Absraarct -We have studied the switching of YBCO thin film resistive fault current limiting devices. Films of 300 nm thickness were deposited on 2 inch and 4 inch sapphire substrates by thermal co-evaporation. Bridges 10 mm wide and 22 mm long (2 inch) or 42 mm long (4 inch) were structured by standard photolithography. Contacts were made by in-situ gold overlayers and soft solder. The gold film was removed from the switching area so that the YBCO film was not shunted. The films were tested by 30 ps DC pulses and 50 Hz AC pulses for 50 ms. We find evidence that at the AC tests heat propagates over several cm under these conditions in sapphire so that hot spots can be avoided even without shunt layer with the prospect of higher switching power. The highest destruction free switching power -the r m s critical current times r m s voltage after switching -was 57 kVA. The highest switching power density achieved was 2.5 kVAkm2. To our knowledge, these are the highest switching power densities observed so far.
Numerical simulations of the combined thermal and electrical behavior have been carried out to study the influence of inhomogeneities along the HTSC length on the quenching behavior. A two-dimensional Finite Difference Method (FDM) has been used to investigate the current-limiting performance of YBCO film with a critical current density around 10' Alcm' on a ceramic substrate. 1% of the length was assumed to have reduced critical current and temperature. The equalization properties of an additional thin conducting layer on the quench process has been demonstrated for varying degrees of inhomogeneity.Furthermore a sample of YRCO film was investigated experimentally and compared to calculated data. The results of the experiments show good agreement with the numerical simulations.
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