This paper describes the unbalanced current theoretical formula of the high-voltage capacitors in a converter station

and with the linear relationship of unbalanced current under the action of different power frequency voltages as the basic principle

the difference between the unbalanced current theoretical value and off-line testing value under low power frequency voltage is accounted for. Through analysis of the cause of the difference from shallow to deep

the conclusion is reached that the key method by which the field maintenance personnel can improve the accuracy of unbalanced current test is through rational and optimized test wiring to reduce electromagnetic interference and appropriately compare theoretical value with off-line test value to ensure the accuracy of the bridge arm unbalanced current off-line test value. Through the capacitor adjustment or replacement

the off-line test values of the unbalanced current are up to requirement for ensuring stable equipment work in operation.