Operating properties of superconducting fault current limiters based on YBCO thin films

We have investigated various operating properties of superconducting fault current limiters (SFCLs) based on 300 nm thick YBa2Cu3O7 (YBCO) films to determine the voltage ratings of the SFCLs as applied to Korean power system. The SFCL consists of 1 mm wide and 26 cm long meander-type YBCO stripes covered with a 200 mn gold layer grown in situ for heat dispersion at hot spots. Measured operating properties included maximum voltage, maximum limited current, response and recovery time under various conditions. Maximum voltage across the SFCL during the quench was independent of fault angle between 0 degrees and 90 degrees while maximum limited current was the highest at fault angles between 60 degrees and 120 degrees due to high current value at the fault instant. The response time showed reverse behavior to maximum limited current. When inductance was inserted into the circuit, the response time rapidly increased with decreasing power factor down to 0.985 while the maximum limited current varied little. Recovery time increased linearly with applied voltage. Considering the above characteristics, particularly the recovery time, it was determined that optimal voltage rating of our SFCL units was below 100 V-rms. (C) 2001 Elsevier Science Ltd. All rights reserved.