Electromechanical Interaction in Rotor Vibrations of Electric Machines

In electric machines the electromagnetic fields interact with the deformations of machine structures. At low frequencies the electromagnetic system may couple distinctly with the mechanical one. This electromechanical interaction changes the vibration characteristics of the machine; e.g., it may induce additional damping or cause rotordynamic instability. To study these interaction effects, an electromechanical simulation model for the rotor vibrations of electric machines was developed. A time-stepping, finite element analysis was used for the solution of these system equations. The complete system is non-linear due to the saturation of magnetic materials. In addition, a spatially linearized version of the complete simulation model was developed. In this model, the effects of nonlinear saturation can be calculated before the actual simulation. The developed simulation models were applied to study the vibration characteristics of a modified 15 kW electric motor. The impulse excitation exerted on the rotor was used as the loading for the transient analyses. The rotordynamic stability was illustrated by plotting the orbits of the rotor with two separate shaft stiffness. In addition, the response signals and frequency response functions obtained by the simulation models were compared. The complete and linearized models yielded almost similar results. These numerical results indicate that the linearized simulation model can be used as a good approximation for the electromechanical interaction in rotor vibrations of electric machines. Moreover, the linearized model is numerically very effective compared to the complete simulation model.