Dynamic harmonic field analysis of a cage type induction motor when magnetic slot wedges are applied

Applying magnetic slot wedges to stator slot openings is an effective means to reduce the slot ripple harmonic components in the magnetic field. To investigate the effect of the wedges in detail, this paper proposes a new harmonic field analysis method that considers the rotor movement dynamically and the harmonic components of the secondary current as induced current by a two-dimensional finite element method (2D-FEM) using a time stepping technique. The differences in harmonic characteristics due to the use of plural wedges (a nonmagnetic wedge and magnetic slot wedges in different dimensions) for the stator slot opening of a three-phase cage induction motor are evaluated using the method. Suitable wedge dimensions to reduce the slot ripple harmonics are determined. From the comparison of calculated and experimental results of secondary current, the proposed method is shown to be appropriate and useful for the quantitative estimation of harmonic fields for induction motors