Asmo Tenhunen

Calculation of eccentricity harmonics of the air-gap flux density in induction Machines by impulse method

The rotor eccentricity creates extra harmonics into the flux-density distribution in the air gap. Together with the fundamental field-component, these harmonics create the total force acting between the stator and eccentric rotor. The paper presents a new application of the impulse method, which enables the calculation of the harmonics of the flux density distribution when the rotor is eccentric. The idea of the application is to move the center point of the rotor from its central position for a short period of time during transient finite-element calculation. The flux-density harmonics are then calculated from the response and excitation signals.

Spatial linearity of an unbalanced magnetic pull in induction motors during eccentric rotor motions

There is an unbalanced magnetic pull between the rotor and stator of the cage induction motor when the rotor is not concentric with the stator. These forces depend on the position and motion of the centre point of the rotor. In this paper, the linearity of the forces in proportion to the rotor eccentricity is studied numerically using time‐stepping finite element analysis. The results show that usually the forces are linear in proportion to the rotor eccentricity. However, the closed rotor slots may break the spatial linearity at some operation conditions of the motor.

Numerical Identification of Electromagnetic Force Parameters for Linearized Rotordynamic Model of Cage Induction Motors

The electromechanical interaction in cage induction motors induces additional forces between the rotor and stator. Recently, a linear parametric model was presented for these forces, and the corresponding model was combined with a mechanical rotor model. The electromagnetic system is usually non-linear due to the saturation of magnetic materials. Thus, the effective identification of the force parameters is crucial. Initially, the parameters were identified numerically from the response induced by the whirling rotor. Later on, a method based on the impulse response analysis was presented. The aim of this study was to present the theoretical background of this impulse method, and to present some useful additional features. The derived equations show the mathematical equivalency of this impulse method and the previous whirling method. The results show that the impulse method is numerically effective. In addition, the feasibility of thus obtained simple electromechanical rotor model was demonstrated.Copyright