Hysteretic Relationship Between Magnetic Flux and Primary Overcurrent in FTI-FCL With YBCO Thin Film Disc

We focused on a flat-type inductive fault current limiter (FTI-FCL) with an yttrium barium copper oxide (YBCO) superconducting thin film made with the metal-organic deposition method. The FTI-FCL consisted of a pancake coil as the primary winding and a YBCO disc as the secondary winding. Normally, the magnetic flux generated by the current flowing through the primary coil is canceled out by that generated by the eddy current induced in the YBCO disc, which reduces the inductance of the FTI-FCL. When an overcurrent is injected into the primary coil, the YBCO thin film shifts from the superconducting state to the flux-flow resistive state, and inductance then appears in the FTI-FCL. This paper describes an experimental and computational approach. The periodic behaviors of the magnetic flux density produced in the FTI-FCL were measured by a pickup coil when the ac overcurrent was injected into the primary winding of the FTI-FCL. The eddy current induced in the secondary YBCO disc and the magnetic flux were calculated by using a finite element method, taking the superconducting n -value model into account. The measured magnetic flux density changed in a hysteretic manner for the injected current. A similar hysteresis characteristic was also derived in the calculation. The experiments and simulations showed that the YBCO thin film disc periodically alternates between superconducting and flux-flow resistive states.