Current limitation using high T-C materials

The superconducting (SC) current limiter is one of the most attractive applications of superconductivity because it is an innovative device without any conventional equivalence. Following the emergence of ultra low a.c. loss NbTi strands in the eighties several devices have been designed and built using these superconductors. The discovery of high T-c materials has created numerous potential applications such as particularly for current limiters. The operation at higher temperatures and the very different nature of the SC oxides compared to low T-c strands deeply modify the limitation process. We have carried out some experiments to study the transition of high T-c samples fed by voltages with the objective of making a resistive limiter. The quench behaviour of sintered and textured Bi compounds have been studied and compared. Grain boundaries play a very important part in the limitation process. The resistive transition seems to begin at the grain boundaries. The complete resistive transition of the sample has never been recorded. The propagation of the transition from the resistive part to the entire sample is very low. To overdrive the quench a magnetic field has been applied. In this paper, the results are reported to show the grain boundaries role in the transition.