| 摘要 |
PURPOSE:To protect overcurrents within the whole speed range by providing a pattern generating means through which an allowable current value is changed in response to the alteration of a cooling effect. CONSTITUTION:A frequency signal F is guided to an allowable-current pattern generator 21, and allowable currents IT corresponding to a cooling effect varying with the speed change of an induction motor 5 are outputted from the allowable- current pattern generator 21. An adder-subtractor 23 arithmetically operates a deviation between peak actual currents IP and allowable currents IT and inputs it to an integrator 24, and inputs an output from the integrator 24 to a comparator 16. The output from the integrator 24 is increased when the motor 5 is brought to overload, and the induction motor 5 is stopped when the output from the integrator 24 is made larger than a value of a setter. |
