Watthour meter with isolation transformers having a feedback loop

Abstract From the Canadian patent

A voltage transducer in a watthour meter for sensing AC line, voltage across a load includes a current transformer having its primary winding connected in series with a current-limiting resistor across the AC source. The transformer includes a secondary coil and a tertiary coil. The current through the secondary coil represents the sensed voltage and is signal conditioned through an integrator circuit for input to a solid-state watt transducer chip. An active circuit is connected across the tertiary coil, with an output feeding a compensating current into the input of the secondary coil. The active circuit includes an RC network at the output of the tertiary coil for providing a loop …