Patent ID: 7696743

Claim:
A zero-phase current detecting apparatus comprising: a zero-phase-sequence current transformer that includes a magnetic core and a detection coil wound around the core, and that detects a zero-phase current flowing in an electric power line; and a feedback loop is made up of a pulse generating unit that applies an excitation pulse signal to one end of the detection coil; a current detecting unit that converts a current flowing through the detection coil into a voltage and outputs the voltage; a peak detecting unit that detects a peak value of the voltage output from the current detecting unit; an adding unit that outputs a difference between a target value and the peak value detected by the peak detecting unit; and a current regulating unit that regulates the current flowing in the detection coil based on the difference output from the adding unit, wherein the zero-phase current is detected based on the difference output from the adding unit as a result of regulation of the peak value so as to be the target value in the adding unit.