Mechanical Simulation and Energizing Tests of HTS Coils for 10 kW Generator Cooled by Liquid Hydrogen

Japan's strategy to import overseas-produced liquefied hydrogen faces an economic hurdle due to liquefaction costs. Efficiently tapping into the cold heat produced by liquid hydrogen is pivotal, with high-temperature superconducting (HTS) devices offering a promising solution. Commercializing a liquid hydrogen-cooled HTS generator that operates alongside a hydrogen gas turbine holds significant promise. This setup eliminates the need for a refrigerator by utilizing cold heat, leading to notable efficiency improvements. A national project is underway to develop liquid hydrogen-cooled HTS generators, with the ultimate objective being to commercialize a 600 MW-class generator. A 10 kW-class demonstration system should be developed and verified in the project. A notable technical challenge in applying HTS coils to large-diameter, high-speed rotating field coils is their mechanical fragility. For the 600 MW system, the anticipated compressive stress due to centrifugal force is approximately 50 MPa. A technology is being developed to realize high-strength coils five times more robust than conventional coils. Mechanical simulations revealed a degradation mechanism, in which the innermost and outermost wire edges of conventional coils are delaminated. Coil casing reinforcement proved effective in reducing the stress in the superconducting layer while maintaining the high current density of the coil. Designing a liquid hydrogen-cooled HTS field coil necessitates a comprehensive understanding of the coil's transport behavior when subjected to liquid hydrogen immersion cooling. Energizing tests for the field coils of the demonstration system were conducted; the HTS coils continued to be energized without thermal runaway, even at a generated voltage of 0.8 mV.