Breakdown of YBCO Thin Films during Current Limiting and Methods of Improving Current Limiting Performance

We performed fault current limiting tests using YBCO thin films and investigated the reasons for their breakdown during current limiting. There were two patterns of film breakdown. One occurred immediately after current. limiting and the other occurred during current limiting. In film breakdown, the quench propagation speed showed almost no change with increasing energy consumption per unit time, but the energy consumption per unit area increased with increasing energy consumption per unit time. Therefore, local areas of the film reached the melting point and arcing occurred. It is therefore concluded that the performance of the films can be improved by decreasing the energy consumption per unit time. Connecting a parallel capacitor to the film in order to limit the energy consumption per unit time is proposed and tested as a measure to improve the current limiting performance of thin films. (c) 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(1): 20-27, 2009; Published online in Wiley InterScience (www.interscience.wiley. com). DOI 10.1002/eej.20709