Characterising the ‘in situ’ Thermal Behaviour of Selected Electrical Machine Insulation and Impregnation Materials

This paper presents results from an analysis of thermal behaviour for alternative slot liner insulation and varnish impregnation materials used in the construction of electrical machines. These materials are typically characterised by the individual material properties altered to suit a particular application. However, the manufacturer provided material data is 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 behaviour 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.