Modification of polyphase induction motor performance by introduction of E. M. F. in secondary

The possibility of obtaining speed adjustment and power factor correction of induction motors by impressing an e. m. f. on the rotor is a subject which has attracted considerable attention in recent years. As compared with the straight polyphase induction motor, the graphical treatment in this case becomes much more involved, if reasonable account is to be taken of all the phenomena. The analytical treatment of the polyphase induction motor is, however, readily extended to the case when an e. m. f. is impressed on the rotor. There appears to be a general impression that in deriving formulas analytically the usual method based on the rotating magnetic field theory is no longer suitable when a voltage is impressed on the rotor, but that it is preferable to resolve the induced e. m. f. in the rotor into two components. This paper is an attempt to show that not only is the rotating field theory still applicable, but that the results can probably be obtained most readily by means of it.