Current limiting properties of YBCO-films on sapphire substrates

This work presents results of switching experiments with meander shaped YBCO-films on sapphire substrates. For the experiments YBCO-layers with a thickness of 0.3 micrometer deposited on sapphire substrates with 2 inch in diameter 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 process. 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 measurements attention was directed to the expansion of the first quenching zone. To detect the expansion several voltage taps along the entire length of the meander were mounted. It is shown that the thermal conductivity of the substrate exerts a strong influence on the quench expansion over the whole sample and therefore on the switching properties of FCLs.