Partial Discharge Investigation of Form-Wound Electric Machine Winding for Electric Aircraft Propulsion

Abstract

Electric machines with high specific power are crucial for the more electric aircraft propulsion. However, the harsh operating environment such as low air pressure and high temperature will challenge the motor’s insulation system and cause partial discharge (PD), which threatens the reliability of the machine. This article proposes a PD-free stator winding design regarding an air-core high-frequency permanent magnet synchronous machine for aircraft propulsion. The experiment and simulation are performed under sinusoidal voltage due to the power quality requirement by the standard for aircraft. PD inception voltage (PDIV) with respect to air pressure and temperature was obtained experimentally for form-wound windings and was analyzed to derive the PD-free criteria. A 3-D stator model was built and used to simulate the electric field and temperature distributions with a finite-element method. In addition, the effect of voids and delamination on electric field distortion was also taken into consideration to allow for a safety margin and meet the PD-free requirement. To achieve high-specific-power requirement and PD-free requirement simultaneously, a multiobjective genetic algorithm was adopted to perform the optimization and obtain the Pareto fronts at various air pressures. Finally, the PDIV value of the designed winding was measured to verify the PD-free design. The main purpose is to combine the experimental results and the simulation tool to obtain an acceptable PD-free design in the meantime achieving high power density, which may provide helpful guidance on motor insulation design for the more electric aircraft propulsion.