The impact of thermal degradation on electrical machine winding insulation

Inter-turn stator short circuits can develop quickly leading to serious damage of an electric machine. However, degradation mechanisms of winding insulation are not yet fully understood. The main contribution of this article is analysis of the impact of thermal ageing on the electrical properties of winding insulation. The insulation samples have been aged thermally at 200-275 °C and for 100-1600 hours. After aging, impedance spectroscopy measurements were undertaken on the samples and equivalent circuit model (ECM) parameters fitted for each measurement. This allows the impact of thermal ageing on ECM parameters to be analysed, giving insight into the changes of the electrical properties of the insulation. Ultimately this will lead to development of new methods for remaining life prediction of electrical machine windings.