| 摘要 |
PURPOSE:To judge whether the resistance value of a liquid resistor is normal or not without disconnecting the resistor from a secondary circuit by supplying a current to the primary widing of an induction motor from a constant-voltage circuit at stopping time, inducing a voltage in a secondary winding, and supplying a secondary current thereto. CONSTITUTION:When the contactor 2 of a main circuit of an induction motor 4 is opened, a switching unit 3 of a constant-voltage circuit is closed to supply a current to the primary winding of the motor 4. When the current value is smaller than the current value necessary to start the motor 4, the motor 4 is not started, but stopped, and the motor 4 is regarded as a transformer. Thus, a voltage according to the winding ratio is induced in the secondary winding, and a current flows to the secondary circuit. The current is detected by a current transformer 5, and the secondary current of the transformer 5 is input to an alarm setter 6. The values corresponding to the upper and lower limits of the normal range of the resistance value of a liquid resistor 7 are set in advance in the setter 6, when it exceeds it, it is regarded as the change in the resistance value of the resistor 7 so that an alarm is output externally. |
