c-Axis YBCO domains for current limiting applications

A superconducting fault current limiter using YBCO single domains requires long elements cut along the ab-planes or along the c-axis. These elements have to be assembled in series in order to produce a limited fault current after the quench to the resistive state under the network voltage. The superconductor total length is much smaller with c-axis elements because their high resistivity after transition contributes to a very high electric field during the current limitation. The critical current density has to be decreased in order to be sure that the Joule effect related to the limiting current does not increase too much the material temperature before its interruption by a current breaker. The inhomogeneously oxygenated YBCO elements limit the current even if the only surface layer is superconducting and produce an electric field up to 5000 V/m. A homogeneous oxygenation without macrocrack is obtained when the thickness along the ab-planes is thin. Several elements have been tested by applying a 20 ms duration fault current in a liquid nitrogen bath at T = 77 K and above. (C) 2002 Elsevier Science B.V. All rights reserved.