Patent ID: 8009394

Claim:
A leak current breaker comprising: a leakage current detecting means for detecting a leakage current flowing through electric lines under testing; a converting means for converting the leakage current detected by the leakage current detecting means into a voltage; an amplifying means for amplifying the voltage output from the converting means; a first harmonic component removing means for removing a harmonic component from the voltage amplified by the amplifying means; a voltage detecting means for detecting a voltage developed in the electric lines under testing; a second harmonic component removing means for removing a harmonic component from the voltage detected by the voltage detecting means; a phase contrast detecting means for detecting a contrast in signal waveform between the voltage from which the harmonic component has been removed by the first harmonic component removing means and the voltage from which the harmonic component has been removed by the second harmonic component removing means; a frequency calculating means for calculating a frequency occurring in a voltage line in which the voltage has been detected by the voltage detecting means on the basis of the signal waveform of the voltage having the harmonic component removed by the second harmonic component removing means; a phase angle calculating means for calculating a phase angle of the leakage current flowing through the electric lines under testing on the basis of the phase contrast detected by the phase contrast detecting means and frequency calculated by the frequency calculating means; a root-mean-square value calculating means for calculating a root-mean-square value of the voltage having the harmonic component removed by the first harmonic component removing means; an earth insulation resistance-caused leakage current component calculating means for calculating a leakage current component arising from an earth insulation resistance included in the leakage current flowing through the electric lines under testing on the basis of the root-mean-square value calculated by the root-mean-square value calculating means and phase angle of the leakage current flowing through the electric lines under testing, calculated by the phase angle calculating means; a judging means for judging whether the leakage current component arising from the earth insulation resistance included in the leakage current flowing through the electric lines under testing and calculated by the earth insulation resistance-caused leakage current component calculating means has exceeded an arbitrary value; and a circuit breaking means for breaking the electric lines under testing on the basis of the judgment made by the judging means.