Temperature Characteristics of Superconducting Thin-Film Fault Current Limiting Elements Using High-Resistivity Alloy Shunt Layers

We have been investigating a superconducting fault current limiter (FCL), in which YBCO superconducting thin films with Au-Ag alloy shunt layers are used. The ability of the films to withstand high electric fields (> 40 V_peak/cm) enables the total length of FCL elements to be reduced, thus greatly reducing the cost of FCLs. In this paper, we report the temperature characteristics of Au-Ag/YBCO composite films with sapphire substrates. Temperature of the film was estimated as average temperature from voltage and current in the films during the over-current period of 0.1 s using the relation between their resistance and temperature. The effect of thickness of the substrate was examined. Temperature data were analysed with the relation between the maximum temperature and joule heating during the over-current period. Data on recovery time are also shown.