Masayoshi Ohya

Phase II of the Albany HTS Cable Project

High-temperature superconducting (HTS) cable systems are expected to be a solution for improvement of the power grid and three demonstration projects in the real grid are underway in the United States. One of these is the Albany, NY HTS Cable Project, involving the installation and operation of a 350 meter HTS cable system with a capacity of 34.5 kV, 800 A, installed between two substations in National Grids electric utility system. A 320 meter and a 30 meter cable are installed in an underground conduit and connected together by a joint, or splice in a vault. In Phase I of this project, the cables were fabricated with DI-BSCCO wire in a 3-core-in-one cryostat structure. After the installation of the HTS cable system, the in-grid operation began on July 20, 2006 and operated successfully in unattended condition through May 1, 2007. In Phase II, the 30 meter section was replaced by a 2G (YBCO) cable. The 2G cable was fabricated with SuperPowers YBCO coated conductors in a 3-core-in-one cryostat. After replacement of the 30 meter section, the joint and one termination were reassembled and the commissioning tests that included initial cooling, critical current measurement and DC withstand voltage test were completed successfully. After the commissioning tests, the HTS cable system with a 30 meter YBCO cable and a 320 meter DI-BSCCO cable was re-energized on January 8, 2008 and started again to operate in a live utility network. This paper describes the latest status of the Albany HTS cable project.

A New HTS Cable Project in Japan

A new HTS cable project supported by Ministry of Economy, Trade and Industry (METI) and New Energy and Industrial Technology Development Organization (NEDO) has just started in Japan. Target of this project is to operate a 66 kV, 200 MVA HTS cable in a real grid in order to demonstrate its reliability and stable operation. Tokyo Electric Power Company (TEPCO) provides the real grid and studies the impact of connecting the HTS cable to the existing conventional facilities in Yokohama. Sumitomo Electric Industries, Ltd. (SEI) designs and manufactures the HTS cable, terminations and joint. Mayekawa Mfg. Co. Ltd. provides a cooling system. Total project period is planned to be 5 years. In 2007, components of HTS cable system were studied and designed. In 2008 and early 2009, the pre-system with a 30-meter cable will be installed in the factory to demonstrate basic performance of the HTS cable and its accessories. Then the 200 MVA HTS cable will be manufactured in 2009 and installed and operated at the site in 2010 and 2011. One of the technical targets in this project is to reduce the AC loss of HTS cable. For this purpose, a new type DI-BSCCO wire with twisted superconducting filaments is planned to be applied in the cable. A 1-meter cable core manufactured with the new wires shows its AC loss as less than 1 W/m/ph at 2 kArms, which is 1/4 of AC loss with normal DI-BSCCO.

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.

Test Results of a 30 m HTS Cable for Yokohama Project

HTS cable demonstration project supported by Ministry of Economy, Trade and Industry (METI) and New Energy and Industrial Technology Development Organization (NEDO) 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-meter HTS cable system with terminations, a joint and a cooling system was installed in SEI facility to confirm their design and performance. Various tests as voltage tests, nominal and over current tests, heat cycle tests, heat loss measurements and so on were conducted and it is verified that the cable has good performances as design. This paper describes the design and test results of a 30-meter HTS cable, and discusses required test items of HTS cables.

Results of Japan's First In-Grid Operation of 200-MVA Superconducting Cable System

A high-temperature superconducting (HTS) power cable demonstration project was started in 2007 to evaluate the cables performance, stability, and reliability. This project aims to operate a 66-kV 200-MVA HTS cable system in a real power grid of the Tokyo Electric Power Company. A 240-m-long HTS cable was successfully installed, and other system components, such as a cable-to-cable joint, terminations, and a cooling system, were also constructed at the Asahi Substation in Yokohama. After several completion and performance tests on the system, the HTS cable was connected to a real grid from October 29, 2012 to December 25, 2013. The in-grid operation had continued for more than one year without any accidental interruption of the operation or troubles of this system. The temperatures and pressures of liquid nitrogen flowing in the HTS cable were controlled to within the target values. After the in-grid operation, the critical current of the HTS cable was measured, and it was confirmed that there was no degradation compared with the initial results. In addition, no partial discharge was observed in periodical measurements. It is concluded that the HTS cable system has good performance and stability for long-term in-grid operation.

