Detection of static and dynamic eccentricities in a permanent magnet motor by monitoring BEMF

One of the major faults of electric motors is a breakdown of bearing because it is the most flexible component under cyclic loading between stator and rotor. Most of bearing faults in electric motors result from localized defect of bearing and generate vibration and noise, which eventually degrades the performance of motor-driven systems. Many researches have been proposed various methods to detect bearing faults by measuring vibration and noise. In electrical point of view, bearing fault changes static and dynamic air gap, which change magnetic field and input current of electric motors. Several researchers studied the diagnostic technique of motor faults by monitoring vibration and current. However, another possible signal of electric motors due to static and dynamic eccentricities is back electromotive force (BEMF) and this research proposes a method to detect static and dynamic eccentricities of a permanent magnet (PM) motor by measuring BEMF. It derives mathematical equations of BEMF due to static and dynamic eccentricities of a PM motor, and performed experiment to validate the derived equations.