To provide a variably speed motor driving system at a low cost in which the same inverted equipment can be shared for driving a main motor and a subsidiary motor.
This system supplies three-phase AC voltage of a specific voltage at a specific frequency to a three-phase induction motor 4 for a feed water pump, from an inverter equipment INV, and drives the pump at a specific rotational speed. In this case, a three-phase bridge rectifying circuit 5 for rectifying the three-phase AC voltage which is outputted from the inverter equipment INV and gas variably frequency and voltage is installed. A variably DC voltage which is identical to the terminal voltage of the three-phase induction motor 4 is supplied to a DC motor 6 for driving a pump for chemical liquid injection. The rotational speed of the DC motor 6 changes almost in proportion to that of the induction motor 4, so that the amount of sterilizing chemical liquid supplied to feed water can be automatically controlled in proportion to the amount of the feed water. Thereby a simple equipment can be constituted at a low cost by using a single inverter, and the installation space can be saved.
ENDO TSUNEHIRO
SUGINO HIDENORI
TAGUCHI YOSHIYUKI
