| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem associated with a conventional ground detector, which detects positive and negative signals of ground current sand if ground fault occurs at the phase control part of an inverter, there are only positive or negative signal, and ground detection cannot be made. SOLUTION: A zero-phase current transformer 5 detects the ground component signals of AC cable way, and when the output exceeds the predetermined threshold + TH1 of a positive side level discriminator 8, it outputs signals. The widths of positive side signals which have exceeded from the duration of the output, is decided by a positive side signal width discriminator 9, and if the predetermined time is exceeded, it outputs pulse signals, while if they are smaller than the criteria level of the positive side signal discriminator 9, a positive side signal latch circuit 12f is actuated, depending on the output of an inversion device 12h, and then if positive side signals at second time are generated, a positive side signal latch circuit 12c is actuated. With such a configuration, the ground detection is executed with only positive side wave form. For negative side too, ground detection is executed in a similar manner. COPYRIGHT: (C)2003,JPO
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