Test of a 1 kA superconducting fault current limiter for DC applications

A low voltage fault current limiter (FCL) having a nominal current of 1 kA has been set up using switching elements based on YBCO thin films fabricated by reactive thermal co-evaporation. The films showed critical current densities exceeding 1 MA/cm/sup 2/ @ 77 K. After patterning and contacting the films, the elements have been assembled in a closed cryostat for operation in a liquid nitrogen bath. The FCL model was successfully tested using prospective fault currents from 25 kA to 150 kA. The electric data show a peak current of 2.7 kA within 1 ms and a limitation to approximately nominal current within 5 ms. Due to this fast response of the YBCO switching elements, FCL coupled grids can be instantaneously decoupled during a fault, leaving the faultless part of the grid practically unimpaired.