Study on recovery current of transformer type superconducting fault current limiter

To introduce Superconducting Fault Current Limiters (SCFCL´s) in a power system, some specifications such as the impedance, the trigger current level, the recovery time and so on are requested. Fault analyses point out that the accuracy of the trigger current level is required in several percents. Therefore, an SCFCL with adjustable trigger current level was proposed, designed and made. Adjustability of the trigger current level was confirmed experimentally. In addition, the SCFCL has good limiting and recovery characteristics. The SCFCL can recover in several tens of msec. It suggests that the SCFCL can recover when the current becomes small enough. In this paper, experimental and theoretical studies on recovery current of the SCFCL are described. Recovery current of the SCFCL was measured and the current of the secondary coil at the recovery operation was calculated. The minimum propagating current of the superconducting wire was calculated and it was compared to the current of the secondary coil just after recovery. Then, it is confirmed that the recovery current of the SCFCL´s of proposed type can be calculated at designing.