Quench Development in Superconducting Fault Current Limiters Based on YBCO Films

We measured and analyzed quench development in superconducting fault current limiters (SFCLs) based on Au/YBa 2 Cu 3 O 7 thin films, taking temperature dependence of thermal parameters into consideration. The SFCLs were fabricated by patterning Au/YBCO films grown on 100 mm-diameter sapphire substrates. They were subjected to simulated AC fault currents for quench development measurement. The samples were immersed in liquid nitrogen during the experiment. The quench resistance increased rapidly first and then moderately fast. The increase slowed down afterwards. Data were analyzed quantitatively with the concept of heat transfer within the SFCLs. A heat balance equation was derived and solved, taking into consideration temperature dependence of thermal parameters of sapphire substrates. The solutions agreed with data well. They explained the quench behavior both prior to and after completion of quench propagation. Dependence of quench development on applied voltages could be also understood quantitatively.