| 摘要 |
A protective relay circuit includes a first a-c level detector or bi-polar threshold circuit to which a polarizing signal VPOL is applied. An output is provided from the first a-c level detector only when the magnitude of VPOL exceeds a predetermined value. Also included is a second a-c level detector or bi-polar threshold circuit to which an operating signal VOP is applied. An output is provided from the second a-c level detector only when the magnitude of VOP exceeds a predetermined value. The output of the first level detector is compared in a coincidence circuit with the output of the second level detector. The detection of coincidence for a predetermined time period, as measured by a characteristic timer, results in an output signal for use in controlling operation of a trip coil of a circuit breaker.
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