Towards a partial discharge free insulation system for the More Electrical Transportation

Currently, electric motor manufacturers install a ground and turn insulation capable of withstanding normal operating voltages without exceeding the dielectric strength of the air. If the electric field generated during operation exceeds this characteristic quantity, there are pre-discharge phenomena, which accelerate the degradation of the insulation and therefore lead to a shortening of the useful life of the machine. The main objective of this thesis was to develop a model capable of determining the so-called Partial Discharge Inception Voltage for random-wound machines and to facilitate the design of their electrical insulation system. In addition to this, an in-depth study was carried out on how to improve the qualification process of electric motors and actuators intended for use in the world of More Electric Transportation. First, it was considered how to effectively test the insulation systems of random-wound electrical machines to prove that they are PD-free. Subsequently, the impact of thermo-mechanical stress due to frequent speed and torque variations was studied. Finally, the impact of partial discharges on insulation at different altitudes was investigated to better understand the potential risk these can have on the correct operation of the machine, since it is easier to trigger them at pressures above sea level. Ultimately, this thesis seeks to provide various tools for a complete study of the reliability of the insulation system of an electric random-wound motor (or actuator) applied to the transport sector, with particular regard to preventing the partial discharge triggering. Nevertheless, a general approach has been adopted that can be extended to the study of other low-voltage machines, such as dry-type high-frequency transformers or hairpin motors.