Tomoo Mimura

Status of Superconducting Cable Demonstration Project in Japan

The HTS cable demonstration project, called the Yokohama Project, supported by Ministry of Economy, Trade and Industry and the New Energy and Industrial Technology Development Organization, was initiated in Japan in 2007. The aim of this project is to operate a 66 kV, 200 MVA high-temperature superconducting (HTS) cable in a network of the Tokyo Electric Power Company to demonstrate cable reliability and stable operation. Total project period was changed from 5 years to 6 years. Chosen as the demonstration site was the Asahi substation in Yokohama. Based on the analysis of the network conditions of the demonstration site, specifications of the HTS cable system were determined. Element technologies were developed and various preliminary tests using short core samples were conducted to confirm the HTS cable design. A 30-meter HTS cable system was manufactured and tested prior to initial demonstration tests. Long-term demonstration tests of the HTS cable system in an actual grid at the Asahi substation are scheduled to be started in 2011.

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.

Update of YOKOHAMA HTS Cable Project

The high-temperature superconducting (HTS) cable demonstration project supported by Ministry of Economy, Trade and Industry and New Energy and Industrial Technology Development Organization has started in Japan. The target of this project is to operate a 66 kV, 200 MVA HTS cable in the live network of Tokyo Electric Power Company in order to demonstrate its reliability and stable operation. The design of the HTS cable with DI-BSCCO has been completed as well as those of a termination and a joint. A 30-m HTS cable system with terminations, a splice, and a cooling system was installed in the SEI facility and confirmed the cable has good performances as design. The HTS cable, splice box, and termination vessels have been manufactured with the same design of a 30-m cable system. By now, the HTS cables have been installed into the conduit at the Asahi substation of Tokyo Electric Power Company. The constructions of splice and terminations have been completed. The HTS cable system at Asahi substation was cooled down in this spring. This paper describes the design and completion test results of the HTS cable system.

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.

Design and production of high-Tc superconducting power transmission cable

The design and production of high temperature superconducting (HTS) power transmission cables was studied. In the production of HTS cable, difficulties are mainly caused by the poor mechanical properties of HTS tapes, because critical currents of the HTS tapes deteriorate due to the strains applied during cable production and usage. Therefore, two basic characteristics of HTS cables were experimentally analyzed to improve HTS cable design and production: (1) the mechanical-electrical properties of the HTS cable; and (2) the properties of electrical insulation. The analysis results indicate that the most important technology is the control of the strains applied to the tape in the cable. Based on the results, the design of the HTS cable was then improved, and the machines at Furukawa Electric fabricated a three-phase prototype HTS cable of 30 m in length. The results of the performance test of the cable demonstrated the proposed design and the production method are appropriate.

Present status of the development of superconducting power cable

In this paper, we focus on our R&D activities in the field of high-temperature superconducting (HTS) power transmission cable, and summarize its present status. Five- to seven-meter cable models and 50-m-long conductors were developed using silver-sheathed Bi-2223 tape wires. A 30-m single-phase cable prototype having a closed cooling cycle was also constructed. Numerical and experimental approaches were carried out to reduce AC losses in these conductors. Based on these activities, we have started a new project to develop a 100-m, 66 kV/114 MVA three-phase power transmission cable system prototype and conduct long-term loading tests. In this project, we aim at certifying its manufacturing ability and its practicability, and also extracting the necessary information for development of a field-level HTS power cable system.

Stability Analysis of HTS Power Cable With Fault Currents

We numerically calculated the transient temperature distribution of flowing subcooled liquid nitrogen in a high-Tc superconducting (HTS) model cable when faults occur. The coolant and cable core temperatures were calculated by numerically solving the heat equation using the finite difference method. In the calculation, we assume that the heat transfer coefficient between the flowing subcooled liquid nitrogen and the cable core surface is described by the Dittus-Boelter correlation. The calculation results reveal that the coolant temperature increases even after the fault has been removed and that it continues increasing until fresh coolant arrives from the inlet. The calculated temperature profile of the coolant agrees well with measured data obtained by conducting over-current tests on a model HTS cable. Using our computational code, we also evaluated the maximum HTS cable lengths that ensure that the coolant remains in the liquid phase for certain fault currents for an HTS model cable.

Development of a High Tc Superconducting Cable

A High Temperature Superconducting (HTSC) cable is expected to transport large electric power with a compact size because of its high critical current density. A 30m 66kV-lkA HTSC power cable system has been developed. The critical currents measured at 67K~80K are 1800A~800A. At the loading test, the 40kV-500A was successfully applied with a constant tan δ and capacitance. During the test, the temperature and pressure of circulating liquid nitrogen were controlled to 72K and 20kPa, respectively. Heat leak through the thermally insulated pipe was estimated as 1.5W/m, which is good performance for a long HTSC 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.