HTS Trapped field magnet based motors for naval applications
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As the Navy conve1is to all electric ships, it is investigating ways to reduce the size and weight of electric propulsion motors. The fundamental challenge is to achieve high torque and low speed in a small motor. To achieve this objective, they have invested in, or are investing in, wound induction motors, permanent magnetic motors, synchronous superconducting magnetic motors, and homopolar superconducting motors. Reliable wound induction motors are available today and have been selected for use in the U.K. Navy, but it is unlikely they can be made significantly smaller. The permanent magnet machines are smaller and further compaction is possible. The limits on energy product provide a lower bound on how small permanent magnet machines can ultimately become. Superconductivity offers the promise of even higher fields leading to smaller size, but the mechanical properties of superconducting wires appear to set a practical limit on minimum size today and for the foreseeable future. We are proposing a study to assess the technical feasibility of achieving small sizes more rapidly by pursuing an alternate approach that is a functional hybrid between today's permanent magnet machines and today's superconducting machines. The proposed program does not require building a new machine at this stage. Rather, key experiments and theoretical analyses will be done to provide the engineering data needed to build and operate this novel machine. Since any resulting machine will likely have conventional topology with unconventional materials, a good knowledge of relevant material system performance under relevant conditions can be used to estimate the ultimate machine performance. This work is particularly significant as the investigations on bulk superconducting >permanent> magnets to date indicate a potential size reduction in a motor of a factor of 10 to 20 over today's superconducting and permanent magnet motors. The proposed work will examine the degree to which the potential size reduction might be achievable in practical motor designs.