(Maintenance and Test Center of Extra High Voltage Power Transmission Co., China Southern Power Grid, Guangzhou 510663, China)

The paper mainly gives an account of the principles of calculating the settings of unbalanced current protection for ∏ configuration of capacitor banks of high voltage direct current (HVDC) filters. It is first proposed that, following the failure of part of the capacitor units, the permitted detuning of the filters and the over-voltage level on the remaining capacitor units in good condition are taken as the basis for protection calculation. The formulae are deducted to calculate the settings of unbalanced current protection in cases where failures of some capacitor units or elements occurred. Based on the calculations of settings for both interfused and fuseless capacitors, the behavior of part of the unbalanced current protection are analyzed and compared with calculation results.