Current limiting properties of YBCO-films on sapphire substrates

This work presents results of switching experiments with meander shaped YBC O-films on sapphire substrates. For the experiments YBCO-layers with a thic kness of 0.3 micrometer deposited on sapphire substrates with 2 inch in dia meter were available, The critical current densities of the superconducters were about 10(6) A/cm(2). The films were coated with additional gold shunt layers to protect them against thermal destruction during the limiting pro cess. Test results with a 30 cm long and 0.4 cm wide sample up to a nominal power of 3.4 kVA (235 V rms and 14.4 A rms) are reported, During the measu rements attention was directed to the expansion of the first quenching zone . To detect the expansion several voltage taps along the entire length of t he meander were mounted. It is shown that the thermal conductivity of the s ubstrate exerts a strong influence on the quench expansion over the whole s ample and therefore on the switching properties of FCLs.