Assessment of Different Cooling Techniques for Reduced Mechanical Stress in the Windings of Electrical Machines

Abstract

Thermal loading can induce mechanical stresses in the windings of electrical machines, especially those impregnated with epoxy resins, which is mostly the case in modern traction motors. Although designers look for cooling techniques that give better performance in terms of the power density and efficiency of the machine, several thermal cycles can lead to fatigue and the degradation of the copper insulation, epoxy and consequently the windings. In this paper, the performance of different cooling techniques has been compared based on the temperature distribution and the mechanical stress induced in the windings. Three-dimensional finite element thermo-mechanical models were built to perform the study. Two different variants of water jacket cooling, two configurations of direct coil cooling and two cases of combined water jacket and direct coil cooling methods have been considered in the paper. The results show that the combined water jacket and direct coil cooling perform the best in terms of the temperature and also the mechanical stress induced in the windings. An experimental set-up is built and tested to validate the numerical results.