DC 5 kA Current Ratio Standards Based on Series–Parallel Self-Calibration DCCs

Abstract

With proper design, accurate current ratios of direct current comparators (DCCs) can be achieved between series and parallel connections of n sections of primary windings with the same nominal number of turns. Based on this principle, a DCC could be calibrated with the windings connected in series, then operated in parallel, at rated current and therefore have its current ratio accurately extended by n times. By keeping the geometric position of the primary windings symmetrically and rigidly fixed to the cores, the leakage fluxes and their effects on the DCC current ratios would be minimized and relatively unchanged between the series and parallel connections. Four DCCs with current ratios of 10 A:1 A to 5 kA:5 A have been developed with relative ratio errors less than 2 × 10 −8 to 5 × 10 −7 , and calibrated by the series parallel method through only four step measurements. These measurement techniques for the selfcalibration of DCCs with current ratios of 10 A:1 A to 5 kA:5 A and corresponding uncertainties from 1.2 × 10 −8 to 1.6 × 10 −7 (k = 2) are described.