The Characteristic Analysis Between Flux-Coupling and Flux-Lock Type SFCL According to Variations of Turn Ratios

Abstract

We have proposed a flux-coupling type superconducting fault current limiter (SFCL) using coils and analyzed its operating characteristics. The SFCL consisted of the primary and secondary coils, which were wound in series each other through an iron core. The superconducting unit, which was based on YBCO thin film, was connected with secondary coil in parallel. Meanwhile, the primary coil and secondary coil with serially connected superconducting unit were connected in parallel in a flux-lock type SFCL, which didn't permit the same inductances between the primary and secondary coils. The short-circuit currents were effectively limited by adjusting the numbers of winding turns of each secondary coil and the winding directions of the coils without a certain limitation in a flux-coupling type SFCL. The flux generated from a coil in normal operation is cancelled out by the direction of windings in the SFCL and the zero resistance behavior of the superconducting unit. In order to compare the influence by turn numbers between coils, the turn number of the secondary coil was varied from 21 to 84 while the turn number of the primary coil was 42 and 63. We confirmed that the flux-coupling type SFCL was significantly efficient in reducing the initial line current after fault initiation. The voltage generated in the superconducting unit was also lowered by reducing power burden of the YBCO thin film in the flux-coupling type SFCL. We considered that this was caused by mutual linkage of the flux between two coils. The current limiting behavior of the flux-coupling type SFCL was more effective for fault current limiting operation.