ENGINEERING PROTOTYPE OF A SUPERCONDUCTING FLYWHEEL FOR LONG-TERM ENERGY-STORAGE

We built a flywheel system with superconducting magnetic bearings. The bearing consists of six melt-textured YBCO pellets mounted inside a c ontinuous flow LN(2) cryostat. A disk measuring <empty set> 190 mm x 3 0 mm was safely rotated at speeds up to 15 000 rpm. The disk was drive n by a high speed three phase synchronous homopolar motor/generator. M aximum energy capacity was 4.8 Wh, maximum power was 1.5 kW. The dynam ic behavior of the prototype was tested, characterized and evaluated w ith respect to axial and lateral stiffness, damping, decay torques (be aring drag), vibrational modes and critical speeds. Experimental data were found to be in agreement with a structural damping model. Rotor u nbalance together with the hysteretic nature of the superconducting ma gnetic bearing gave significant contribution to the overall losses. At a background pressure of 6x10(-4) mbar, the coefficient of friction ( drag-to-lift ratio) was measured to be mu = 9x10(-6). The experiments demonstrate the applicability of superconducting magnetic bearings in highly efficient, kinetic energy storage systems.