Degradation characteristics of YBCO coated conductors due to fault-current in power cable applications

In high temperature superconductor applications used in electric power devices, YBCO coated conductors may be subjected to short-circuit fault-currents that are 10-30 times the normal operating current. These over-currents cause heat generation, resulting in I_c degradation of the YBCO coated conductor. Therefore, it is necessary to fully investigate the degradation characteristics of YBCO coated conductors. We previously conducted preliminary experiments on the degradation of YBCO sample tapes resulting from the over-current pulse drive. In this study, we analyzed the waveform of fault-current that is supposed to flow into the YBCO coated conductor when a short-circuit fault occurs in a power cable application, by using a newly developed numerical simulation program. We also carried out experiments in which an over-current with the analyzed fault-current waveform was applied to two YBCO sample tapes. We then investigated the degradation characteristics, focusing on the amount of current permitted. Experimental results showed that both the sample tapes (initial I_c = 118.6 A and 123.2 A) were degraded by applying an over-current with a peak value of 320 A.