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We constructed a test stand of 20 m-class DC superconducting power transmission cable in Chubu University, in 2006. The cable consisted of thirty-nine Bi-2223 HTS tapes in two layers; nineteen tapes were used in the first layer and twenty tapes were used in the second layer. One of the features of the cable is that each HTS tape in the first layer is electrically isolated. Therefore, we can apply the current to the individual HTS tapes in the first layer. We measured critical current of the one HTS tape in the first layer when current was applied to the other HTS tapes, and compared the result with the magnetic field calculation due to the applied current. The critical current increased by 2 4% when the current was applied to all other eighteen HTS tapes in the same layer. From the magnetic field calculation, we concluded that the self magnetic field of the measured HTS tape was eliminated at the tape edge by the applied magnetic field from the neighbor HTS tapes, and then the critical current increased.

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The 200-meter DC cable test facility was constructed in Chubu University. The cryogenic pipe is composed of two pipes, and the material of the inner pipe is stainless steel (SS304). The outer pipe is the straight pipe, and made from the iron steel because of high strength, low cost and not low temperature. If the cable structure is co-axial, the magnetic field is not generated outside the cable, and the ferromagnetism of the iron steel is not affected to the electric circuit. However, if the single core cable is used, the ferromagnetic effect of the outer pipe should be considered. Therefore, we measured the inductances of the cable after the construction of the experimental device. The measured inductance of the co-axial cable is matched with the analytical value, and it is very small. But the measured inductance of the single core cable configuration, it is 0. 4 mH. This is a large value, and therefore we can save the inductor in the power converter. Moreover, the energy storage can be available in the grid power line if large current operation is used.