Design of ReBaCuO-coated conductors for FCL

The superconducting (SC) fault current limiter (FCL) improves the security and the power quality of electric networks; these are the two essential demands of today. The device must fulfil several requirements in normal and fault operations, and must operate under a variety of conditions. Low prospective current faults represent the most severe conditions. Proper design of the ReBaCuO-coated conductor is essential for safe and optimized operations. The design of the superconducting conductor is mainly based on thermal criteria. The minimum superconducting conductor volume is given by its enthalpy and the limited current through the SC conductor. The superconducting quantities play only a small role in the design. A high resistivity conductor reduces the ReBaCuO volume. Of other considerations to be taken into account, the quench homogeneity is one of the most important for resistive FCLs. The coated conductor architecture and design can help to reduce the consequences of quench inhomogeneity along the conductor. The presented arguments, for a high limited current forcing the conductor to quench uniformly and for a moderate conductor resistivity to reduce the temperature differences, are supported by experiments carried out utilizing two rather different coated conductors in various limiting conditions.