Investigation in to energy efficiency of an electrical generator with a superconductor element as a rotor
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This dissertation investigated in to a new type of electrical generator where a rotating High Temperature Superconductor thin film disk, acts as a "magnetic flux shield" creating a rate of change of flux and hence inducing a voltage in a secondary coil. A preliminary analysis was done using a Finite Element Modeling tool to ascertain the feasibility of construction of a hemispherical shaped superconductor rotor for a generator. For the very high flux density values used and almost negligible air gap in the model that was used for the preliminary analysis, an appreciable output was realized. As the results of the preliminary analysis looked appreciable, a prototype model was built, but with a circular superconductor disk instead of a hemispherical superconductor, as hemispherical superconductor material became difficult to obtain. The investigation process therefore included an experiment conducted on the laboratory prototype generator and simulation of the prototype model using the Finite Element Modeling tool. Experiment was performed with three different permanent magnet configurations and efficiency of energy conversion was obtained. Due to a comparatively large air gap and flux fringing there was little flux available for creating a large rate of change of flux and hence there was no appreciable output. The efficiency of energy conversion was very low. Using a Finite Element Analysis tool, the prototype generator was simulated and the voltage values were calculated and compared with the experimental values. It was observed that the experimental values of the voltage induced followed more closely to the simulated values of the induced voltage, when the entity that represented superconductor, was assigned a permeability value in the range of 1E-3 to 0.1. It was also observed that voltage levels induced in the secondary, for smaller magnetic strength was larger than that of the voltage levels for the higher magnetic strength. This was attributed to the ratios of different diameter (of the disk) to the height of the disk above the permanent magnet ratios. This hypothesis was also verified by simulations. The reluctance value of the YBCO thin film superconductor disk was calculated. The efficiency calculations of the electrical generator showed that prototype electrical generator built had a very low efficiency.