Verification tests of a 66 kV HTSC cable system for practical use (first cooling tests)

Tokyo Electric Power Company and Sumitomo Electric Industries, Ltd. have been jointly developing elementary technologies for an high temperature superconducting (HTSC) cable system, such as conductor wound with HTSC wires, thermal insulation pipes, terminations and so on. Verification tests of a 100 m HTSC cable system integrating these elementary technologies have been conducted in collaboration with Central Research Institute of Electric Power Industry (CRIEPI) to verify its long term electric and cryogenic properties. The cable conductor is composed of four layers of Bi-2223 wires wound spirally around a former. Polypropylene laminated paper impregnated with liquid nitrogen is adopted as cable insulation for its properties of high insulation strength and low dielectric loss. HTSC wires are also wound around the electrical insulation to form an electrical and magnetic shield. To reduce heat invasion from ambient temperature part, multi-layer insulation is wound between the co-axial stainless corrugated pipes where high vacuum is maintained. The cable was partially installed into a ∅ 150 mm duct and formed in a U-shape. Each end has a splitter box and three terminations. The cable and the terminations are cooled using two separate sets of a pressurized and sub-cooled liquid nitrogen cooling system. The cable has been developed and laid at CRIEPI's test site and long-term tests have been under way since June, 2001. This paper presents the design of the cable and some results of the first cooling tests.