Low voltage application is usually used for field test of high voltage capacitor in converter station. Theunbalanced current is tested directly through the micro ammeter

which is influenced greatly by the internal resistance of micro ammeter and the electromagnetic interference in the field and is difficult to measure directly and accurately. In this paper

the cause for the large error in unbalanced current field measurement is analyzed theoretically and verified by simulation

a new measurement method is proposed

that is to apply the high voltage AC signal to the capacitor tower and calculate the unbalanced current by way of measuring the unbalanced voltage of the bridge arm and through the equivalent impedance of the capacitor tower. The new method proposed in this paper can eliminate the influence of inner resistance

the measurement equipment and interference at site on the accuracy. It is shown by the site test result that the new method has clear theoretical idea and can improve effectivelythe accuracy of unbalanced current measurement.