Mutual inductance current transducer for AC electric energy meters

Claim 1

An AC electric energy meter comprising: an electronic measuring circuit processing analog signals responsive to the line current and the line voltage components of an alternating current electric energy quantity to be measured for producing electronic signals representative of quantized amounts of electric energy; means for producing an analog signal responsive to said line voltage component; and current sensing transducer means for producing an output signal proportional to said line current component, said current sensing transducer means including conductor means for series connection with said line current component, said conductor means having a primary winding portion for producing magnetic flux responsive to variations of said line current component; said transducer means further including a secondary winding; said transducer means still further including a magnetic core made of a soft magnetic material having said primary winding portion and said secondary winding disposed about said magnetic core in an inductively coupled relationship, said magnetic core further having opposite ends separated by a space equivalent to a predetermined air gap so that said magnetic core and the space between the ends thereof couple said magnetic flux with said secondary winding for having an electromotive force generated therein proportional to the time derivative of said magnetic flux, and said secondary winding having a pair of output conductors for producing a current responsive analog signal having a voltage proportional to the time derivative of the line current component for connection to a high impedance low level signal input circuit of said electronic measuring circuit; said current sensing transducer means including magnetically saturable shunt bar members which extend from one to the other of said opposite ends of said magnetic core for partially shunting said magnetic flux across said core space and being operable in a substantially unsaturated condition only below a predetermined low level of said magnetic flux to provide compensation for magnetic flux in said core at low levels of input current to said transducer means.