Development of 22 kV HTS Triaxial Superconducting Bus

When conventional power cables are replaced with superconducting ones, it is necessary to realize a large transmission capacity with a low heat-road from an economic standpoint. In this regard, the isolation power bus (IPB), which is used to connect a generator to a step-up transformer in power plants, is one of the potential candidates to achieve this. We have been developing a 22 kV class triaxial superconducting bus as an alternative to the IPB in which Y₁Ba₂Cu₃O_7-d tapes are used, and we have already reported a basic design. In this study, we fabricated 22-3 kA class test cables and terminations to verify the design ansd investigate the properties of the system. A 7-m-long superconducting test cable was manufactured by using industrial winding machines and critical current I_c values, and voltage withstand tests were performed. The I_c value of each phase was 4 kA or more at 77 K, which was almost equal to the value of the design. In addition, the withstand voltage was higher than the ac withstand voltage of 50 kV and the lightning impulse of 125 kV. Furthermore, thermal loss to the cryogenic region from the cable and terminations was calculated, and the flow pattern and the pressure loss of liquid nitrogen in a 100-m-long cable were simulated by using a FLUENT simulation software. The cryogenic system could be designed based on the simulation. The termination design was the most difficult because heat insulation and dielectric insulation for a high voltage had to be realized. We tested various kinds of heat insulation techniques with several vacuum levels to develop an appropriate design.