Assessment and improvements of inorganic insulation for high temperature low voltage motors

The increase of internal temperature capability of electrical machines is a major challenge for building high power density actuators for many applications in transport systems and in aerospace industry. Today, the main limit is the thermal class of the organic Electrical Insulation System (EIS), but a breakthrough toward very high temperature is possible with inorganic insulation technologies. An inorganic EIS is proposed and tested for designing motors able to work permanently up to 500 °C in the heart of windings. After a review of several high temperature (HT°) insulation solutions, the paper focuses on currently available ceramic-coated wires insulated with a very thin inorganic layer, which is a favorable solution for high current densities in machines of small sizes. The electrical limits of this technology are investigated, the weak points of the HT° wire are circumvented using impregnating cements able to provide adequate mechanical and electrical properties up to 500°C for designing HT ° electrical machines fed by a standard PWM inverter connected to the HVDC bus of the more electric aircraft, for example.