Precharge Switch: A Strategy to Suppress the Inrush Current of High Voltage Capacitor

When a circuit breaker switches on high voltage shunt capacitors, high inrush current will occur and may induce restrike, which will harm the power system and some electrical devices. This paper firstly calculates the expression of the capacitive current accurately when the high voltage shunt capacitor switches on, and get the steady component and the transient component of the capacitive current respectively. Then proposes a precharge strategy to suppress the inrush current caused by capacitor switching on according to the calculation results. The proposed strategy can make the transient component of closing current zero or minimum. The target value of precharge is obtained by the theoretical derivation. Then a precharge strategy for single-phase, two-phase and three-phase precharging is proposed and a topology of precharge device is put forward based on the target value. Finally a PSCAD simulation model is built to validate the proposed precharge strategy. The simulation results show that the inrush current can be limited under 1.7p.u. The single-phase precharge can reduce the inrush current by 70%, and two-phase precharge can make the three-phase closing inrush surge rate over 50%. The duration time of closing transient is sharply shortened as well. Thereby the effectiveness of the proposed precharge strategy is verified.