On the capability of heat dissipation in thermally aged electrical machines

Thermal aging is one of the main causes of progressive deterioration of the insulation system in electrical machines. This because the thermo-physical properties of dielectric materials can undergo severe changes when exposed to high temperature. Accordingly, thermal aging has a twofold effect, namely, shortening the expected insulation lifetime and influencing the heat transfer / dissipation towards the surrounding. This paper aims at analyzing the second aspect through an in-depth experimental investigation. A case-study motor is thermally modelled with the purpose of quantifying the extent and magnitude of thermal conductivities change, resulting from the insulation thermal aging. As an outcome, it is found that the hot-spot temperature in a thermally-aged machine can be considerably higher than its unaged counterpart, for given operating and boundary conditions.