| 摘要 |
PROBLEM TO BE SOLVED: To provide an insulation monitor which is small and is capable of identifying a phase, in which degradation in ground insulation has occurred. SOLUTION: A zero-phase current of a three-phase electric path 7 is measured with a zero-phase current transformer (ZCT)1, while the voltage of each phase is measured with a voltage-measuring device 2. With the use of a bandpass filter 9, a fifth-order harmonics components which are harmonics components other than the fundamental wave component and a 3n-th order harmonics is extracted among the detected outputs of the ZCT1 and the voltage-measuring device 2. The phase relationship, between current and voltage of the frequency component that has been extracted, is acquired with a calculation processor 3. By analyzing in accordance with a prescribed analyzing algorithm, the amount of leakage current caused by a ground capacitance is removed from the leakage current of the three-phase electrical path 7, to calculate the amount of leakage current caused by a ground insulation resistance. At the same time, a phase where the ground insulation resistance, which is the cause of leakage current, has dropped is identified. No arrangement for applying a low-frequency voltage component for measurement is required, which results in reducing the size of the monitor. COPYRIGHT: (C)2005,JPO&NCIPI
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