Quench behavior of superconductors during the operation of superconductor-triggered fault current limiters

In the first-peak non-limiting type superconductor-triggered fault current limiter (STFCL), which was developed by the collaborative work of KEPRI and LSIS, the first half cycle of fault currents is passed, unlimited. Due to these characteristics, information needed for the fault judgments can be provided to the protection relays, which is useful for the protective coordination of power system. In this fault current limiter, superconductors are used as a fault detector that does not generate resistive loss in normal operation state. Therefore, high J(c) and fast occurrence of large resistance are the essential properties of superconductors for the application to fault detectors. In this study, for the design of superconducting fault detector (SFD), we investigated the quench behavior of two kinds of superconductors, stabilizer-free coated conductors (SF-CC) and Au/YBCO/sapphire substrate, during the operation of the first-peak non-limiting type STFCL The dimension of SF-CC was 12 mm wide x 1000 mm long and that of Au/YBCO/sapphire was 20 mm wide x 100 mm long. Their critical current (l(c)) values were 250 A and 200 A. respectively, and the critical temperature (T-c) was both 90 K for both superconductors. When fault currents of over 3 kA were applied, the STFCL carried out the current limitation successfully. At the beginning of the quench, SF-CC generated a resistance of 150 m Omega, and 394 m Omega was generated in the Au/YBCO/sapphire substrate, when 150 V-rms was applied. After the first half cycle, the resistance of the superconductors increased up to 263 m Omega, and 846 m Omega, respectively, and the temperature reached 132 K and 127 K. In addition, we also investigated the recovery characteristics of the SFDs. The SF-CC and Au/YBCO/sapphire substrate recovered the superconductivity by 353 ms and 357 ms, respectively. Based on the results of the analysis, we determined the required length of the superconductors for the SFD application. (C) 2009 Published by Elsevier B.V.