| 摘要 |
PURPOSE:To detect the generation of an arc without expecting the extinction of an arc current by detecting arc current on conditions that the current value is above the prescribed value and yet of irregular variation. CONSTITUTION:A differentiation circuit 6 passes through the portion of current variation. In the accident excluding an arc of the short in power system, etc., however, the current value is hardly changed and it is not passed through. The arc current in a power system and a troubled current are therefore discriminated by whether or not they can pass through the circuit 6. The size of the output of the circuit 6 is compared with the reference voltage by a level discriminating circuit 7 and in case of the output of the circuit 6 being larger a point (d) becomes a high level. When the high levelled condition is continued for the prescribed time, then, the point (d) becomes a low level and a relay contact 11 is turned on with the excitation of a relay coil 9. An over-current detecting circuit 5 is motioned similarly and turns a relay contact 10 on when the over-current holds the current value beyond the prescribed for the prescribed time. At the time when the prescribed time proceeded after the generation of an arc, relay contacts 10, 11 are turned on and an arc generation output signal is outputted, and the detection of the arc generation is enabled without expecting the extinction of an arc current.
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