Loading Effect on Induction Motor Eccentricity Diagnostics Using Vibration and Motor Current

Abstract

Diagnostics of an induction motors is serious issue for improving plant reliability. Air gap eccentricity between rotor and the stator can lead to power loss, decrease in efficiency, current spikes, and other complications leading to premature failure of a motor. Motor current signature analysis (MCSA) and vibration data are commonly used for diagnosing induction motor problems. However, the effect of mechanical loading on the fault signature is not clear. This paper will present a comparison of vibration and motor current signals for induction motor subjected to different levels of torque, unbalance and misalignment loading air gap eccentricity fault signatures. Experiments were performed on intentionally faulted motor with varying degrees of static air-gap eccentricity. Different levels of mechanical torque, unbalance and misalignment loadings were applied to the rotor side. The data was analyzed using both vibration and motor current sensors. Results indicate significant components in motor current signature to due rotor eccentricity and torsional mechanical loadings. Vibration spectra do not provide a clear picture air gap eccentricity fault. But 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.