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Description
High temperature superconductors (HTS) are being applied to electric power systems such as generators, motors and reactors. Researches on HTS wind turbine generators are now focused on increasing efficiency and capacity. In the HTS generators, a large magnetic air gap exists because of needed space for a cryostat wall and thermal insulation. Consequently, the reactance is lower than that in a conventional machine. A lower reactance provides a faster dynamic response and a higher load capacity. On the other hand, it leads to a higher fault current and a larger transient torque under short circuit conditions. It would be very challenging to design the mechanical structure of a generator to withstand such a high peak torque since usually the generator structure is designed for three times the rated torque. To do this, a performance evaluation system (PES) is required to test the HTS field coil and structures before it is installed in the HTS generator. The output torque and Lorentz force of an HTS generator must be carefully investigated due to the high current density and magnetic field of the generator. In this paper, the design and feasibility study of a PES for a large-scale HTS generator under short-circuit conditions are presented. Based on the specifications of the 10 MW class HTS generators, the stator and field current, torque, and force of the HTS coil were analyzed under normal and short-circuit conditions. The PES was designed based on the results of electromagnetic analysis using FEM program. The analysis results were compared with full generator model to confirm the possibility of PED. We conclude that the HTS field coil can be practically tested using the proposed PESs whether the structure of the coil can withstand the high torque and force of the generator under normal and short-circuit conditions through stator and field current control. The proposed PES design and analysis results can be effectively used for the development of large-scale HTS wind power generation systems.
