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Considering the deterioration characteristics of 2G hightemperature superconducting (HTS) tapes is necessary to design a mechanically and electrically robust superconducting coil. In this study, the deterioration characteristics of 2G HTS tapes such as the critical current ( I ) and n value are determined according to the electrical breakdown applied. AC, DC, and lightning impulse (IMP) voltages are applied to 2G HTS tapes stabilized by various materials to verify their deterioration characteristics. It is found that the degree of deterioration is dependent on the applied voltage and the type of 2G HTS tape. This implies that the deterioration characteristics of the 2G HTS tape by the discharge is influenced by the total energy of the input voltages whereas the variation in deterioration according to the type of the 2G HTS tape is a result of the electrical resistivity and hardness of the stabilizer material. Deterioration characteristics of 2G HTS tapes damaged by discharge voltages are analyzed by using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). [ABSTRACT FROM AUTHOR]

A high-temperature superconducting (HTS) coil system often operates in an environment cooled with liquid nitrogen (LN). However, it could be surrounded in part by gaseous nitrogen (GN) as a result of film boiling due to thermal quenching. This may negatively affect the dielectric reliability in a composite dielectric system relative to that of a liquid dielectric system because the intensity of the electric field increases at the gaseous dielectric layer. The increase in the electric field intensity with the gaseous dielectric layer may degrade the dielectric reliability of the HTS coil system. This study investigates the dielectric characteristics of a composite insulation system with GN and LN to design an HTS coil system with high reliability in a quench state. The dielectric experiments use a sphere-to-plane electrode system made of copper, and three types of voltages (AC, DC, and lightning impulse) are applied to the sphere electrode with a grounded plane electrode. The electrical breakdown voltage of the composite dielectric system is measured and analyzed with respect to the height of the gaseous nitrogen layer. Finally, the dielectric characteristics of the composite dielectric system corresponding to a given height of the gaseous nitrogen layer are compared with those of GN and LN dielectric systems. [ABSTRACT FROM AUTHOR]