Diagnostics of rotor-cage faults supported by effects due to higher MMF harmonics

The main task of this paper is to analyze changes in the Fourier spectra of the stator phase currents due to arbitrary faults of an induction motor cage. In the work special attention has been paid to the effects caused by higher MMF harmonics to look for its application in cage fault diagnostics. In order to do it, a mathematical model of induction motors with faulty cage accounting for higher MMF harmonics of all windings has been developed in the paper. Commonly, the state of a cage is examined on the basis of the component of the stator phase current with frequency (1 - 2s)f₀. In the paper it is shown that for some cage faults this component can be insufficient for correct diagnosis and additional components in stator currents generated by higher space harmonics can support a diagnosis.