Characterising the performance of selected electrical machine insulation systems

This paper presents results from an analysis of alternative slot liner materials used in the construction of electrical machines. The slot liner material has a vital safety critical function within a machine assembly, providing electrical insulation between the winding body and stator core pack. Performance measures for the slot liner material include the dielectric breakdown voltage, tensile strength, thermal conductivity and thermal class, amongst others. There is a large variety of slot liner materials available on the market with the material properties altered to suit a particular application. Some of these material properties are strongly dependent on the components and processes employed in construction of the complete winding assembly e.g. type of the winding impregnation and/or method used in impregnation of the stator/winding assembly. Consequently, the manufacturer provided data is usually inadequate when comparing various insulation systems and their individual elements for a particular machine construction. This research is focused on the conductive heat transfer phenomenon from the winding body into the machine periphery in context of the slot liner material used, for a given impregnation type and method. The repeatability of the winding manufacture process is also investigated. Three alternative slot liner materials with different thermal conductivity and ability of absorbing varnish impregnation have been chosen for prototyping of representative stator/winding hardware exemplars. This has been supplemented with a batch manufacture of the stator-winding hardware exemplar for a selected slot liner material. The proposed experimental approach allows for the complete insulation system to be evaluated accounting for the assembly and manufacture nuances. The results suggest that the use of a particular slot liner has an impact on the winding heat transfer and also implications regarding appropriate manufacture and assembly processes used, i.e. some of the materials require special handling. The experimental work has been supplemented with theoretical analysis to provide a more comprehensive insight into the winding heat transfer phenomena.