Comparison of thermal stresses developed during transients on a damaged rotor cage

Structural defects in the rotor cage of large electrical machines significantly impact their expected operational lifetime. This work simulates the stresses developed in a damaged rotor cage during different transient profiles and for different sizes of the imperfection. A combined model featuring electrical, thermal and mechanical stages as well as three different meshes reflecting a progressing narrowing of one of the bars in its junction to the end ring are used for this purpose. The results qualitatively agree with a previously presented fatigue test and show that under severe conditions the capability of aluminum to absorb stress is limited, and a state of plastic deformation is rapidly reached. The effect of a possible mitigation strategy is also studied.