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Sagamihara, Japan

Matsumura R.,Tokai University | Yamada Y.,Tokai University | Hikichi Y.,SWCC Showa Cable System Co. | Hironaga R.,SWCC Showa Cable System Co. | And 3 more authors.
Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals | Year: 2016

High Temperature Superconducting HTS current lead has been prepared by the TFA-MOD processed YBCO tapes. The YBCO tape has higher critical current density Jc and better magnetic property than the Bi2223 tape. Furthermore, thermal conductivity of YBCO tape with thin Ag layer is much lower than that of Ag-sheathed Bi2223 tape. The critical current of the YBCO tapes ranges from 150 A to 190 A in liquid nitrogen and self-field. A current lead is composed of eight YBCO tapes, Cu end caps and a pair of stainless steel boards. Rogowski coils and Hall sensors used for estimation of current distribution are attached on each YBCO tapes. The transport current of 1000 A was carried with no voltage on every YBCO tape at 77 K. The voltages between Cu cap and YBCO tapes almost linearly increased with increasing transport current, and they range from 0.206 mV to 0.234 mV and 0.210 mV to 0.230 mV at 1000 A, respectively. The low voltages correspond to 0.206 μω to 0.234 μω and 0.210 μω to 0.230 μω. The low contact resistance results in low joule heating at Cu joints. The current calculated by Rogowski coils in eight YBCO tapes varies from 4 A to 179 A at 1000 A and sweep rate of 200 A/s. Therefore, the imbalance among eight YBCO tapes is evaluated to be 175 A. The current of eight YBCO tapes calculated by Rogowski coils sums up to 1001 A, which is the slight difference of 1 A in comparison with transport current of 1000 A. Rogowski coils and Hall sensors are effective at evaluating of current distribution for current lead. © 2016 The Japan Institute of Metals and Materials. Source


Yamada Y.,Tokai University | Sakai S.,Tokai University | Shiohara K.,Tokai University | Ishii Y.,Tokai University | And 4 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2010

HTS current leads have been prepared by the TFA-MOD processed YBCO tapes. A current lead unit is composed of five YBCO tapes soldered to Cu caps at both ends and a GFRP board. The YBCO tape is 5 mm in width, 190 mm in length and about 120 μm in overall thickness. The YBCO superconducting layer, 1.5 μm in thickness, is formed on oxide buffer layers of GZO and CeO2 deposited on Hastelloy substrate tapes. Transport current is supplied through Ag layer deposited on YBCO layer. The YBCO tapes with critical current of about 170 A at 77 K in self-fields have been used for two 500 A-class current lead units. The transport current of 800 A was stably carried in liquid nitrogen without any voltage appearance on each tape. The voltage between both Cu caps linearly increased with increasing current, and it was about 350 μV at 500 A. The low voltage at Cu joints results from low contact resistance between YBCO tapes and Cu caps, and causes small Joule heating at the Cu joints. Furthermore, the transport current of 1400 A was successfully applied in the current lead combined with two units in parallel. The heat leakage of the current lead unit composed of five YBCO tapes and a GFRP board between 77 K and 4.2 K is calculated to be 47 mW/0.5 kA, which is much smaller than that of conventional Cu current lead (1.2 W/kA). The small heat leakage results from high current performance and low thermal conductivity in the present HTS current lead. © 2006 IEEE. Source


Shiohara K.,Tokai University | Sakai S.,Tokai University | Ishii Y.,Tokai University | Yamada Y.,Tokai University | And 6 more authors.
Physica C: Superconductivity and its Applications | Year: 2010

Two superconducting current lead units have been prepared using ten coated conductors of the Tri-Fluoro-Acetate - Metal Organic Deposition (TFA-MOD) processed Y1Ba2Cu3O7 δ (YBCO) coated conductors with critical current (Ic) of about 170 A at 77 K in self-field. The coated conductors are 5 mm in width, 190 mm in length and about 120 μm in overall thickness. The 1.5 μm thick superconducting YBCO layer was synthesized through the TFA-MOD process on Hastelloy™ C-276 substrate tape with two buffer oxide layers of Gd2Zr 2O7 and CeO2. The five YBCO coated conductors are attached on a 1 mm thick Glass Fiber Reinforced Plastics (GFRP) board and soldered to Cu caps at the both ends. We prepared two 500 A-class current lead units. The DC transport current of 800 A was stably applied at 77 K without any voltage generation in all coated conductors. The voltage between both Cu caps linearly increased with increasing the applied current, and was about 350 μV at 500 A in both current lead units. According to the estimated values of the heat leakage from 77 K to 4.2 K, the heat leakage for the current lead unit was 46.5 mW. We successfully attained reduction of the heat leakage because of improvement of the transport current performance (Ic), a thinner Ag layer of YBCO coated conductor and usage of the GFRP board for reinforcement instead of a stainless steel board used in the previous study. The DC transport current of 1400 A was stably applied when the two current lead units were joined in parallel. The sum of the heat leakages from 77 K to 4.2 K for the combined the current lead units was 93 mW. In comparison with the conventional Cu current leads by gas-cooling, it could be noted that the heat leakage of the current lead is about one order of magnitude smaller than that of the Cu current lead. © 2010 Elsevier B.V. All rights reserved. Source

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