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Description
Offshore wind turbines are becoming an integral part of the future large-scale renewable generation initiatives. It is envisioned that to upscale offshore wind turbines in the range of 10+ MW power, superconducting (SC) technologies must be explored. Several partial and fully SC machine designs have been proposed and demonstrated for offshore direct-drive wind turbines. It is theoretically shown that the fully SC machines can further improve the efficiency and power density of wind turbines while lowering the levelized cost of energy. However, fully SC machines pose many technical risks, which must be addressed before commercial application. A key challenge of fully SC machines is high ac losses generated in the armature winding. These losses pose a significant barrier to the use of fully SC machines in high-speed applications. But, it is expected that direct-drive wind turbine ac losses can be handled due to their low frequency.
Most of the fully SC machine designs in the literature are primarily focused on EM designs and validating their electrical performance. However, the practical implementation of these machine designs heavily depends on the accuracy of estimated ac losses and associated cryocooler design. Therefore, extensive attention must be paid to validating ac loss evaluation and mitigating these ac losses for a feasible machine design. This paper presents a detailed evaluation of ac losses of a 10-MW fully superconducting machine. An inside-out synchronous machine with MgB2 race rack coils is investigated in this research. A rigorous ac loss calculation utilizing finite-element analysis is performed using different ac loss models available in the literature. Further, these analytical results will be validated against experimental results conducted on individual race rack coils. After the ac loss models are validated, an optimized machine model will be obtained which limits the ac losses to a manageable level.
