Rotordynamic Simulation Method of Induction Motors Including the Effects of Unbalanced Magnetic Pull

In rotating electrical machines, unbalanced magnetic pull (UMP) is unavoidable phenomenon because it results from manufacturing tolerance and machine vibration. From the viewpoint of rotordynamics, the UMP results in additional vibration and bearing wear. These effects are gaining interest owing to the increase in the demand for high speed electrical machines. This poster presents the rotordynamic simulation method of induction motors including the effects of unbalanced magnetic pull (UMP). The developed simulation method including rotor eccentricity and UMP force models is simplified, but still accurate for applying to the actual design process of induction motors, i.e., these models are optimized for rotordynamic simulation of induction motors. First, axial-varying mixed rotor eccentricity is modeled based on time-step rotordynamic simulation concept. This eccentricity model can include static, dynamic and axial-varying eccentricities simultaneously for considering actual rotor eccentricity condition. Second, a simple analytical UMP model is used for calculating resultant UMP forces with several assumptions. This model uses the magnetizing current without calculation of the rotor current and the effects of the slot opening and saturation are initially incorporated into the model by using the Carter factor. To improve the accuracy of the model, the magnetizing current is calculated by the finite element analysis (FEA), and the proposed correction factor is built into the model. This correction factor is also calculated by the FEA. Based on the developed rotor eccentricity and UMP calculation model, rotordynamic simulation process within the induction motor design process are proposed and tested in a standard four-pole induction motor. The simulation results show that inclusion of the UMP force reduces the critical speeds and generates electromagnetic excitation. The study further shows that the effects of UMP vary with a change in static eccentricity, dynamic eccentricity, slip and bearing stiffness. Finally, based on the results, a utilization plan of the developed methods is proposed.