Some concepts involved in the analysis of the magnetic field in cage induction machines

The precise meaning of terms widely used in the analysis of harmonic fields in the airgaps of rotating machines is examined. The available methods of analysis of induction-motor fields are compared, and a simplified approach to field harmonics involving the concept of modulation is outlined. The flux components observed at stator and rotor in a cage-rotor machine are classified, and their relative significance in producing loss is examined by experiment. An unusual method of displaying the total flux spectrum is demonstrated, and this clearly shows that considerable simplification is possible by neglecting certain harmonics that, in the case of loss, are relatively unimportant.