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This article presents the design of a superconducting (SC) rotor with a spoke supported structure that minimizes the heat loss and enables the motor to be cooled by one cryocooler. The main challenge with the SC machines is the need to maintain the SC coils at cryogenic temperatures. Though usually placed in the vacuum, the cryogenic coils still receive a large amount of heat through the conduction of the torque tube which connects to the ambient temperature. The heat flown into the system exceeds the cooling capacity of a cryocooler and requires the boiling of cryogen, which comes with a more complicated and bulky hardware system. The SC rotor proposed in this article uses a spoke system to support the cryogenic windings. Connecting the windings to the shaft, the flexible spokes with low thermal conductivities transfer the torque from the windings to the shaft. The spoke system has much lower thermal conductivity than a traditional torque tube. Preliminary results show that with the ambient temperature 298 K and the cryogenic temperature at 40 K, the total heat transfer rate from the ambient environment to the cryogenic environment is less than 0.1 W, within the capability of a cryocooler that can be mounted on the rotor. The cryocooler is arranged concentrically with the shaft of the rotor. Thermal straps connecting the cold end of the cryocooler to the windings to conduct the heat. An analytical model is built for the rotor. The rotor’s mechanical property and its thermal behavior are analyzed jointly so that the spoke system is optimized for high stress and lightweight. A physical model is also built to test the cryocooler performance in the rotational environment. A previous study shows that the sterling-cycle cryocooler performance has not deteriorated at 1800 rpm at the temperature of 100 K. The proposed design involves a lower operating temperature at 40 K and a high vacuum environment surrounding the cold head. [ABSTRACT FROM AUTHOR]

Offshore wind turbines are the key enabling technology to increase the green energy penetration in the electricity market. Increasing the power generation per tower and reducing the levelized cost of energy are the two significant problems faced by wind turbine manufacturers. Traditional turbine manufacturers use rare-earth permanent magnets (PMs) to increase the air-gap flux density and maximize the machine outer diameter (OD) to increase the torque output. Since the air-gap flux density achievable with available PM is limited, increasing the power output of a traditional generator invariably leads to a significant increase in the volume and mass on top of the turbine tower and associated manufacturing, transportation, and installation costs. Superconducting (SC) wind turbine generators offer 5 to 10 times the air-gap flux density of a PM generator, and a corresponding increase in specific power and power density. Previous MW scale SC wind turbines designs used heavy back iron in the design, iron saturation limits the achievable air-gap flux density in the designs and resulted in bulky generators and moderate efficiency. In this article, a hybrid design approach is proposed to reach an ultrahigh field (5 to 10 times of PM air-gap flux density) and high efficiency (>98%) SC wind turbine for offshore wind turbine. An additional stray field limitation is introduced for safety concerns and shielding techniques are explored. Electromagnetic, mechanical, and cooling designs are provided to support the feasibility of proposed SC wind turbines. A nacelle integration inside a commercially available 6 MW wind turbine is shown to demonstrate the size comparison of the proposed generator. [ABSTRACT FROM AUTHOR]