Towards Practical Quantification of Induction Drives Mixed Eccentricity

As far as industrial applications of induction drives are concerned, one of the most critical issues is the statement of acceptable mixed eccentricity degree and of other mechanical abnormal conditions. These troubles cause characteristic spectral components in many drive quantities, but for economic reasons the electrical quantities, already sensed for drive control purposes, are preferable; among them current signals (i.e. MCSA) are the electric signals of choice to detect the machine conditions. Each trouble produces spectral lines at typical frequencies in the stator current: monitoring them is a usual procedure but the threshold to discern acceptable intrinsic defects from alarming situations is hardly defined. This paper presents an attempt to formulate a mixed eccentricity index developed through the interaction between static and dynamic eccentricity on stator windings and rotor cage. The index can be detected by a no-load test without any spectral resolution problem and it does not require any preliminary knowledge of machine health condition.