Over-current testing of HTS tapes

High-temperature superconducting (HTS) transmission cables are subjected to short-circuit fault currents 10 to 30 times the normal operating current and lasting up to 15 cycles. These over-currents will drive the HTS conductor normal and generate heat during the fault. A concern is whether the fault current will either electromechanically or thermally damage the HTS conductor and degrade it or burn-out the tape altogether. Electromechanical and thermal limitations of over-current pulses were measured on BSCCO and YBCO tapes in a liquid nitrogen bath. With pulse lengths as short as 35 ms, it is found that single BSCCO and YBCO tapes can be pulsed to at least 1 to 1.2 kA without being damaged electromechanically. Longer pulses at moderate (450-750 A) over-currents indicated that HTS tapes can be heated transiently to over 400 K without suffering degradation. Thus, it is likely that other considerations of the cable rather than the HTS tape itself would set the limit for short-circuit fault protection.