6．Flywheel energy storage system with high temperature superconducting magnetic bearings

A structure was designed for suspending a flywheel on completely contactless high temperature superconductor bearings driven by a contactless coupling.
Completely contactless levitation and rotation was successfully demonstrated on a small scale.

One adaption of superconducting technology for use in conventional railways to further improve energy efficiency is anflywheel energy storage system which support aflywheel with superconducting magnetic bearings (SMB).The SMB comprised of a superconducting coil and bulk superconductor to eliminate friction resistance of the rotor part.

Cooling of the rotating bulk superconductor was achieved in the new design with a proposed refrigeration system instead of liquid nitrogen cooling. A small scale prototype of the design was produced for further tests (Fig.1). In this device, the magnetic bearings are composed of a high temperature superconducting coil as the fixed part and a bulk high temperature superconductor for the rotating component (Fig.2).

The device successfully realizeda contactless levitation of a flywheel.Improving the performance of the fixed element in the bearing structure, the flywheel was rotated over 2,000 revolutions per minutes (Fig.3) using permanent magnet coupling in order to drive contactless. Future work is aimed atproducinga 10 kWh storage device to meet railway sector requirements.

Fig.1 Small scale prototype device for testing the high
temperature superconductor magnetic bearing system.
- Fig.2 Illustration of the superconductor flywheel
- Fig.3 Illustration of test result of completely
  contactless levitation / rotation