| 摘要 |
PURPOSE:To make it possible to control one of two motors continuously by a method wherein when the total r.p.m. of the motors is more than 150% which corresponds substantially to the maximum capacity of a frequency converter, the other motor is made to be driven through a commercial power source so that no load larger than the maximum capacity of the frequency converter is applied on the frequency converter. CONSTITUTION:In case where it is necessary to supply large power to the motors M in order to keep the temperature of feed water in the cold water tower 10 at a set value, a control device 12 turns switches SW1 and SW4 ON on the base of the detecting value of a detecting means 11 and one of the motors, namely the motor M 1 is driven by the commercial power source while the other motor M2 is driven by the frequency converter 14. Next, a PID controler 13 controls the rate of frequency converter 14 to a desired value so that a blower generates an amount of blowout air sufficient to keep the feed water temperature constant. Accordingly, the motor M1 rotates with 100% r.p.m. while the motor M2 is driven by a frequency changed electric current depending on the condition of load applied thereon and the rotation of the motor M2 is controled continuously.
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