Overcurrent characteristics of 1 m long superconducting model cable using YBCO coated conductors

In applications to power transmission cables, a number of YBCO tapes would be assembled and wound spirally on a Cu former. The YBCO tapes and the Cu former would be connected in parallel and could be subjected to short-circuit fault currents 10 to 30 times the operating current. The fault currents would drive the YBCO tapes into the normal state and thus generate Joule heating for the duration of the fault. Therefore, in order to examine the stability and feasibility of YBCO power transmission cables, it is important to demonstrate the redistribution of the transport current and the electromagnetic coupling between the YBCO tapes and the Cu former during a short-circuit fault current. We constructed a 1 m long superconducting model cable and subjected it to an overcurrent with a peak of 31.5 kA_rms for a duration of 2.0 s, as established by JEC (Japanese Electrotechnical Committee), in a liquid nitrogen bath. We examined the redistribution of the transport current between the YBCO sample tapes and the Cu former by using Hall probes. In addition, we developed a novel computer code based on the finite element method and an equivalent circuit in order to clarify the characteristics of the redistribution of the transport current and the thermal behaviour within the cable. Finally, we designed a 10 m long cable that would reach the degradation temperature of the YBCO tape due to the fault currents.