Flywheel generators

Unusual power supply for the ASDEX Upgrade fusion device

The electric energy needed by the ASDEX Upgrade fusion experiment to power its magnetic field coils and plasma heating facilities is supplied by large flywheel generators. An experimentation pulse in ASDEX Upgrade requires an electric power of 400 megawatts lasting 10 seconds, i.e. half as much as the whole district of Munich. Such an abrupt grid load is not permissible; so the electric energy for ASDEX Upgrade cannot be taken directly from the grid. Instead the flywheel generators gradually take the energy needed from the grid, store it and then pass it on to ASDEX Upgrade in a single pulse.

The biggest flywheel generator at IPP can store 1,514 megajoules or 421 kilowatt-hours of useful energy. It is used primarily for the main field coils of ASDEX Upgrade. The 220-ton flywheel is accelerated in 30 minutes by a grid-supplied drive motor from stationary to 1,650 r.p.m.. Its circumferential velocity can attain 900 kilometres per hour, i.e. almost the speed of sound.

During an experimentation pulse the flywheel then drives a three-phase generator, whereupon it decelerates to 1,270 r.p.m.. The three-phase generator can supply up to 155 megawatts of power for about 10 seconds. Once it has unloaded, the flywheel generator is restored to full power every six minutes.

The EZ2 flywheel generator at IPP: the large flywheel mass in the centre is connected on the left with a drive motor that slowly brings the flywheel to full power. When switched over to generator operation the fast-rotating flywheel mass then drives the generator (right), which produces a strong current pulse for ASDEX Upgrade.
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