Shirou Nakamura

Design of a large current-type fault current limiter with YBCO films

Superconducting fault current limiters (FCLs) with YBCO films are under development in a national project in Japan. In this project, Mitsubishi Electric Corporation is in charge of the development of a large current-type FCL with a target capacity of 1 kA/200 V. To develop the FCL, numerical simulations on the combined thermal and electrical behavior of the device have been carried out considering inhomogeneity. The thermal stress of the FCL has also been studied by FEM using the calculated temperature profile. Here, the assumed size of a YBCO film on a sapphire substrate with a metal shunt layer is 30 mm in width and 100 mm in length. The critical current (I c ) of the film is assumed as 210 A +20% or -20%. The main results are as follows: (1) 16 films are arranged as a series of two stacks each consisting of eight films in parallel. (2) A polygonal arrangement is adopted for the YBCO films to obtain uniform current distribution. (3) The maximum temperature is 150 K and the thermal sink on the film effectively reduces temperature increase. (4) The thermal stress caused by the temperature gradient is <10 MPa. Therefore, mechanical breakdown is not a serious problem with this device.

Experiment of a 100Wh-Class Power Storage System using High-Tc Superconducting Magnetic Bearing

A superconducting magnetic bearing exhibits low rotational loss. Accordingly it is likely to form an efficient power storage system in combination with a flywheel. We developed a 100Wh-class flywheel type power storage system using high-Tc superconducting magnetic bearing. We prepared Y-based oxide superconductors with MPMG method and Pr-based permanent magnets for the magnetic bearing. The flywheel has the maximum diameter of 250mm and weight of 27.5kgf. A storage energy of the flywheel is 0.2MJ(=55Wh) at nominal speed of 17000rpm.

4K Three-Stage Gifford-McMahon Cycle Refrigerator for MRI Magnet

The authors have succeeded in the development of a 4K Gifford- McMahon cycle cryogenic refrigerator capable of eliminating the evaporation of helium from a superconducting MRI magnet. We installed this refrigerator in a superconducting MRI magnet and established that it actually eliminated evaporation and was capable of stable operation.

A Conceptual Design of a Superconducting Magnet for a Magnetic Levitated Train Using a High Tc Oxide Superconducting Wire

A conceptual design of a superconducting magnet for magnetic levitated train (MAGLEV) using a silver sheathed wire of high Tc oxide superconductor is studied. In the conceptual design, the superconducting magnet is operated by persistent current at 20K. The efficiency and the reliability of refrigerator are high at 20K. The critical current density of 6x104 A/cm2 is required at 5T for the conductor. The coil is stable against disturbance, because the minimum quench energy is large. On the other hand, the quench propagation velocity of the coil is low. The coil needs active quench protection.

Cryogenic and electrical performance at a factory test of a rotor for 70 MW class slow-response excitation type superconducting generator

70 MW class superconducting generators are under development as a national project in Japan. This is an eleven-year program which commenced in 1988. The manufacturing of the slow response excitation type rotor was completed at the beginning of 1996, and performance test of the rotor was carried out in the factory at the beginning of 1997. The factory test has been completed successfully. This paper describes the factory test results of the cryogenic performance and the electrical performance.

Stabilization of CuNi/Nb-Ti superconductors by MgO powder

Abstract The CuNi/NbTi superconductor of a persistent current switch (PCS) with high normal state resistance is very susceptible to external disturbances. To stabilize the PCS, it is necessary to improve its mean thermal conductivity. A MgO powder coating was used on the surface of the conductors as a stabilizer. The thermal conductivity of MgO is two orders of magnitude larger than that of CuNi at

Cooldown of a 30 MVA Superconducting Synchronous Conductor

Since superconducting generators have various merits, such as increased efficiency, reduction in dimensions and weights, improvement in system stability and possibility of increase in terminal voltage, intensive research efforts for the development of them are being made in USA, USSR, France, West Germany, Japan, etc. The development and performance evaluation tests of experimental units of several tens of MVA have been finished in many countries, and at present manufacturing programs for demonstrating units of several hundreds of MVA aiming at general evaluation tests involving their economic efficiencies and reliabilities are under way in each country.

Advanced Design for Load Capable Superconducting Bearings

Superconducting bearings have some room for improvement in loading capacity and cost, the authors examined the effects of gaps between magnets and superconductors, width and thickness of magnets, thickness of superconductors, and combination of plural ring magnets. Four advanced design rules were obtained.

Acoustic emission monitoring on a model field winding for the 70 MW class superconducting generator

Abstract Acoustic emission monitoring on a model field winding for the 70 MW class superconducting generator was performed during cooldown, excitation and quenches to diagnose the integrity of the model field winding and improve the reliability of the field windings for the generator. The results confirm that the acoustic emission signals are mainly due to conductor motions which cause premature quenching of the winding. It is therefore important to support the field windings as rigidly as possible to prevent conductor motions and to increase the stability of the field windings.