Currents and vibrations in asynchronous motor with externally induced vibration

This paper presents an experimental investigation of the airgap variation model for vibration and current harmonics relationship in induction motors. To this aim, an external vibration source was employed, together with ball bearing alterations in order to decrease stiffness. The direction of the external vibration is radial with respect to the axis of the electric machine under test. To maximize the effect of externally induced vibrations, the frequency chosen was near the flexural resonance of the rotor, determined by FEM analysis. During tests both currents and vibration of the machine were acquired. The test rig allowed to vary speed, vibration level and bearing stiffness. An electromagnetic brake provided a variable output load for the electric machine. The focus of the paper is the review of fault models used in literature. Radial effects are usually visible only in case of large failures that result in air-gap variations, as the experiments confirmed.