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A significant challenge in the design of fully superconducting (SC) machines is managing ac losses in the SC armature. Recent developments in MgB2 superconducting conductors promise low ac loss conductors suitable for fully SC machines. This paper presents an optimized design targeting low losses and low weight for a 10-MW fully SC generator suitable for offshore wind turbine applications. An outer rotor air-core machine topology is investigated to optimize the design with low weight and low losses. An active shielding concept is used to minimize the pole count without adding excessive weight. This enables a reduction in the electrical frequency for a practical design by a factor of 4 to 5 over current designs, driving ac losses and active components weight lower by an order of magnitude. In this study, armature current is varied to control electrical and magnetic loading in order to minimize losses. A pole count study is conducted to identify the design space suitable for MW scale machines. A comparison is made between active shield, passive shield and a hybrid topology to address the benefits of an active shield for weight reduction. Results suggest that low-pole-count designs with MgB2 conductors will enable machines with less than 1 kW of ac losses. 

{Fully superconducting (SC)machines hold immense promise for high-power-density and higher efficiency machine solutions for offshore wind turbine applications. In this paper, a 10MW air-core fully SC machine is designed for offshore wind turbine applications. This machine design is considered with inside armature coils and outside rotating field coils. In this topology, shield iron can be eliminated or reduced by replacing it with shield coils which contain the magnetic flux inside the machine. This machine is attractive for off-shore wind turbine application due to its high-power density and high efficiency compared to a conventional shield iron design. However, due to the introduction of additional shield coils, this topology uses relatively more amount of SC material than a conventional shield iron design. Therefore, a tradeoff between the shield coils and the shield iron is explored in this paper. In addition, machine designs with different pole-counts are investigated to identify the optimal pole-count design for a low-speed application. A detailed ac loss calculation is evaluated for the machine and required cryocooler power is evaluated to obtain the machine efficiency.