A 250 kW/5 kWh engineering prototype Flywheel Energy Storage System (FESS) was designed, fabricated and component tested by Adelwitz Technologiezentrum GmbH (ATZ) and L-3 Communications Magnet -^sMotor GmbH (MM). A heavy - load vertical 0.6 ton rotor is suspended totally magnetically by an HTS radial-passive bearing on the top together with a PM bearing at the bottom. Further features are the flywheel rotor body which is manufactured from carbon fibre reinforced plastics (CFRP) in a multi-rim version and combined with an integrated high-power motor/generator. A 35 W/77 K single- stage Gifford McMahon cryo-cooler is cooling the HTS bearing to a temperature of 45 - 60 K. Functionality and efficiency of the magnetic bearing configurations, rotor control concepts and motor/generator power electric system is considered and established. Bearing stiffness parameters, damping performance, and rotational friction are measured. Testing of further components under vacuum conditions confirmed that low bearing drag and wear- free operation can be attained. The motor-generator operates with a power in excess of 250 kW and an efficiency of > 92%, including the losses of the inverters. A redundant mechanical touchdown bearing system can be activated to restore the rotor position. The separately tested flywheel components are now in the assembling status expecting first machine tests in November 2007. After studying and measuring all FESS parameters in -house the dynamical storage device will be tested in a German E.ON power station under industrial conditions.
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