Tadao Ezaki

On the Resistive State of Current-Carrying Rods of Type 2 Superconductors in Longitudinal Magnetic Fields

The resistive state of the current-carrying type 2 superconducting rod in a longitudinal magnetic field was studied for Pb-T l alloys. The herical structure composed of two kinds of domains was found from the measurement of the potential distribution on the sample surface. The larger domain was confirmed directly to be in a flux flow state and the other domain was estimated to be in a normal state by some theoretical considerations. The direction of the boundary between these domains was dependent only on the direction of magnetic field at the surface.

Results of tests on components and the system of 1 kWh/1 MW module-type SMES

A full system of 1 kWh/1 MW superconducting magnetic energy storage (SMES) has been completed early this year. This SMES is the first step to the realization of practical SMES system for power line stabilization. Main points in its design are two module type arrangement of six coils having three coils and one converter as one unit of module, modified-D-shaped coils with mechanical supports, liquid helium vessel type cooling of coils, and high-temperature superconducting current leads. The first test experiment was carried out on the site recently. The above design points were examined. A preliminary test for power line control was also made in the distribution line at the site. Satisfactory results were obtained.

Development of a 1 kWh-class module-type SMES-design study

The authors are planning to build a 1 kWh/1 MW (maximum stored energy/maximum power capability) module-type SMES (named ESK; experimental SMES of Kyushu Electric Power) as a first step towards the realization of practical SMESs for power line control. The main points of the design are those of: module-type coils for the development of SMES capacity scale-up; the choice of low loss stranded cables for reducing pulse operating loss; the choices of modified D shape coils and the reduction of stresses in the conductor-which become more serious in scaling-up and high-T/sub c/ superconductor (HTSC) current leads for covering weak points due to thermal loss in a module-type SMES which need many current leads. Some other points are also studied such as the design of the cooling system in which a single coil quench does not induce that of others, and harmonics suppression in the SMES power converter system.

Flux Flow in a Current-Carrying Cylinder of Type 2 Superconductor in a Longitudinal Magnetic Field

In the resistive state of current-carrying type-2 superconducting cylinders with longitudinal magnetic fields, the existence of a helical structure composed of the flux-flow domain and the normal-like domain has been suggested experimentally. Based on this helical structure, the expressions of the induced electric field and the induced paramagnetic magnetization are derived with the aid of the critical-state model. The present derivations are applicable only when the magnetic field generated by a transport current is smaller than the longitudinal magnetic field, and the results show fairly good agreements with the observed data of this range.

Experimental study of SMES system with DC intertie for power line stabilization

A superconducting magnet energy storage (SMES) system for power-transmission-line stabilization is studied using an experimental model system. It has a DC intertie section using convertors in an AC transmission line, with SMES used in series in the DC section. The distinctive characteristics of this system are that independent stabilization can be made for each AC line and that the power flow through the DC section can be controlled. The model system has pulsewidth-modulated GTO (gate-turn-off) converters, a superconducting pulse magnet, and a simulated power line system with generators. Measured characteristics of the system are discussed. Results of some simple line-fault experiments are shown.<<ETX>>

Scaling law of fringe fields as functions of stored energy and maximum magnetic field for SMES configurations

Although a SMES (superconducting magnetic energy storage system) has attractive potential for power management and quality control, the fringe field from the SMES restricts its site location. The fringe field outside a coil is expanded in a series of Legendre polynomials. The results are applied to the fringe fields of various SMES configurations, such as a single solenoid coil, toroidal coil, axially displaced coil. The derived fringe fields are scaled as functions of both the stored energy E and the maximum magnetic field B/sub m/, which are the main parameters of superconducting coil design. The fringe fields decrease as E/B/sub m/, (E/sup (n+2)//B/sub m//sup (2 n+1)/)/sup 1/3/, and ( E/sup 5//B/sub m//sup 7/)/sup 1/3/, for a single solenoid, toroidal coil, and axially-displaced coil configurations, respectively, where n is the number of coils.

Design of a Modified D Shaped Toroidal Coil for 1kWh/1MW Experimental SMES

In the development of ESK(Experimental SMES of Kyushu electric power, 1kWh/1MW) which is a toroid type coil composed of 6 elementary coils wound by strand cables, problems of mechanical force mat might be connected with mechanical disturbance in coils are very important. To reduce this force, a new coil shape is proposed named “modified D shape” that has two straight parts mechanically connected to each other by support material as well as two curved parts having the shape with no bending moment. It is made clear that the reduction of floor area(2/3) as well as that of tension (1/2) without the increase of amount of conductor are shown to be attained by calculation.

Analytical models for a mechanical strain of a modified D-shaped toroidal coil for 1 kWh experimental SMES

Several interesting characteristics in the strain force measurement of the supporting structure of the modified D-shaped toroidal coil for 1 kWh experimental SMES (ESK) have been observed. A simple analytical model is developed to simulate the measured characteristics. With this model, the mechanical behavior of the superconductor in the coil is studied. Calculated results based on this model show good agreement with the observed characteristics. Mechanical losses of the superconducting coil are also discussed using this model.

Study of SMES System with DC Intertie for Power Line Stabilization

A new superconducting magnet energy storage (SMES) system proposed by one of authors for power transmission line stabilization is studied by an experimental model system and computer simulation. It has a SMES in a dc intertie section connected to ac transmission lines via convertors. The distinctive characteristics of this system is that independent stabilization can be made for each ac line and also that the power flow through the dc section can be controlled. For verifying these characteristics we developed a model system consisted of a superconducting pulse magnet (lOOkJ), pulse width modulation (PWM) convertors, simulated power line system with a generator (lOkVA) and a short-circuiting device to give power line fault.

Solenoid Type Shielding Coil Systems for a Small Scale SMES

One of the difficulties of a small scale SMES for applications such as power line control is a high pulse loss due to its rapid change of magnetic field at short time energy transfer. To reduce it, a shielding coil system, which is composed of a main superconducting coil and a normal shielding coil connected in parallel, was proposed. For the medium scale SMES, we have showed the possibility of a toroidal type shielding coil system which produces small stray field in environment. A solenoid type coil system, however, seems to be appropriate for a small scale one, because a coil system of solenoid configuration brings advantages of an ease of magnetic force support and a simple cryostat system. The stray field is restricted in narrow area due to its small dimension. A simple solenoid shielding coil, however, might give somewhat of field fluctuations to a main superconducting coil, and then correction shielding coils should be arranged in the system. The proper arrangements of correction shielding coils are discussed in terms of the reduction of field fluctuations on the superconducting coil.