A Transformer-Ratio-Arm Bridge for Measuring Large Capacitors Above 100 Volts

A high-voltage bridge suitable for measuring capacitance ratios up to a million to one is described. The high ratio is realized by cascading a two-stage current transformer to a bridge based on the current comparator principle. Circuits that compensate for the lead impedances of large capacitors are presented. The bridge is direct reading in the capacitance ratio and the dissipation factor and the uncertainties for both components are less than 10 parts per million (ppm).