Over-Current Characteristics of a 20-m-Long YBCO Model Cable

To achieve large current capacity and mechanical flexibility, high-temperature superconductor (HTS) power transmission cables consist of a number of YBCO coated conductors, which are assembled and wound spirally on a Cu former. In practical applications, superconducting cables might be subjected to short-circuit fault currents that are 10 to 30 times the operating current. Therefore, in order to ensure the stability and feasibility of HTS power cables and protect them from fault currents, it is important to estimate the redistribution of the transport current and electromagnetic coupling among the conductor layer, shield layer, and Cu former. In this study, we carried out experiments on a 20-m-long YBCO model cable, which was composed of two jointed 10-m-long YBCO model cables. Over-current with a peak of 31.8 kArms and a duration of 2.02 s was applied to the model cable. We performed numerical simulations using a newly developed computer program based on the 3D finite element method (FEM) in order to clarify the electromagnetic and thermal behaviors of the YBCO model cable in the presence of an over-current.

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.

Over-Current Characteristics of 66-kV RE123 HTS Power Cable

In Japan, the development of the 66-kV-class superconducting power cable was begun in 2008 as a national project. A high-temperature superconducting (HTS) power cable typically consists of a copper former, HTS conductor layers, electrical insulation layers, HTS shield layers, and copper shield layers. 66-kV-class superconducting power cables may be subjected to a fault current of 31.5 kArms for 2 s. Therefore, in order to ensure the stability and feasibility of superconducting power cables, we need to investigate these cables with respect to their thermal characteristics and current distribution under fault conditions. In this study, we carried out over-current experiments on a 2-m-long HTS model cable. We also performed numerical simulations on the model cable by using a computer program developed by us on the basis of a 3D finite element method (FEM) and an electrical circuit model.

Current-carrying capacity of single layer cable using superconducting Bi-2223 tapes in a parallel magnetic field

It was theoretically shown by the authors that the current-carrying capacity of superconducting dc power cable can be enhanced by choosing a force-free configuration under a parallel magnetic field produced by the current flowing back in the outer shielding conductor. This was experimentally checked for a single layer cable using Bi-2223 tapes in an applied parallel magnetic field. It was found that the current-carrying capacity took on a peak value under the force-free condition for the total magnetic field, including the self-field. This shows that the proposed structure is suitable for practical dc power transmission. The possibility of the innovative dc superconducting power cable with multi-layers with higher current-carrying capacity is discussed.

Development of RE-123 Superconducting Cable

High temperature superconducting (HTS) cables are expected as a large capacity cable with lower transmission loss. Numerous HTS cable demonstration projects using Bi-2223 superconducting wires are being promoted around the world for practical utility usage. RE-123 coated conductors, which are still at the research and development stage, will also be applied to several demonstration projects in coming years in addition to Sumitomo Electrics world first 30-m HTS cable project using RE-123 conductors which was successfully energized in early 2008. As wire and cable manufacturer, Sumitomo Electric has also been developing its own RE-123 conductors, and has succeeded in fabricating a 200-m-class conductor. One of the important challenges associated with the use of RE-123 conductors in power cables is to ensure stability against over-current. In order to evaluate over-current characteristics, a 10-meter ldquo3-in-Onerdquo RE-123 superconducting cable was manufactured and over-current tests were performed. No Ic degradation was observed after exposure to over-currents with a maximum current of 31.5 kArms for 2 s (120 cycles), which meets the requirements for 66-77 kV class power cables in Japan. It was confirmed that RE-123 conductors have satisfactory over-current characteristics for use as superconducting cable wires.