Theoretical Analysis of Lateral and Torsional Vibrations Coupled by the Electromagnetic Air Gap Field of Soft Mounted Induction Motors Under Torque Excitation

Purpose In the paper a theoretical analysis is presented in which lateral and torsional vibrations are coupled by the electromagnetic air gap field of soft mounted induction motors under torque excitation. Methods The mathematical formulations are derived based on a multibody vibration model of an induction motor mounted on a soft foundation and coupled with a load machine, taking into account torque excitation by dynamic air gap torques of the induction motor and dynamic torques of the load machine. Results By analyzing the differential equation system, the influence of the torsional electromagnetic coupling in the air gap of the induction motor is shown, leading in combination with an elastic foundation to a coupling between lateral vibrations of the induction motor and the torsional vibrations of the drive train. Beside the mathematical analysis also a numerical example is presented where the lateral and torsional vibrations of a 2-pole induction motor with journal bearings and flexible rotor, mounted on an elastic steel frame foundation and coupled with a load machine, are analyzed. Conclusion In addition to typical lateral vibrations of soft mounted induction motors, such as bearing housing vibrations, relative shaft vibrations and foundation vibrations, also the torsional vibrations of the drive train are discussed and their coupling by the electromagnetic air gap field could be shown. Finally, the paper serves as a theoretical academic/scientific basis for future research, from which measurements and detailed finite element analyses can be derived, leading to practical benefits for engineering.