| 摘要 |
PROBLEM TO BE SOLVED: To shut off the power source circuit of a DC motor and an AC power source line immediately when there is a shorting fault of the DC motor by shutting off the AC power source line by activating a circuit breaker, thereby stopping the DC motor in case pump voltage falls down to reference voltage or below. SOLUTION: If the shorting of a coil of the DC motor 5 occurs at the time of current supply to a DC pump 5, overcurrent flows instantaneously to the DC motor 5 but the switching operation is instantaneously stopped by an overcurrent protection circuit 25 disposed at a switching power source 2 and, therefore, the voltage impressed to the DC motor 5 turns to 0. Then, the voltage drop is detected by a pump voltage drop detecting circuit 35 and the signal of the motor voltage zero is sent to a shutting section 63 of the circuit breaker 6, by which the power source circuit 10 and the AC power source line are shut off and the supply of the current to the DC motor 5 may be stopped. Since both are shut off immediately without the continuation of the operation until abnormality occurs and, therefore, safety is improved.
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