Rise aspect of limiting inductance of superconducting fault-current limiter with two YBCO thin-film disks

A flat type of the superconducting fault current limiter (FCL) was investigated to find out its inductance components and magnetic-flux linkage in a coil over a wide ac current range. This FCL consists principally of a pancake coil stacked on a YBCO thin-film disk. Two types of the miniature model FCLs were constructed: 1) a one-layer coil and one YBCO disk (called `basic structure´) and 2) one-layer coil sandwiched by two YBCO disks (called `sandwich structure´). Results of current-carrying experiment showed that the sandwich structure had the residual inductance of 20 μH at low currents below 12 A_peak, but raising the inductance to 84 μH at currents above 12 A_peak. The sandwich structure also proved to contribute reduction in the residual inductance, in comparison of the basic structure. The magnetic flux linkage in the coil was evaluated to interpret the behavior of the proposed FCL. The YBCO disk was found to generate the resistance when the instantaneous-current magnitude increases toward the peak value, whilst generating no resistance at an instant time after the peak current.