Analysis of electrodynamic transients in High Temperature Superconducting tapes and coils

This thesis deals with the losses generated during electrodynamic transients in second generation High Temperature Superconductors (HTS). The various aspects are first investigated at the conductor level and then extended to coils wound with such tapes. Two numerical models are presented to investigate losses in coated conductors due to a combination of an AC transport current and an AC magnetic field. The first model implements a FEM analysis based on the H-formulation, while the second one implements an integral analysis based on the A-V formulation. Furthermore, a methodology is presented to determine the influence of the configuration of the voltage measurement circuit on the AC losses measured in tapes, calculating a corrective factor to be applied to the experimental results. Then, an electromagnetic methodology and a post-processing technique for the acquired signals are developed to measure the AC losses in different tapes. The method does not involve the use of lock-in amplifiers and has some advantages over traditional techniques. Whereupon, the defect-irrelevant behaviour of a no-insulation (NI) HTS coil in a pancake-wound configuration, in which some defects are intentionally inserted at desired locations, is verified. The results of the experiments carried out at different temperatures are treated to determine the parameters of a simple equivalent circuit. Secondly, the electrical characteristics of two HTS coils in a layer-wound configuration, with and without insulation and having almost identical geometric parameters, are compared. The distinct electric field profiles acquired during tests are explained by the use of an equivalent lumped parameter circuit, which allows to derive the current distribution between the turns. Finally, the same layer-wound coils are supplied with an AC current and their power dissipation is measured experimentally. The measurements are discussed and correlated with the results obtained through two models which can describe the different power dissipation mechanisms involved.