Air-Gap Flux Analysis for Cage Rotor Diagnosis

Abstract

The fault diagnosis of an induction motor by analyzing the abnormal frequency components of the current or power waveform has been already proposed by the authors, and its characteristics with faulty cage rotor such as broken bars have been presented also. As the results, it becomes clear that the amplitude of abnormal component of the stator currents and so on, increases with the number of broken bars, while it decreases with the number of broken end-rings, in the case of consecutive fault positions within 90 degree in electrical angle. So, in this paper the more direct diagnosis methods by detecting the air-gap flux are investigated to avoid the above inconsistency.
In this paper we discuss in detail the relation between the various fault conditions and the MMF distributions of a three-phase induction motor with faulty cage rotor such as broken bars and endrings, and analyze quantitatively the search coil output and its harmonic component to detect those faults adequately from the air-gap flux density. The measured results obtained by the artificially faulted machine demonstrate the availability of those analytical results and this diagnosis method.