Masaharu Minami

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.

Fundamental study on high Tc superconducting magnetic bearings for flywheel system

Basic quasi-static tests of superconducting magnetic bearings are carried out using YBa/sub 2/Cu/sub 3/O/sub 7-/spl alpha// (YBCO) and Nd-Fe-B permanent magnets. In the thrust type tests, two kinds of c-axis oriented YBCO bulks are used. These YBCO bulks are produced by a melt process using a seed crystal. The measured maximum repulsion pressure between the YBCO and the magnet between the YBCO and the magnet is 0.14 MPa at 77 K under the zero-magnetic-field cooling condition. This repulsion pressure, which is a top level value, enables the authors to consider the application of the superconducting magnetic bearings. The attractive forces between the YBCO and the magnet under the field cooling condition are also measured at 77 K. In the radial type tests, the force between a ring-shaped YBCO bulk and a shaft combined with multi-ring magnets are measured in the liquid nitrogen. A simplified formula is proposed to evaluate the repulsion force. As an application of the superconducting magnetic bearings, a flywheel system is preliminary designed for the energy storage of one kilowatt-hour. The flywheel, which is made of fiber reinforced plastic, is a ring shape having an outer diameter of 600 mm and a height of 100 mm.<<ETX>>

Improvement and enlarging of the CFRP flywheel with superconducting magnetic bearings

Superconducting flywheel usually adopts carbon fiber resin mold plastic (CFRP) material that has the basic characteristics such as higher strength and lighter weight. Stabilized rotation of flywheel requires lower unbalance individually about flywheel and supporting disc. And supporting disc is needed to steadily follow the expansion of the inside diameter on the flywheel by centrifugal force and keep the concentricity of the flywheel and its own rotating axis. We developed the flywheel rotor, which was composed of CFRP flywheel, and partially spherical supporting disc made of high strength aluminum. They were combined with expanse fitting each other and most precisely machined to realize the extremely precise axial symmetric shape and enable to be supported and driven at the point near the center of gravity. We manufactured and confirmed that the flywheel rotor rotated up to peripheral speed of 628 m/s quietly without permanent set.

Study of a high-Tc superconducting magnet made with Bi-2212/Ag Rutherford cable

A high temperature superconducting magnet using newly developed Bi-2212/Ag Rutherford cable was trial manufactured as a partial model for a 10 T magnet. The developed magnet consists of 4 double pancake coils constructed from a Rutherford cable with a critical current of 3.5 kA at 4.2 K, 0 T. The magnet has inside and outside diameters of 100 mm and 180 mm, respectively and is 75 mm long axially. The coil successfully operated with DC 1.25 kA and 1.5 kJ was stored stably. A maximum magnetic field of 2 T with A current of 1.47 kA was confirmed in liquid helium. Also, the authors performed excitation tests under the high-speed rate of change of magnetic field (0.54 T/S) and 300 cycles simulating alternating operation, and estimated the value of AC losses at 5.3 W using the change of liquid helium level.

Development on CFRP Rotor for 1kWh Superconducting Flywheel System

A full-scale CFRP flywheel for 1kWh superconducting flywheel system with the outer diameter of 600mm was manufactured, and it has been confirmed that the rotor was able to rotate having the margine of the speed of 1.35 times to designed rotating speed, 20000rpm. A multi-layered construction supporting with the partial spherical membrane-type structure rigidly fixed to the rotor was used.

Influences of separate position to radial direction between bulk superconductor and permanent magnetic ring about magnetic levitation and rotating characteristics

Abstract The segmental structure of bulk superconductor will be needed designing ultra-large scale high temperature superconducting magnetic bearing for MWh class superconducting flywheel. The N–S poles of permanent magnetic ring assembly were arranged alternately to radial direction and the influences to magnetic levitation and rotating characteristics of the separate position of bulk superconductor to radial direction were tested. It was found when the separate position of bulk superconductor was coincided with the joint of the N–S poles of permanent magnets, both the magnetic levitation and the rotating characteristics were the same as the case of non-separate superconductor. When its position was the center of one side pole of permanent magnets, the levitation was the same as the case of non-separate superconductor, but the behavior of rotating characteristics changed and the loss increased as compared with the case of non-separate type.

Investigation of Characteristics of Axial Gap Type Superconducting Magnetic Bearing for 1kWh Flywheel

We have tackled with the improvement of the superconducting magnetic bearings and manufactured the newly developed facility which has possessed the cooling device with cryogenic refrigerator and the driving device for the completely floating rotational elements, and can be utilized to research and development for various type of the bearings. We have confirmed the small loss of 0.26W about the axial gap thrust bearing of 238mm diameter at speed of 3000 min2212;1 and load of 281N. We introduce the test facility and report the test results.

Evaluation of magnetic force characteristics in High-Tc super-conducting flywheel

We developed the numerical analysis of magnetic force characteristics in high-Tc bulk superconducter. In analysis using the measured Jc, We obtained good agreements with experimental results under different magnet diameter condition. The results show that we obtained anticipation method of magnetic force characteristics of high Tc superconducting bearing. Moreover we evaluated the magnetic force of 1kWhr superconducting flywheel system which arranged plural circular superconductors. It was confirmed good agreement with experimental results. So we will be able to evaluate the magnetic force characteristics of flywheel system without many experimental examinations.

Proposal of 40 MWh Hybrid Power Storage System with Super-conducting Flywheel and HTc-SMES

A 40 MWh hybrid power storage system with Superconducting Flywheel and a high-temperature Superconducting Magnet Energy Storage system (HTc-SMES) is proposed. A Flywheel is used for a base load with power of 10 MW during four hours, and SMES is used for instantaneous power of 10 MW during one second. The principal characteristic of this hybrid power storage system is that a single power conditioning system can be commonly used.

Tests on Small Sized Rotary Model of Flywheel with High Temperature Superconducting Magnetic Bearings

In order to investigate the levitating and rotating characteristics of high temperature superconducting magnetic bearings with newly developed superconducting bulk materials and permanent magnets, the small sized model rotor with 80mm diameter was fablicated and tested. The single grain bulk materials and Nd-Fe -B permanent magnets including Pr were combined. A steady roration of 2.2kgf rotor at 12,100rpm (energy storage : 0.3Wh) was confirmed by rotating the shaft with the turbine. Furthermore it was shown that a multi-ring construction would be applicable for a low stress type CFRP flywheel in a conceptual design of lkWh flywheel.