Leakage current calculation device and method for calculating leakage current

Abstract

Provided is a leakage current calculation device capable of calculating an accurate leakage current value in which the effect of noise has been suppressed. The configuration comprises: a to-ground voltage measurement means for measuring, over a predetermined interval, to-ground voltages inputted in each phase of a three-phase motor; a zero-phase current measurement means for measuring, over a predetermined interval, a zero-phase current, which is the to-ground leakage current that flows through the three-phase motor; a basic AC voltage waveform extraction means for extracting, from the to-ground voltage, a basic AC voltage waveform having a frequency in the same phase as the to-ground voltage of each phase; a frequency component extraction means for extracting, in the frequency band containing the frequency of the basic AC voltage waveform, a zero-phase current component of said frequency band; and a leakage current value calculation means for calculating the leakage current value Icos θ flowing through the to-ground resistance component, excluding the to-ground capacitance component of the three-phase motor, among the to-ground leakage currents by integrating the zero-phase current components of the frequency band in an interval corresponding to gap between zero-crossings of the basic AC voltage waveform.