A flywheel energy storage system (FESS) is a power storage device that stores electrical power by rotating energy. The FESS we develop has a large capacity to charge electrical power from a solar power system and other renewable generators and discharge the power to power networks. A superconducting magnetic bearing developed by Furukawa Electric and Railway Technical Research Institute levitates the rotating shaft for high speed and low friction with the disk weight of about 7-10 tons and rotating speed of about 6000-9000 rev/min. Characteristically, a combination of a REBCO HTS bulk and a REBCO HTS magnet is adopted as the HTS bearing.
Furukawa chose a YOROI coil structure developed by Chubu Power Company for the HTS magnet of the magnetic bearing. Double pancake coils were fabricated, and an excitation test was conducted while the coil was conductivity cooled by a GM refrigerator at lower than 50 K. We successfully confirmed that the magnetic field was achieved to a design value of 1 T. After the excitation test, the levitation test was carried out using one YBCO bulk and two double pancake coils to produce the satisfactory levitation force.