Shigeo Nagaya

System Coordination of 2 GJ Class YBCO SMES for Power System Control

YBCO superconducting wire has a relatively low decrease in power distribution at high temperatures and under a high magnetic field. A high-intensity substrate is used for the wire, so the wire has high machine characteristics. Therefore, it is expected that this wire can be used for large-scale high magnetic field coils. Here, coordination between the SMES system for 100 MVA/2 GJ class load fluctuation compensating was conducted using IBAD/CVD-YBCO wire. The SMES system includes a toroidal type YBCO coil consisting of 180 compact, high magnetic field multi-unit coils, a large coil cooling system that uses the conduction cooling method, which does not use a refrigerant medium, and a multi-cell power converter that achieves multi-unit coil connection with relatively low current and low voltage. Studies were conducted for each individual device and for the whole system. Based on the study plan in this paper, it has become possible to develop and coordinate each device of the 100 MVA/2 GJ class power system load fluctuation compensation SMES system using YBCO wire, which up until now had seem impossible as an actual system.

Study of 10 MW-Class Wind Turbine Synchronous Generators With HTS Field Windings

We study the electro-magnetic design of 10 MW-class wind turbine generator with high temperature superconducting field winding by using the FEM analysis. The design examples are presented and the generator characteristics are investigated. The 10 MW-class HTS wind turbine generator is considered to be feasible from the stand point of the electro-magnetic design. In this study, 8-pole and 12-pole generators are investigated. From the results, it is considered that the 8-pole design is preferable compared with the 12-pole design. The analysis also reveals the small synchronous reactance of the HTS wind turbine generator. Therefore, proper protection is necessary for the large short circuit current.

The reversible strain effect on critical current over a wide range of temperatures and magnetic fields for YBCO coated conductors

The strain effect on critical current (Ic(?)) in Y Ba2Cu3O7 ? ? (YBCO) coated conductors was evaluated at temperatures in the range 20?83?K under magnetic fields parallel to the c-axis up to 10?T. The peaked reversible variation of Ic with applied uniaxial strain was confirmed in the self-field at all tested temperatures. The strain sensitivity increases with increasing temperature, resulting in a more pronounced reversible suppression with strain at higher temperature. Interestingly, it was found that the peak strain corresponding to the maximum of Ic shifts to the compressive side with decreasing temperature. Such a peak shift cannot be explained by a change in the thermal residual strain of the YBCO film, suggesting that the peak strain of the Ic(?) in YBCO coated conductors is not determined only by relaxation of the residual strain. The strain sensitivity of Ic(?) at 60?K becomes greater with increasing magnetic field, while the influence of the magnetic field is much less pronounced at 20?K. The in-field Ic(?), including the compressive strain region as well as the tensile region, shows a double peak behavior at low magnetic field at 77 and 83?K. The temperature and magnetic field effect on Ic(?) in YBCO coated conductors is discussed considering flux pinning within the grains and on grain boundaries.

Study on high temperature superconducting magnetic bearing for 10 kWh flywheel energy storage system

Flywheel energy storage systems with high temperature superconducting magnetic bearings are expected for load leveling use. A 1 kWh flywheel of 600 mm diameter was developed and the maximum energy storage of 1.4 kWh at 20,000 RPM was attained. For the development of a large capacity flywheel system, it is necessary to sophisticate the cooling system and improve the performance of the HTS magnetic bearing. So, an advanced cooling system of the bearing with a cryogenic refrigerator has been developed, and also the bearing characteristics in several cooling conditions have been investigated. It has been confirmed that the repulsive force of the bearing at 50 K was 1.5 times of its value at 80 K, and the rotating loss of the bearing at 50 K was one third of its value at 80 K, but the lateral magnetic stiffness at 50 K became small in comparison to that of 80 K. On the basis of the above results, an HTS magnetic bearing for 12.5 kWh flywheel system is under development.

Development of magnetic refrigerator for room temperature application

This paper describes experimental results of a magnetic refrigerator operated at room temperature. Spheres of Gadolinium, 2.2 kg in weight and 0.3 mm in diameter, are used as a magnetic working material. The magnetic materials were divided into two vessels and reciprocated between high and zero magnetic fields. High magnetic field up to 4 T was applied by a cryocooler cooled superconducting magnet. Refrigeration capacity of 100 W was obtained with operating frequency of 0.167 Hz. Details of the magnetic refrigerator construction and experimental results are presented.

