Melt textured superconductors : Tailoring properties for current limitation

The Fault Current Limiter (FCL) is one of the most promising devices for the electrotechnical applications of High Temperature Superconductors. Several designs and materials alternatives have been considered for integration into this system. In this work we review first the concept of FCL and then we report the progress carried out in the development of bulk Melt Textured Growth (MTG) YBCO for resistive and hybrid FCL. The main problem of using MTG YBCO ceramics in current limitation at 77 K is that the high critical currents can generate hot spots. Our strategy to minimize this problem has been either to dope MTG bars, grown by the Bridgman technique, with metallic ions (Mg, Zn, Ni) which reduce Tc and hence Jc or to dimension the triggering element to the quench size around electrical contacts. The chemical and superconducting homogeneity of these elements were tested and the performances for current limitation were analyzed. Quench currents up to 4000 A were measured in undoped YBCO bars. On the other ...