Electromagnetic-Thermal Coupled Analysis Considering AC Losses in REBCO Windings of 10 MW Fully Superconducting Synchronous Generators Cooled by Subcooled Liquid Nitrogen for Electric Aircraft

A large AC loss is generated in armature windings composed of a REBa2Cu3Oy (REBCO, RE = rare earth, Eu, Gd, etc.) wire in a fully superconducting synchronous generator. In aircraft applications, liquid nitrogen is suitable for cooling windings because of its specific heat capacity and dielectric strength. The evaporation of liquid refrigerant significantly decreases the dielectric strength, which results in an increase in the risk of accidents by discharging. For safe operation, the temperature in the generator is set below the boiling point of nitrogen (similar to 77 K). We calculated the temperature rise caused by the AC loss and others by applying a method that estimates the AC loss from the experimental results. This paper addresses the electromagnetic-thermal analysis in finite element method to calculate the temperature rise and proves the feasibility of a fully superconducting generator cooled by liquid nitrogen, that is, the temperature is maintained below 77 K. The output power is 10 MW. The temperature of liquid nitrogen was assumed to be 65 K, and its flow speed was set as a parameter. Additionally, we confirmed that designing a method that determines the number of parallel conductors of REBCO windings considering the temperature rise can enhance the output power density.