Evaluation of Heat Inleak in a Model Superconducting Coil Module for a Wind Turbine Generator With Iron Cores

Wind turbines larger than the present 5 MW class have recently been developed because adoption of larger capacity turbines can increase the total capacity of a wind farm. The realization of compact and lightweight superconducting direct-drive generators is desired. From a cost standpoint the salient-pole iron-core rotor design is superior, because it requires much less amount of expensive high-temperature superconducting (HTS) wires than air-core HTS rotors. In this study we have investigated how to compose a salient-pole 10 MW-class HTS rotor and selected a coil-module system with a warm iron core in which only the HTS racetrack coils are cooled. Based on basic consideration of the coil support system and the structure of the vacuum vessel, we fabricated a model coil module in which an approximately half-sized dummy coil made of copper bar is cooled in a doughnut-shaped vacuum vessel. Cooling tests using liquid nitrogen and liquid helium were successfully performed, and the amount of heat inleak was evaluated. We estimate that the heat inleak in a 10 MW rotor can be less than 500 W.