In Japan, the replacement of old, large-capacity pipe-type oil-filled (POF) cables is planned for around 2020. Replacing these with low-capacity cross-linked polyethylene vinyl sheath (CV) cables however requires additional circuits, which is impractical due to the difficulties in constructing new cable tunnels in urban areas. Because high-temperature superconducting (HTS) cables fit within the large-capacity, low-loss power transmission network using compact conduits, HTS cables are expected to offer an innovative solution to these technical bottlenecks. Therefore, HTS cables have been identified as one of the key technologies for the development of next-generation power transmission grids.
During the first three years (2008-2010), Sumitomo Electric Industries in collaboration with, ISTEC, Kyoto University and Waseda University developed the elemental technologies for the HTS cable.
The key technologies for the AC loss reduction were the development of a low-magnetic textured
substrate and the slitting of a wide REBCO wire into narrow strips. SEI has developed a new type of
textured metal substrate referred to a clad-type substrate. The magnetization loss in the clad-type substrate is one twenty-fifth that in a conventional Ni-alloy substrate. The developed REBCO wire is composed of a 120-μm-thick clad-type textured metal substrate, CeO2/YSZ/CeO2 buffer layers, a GdBa2Cu3Cux (GdBCO) superconducting layer, and a stabilizing Ag layer. A 30-mm-wide wire was slit into 4-mm-wide strips, and each strip was coated by electroplating with 20-μm-thick copper. A cable core with 4-layer conductor and 2-layer shield was manufactured using these 4-mm-wide strips, and the AC loss characteristics were evaluated. The measured AC loss was 1.8 W/m/phase@5kA, thus achieved the AC loss goal. Using this design, test samples were prepared to conduct fault current tests (max. 31.5 kA, 2 sec).
In the next two years (2011-2012), a 15 m-long cable system will be built for testing. The 15 m-long demonstration system will be cooled and subjected to various tests, including those for electrical, thermo-mechanical, and heat-loss measurement. After the confirmation of the nominal current and voltage performance, a long-term operational test will be performed to verify whether the HTS cable system is capable of handling the rated current and voltage for thirty years.
Source: Masayoshi Ohya (Superconductivity & Energy Technology Division Sumitomo Electric Industries, Ltd.). Superconductivity Web21 (January 16, 2012).