Novel Investigation of Influence of Torsional Load on Unbalance Fault Indicators for Induction Motors

This paper investigates how the torsional load affects two vibration-based unbalance fault indicators. This investigation is important for unbalance fault diagnosis in multiple constant load conditions, which are unavoidable for many rotating machines. Coupled flexural–torsional dynamics of an unbalanced disc–shaft system, as the representative of an induction motor, is investigated via a continuous shaft–beam model. Numerical investigations reveal that the fundamental rotating intensity of the transversal acceleration is independent of the torsional load. So, the novel speed-invariant version of this indicator, which is obtained by normalizing the fundamental rotating intensity by the fourth power of the rotational speed, is also load-independent. The comprehensive experimental trials confirm load-independency of the considered two unbalance fault indicators. The important novel outcome is that, by conducting numerical analysis and comprehensive experimental trials with a belt conveyor system under various constant loading conditions, the load-independency of the fundamental rotating harmonic intensity as well as novel speed-invariant unbalance feature are justified.