Comparative study of thermal properties of electrical windings impregnated with alternative varnish materials

The thermal design‐analysis of devices with electrical windings impregnated using varnish materials is frequently challenging. This is due to difficulties in predicting theoretically the equivalent thermal properties for the composite materials, such as impregnated windings, in a reliable manner. The existing approach makes use of the impregnation ‘goodness’ factor, which allows for imperfections associated with the winding impregnation to be accounted for. This, however, requires experimentally derived data from appropriate material samples or machine assemblies. Considering relatively large range of commercially available varnishes, such data are often limited and are not readily accessible. In this investigation, a set of three alternative varnish materials commonly used in impregnation of low‐voltage electrical windings has been evaluated. To provide better understanding of the material impregnating properties, data from multiple impregnations are also provided. The experimental findings have been supplemented with theoretical analysis on the impregnation ‘goodness’ and stator‐winding contact thermal resistance for a selected winding construction. To highlight the importance of appropriate input thermal material data, a case study machine design is thermally analysed.