EFFECTS OF ROTOR ECCENTRICITY AND PARALLEL WINDINGS ON INDUCTION MACHINE BEHAVIOR - A STUDY USING FINITE-ELEMENT ANALYSIS

An eccentrically-positioned rotor in a rotating electric machine experiences a strong unbalanced pull toward the short side of the air gap. The air gap flux density and magnetic force distributions exhibit new harmonics resulting from the nonuniform air gap. Use of parallel windings reduces the net unbalanced pull by allowing different amplitude currents to flow in the parallel branches. In this paper, rotor eccentricity and the effect of parallel windings in an induction motor are investigated by means of a transient finite element model. Magnetic flux density and force distribution harmonics generated by the model are presented for the cases of static and dynamic rotor eccentricity, with various combinations of series and parallel stator winding connections. These results are compared with those obtained from a centered rotor case. Examples of the action of parallel- connected windings to reduce the effects of rotor eccentricity are given.