| 摘要 |
PROBLEM TO BE SOLVED: To provide a differential current monitor in which a differential current monitoring logic is standardized by substantially eliminating the need for setting a timer at each site. SOLUTION: The differential current monitor comprises: a differential current detection circuit 1 for comparing a current flowing into a power facility apparatus with a current flowing out therefrom, and detecting the differential current of unbalance component corresponding to a fault current at the time of tripping a circuit breaker by outputting a trip signal upon occurrence of fault in the apparatus; and a differential current monitoring timer 4 for locking output of the trip signal until the differential current of unbalance component sustains for a predetermined time or longer. The monitor is further provided with: a circuit 2 for detecting the second harmonic from a current signal; and a gate circuit 3 for stopping output from the differential current detection circuit 1 to the differential current monitoring timer 4 when the detected second harmonic is not lower than a predetermined level. COPYRIGHT: (C)2006,JPO&NCIPI
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