100:1 Step-Up Amplifier-Aided Two-Stage Current Transformer with Small Ratio Errors at 60 Hz

An electronically aided 100:1 step-up two-stage toroidal current transformer is described which has very small ratio error. Two-stages of amplifier aiding are used. One stage reduces significantly the burden seen by the transformer while the other enables almost exact ampere-turn balance to be achieved between primary and secondary currents within the inner core of a two-stage arrangement. Practical operation of the circuit is described, together with analysis of circuit stability considerations at low and high frequencies. Measurement techniques are included and the effect of practical circuit performance upon the current ratio error is discussed.