INRUSH CURRENT SUPPRESSION RESEARCH ON 750 KV FILTER SWITCHING

The switching of AC filter in HVDC transmission project can cause serious inrush current and overvoltage, which causes damage to the high-voltage equipment and cause the imbalance protection of the AC filter to frequently false operation. Closing resistors or phase-controlled technology are usually used to restrain the inrush current. In a converter station of Northwest Power Grid, the closing resistor has failed to effectively restrain inrush current many times. For the actual working conditions of this converter station, this paper simulated and analysed the closing inrush current and overvoltage of different closing resistors and the phase-controlled technology. The results show that overvoltage cannot be significantly restrained as closing resistor increases from 400 ohms to 1500 ohms, but the inrush current increases greatly. For BP11/BP13 filters, the inrush current is 4.8 p.u. when closing resistor is 1500 ohms; while it can be limited to 2.9 p.u. by adopting the phase-controlled technology. The research results can provide a basis for HVDC engineering design and equipment selection.