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

Abstract

This paper presents an optimal method for rotordynamic simulation of induction motors, including the effects of unbalanced magnetic pull (UMP). The developed simulation method containing the UMP model is simple but still accurate for the actual design process of induction motors. The UMP model is simplified by using the magnetizing current without calculation of the rotor current. 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 also built into the model. Moreover, mixed eccentricity is modeled and applied to the time step rotordynamic simulation for considering the actual rotor eccentricity condition. Based on the developed UMP and eccentricity models, rotordynamic simulation methods 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.

Winding Tensor Approach for the Analytical Computation of the Inductance Matrix in Eccentric Induction Machines

“…These constraints can be formulated as in (26). The old set i b of n b + 1 rotor currents (n b − 1 current loops that include the bars plus two end ring currents) can be obtained from the new set i r of n b − 1 currents (just the current loops containing the bars), using (32) and (33), as…”

“…Using the circuit transformation tensor C i in (34), which transforms branch resistances into loop ones, as in [57,58], the resistance matrix of the rotor R r that includes the current constraints (32) and 33is…”

“…Besides, in case of a faulty machine, the air gap length or the configuration of the windings may become asymmetrical, making it difficult to use labour-saving procedures that are valid only for symmetrical conditions. In particular, the eccentricity fault [32,33] gives rise to a non-uniform air gap length, which becomes a function of the angular coordinate. Moreover, this function can be different for each rotor position [34].…”

Unbalanced Magnetic Pull Effects on Rotordynamics of a High-Speed Induction Generator Supported by Active Magnetic Bearings – Analysis and Experimental Verification

“…The parameters in the model were estimated by using an impulse method based on FEA. Kim et al [5], [6] developed a rotordynamics simulation method based on a mixed rotor eccentricity model for time-step analysis in an induction motor. They proposed an optimal way to calculate the UMP force by using a simple analytical model and its update with FEA.…”

“…The objective of this study is to simulate the effect of UMP in an actual industrial induction machine accurately and efficiently by using a previously studied semi-analytical UMP model [6], and then verify the results experimentally. Specifically, the study focuses on a method to verify the UMP effect on rotordynamics rather than the UMP force itself because the vibrational effect of the UMP is directly related to the rotordynamics of the machine.…”