Shaping of Melt Textured Samples for Fault Current Limiters

Abstract

Resistive fault current limiters require long length of superconducting materials with relatively low sections. Meander is now a frequently used geometry for this type of application. Nevertheless, the shaping of a textured sample is a quite delicate operation because of its brittle character. Cracks are often observed in the final meander and reduce the life time of these samples. Recently, we have presented a new process that allows overcoming this problem. Sintered pellets are drilled to adopt the chosen geometry. Then, the texturing process is performed. By this way, no large mechanical stresses are applied to the fragile textured samples. Here, the idea is to reproduce the meander pattern. Holes performed do not cross the whole sample thickness but alternatively emerge from top or bottom of the pellet. Slices extracted from the textured samples face like meanders. Different geometries have been tested with holes emerging perpendicular to the (ab) planes or parallel to the (ab) planes. The annealing time under oxygen flow has been studied to fit the required critical current densities values, which were evaluated through transport measurements at 77 K. SEM studies allow comparing both configurations and in particular the crack existence. The quality of the textured material around the holes was found to be not deteriorated compared to the bulk microstructure. Finally, the influence of the holes on the texture quality was studied by neutron diffraction.