Tsukushi Hara

Development of a new 6.6 kV/ 1500 A class superconducting fault current limiter for electric power systems

A superconducting current limiter comprising a noninductively wound AC superconducting coil (trigger coil) connected in parallel with a limiting coil was developed. A model electric power system for the application of this type of superconducting current limiter was created, 400 V/100 A class model superconducting current limiters were fabricated, and various current limiting tests were performed with respect to short-circuit currents and phases varied over a wide range. The results demonstrate that the proposed current limiter possesses performance characteristics fully adequate for application to the model system. A 6.6 kV/1500 A class superconducting trigger coil was developed, with a scale permitting, in principle, validation tests of applicability to actual power systems. This coil was demonstrated to be capable of limiting short-circuit currents by a factor of 1/30, and was subjected to detailed evaluation of current-limiting characteristics. >

6.6 kV/1.5 kA-class superconducting fault current limiter development

The authors have developed and tested a 6.6-kV/1.5-kA-class fault current limiter wound with a 42-strand AC superconducting wire having ultrafine NbTi filaments in a high-resistivity matrix. In experiments, voltages up to 7.2 kV were applied to the limiter with phase angles of 0, 45, and 90 degrees . The limiter was able to limit the fault current to 1.8 kA from the 55-kA short-circuit current that would flow in a circuit without a limiter. >

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.

50-m long HTS conductor for power cable

The long conductor fabrication is one of key technologies to realize the High-T/sub c/ superconducting power cable. A 50-m long conductor was fabricated by helically winding the High-T/sub c/ superconducting tape onto a former with a winding machine. The conductor consisted of ten layers of Ag-sheathed Bi-2223 tape which had a high critical current density of 10,000 A/cm/sup 2/ (at 77 K). AC losses and layer-by-layer current distribution were measured, feeding AC current of 100 to 2,000 Arms to the conductor cooled by LN2. The results showed that most of the current flowed in the outer layers where the impedance was low, and that AC losses were remarkably reduced by making the current distribution uniform.

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.

HTS large scale application using BSCCO conductor

The basic property of high-Tc superconducting cables (HTS cables) using Bi-2223-based Ag-sheathed multifilamentary wire (Ag-sheathed wire) have been investigated for the realization of large-scale and compact cables, these being replaceable with conventional cables in existing ducts or tunnels. The AC performance of multi-layer HTS conductors, and three-phase HTS cables with coaxial superconducting magnetic shielding structure was evaluated. The characteristics of the HTS conductor and cable models of long length was investigated on a 50 m scale.

Feasibility study of compact high-T/sub c/ superconducting cables

A conceptual design of a compact high-T/sub c/ superconducting cable was developed by using the Bean model. The experiments suggested that the Bean model provides a rough evaluation of hysteresis loss in high-T/sub c/ superconducting wires, which is supposed to be the main component of AC loss. A compact high-T/sub c/ superconducting cable was designed using a method based on the Bean model so that it could be installed in existing cable ducts. The results indicated that a compact high-T/sub c/ superconducting cable system can increase the power transmission capacity without the need to construct new cable ducts or tunnels. It has also been found that the high-T/sub c/ superconducting cable system is acceptable with regard to such system aspects as stability and short-circuit capacity. >

Superconducting fault current limiter development

The authors have developed and tested a 400-V 100-A-class fault current limiter wound with AC superconducting wire with ultrafine NbTi filaments. The limiter consists of noninductively wound superconducting trigger coils and a superconducting limiting coil which acts as a reactor. Excessive fault currents initiate quenching in the trigger coils and these currents, which have flown in trigger coils in nonfault conditions, are commutated from the trigger coils to the limiting coil. In an experiment, a fault current level was successfully limited to 120 A with a limiter whose terminal voltage at the limiting condition was 420 V.

Characteristics of the flexible high Tc cable conductor

Abstract Flexibility and a.c. characteristics of Bi-2223 Ag-sheathed multifilamentary superconducting wire (Ag-sheathed wire) were investigated for cable conductors. For the application of a power transmission cable, it is important to note the properties of the high T c superconducting (HTSC) cable conductor. Several types of flexible conductors were fabricated by spiral winding on flexible mandrel. The bending property was investigated in a 1.4 m/3-layer conductor and a 5 m/8-layer conductor. The critical current I c of the 5 m/8-layer conductor was measured under the bending strain of 1.3 m radius in liquid nitrogen. The conductors I c was 3000 A, and the J c was 13,000 A/cm 2 . Using the 0.7 m conductor, we investigated the relation between the a.c. loss and the number of layer of the cable conductor.

Estimation of AC losses of polycrystalline YBCO by two different methods

AC losses of polycrystalline YBa/sub 2/Cu/sub 3/O/sub y/ were evaluated using AC transport and magnetization techniques. As alternating currents were passed through a cylindrically sintered specimen, effectively resistive voltages were detected by means of a lock-in amplifier and were shown to be linked with AC losses of the specimen. The field dependence of magnetically estimated AC losses for a small chip, synthesized in the same manner, exhibited a plateau region beginning at several tens of oersteds. This field was found to be equal to the self-induced magnetic field created by the DC critical current of the cylindrical specimen and could be attributed to the grain decoupling field. Below this field, the two methods provided almost equivalent AC losses, which also semiquantitatively agreed with theoretical estimation using C.P. Beans (1962) critical state model.<<ETX>>