Diagnosis of eccentricity in induction machines working under fluctuating load conditions, through the instantaneous frequency

This paper introduces a methodology for diagnosing mixed eccentricity fault in squirrel cage induction machines which work under variable load conditions in generator or motor mode; the method is based on the extraction of the instantaneous frequency of the fault related component of stator currents during speed transients, caused by load changes. It is shown that under these conditions, the instantaneous frequency plot of the main fault component versus the slip is a straight line with a specific slope and offset. In addition and for a given pole pair number, this pattern is not dependent on the machine features, nor the way in which the load changes. Besides, the practical methodology of this technique is introduced for diagnosing mixed eccentricity. The approach is validated by laboratory tests.