Abstract
Poly Pha c Induction Motor is an asynchronous motor and rues with a slip fro n the synchronous speed or the speed of the speed of the rotating field flux.
The slip of nduct on motor changes with the mechanical load and gives some flexibilities between the motor and the load.
For the requrirements of a constan speed runing with adj sta le speed the Induction Motors are more reliable than Synehron us Motor which has a consant speed without slip for any n_echanical load.
Induction Motor, however, has a nature to slip down for any mechanical load to produce the torque just equal to that of the load.
The writer explains a combination of Induction motor and a special frequency changer to keep the speed constant and independent to the primary frequency, primary e. m. f. and the mechanical load.
The idea of the principle is to keep the difference between the primary frequency f1 and secondary frequency f2 constant by a special frequency changer.
Speed of Induction Motor is repres nted by
n=120(f1-f2)/P
P=Number of Poles of the Induction Motor.
The secondary frequency of the frequency changer is represented by
f2=f1-n'P'/120
P'=Number of poles of the frequency changer.
n'=Number of revolution of the frequency changer.
Substituting the above equation to the value of n, we have
n=n'P'/P
For the constant values of P and P', n is proportional to n' which may easily be kept constant and therefore the speed of Induction motor should be constant and also adjustable by regulating the speed of the frequency charnger n'.
