Recovery Characteristics of GdBCO Series-Connected Non-Inductive Coil in Pressurized Liquid Nitrogen for a Resistive SFCL

A SFCL (Superconducting Fault Current Limiter) is expected to limit a fault current and to improve system stability and operation flexibility in electric power system which is becoming more and more complicated and larger-scale. In order to put SFCL into practical use, it is important for quick recovery to improve the cooling property of a superconducting wire. Especially in resistive SFCL, the superconductor turns to the resistive state for current limiting performance, then the temperature of the superconductor rises up to the film boiling regime of LN2 heat transfer characteristics. After the fault, the SFCL should recover to the superconducting state (stand-by for repetitive fault) within a short period according to the circuit breaker operation. In this study, to improve current-limiting capability, we used GdBCO series-connected Non-inductive coil for the resistive SFCL and investigated the effect of different applying pressure for improvement of its recovery characteristics. In addition, we observed the difference of the boiling phenomena on the surface between under pressurized condition and under ambient pressure by a high-speed video camera.