Optimized current path pattern of YBCO films for resistive uperconducting fault current limiters

High critical current density, high n value and fast recovery characteristics of YBCO thin films are attractive characteristics for developing resistive type fault current limiters (FCLs). In order to get desirable resistance during quench state, it is important to design optimum current path etched on the surface of YBCO films, Therefore it is needed to determine the optimum current path patterns of YBCO thin films in order to prevent the distortion caused by both localized heat caused by excessive fault currents and breakdown occurred from intensification of electric field during quench period. In this study, to clarify the optimum current path design of YBCO films, electromagnetic analysis of various current paths including meander pattern, spiral pattern, and bi-spiral pattern were considered and to verify the analysis results, experimental tests including quench test, and insulation tests were performed. From the analytical and the experimental results, it was concluded that bi-spiral pattern of YBCO thin film was rather effective for quench and insulation than the other patterns. Finally, this bi-spiral current path pattern was adopted for YBCO thin film design for developing 6.6 kV/200 A 3 phase resistive fault current limiters, and it was possible to get satisfactory results.