A frequency-compensated high-voltage current-comparator-based capacitance bridge for shunt reactor loss measurement

A current-compensating technique for making a high-voltage current-comparator-based capacitance bridge insensitive to frequency fluctuations when used for measuring shunt reactor loss is described. A compensating current, proportional to twice the change in the current through the reference capacitor due to frequency fluctuations, is forced into the comparator winding through which the current from the reference capacitor passes resulting in a current in that winding having frequency characteristics similar to those of the reactor current. This compensating current is derived from a reduced replica of the applied high voltage or from the current through the reference capacitor. It need not be supplied with great accuracy for it is only a small fraction of the reference current. Thus the effect of frequency fluctuations on the inductive balance of the bridge is eliminated without sacrificing the inherent high accuracy of the high-voltage current-comparator-based capacitance bridge.