Resistance development in superconducting fault current limiters prior to quench completion

We investigated the resistance development in resistive superconducting fault current limiters (SFCLs) based on YBa₂Cu₃O₇ thin films prior to quench completion. The behavior of resistance during this time period is important for the development of SFCLs since it is closely related to the current limitation speed of SFCLs. The 0.3 μm thick film of 2 inch diameter was coated with a gold layer of 0.2 μm thickness and patterned into 2 mm wide meander lines. The SFCL was subjected to simulated AC fault current for resistance measurements. It was immersed in liquid nitrogen during the experiment. The resistance first increased rapidly and the increase slowed down. It was a superposition of an oscillatory component to a slowly varying background. The background increased rapidly and then slowly with time, and linearly with source voltage. The oscillatory component was small, of constant amplitude, and independent of source voltage. These results could be explained quantitatively with the concept of quench propagation, which was caused by heat transfer within the film and a transition to a resistive state. A simulation function was derived from a heat balance equation. Data fit well to this function.