Estimation of Equivalent Thermal Conductivity for Electric Machine Windings Using Conformal Mapping Method

Abstract

It is important to predict the temperature distribution in the windings of electric machines, where the thermal model of an equivalent homogeneous material is used to simulate the winding conductors as well as the insulation and impregnation between the conductors. This article presents an analytical method for better estimating the equivalent thermal conductivity of the windings. According to the periodicity and symmetry of the heat flux field in the windings, the windings are segmented into square units, while the equivalent thermal conductivity of the whole windings is replaced with those of square units. Conformal mapping and equivalent transformation are used to reduce the complexity of solving the equivalent thermal conductivity of each square unit. Comparative study shows that the proposed analytical model is more accurate than the commonly used models. The partial stator temperature simulation was done to further verify that the proposed analytical model can be well applied to the actual windings. Experiments were conducted by fabricating and testing various winding samples, and a comparison between the finite volume method (FVM) thermal simulation and experimental tests verifies the accuracy of the proposed model.