Estimation of Equivalent Thermal Conductivity for Electrical Windings with High Conductor Fill Factor

In order to improve accuracy and reduce model setting up and solving time in the thermal analysis of electrical machines, the multi-material winding region is frequently homogenized. A typical electrical winding is an amalgam of the conductor material, electrical insulation, impregnation and imperfections like air cavities, which depend on the impregnation material and technique, among other factors. This makes the winding assembly one of the most challenging region in thermal design of electrical machines. This paper presents an analytical method for estimating the equivalent thermal conductivity of impregnated windings formed with round profile conductors. The existing analytical methods are limited to windings with conductor fill factor up to 40%. However, the ongoing development in fabricating windings enabled winding arrangements with much higher conductor fill factors, up to 85%. Such high conductor fill is very desirable as it reduces the winding DC power loss while improving the thermal path for the generated heat. Thus, providing a reliable analytical approach for the estimation of the equivalent thermal conductivity, applicable across a wide range of conductor fill factors, is very desirable. This paper presents a detailed description of the proposed approach, supplemented with measured data from tests on hardware winding material samples (WSs). An illustration of a practical use of windings with high conductor fill factors is also provided, highlighting the benefits of such configuration.