Fault current limiters (FCLs) are devices to suppress fault currents in electric power systems, and they play an extremely important role in the electric power industry. This paper first reviews the necessity of FCLs, and the research and development status of various types of FCLs in the world. Second, an experimental evaluation of a single-phase FCL system is provided. This FCL system was fabricated by assembling the various components required, such as superconducting coils, high-Tc superconducting current leads, refrigeration devices, etc. Current limitation was completed almost instantaneously, and fully adequate current limiting performance was achieved.
The effects of thermal fluctuation on the current vs. voltage characteristics in high-Tc superconductors are discussed based on a Monte Carlo simulation for the dynamics of fluxoids pinned by random point pins. Near the transition temperature (TGL) between the vortex glass state and the vortex liquid state, it is shown that the fluxoid pinning characteristics obey simple scaling laws characterized by the static and dynamic critical exponents (ν and z). Tangible expressions for the scaled master curves of the electric field vs. current density characteristics at T-TGL are shown. Some remarks are given regarding the difference between the observed scaled master curves over a wide temperature range and those expected to be observed inside the critical regime of T-TGL. It is pointed out that the low-frequency a.c. losses can be discussed by starting from a generalized critical state model.
In this paper we propose a new combination of high Tc superconducting levitation and ring-shaped flywheel energy storage systems. Superconducting levitation is appropriate for rotating a ring-shaped flywheel which has neither shaft nor hub, because it is a non-contact and automatically stable levitation without any control systems. The levitation properties such as static and dynamic lateral stiffnesses, lateral damping, and lateral vibration during rotation have been investigated using a small-scaled experimental machine consisting of 16 bulk superconductors 46mm in diameter and a ring-shaped flywheel about 300mm in diameter. The spring constant increased as the levitation gap height decreased, and the dynamic spring constant was slightly higher than the static constant. The damping coefficient increased as the gap height decreased and the vibration amplitude increased. The experimental critical speed was in good agreement with the calculated one using a one-degree of freedom model. Finally, the possibility of large-scaled practical systems is discussed from the viewpoint of superconducting levitation.