The Compensated Current Comparator; A New Reference Standard for Current-Transformer Calibrations in Industry

The compensated current comparator combines in one device the high ratio accuracy of the three winding ratio transformer or current comparator with the energy-transfer properties of a normal current transformer. Its ratio error is very small and so independent of the energy-transfer function that it can be operated at very high burden. Even negative burdens may be imposed, and, when operated in this mode, the device fulfils the functions of a high-current primary supply transformer. As such, it is highly suited to in situ calibrations in industry. Construction details of a multiratio compensated current comparator, covering all normally encountered ratios from 5/5 to 1200/5, are given. Its ratio accuracy, for burdens up to 750 va, is better than five parts per million. A test set, for use in calibrating current transformers up to errors of one per cent and 100 minutes, is also described. The set employs three conductance and three capacitance decades, with a three-position range switch, and is direct reading.