Noninvasive Measurements and FEM Analyses for Estimating the Rotor Bar-Lamination Contact Resistance

This research work investigates the phenomenon of interbar currents in induction motors equipped with die-cast aluminum cages. Flowing in the lamination and distorting the bar current distributions, the interbar currents cause additional stray losses as well as an increase of the joule loss in the cage bars. The contact resistance between the bars and the rotor laminations is the key modeling element for a correct prediction of the interbar currents and the related extra losses. The study presents a new noninvasive method to obtain a reliable estimation of the contact resistance. The proposed hybrid approach is based on a mix of experimental data and Finite Element method (FEM)-based simulation results. A reliable three-dimensional FEM model of a four-pole 15-kW induction motor with closed rotor slots has been used to investigate the impact of variable contact resistance on the interbar currents, rotor joule losses, and the voltage drops along the bars, opening a new perspective for this complex phenomenon and its impact on the stray losses. Finally, the proposed methodologies are critically discussed and the obtained results compared with other relevant research works.