Current variation in a rotor bar during transients due to a hot spot

This paper presents an initial study to provide further insight on the conditions under which a natural bar breakage was reproduced experimentally. With this aim several magnitudes at a rotor bar's narrowing (hot spot) in an induction motor during heavy transients: long startup and plug stopping, are calculated in order to compare it with the experimental data, which suggested that the bar breakage process can be modelled by thermal fatigue. A combined analytical electrical and thermal procedure is used to obtain the current and temperature distribution in the cage based on values previously computed by 2D electromagnetic FEM, whilst the temperature, resistance and final stresses at the defect are calculated by Finite Element Analysis. The results show that the asymmetric heating alters the current distribution in the cage throughout the transients and that the interbar currents play a fundamental role in the evolution of the defect.