Turbo generator model with governor and exciter.
One-mass model, turbine- and generator-rotor represent one single
rigid mass.
The machine inertia is determined by the inertia time constant
H.
Steady-state initialisation:
If combined with 'Control.Setpoints.Set_w_p_v' or similar, the
setpoint values p_set and v_set are determined at
initialisation from initial active power and voltage. The
corresponding value for the speed w_set is determined by
the system frequency system.f0.