High Efficiency Megawatt Motor Thermal Stator Preliminary Design

The High Efficiency Megawatt Motor (HEMM) is being designed to meet the needs of Electrified Aircraft Propulsion (EAP). The key objective of HEMM is to establish a motor technology which simultaneously attains high specific power (>16kW/kg ratio to electromagnetic weight) and high efficiency (>98%) by judicious application of high temperature superconducting wire and integrated thermal management. This paper describes the design of the first full size prototype stator for the HEMM motor. This prototype will be used to retire development risks for both the thermal management system design as well as manufacturing challenges. The stator must be able to operate up to a 500 amps without internal temperatures exceeding 200°C. Key features of the stator are liquid cooling of the coils by circulating fluid between the rotor and the stator, a slotless core, and a vacuum tube that houses the rotor. Having the rotor in a vacuum minimizes the heat transfer to the rotor from the stator. This is critical to maintaining cryogenic temperatures on the rotor coils. Addressing the thermal management challenges of the stator involves a combination of minimizing the losses to reduce the heat load and optimizing the cooling system by maximizing the conductive heat transfer in the coils and the convective heat transfer from the coils to the fluid. Manufacturing challenges being addressed include: vacuum pressure impregnation of the assembly with epoxy, winding and fabrication of the vacuum chamber. As this paper will show, the design is feasible from a manufacturing standpoint and the analysis indicates that it will be possible to achieve the performance goal of operating up to 500 amps without internal temperatures exceeding 200 °C