| 摘要 |
PURPOSE:To improve the accuracy of the level sensing of the currents of an accident by enabling an output only when the voltage of a power circuit is sufficient for operating a control circuit. CONSTITUTION:Outputs from current transformers 21, 22 detecting the currents of AC cable ways 11, 12 are converted into currents in the single direction by a rectifier circuit 30. A power circuit 500 and current detecting resistors 40-42 are connected in series with an output terminal for the rectifier circuit 30, and potential difference among both ends of the current detecting resistors 40-42 is amplified respectively by differential amplifiers 60-62. A keying circuit 120 is controlled by outputs from these differential amplifiers 60-62, and an interrupting mechanism is operated. An under-voltage operation inhibition circuit 50 inhibits closing from opening in the keying circuit 120 when the voltage of the power circuit 500 is insufficient for working the differential amplifiers 60-62 and a time limit circuit 70.
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