Development of an indoor 40.5 kV vacuum circuit breaker for back-to-back capacitor bank switching duty

Abstract

Vacuum circuit breaker (VCB) is a mature technology which is commonly used in medium voltage power systems worldwide. However, it is still facing challenges to switch capacitive current, especially for back-to-back capacitor bank switching. The main reason is that the inrush current can cause serious damages to the contact surfaces and further deteriorate the high voltage withstand ability of the vacuum gap. The objective of this paper is to develop an indoor 40.5 kV VCB which is exclusively used for back-to-back capacitor bank switching. The main circuit of this VCB adopted vacuum interrupter series technology, which adopted different contacts (CuW and CuCr), separated functions and specified operation sequence to deal with the challenges of high frequency inrush current and withstanding of (1-cost) recovery voltage. In order to satisfy the frequent operation duty, permanent magnetic actuator and simplified linkage arrangements were used during mechanical designing. The type tests were successfully passed, showing that no restrike or NSDD occurred during 1200 A back-to-back capacitor bank switching test. The mechanical life reached 30,000 cycles, and the short circuit current interrupting capability was 31.5.