Theoretical analysis of shaft vibrations in two-pole induction machines considering static rotor eccentricity

Abstract

The paper shows a theoretical analysis of the shaft vibrations in two-pole induction machines, caused by a static rotor eccentricity. By neglecting field damping effects and considering maximum homopolar flux, a maximum radial magnetic force is calculated -as a worst case -acting on the rotor in the direction of the smallest air gap and oscillating with double supply frequency. This magnetic force is implemented into a simplified analytical rotor dynamic model, considering the oil film stiffness and the damping of the sleeve bearings. Based on this model the equations of motion of the shaft centre and the shaft journals are derived and the orbit movements are mathematical described. Additionally the paper shows that elliptical orbit movements of the rotor occur and that the amplitudes of the shaft vibrations are not only influenced by the magnitude of the magnetic force but also by the direction of the magnetic force.

Analytical Identification of Magnetic Faults Induced by Material Properties and Mechanical Tolerance in PM Synchronous Motor

“…The authors show that UMP can be quickly predicted by their developed Magnetic Equivalent Circuit (MEC) approach when the relative rotor eccentricity is less than 25% of the normal air-gap. Based on the motor shaft movement orbit from a mechanical point of view, Werner [8] uses shaft vibration signals to study induction motor static UMP due to the static eccentricity fault. On the other hand, Rajagopalan et al [9] use a field reconstruction method to study static UMP in a Permanent Magnet Synchronous Motor (PMSM) Bi et al [10] analyzed and calculated dynamic UMP within one motor revolution.…”

Rotor Vibrations in Electrical Machines Due to Electromagnetic Forces

“…In [5] the influence of the magnetic pull on the radial stability is investigated using such a model. A more sophisticated one is used in [6], where the focus lies on the investigation of the static eccentricity.…”