Abstract
The lifetime of an electrical machine mainly depends on the thermal overloading. Modern day applications of electrical machines on one hand require compact machines with high power density, while on the other hand force electrical machines to undergo frequent temperature cycling. Until recently, in the case of electrical machines, the main factor related to the degradation of the winding insulation was thought to be the thermal oxidization of the insulation materials. It has now been revealed that thermal overloading can also induce mechanical stress in the windings of electrical machines, which over time could lead to fatigue and degradation. In this paper, a comprehensive study of the thermally induced mechanical stress in the windings of an electrical machine is presented. The study is performed using combined thermo-mechanical models. The numerical results are validated by experiments on a segmented stator winding set-up.
Highlights
IntroductionSeveral modern day applications cause the temperature in the drive-train to vary continuously
Several modern day applications cause the temperature in the drive-train to vary continuously.In industrial drive-trains, for example, in weaving looms, the variation can be cyclic
[24],could rapid thermalcause cycling with discharge the winding temperature some reports on effects of mismatch of thermal expansion coefficients were found, the actual study greater than 120 ◦ C could lead to the fatigue crack between the copper and the insulation or within the on the thermally induced mechanical stress in the windings of an epoxy impregnated traction motors insulation was layers
Summary
Several modern day applications cause the temperature in the drive-train to vary continuously. In industrial drive-trains, for example, in weaving looms, the variation can be cyclic. In applications such as electric vehicle drive-trains, the temperature variation can be non-cyclic. The temperature variation in the drive-trains has significant effects on all its components, especially the power electronics and the electric motors [1]. One main source of heat in an electrical machine is the power loss in the stator winding. Improper heat removal leads to reduced lifetime of the windings [6] and the machine, due to the degradation of copper wires and the coatings which is caused by rapid oxidization of the coatings [7]. The difference in the coefficient of thermal expansion between the epoxy, coating and the copper wires might lead to thermally induced mechanical stresses in the windings which subsequently cause degradation of the windings
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