Characterizing the in situ Thermal Behavior of Selected Electrical Machine Insulation and Impregnation Materials

This paper presents results from an analysis of thermal behavior for alternative slot liner insulation and varnish impregnation materials used in the construction of electrical machines. These materials are typically characterized by the individual material properties altered to suit a particular application. However, the manufacturer provided material data are usually inadequate when comparing the complete insulation systems. This research is focused on the conductive heat transfer from the winding body into the machine periphery in context of the complete insulation system. An experimental approach using the stator-winding segment subassembly has been adopted here, for the representative in situ heat transfer measurements. The effects of impregnation “goodness,” in volume manufacture repeatability, and individual versus in situ material physical properties on the stator-winding thermal behavior are discussed in detail. The results suggest that the use of a particular slot liner insulation and varnish impregnation has a prominent impact on the winding heat transfer, as well as appropriate manufacture and assembly processes used. The experimental work has been supplemented with theoretical analysis to provide a more comprehensive insight into the winding heat transfer phenomena; in particular the winding-to-slot contact thermal resistance.