Thermal Analysis and Design of a Cryogenic Cooling System for 10 MW Class High-Temperature Superconducting Generators for Wind Turbine

Abstract

This thesis focuses on two main targets. First, the thermal design of the cooling system for the 10 MW-class HTS synchronous generator (HTSSG) is enhanced to diminish thermal absorption from room temperature whenever the cryocooler fails. This step focuses on the most major losses of (1) generator rotor losses including conduction loss of current leads, conduction loss of torque tubes, radiation loss, superconducting losses (taking account of mechanical lap joint Joule heating loss and intrinsic n-value loss), and (2) conduction loss of system supporting rods and natural convection occurring in the heat exchangers, as well. To get maximum elimination of these losses, the numerical method was applied to optimize the design of a current lead and a torque tube, respectively. Finally, the possibility of constructing an HTS field coil can be maintained at a constant low temperature without an external power source or an external supply of cryogen is demonstrated. Hence, the performance of the cooling system is observed for various cryogens to investigate the feasibility of using solid cryogen as a “thermal battery”. It will optimize the total volume of solid cryogens to remain in the HTS field coils, which are kept in a cryostat, and kept below a certain temperature as long as desired.