Tests and Simulations of Different YBCO Tapes for FCL

Abstract

The superconducting (SC) fault current limiter (FCL) is very effective to enhance the security and the power quality of electrical grids, two real demands today. This explains the great interest throughout the world. The YBCO tape characteristics are very important for the FCL. They play a part in the design itself (length and section) and in the behavior especially under low prospective current faults. These certainly are the most severe operation conditions for SC tapes, which inevitably show some inhomogeneities along their length. The three phases clear short-circuit, a rather rare event in fact, does not represent the most severe requirement for the SC element. We have tested different YBCO coated conductors in variable voltage conditions. Modeling has shown that these easy experimental conditions lead to the same results compared to variable prospective fault currents. The SC tapes present very different behaviors. Numerical simulations complete these experiments. The influence of the silver thickness is studied especially in terms of electric field under limitation and of conductor inhomogeneity consequences for low prospective currents. Temperature excursions in the lowest Ic part of the tape are investigated. A compromise should be found between the design (minimum volume) and a safe behavior.