[132] Determining induction motor air-gap eccentricity using vibration and motor current signature analysis (MCSA)

D Chen and S Ganeriwala
SpectraQuest Inc, 8227 Hermitage Road, Richmond, Virginia 23228, USA. 
Email: suri@spectraquest.com 

Diagnostics for induction motor faults is a serious issue for the improvement of plant reliability. Air-gap eccentricity between the rotor and stator can lead to power loss, a decrease in efficiency, current spikes and other complications, leading to premature failure of a motor. Motor current signature analysis (MCSA) and vibration data are being promoted for the diagnosis of induction motor problems. This paper will present a comparison of vibration and motor current signals for air-gap eccentricity fault signatures of an induction motor. Experiments were performed on an intentionally faulty motor with varying degrees of static air-gap eccentricity. Different levels of mechanical torque, imbalance and misalignment loadings were applied to the rotor side. The data was analysed using both vibration and motor current sensors. The results indicate significant components in the motor current spectrum due to rotor eccentricity. Vibration spectra results are inconclusive for these faults. However, vibration data provide a better indication of mechanical faults than the motor current data. The results suggest that both motor current and vibration measurements are required for more complete diagnostics of induction motors. 
Keywords: induction motor diagnosis, air-gap eccentricity, vibration signature analysis, motor current signature analysis, imbalance, misalignment.