2 Faults in Induction and Synchronous Motors Bilal Akin, Ph.D. Texas Instruments
Mina M. Rahimian, Ph.D. Texas A&M University
2.1 Introduction of Induction Motor Fault This section briefly summarizes motor fault conditions and their cause, especially for the induction motor. The eccentricity related faults, broken rotor bar faults, bearing faults, and stator faults, which account for more than 90% of overall induction motor failures, are considered [1–3]. 2.1.1 Bearing Faults Bearing faults account for more than 40% of all electric motor failures [5–7]. Most of the bearings in industrial facilities run under nonideal conditions and are subject to fatigue, ambient mechanical vibration, overloading, misalignment, contamination, current fluting, corrosion, and wrong lubrication. These nonideal conditions start as marginal defects that spread and propagate on the inner raceway, outer raceways, and rolling elements (see Figure 2.1). After a while the defect becomes significant and generates mechanical vibration causing acoustic noise. Basically, bearing faults can be classified as outer raceway, inner raceway, ball defect, and cage defect, which are the main sources of machine vibration. These mechanical vibrations in the air gap due to bearing faults can be considered as slight rotor displacements, which result in instant eccentricities. Therefore, the basic fault signature frequency equation of line current due to bearing defects is adopted from eccentricity literature [10]. Mechanical vibration, infrared or thermal, and acoustic analyses are some of the commonly used predictive maintenance methods to monitor the health of the bearings to prevent motor failures.
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