Quench properties of superconducting fault current limiters with a protective coating

We investigated the quench development in resistive superconducting fault current limiters (SFCLs) with a protective coating. The protective coating is needed to protect the SFCL from moisture in the air, but should not have an adverse effect on the quench properties of the films. The 300 nm thick YBCO film coated in situ with a gold layer was first patterned into meander lines by photolithography, and then coated with teflon by spin-coating. The SFCL was subjected to simulated AC fault currents for quench measurements. It was immersed in liquid nitrogen during the experiment for effective cooling. The coating retained its form throughout repeated quenches in liquid nitrogen. Moreover, quench properties did not change for thin coatings. The quench resistance of SFCLs with a protective coating was similar to that without a coating. This enables one to use a protective coating without compromising the performance of SFCLs. The quench development in SFCLs with a coating of different thickness was explained with the concept of heat transfer to the coating and the liquid nitrogen.