Patent ID: 8421444

Claim:
A device for sensing electrical current in an electrical distribution system, said device comprising: a first magnetic core having a first permeability and a second magnetic core having a second permeability higher than said first permeability, a primary winding comprising P turns coupled with said first and second magnetic cores and connected to a source of current to be measured, a measurement winding comprising M turns coupled with said first and second magnetic cores so that said current to be measured in said primary winding induces current in said measurement winding, a sense winding comprising S turns coupled with said second magnetic core, said measurement winding having a greater number of turns than said sense winding, an amplifier coupled to said sense winding for receiving a voltage developed across said sense winding and producing a compensation current in response to said received voltage, said amplifier having an output coupled to said sense winding to feed said compensation current through said sense winding to reduce said voltage developed across said sense winding voltage to substantially zero, a burden resistor coupled to said measurement winding and said sense winding for receiving the sum of said current induced in said measurement winding and said compensation current, and an attenuation circuit receiving said compensation current and attenuating said compensation current, before the summing of said compensation current with said current induced in said measurement winding, to compensate for the difference between the number of turns in said sense winding and the number of turns in said measurement winding.