuum interrupters

Standard vacuum circuit breakers are required to fulfil various needs, e.g. the interruption capability, breaking/making operations. More and more commercial vacuum circuit breakers have to switch capacitive currents in different networks. Further to line and cable charging circuits, single capacitor bank and back-to-back capacitor banks have to be switched with lowest frequency possible. Late breakdowns are potentially dangerous to the installation as they could lead to the build-up of high switching overvoltages that can be harmful to the equipments. IEC and IEEE standards define switching circuits with the main parameters of peak inrush current, inrush frequency and capacitive breaking currents. Real applications often deviate from these parameters. The paper presents the results obtained with a special designed vacuum interrupter designated for capacitive switching investigations. The test was performed at high power station. Various single-bank and back-to-back capacitor bank switching tests have been done with several inrush parameters and capacitor bank current values. The goal of the investigations was to make a statistical correlation between the late breakdowns and potential sources of failure.