Lateral vibrations of soft mounted converter-fed induction motors caused by dynamic air gap torques: a mathematical analysis of orbital movements

摘要

This paper shows that dynamic air gap torques in converter-fed induction motors may not only cause torsional vibrations in the drive train, but may also cause lateral vibrations of the motor itself-including bending vibrations of the rotor shaft-, if the motor is mounted on a soft foundation. Based on a simplified analytical model, the mathematical correlation between rotor-stator interaction, oil film characteristics of sleeve bearings, the influence of a soft foundation-coupling angular and lateral displacement of the stator-and excitation from dynamic air gap torques is shown. In addition to the absolute orbits of the rotor, stator, shaft journals and bearing housings, also the relative orbits between rotor and stator and between shaft journals and bearing housings are mathematically described. Further, the paper shows the influence of the oil film coefficients of the sleeve bearings on the elliptical shape of the orbits. Therefore, the paper presents a possibility to optimize the whole system-converter, motor and foundation-concerning lateral vibrations, caused by dynamic air gap torques.