| 摘要 |
PROBLEM TO BE SOLVED: To provide a method and an apparatus wherein leakage part of current is detected with satisfactory accuracy by measuring only a zero-phase current and a high detection accuracy is realized without an additional facility such as an injection transformer or the like. SOLUTION: An initial vector quantity IO<SB>1</SB>of the zero-phase current is calculated on the basis of the zero-phase current in an initial state to start an insulation monitoring operation while a power-supply voltage is used as a reference quantity (Measuring step S101 in the initial state), and the vector quantity IO<SB>1</SB>is stored (Storage step S102 in the initial state). A monitoring vector quantity IO<SB>2</SB>of the zero-phase current is calculated on the basis of the zero-phase current measured in an ordinary state after the end of the initial state while the power-supply voltage is used as the reference quantity (Measuring step S103 in the ordinary state). A difference vector quantity IO<SB>21</SB>between the monitoring vector quantity IO<SB>2</SB>and the initial vector quantity IO<SB>1</SB>is calculated, an insulation defect identification process is performed on the basis of a vector-quantity decision condition that an absolute value of the difference vector quantity IO<SB>21</SB>is larger than an insulation-defect threshold value Ik (Determing step S104 of the insulation defect), and the insulation defect is determined when the vector- quantity decision condition is established. COPYRIGHT: (C)2003,JPO
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