A Self-Balancing Current Comparator

The development and construction of a self-balancing current comparator is presented. In principle, the instrument incorporates in one unit a current transformer and a current comparator. The transfer of power from the source to the burden is achieved with the current transformer. The current comparator detects the error current of the transformer and controls a feedback amplifier which supplies the error current to the burden. At the terminals, the overall instrument is equivalent to a very accurate nonreciprocal current transformer. At power frequencies, its current ratio differs from the turns ratio by less than half a part per million. A number of ratios from 10 to 1 to 1000 to 1 is available. Applications of the instrument are discussed.