Design and evaluation of 66 kV class RE-123 superconducting cable

In the new national project, as wire and cable development, Sumitomo Electric Industries, Ltd. (SEI) is trying to develop a 66 kV/5 kArms high temperature superconducting (HTS) cable with its own REBa₂Ca ₃O_x (RE-123, RE = rare earth element) coated conductors. In an actual power grid, an inflow of current higher than the normal rated power (fault-current) can occur. The maximum fault-current condition is set at 31.5 kArms for 2 s for 66 kV-class transmission system in this project. Therefore, one of the technical targets in this project is to design the wires and cables to survive at this fault-current condition. As the first step, the prototype HTS cable was designed against the fault-current condition of 31.5 kArms for 2 s. The wires have copper plating as a stabilizer layer not to be damaged by over-currents. The designed HTS cable has a copper former and copper shield layers in parallel with the HTS conducting layers and HTS shield layers, respectively, to control the temperature rises in the cable core at fault-current conditions. As the second step, a sample HTS cable core was fabricated and fault-current tests were conducted to check its soundness. The temperature rises in the cable core were measured under various fault-current conditions. The critical current of the cable core was measured before and after the fault-current tests, and no deterioration in the critical current characteristics was observed. However, there was slight degradation of the n value. The investigation will be conducted, and the results will be fed back to designs of the RE-123 wires and cables.