Kimiyoshi Matsuo

Development of in-plane aligned YBCO tapes fabricated by inclined substrate deposition

Abstract High temperature superconducting thin film tapes, which consist of a flexible metal substrate, buffer layer, and Y 1 Ba 2 Cu 3 O x (YBCO) layer have been developed for power application. Ni-alloy tape was used as the substrate. Both the YBCO layer and the buffer layer were formed by pulsed laser deposition (PLD) because of an advantageous of high deposition rate. Inclined substrate deposition (ISD) was developed to introduce in-plane alignment for the buffer layer on the non-textured metal substrate. YBCO films epitaxially deposited on the ISD buffer layer by normal PLD had high J c values over 10 5 A/cm 2 at 77 K. For verification of high rate productivity of the PLD/ISD method, we demonstrated high rate deposition of the yttria stabilized zirconia buffer layer and YBCO superconducting layer. We also performed continuous deposition of over 10 m YBCO thin film tapes with a reel-to-reel substrate transfer system combined with 200 W high power laser equipment.

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

Abstract 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 CRIEPIs 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.

Development of a 100 m, 3-core 114 MVA HTSC cable system

Abstract We have started a project to develop a 100 m 3-core 66 kV/1 kA/114 MVA high temperature superconducting (HTSC) cable system to certify the manufacturing capability and the practicability of an HTSC cable system for use as actual power system equipment. The cable is designed based on the results of a 30 m, 3-core test cable. The cable is composed of a conductor and a shield wound with Ag–Mn sheathed Bi-2223 tapes, electrical insulation with polypropylene laminated paper impregnated with liquid nitrogen and thermal insulation with co-axial corrugated pipes. The three cores are housed in this thermally insulated pipe. The cable has been developed and laid at CRIEPIs test site and long-term tests have been under way since June.

High-Tc superconducting power cable development

Abstract We have been developing a high- T c superconducting power cable in order to cope with the continuous increase in power demand. Summarized herein are the results of our activities. Wire development and element development, including 50 m conductor developments and 30 m single cable prototype tests, have been conducted. Based on these researches, we have begun a new project of developing a 100 m, 66 kV/100 MVA three-phase power cable prototype. So far, we have designed the cable system, and have also estimated loss characteristics of the cable. We hope to certify the manufacturing ability and practicability, and also to extract necessary subjects for developing a field level power cable.

Experimental results of a 30 m, 3-core HTSC cable

Abstract A high temperature superconducting (HTSC) cable is expected to transport large electric power with a compact size because of its high critical current density. We have been developing a 3-core 66 kV class HTSC cable, which is applied to the ∅150 mm duct, and is composed of a conductor and a shield wound with Ag–Mn sheathed Bi-2223 tapes, electrical insulation with polypropylene laminated paper impregnated with liquid nitrogen and thermal insulation with co-axial corrugated pipes. A 30 m, 3-core cable system has been constructed to verify the 3-core performance after its production, laying and cooling. The cable had good performance to mechanical stress in the factory process. The critical current of the cable was more than 2.4 kA at 77 K. The AC loss of the conductor part was 0.5 W/m/phase at 1 kA rms, which agreed well with the calculated value of the spiral pitch adjustment technique. A 130 kV rms AC was successfully applied without any change in tan δ and capacitance. As a next step, a 100 m HTSC cable has been designed and developed based on these experimental results.

V–t characteristics for partial discharge inception of high temperature superconducting power cable

Abstract In this paper, we investigated the partial discharge (PD) inception and V – t characteristics in liquid nitrogen (LN 2 )/polypropylene laminated paper (PPLP) composite insulation system for the application to high temperature superconducting cable. Especially, we examined PD inception characteristics influenced by butt gaps in PPLP layers. Experimental results revealed that the PD inception strength in the butt gap was obtained as a function of butt gap thickness. Furthermore, life time indices n of the V – t characteristics at PD inception were experimentally identified and the dependency on the surface pressure of PPLP was clarified.

Development of important elementary technologies for a 66 kV-class three-phase HTS power cable

Abstract High T c superconducting (HTS) cables are expected to serve as underground power lines supplying electrical power to densely populated cities in the future. TEPCO and Furukawa have developed compact HTS cables that can replace the old cables in their existing ducts under metropolitan Tokyo. To connect HTS cables with actual electrical networks requires confirmation of long-term reliability of the electrical insulation and the ability to withstand accidents caused by short circuit. This report gives the results of our examination of these problems.

Electrical properties of YBa2Cu3O7−x tapes fabricated by ISD method

Abstract We have been developing YBa 2 Cu 3 O y (YBCO) wire fabricated by the inclined substrate deposition method. For investigation of advantages of these wires, electrical properties were studied. The J c measured as a function of the temperature and the magnetic field reveals that the YBCO wire has good J c – B – T property. The current–voltage characteristics of a 1 m-long wire shows that the worst section tends to dominate the performance of the wire. Transport ac losses were measured for the 1 m-long wire and were found to be consistent with the values derived by Norriss ellipse model.

Development of 66 kV-class high-Tc superconducting power transmission cable: remarkable decrease in AC losses and production of prototype cable

Abstract TEPCO and Furukawa have been developing a compact 66 kV-class high- T c superconducting (HTS) cable that employs two new important technologies. One technology reduces AC losses of HTS cable. In our studies, we found that using twisted filaments in the HTS tapes in the multi-layer conductor and adjusting winding pitches of layers dramatically reduces AC losses. Another technology is related to the mass production of HTS cable. To facilitate mass production, we improved the cable design. A three-phase prototype HTS cable was then successfully fabricated with machines at Furukawa Electric. The results of the performance testing of the cable demonstrated that the proposed design and the production method were appropriate.

HTS transposed cable conductor and round shape strand

Abstract Bi-2223 round shaped strands were developed for realizing a HTS transposed cable conductor. The maximum critical current density ( J c ) of a short sample was 3.2×10 8 A/m 2 without external magnetic field at 77 K, and the J c of 50 m class long length strands was 1.6×10 8 A/m 2 at the same condition. We prepared subcables consisted of the round shape strands. Using subcables, a HTS transposed conductor was fabricated, and investigated the DC and AC performance. The conductor I c was 900 A as 10 −4 V/m (77 K, 0 T) criterion. Measured AC loss was compared with the theoretical loss considering of the magnetic field distribution and J c – B dependence of the strand. It was confirmed that the experimental and theoretical values were nearly identical.