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.