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.