A microprocessor-controlled high-voltage current-comparator-based capacitance bridge

A microprocessor-controlled high-voltage current-comparator-based capacitance bridge is described. The bridge has a capacitance ratio and a dissipation factor (loss tangent) measurement range of 1/1 to 100/1 and 0 to 10%, respectively, with a resolution of 1 PPM (part per million). To accommodate capacitance ratios larger than 100/1 (up to 100000/1) and load currents of up to 1000 A, an additional range-extending two-stage current transformer is employed. The overall accuracy of the bridge including the ratio extender is better than 5 PPM in both magnitude and phase. The automatic balancing feature facilitates the use of the bridge for accurate load loss measurements of large high-voltage inductive loads, such as shunt reactors and power transformers. It allows tracking of the changes in the inductive and loss tangent balance due to power frequency fluctuations and heating effects, respectively