Effect of load on detecting mechanical faults in small induction motors

Mechanical conditions, such as load unbalance and shaft misalignment in induction motors can be detected by monitoring specific components in the stator current frequency spectrum. Previous work tested these mechanical conditions for the cases of no-load and full-load conditions in small induction motors, assuming that the effect of load on the detection scheme between these two conditions is linear. This paper examines the effect of changing the load of the motor on detecting these mechanical conditions in both the current and vibration spectra. The paper shows that the spectral components associated with mechanical conditions do not always linearly change as the load varies. It shows that other factors, such as mechanical resonance in the coupled systems, affect these spectral components. Experimental results for testing different types of mechanical faults, with the load changing from no-load to full-load, are shown.