An overview of the development of instrumentation and measurement techniques at the National Research Council of Canada, based on the current-comparator technology, for calibration of non-conventional instrument transformers with non-standard rated outputs, is presented. The instruments include: (1) a wide dynamic range transimpedance amplifier for operation of input currents from 1 A to 1000 A with means for modifying the in-phase and quadrature components of the output voltage (rated 10 V) within a +/- 10-percent range; (2) a high-voltage high-current transconductance amplifier with output current ranges of 10 A, 100 A, and 1000 A; (3) a voltage ratio standard also with means for modifying the in-phase and quadrature components of the output voltage (rated 100 V) within a +/- 10-percent range. The current-comparator technique is used to obtain accuracies of better than 20 ppm (parts-per-million) in both magnitude and phase of the associated outputs of these instruments.
