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