Performance of modular SFCL using REBCO coated conductor tapes under repetitive overcurrent tests

Recently, the REBCO coated conductor tapes have shown great improvement in the critical current value along with excellent thermal and mechanical properties, turning it more cost attractive to develop superconducting fault current limiters (SFCLs). In spite of these evolutions on the I_c and n-index values, the effect of inhomogeneity on long tape lengths must be investigated, in particular, for application in resistive-type SFCLs where several hundred meters must be used for 15-kV voltage level units. The degradation or irreversible damage in REBCO tapes assisted by an optimized external shunt resistor was investigated on 12-mm-width tapes submitted to repetitive overcurrent tests. A modular unit with six stacks of 0.7-m-length tapes was built and tested by applying repetitive overcurrent during 80 ms, with recovery time intervals from 1 to 3 s (under load and no-load conditions), for prospective current levels from 0.8 to 3 kA, with the limiting factor of 1.7 and 3.2. The resistive type of SFCL, which is assisted by external shunt protection, indicates reliable operating conditions after 100 tests with the fault current level of 3 kA.