Taro Matsuoka

Test of REBCO HTS Magnet of Magnetic Bearing for Flywheel Storage System in Solar Power System

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.

Quench Protection of YBCO Coils: Co-Winding Detection Method and Limits to Hot-Spot Temperature

A quench detection method of a high-temperature superconducting (HTS) coil using a cowinding method is studied. It is experimentally shown using a small YBCO test coil that the cowinding method is highly effective in canceling the inductive voltage component and can detect a quench occurring in an HTS coil with high sensitivity, compared with a commonly used bridge-balance method. An HTS coil is damaged by a quench when hot-spot temperature exceeds a certain threshold. The authors also experimentally investigated conditions to keep the hot-spot temperature of coils wound of YBCO tapes below a safe level, using the highly sensitive cowinding quench detection method.