HTS conductors for magnets

We have successfully improved the J/sub c/ value of Bi-2212 round wire to 500 kA/cm/sup 2/ at 4.2 K in self-field. The J/sub c/ value strongly depended on the filament size, aspect ratio, and geometry. Adjusting the filament size made it possible to obtain wires with J/sub c/ values higher than 450 kA/cm/sup 2/ in a range of wire diameters from 0.8 to 1.3 mm. The J/sub c/ value remained constant up to an applied tensile strength of 150 MPa. A 1 + 6 stranded cable fabricated using 1.02 mm diameter wires carried an I/sub c/ value of 4.5 kA at 4.2 K in self-field. A 16-strand Rutherford cable could also be fabricated using this wire.

Development and performance results of 5 MVA SMES for bridging instantaneous voltage dips

The superconducting magnetic energy storage system (SMES) of output 5 MVA has been developed to bridge instantaneous voltage dips. The field examination is executed by setting up this system at the new and large liquid crystal factory in Japan. The developed SMES system can store up to 7.34 MJ of magnetic energy in superconducting coils using the NbTi Rutherford conductor. The maximum output of the developed SMES is 5 MVA, and the system can discharge the output for one s. The operating current of the coil is 2.7 kA, and the rated voltage is 2.5 kV. The field examination was started in July 2003. During the field test, we will confirm the performance of bridging instantaneous voltage dips by SMES, the long-term drive reliability and the standby loss characteristic.

Stress Tolerance and Fracture Mechanism of Solder Joint of YBCO Coated Conductors

YBCO coated conductors have been expected to be applied to superconducting magnetic energy storage (SMES) due to high critical current density under high magnetic field and possibility of reducing cooling cost. Solder joints are essential to fabricate a high Tc superconducting coil for SMES system which requires long length of coated conductors. Not only low joint resistance but sufficient mechanical strength is needed, since conductors are exposed to large electromagnetic force generated by large transport current and high magnetic field. In the present study, influence of tensile load on transport property through the joint was investigated. The solder joint with sufficiently low resistance of 5.3 nOmega was attained before loading. Such joint can carry the load up to 650 N without substantial degradation. For further applied load, degradation attributed to fracture at the edge of the conductor is firstly observed. Overall fracture is caused by delamination at the interface between YBCO and CeO2 . As a result, importance of interfacial strength between the superconducting and buffer layer is revealed to realize both low joint resistance and mechanical strength for solder joint.

Conceptual Design of HTS Coil for SMES Using YBCO Coated Conductor

High Tc superconducting (HTS) toroidal coil using YBCO coated conductor is designed for 70 MJ class superconducting magnetic energy storage (SMES) for power system control. Its configuration and shape are optimized by means of genetic algorithm (GA) to minimize the required length of the conductor. The optimization is performed for two kinds of constrains, i.e., maximum electric field or flux flow loss of the coil, which are calculated by means of finite element method (FEM). The FEM analysis considers quantitative current density (J)-electric field (E) expressions based on percolation transition model. It is shown that the great transport performance against magnetic field of YBCO coated conductor can realize a very compact SMES coil compared with an existing Nb-Tis one.

Development of MVA class HTS SMES system for bridging instantaneous voltage dips

A SMES system of MVA class for bridging instantaneous voltage dips has been developed using Bi-2212 wire. The Bi-2212 wire has high-performance conductive characteristics that do not deteriorate at a low temperature in high magnetic fields beyond 10 T. These characteristics enable a compact design of a SMES system of the Bi-2212 wire. In addition, coils of the Bi-2212 wire can be adequately insulated due to a high temperature margin. Therefore, the SMES system designed by using the coils has advantages to enhance dielectric strength and output power of the system. In our previous study, a SMES system consisting of 4 unit coils was constructed and the various properties were examined. Up to the present, the total 18 unit coils were stacked to make a coil system (outer diameter: 700 mm, height: 554 mm, stored energy: 984 kJ) and installed into a SMES system of 1 MVA for bridging instantaneous voltage dips. Also, the cooling system of the HTS SMES has been improved. The characteristics of the conduction cooled HTS coils of 1 MJ class were investigated in the operations of 1 MVA SMES system for bridging instantaneous voltage dips. Thermal reliability was verified during each operations of exciting, standby, bridging and current damping. Moreover, the repetitive bridging operations even worked out every 5 minutes. Advantages of the conduction cooled HTS coils for SMES were verified.