| 摘要 |
PROBLEM TO BE SOLVED: To reduce shock and noise in a power source switchover and ensure a low-cost and reliable structure, in a variable-speed man conveyor. SOLUTION: A variable-voltage, variable-frequency(VVVF) device 1 converts a three-phase alternating current from commercial power sources R to T into a three-phase alternating current of a variable voltage and a variable frequency, and supplies it to a driving induction motor 2. With starting contacts 16a to 16c opened, the VVVF device 1 generates an alternating current having a lower frequency than the commercial power sources R to T and gradually increases the frequency until it reaches the frequency value of the commercial power sources R to T, when the motor 2 is disconnected from the VVVF device 1 and left idling. After the lapse of a fixed time, when the residual voltage of the motor 2 drops, contacts 17a to 17c are opened to connect the motor 2 to the commercial power sources R to T for a high-speed operation.
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