Method for operating generator unit and safety shut-off arrangement

The invention relates to a method for operating a generator unit having an electric machine, which has a rotor winding (16) and a stator winding (12), and a rectifier (14) connected to the electric machine, via which rectifier the electric machine is connected to an on-board electrical system (10), and to a corresponding safety shut-off arrangement (24), when an excitation voltage is applied to the rotor winding (16) in order to generate an excitation current via the rotor winding (16) and thus an output voltage is provided at the rectifier (14), the magnitude of the output voltage is determined, the rotor winding (16) is de-energized by means of a first switching-off path when the output voltage reaches or exceeds a predetermined first safety threshold value for a time greater than a predetermined first safety time, and wherein the rotor winding (16) is de-energized by means of a second switching-off path, the regulator output connected to the rotor winding (16) is short-circuited by means of a second switch