School of Electrical, Computer and Telecommunications Engineering


A literature review of the state of the art of HTS AC losses and power devices determined that the subject of low AC loss HTS tapes required additional work and input and that these could be applied to HTS transformers to obtain a device with lowered AC loss compared to using straight filament tape. A procedure for manufacturing short lengths of twisted filament tape, with novel matrix alloys, and physically distinct filaments was developed. Two alloys were used for the matrix material and the range of twist pitches was from 4 to 20 mm. Tapes samples with twist pitches of 10 and 8 mm were produced with Ic's of 40 A. The AC losses were measured at power fi-equencies in fields up to 0.04 T using a pick-up loop and a lock-in amplifier technique. Control samples of HTS tapes with straight filaments were found to have an AC loss which was predicted very well by the estabhshed equations in the literature. Some twisted filament samples had an AC loss signature that showed a significant lowering of the losses in the range of 0.01 to 0.03 T. No straight filament samples, however, were found to have lowered losses, including those with novel matrix alloys. Suitable materials for use at liquid nitrogen temperatures that can electrically insulate HTS tapes were investigated. It was found that many commonly available materials can be used in liquid nitrogen, however, the application method and adhesives must be considered. A range of pancakes and coils were manufactured using those insulation materials found most suitable. A suitable construction technique was investigated to manufacture robust potted pancake and solenoid coils and these coils were found to give negligible degradation in the Ic after thermo-mechanical testing.



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