Assembly and Soldering Procedure of Nonstabilized YBCO Coils for 1000 A SFCL

The superconducting fault current limiter (SFCL) is the superconducting device for electrical applications closest to overcome the commercialization threshold. Device and operational costs due to resistive electrical connections and ac losses can be minimized by reducing superconducting tape length and power dissipation in the cryostat. Pursuing this goal, we realized anti-inductive coils of YBCO tapes without a copper stabilizing layer. The higher normal-state resistance allows considerable reduction of the necessary length, for the same current limitation factor. The focus of this work is on the soldering procedure and reinforcement of the superconducting tapes, which is particularly challenging when it is protected by only a 2-μm-thin Ag layer. Our developed procedure enabled the realization of the successfully tested single phases of the 9-kV/15.6-MVA resistive SFCL, currently under development at Ricerca sul Sistema Energetico-RSE S.p.A.