Estimation of Dynamic Resistance Variations in YBCO Thin Film for Optimization Design of Superconducting Fault Current Limiter

Dynamic resistance variations in YBCO thin films during the transition from superconducting condition to normal (S/N transition) is important for the design of a superconducting fault current limiter. In this study, the overcurrent characteristics of YBCO thin films were measured. The results show that the rate of variation in resistance generated in the YBCO thin film depends on the current through it. The relationship between the rate of variation in resistance and the current changed when the normal zone propagation reached each electrode of the thin film. The resistance value hardly changed after the end of the propagation. This result shows that the resistance variation caused by the temperature rise of a normal conducting zone is much smaller than that caused by S/N transition. Furthermore, the resistance variation characteristics do not depend on the amplitude of the overcurrent. The generated resistance values are estimated by the resistance variation characteristics. The estimated resistance value agrees with the measurement during the first half cycle of the overcurrent.