Windings of electrical machines are impregnated with an epoxy resin to enhance cooling. However, as copper and epoxy have a different thermal expansion coefficient, so-called, thermally induced mechanical stress occurs in the stator windings. This mechanical stress can lead to fatigue and degradation of the insulation over time, causing the machine to fail. Two elements have a significant impact on this mechanical stress: the load pattern and the cooling system. The former can lead to thermal cycling and the latter can have an impact on the temperature distribution in the motor and thus also the mechanical stress.
The first step is to get started with thermal models that are available in the literature and to validate these on a setup to estimate the previously mentioned mechanical stress. This lumped parameter model will be tested primarily during static loading. Once the static behaviour is correctly modelled, the thermal model will be enhanced to incorporate thermal cycling. To validate the model for this phenomenon, a dynamic load cycle will be imposed to the device under test (stator of an induction machine).