Final answer:
To maintain a 400 Hertz (Hz) alternator output frequency on large turbojet or turbofan engines, control systems, synchronization, and governor systems are used.
Step-by-step explanation:
To maintain a 400 Hertz (Hz) alternator output frequency on large turbojet or turbofan engines, several methods are used.
1. Control Systems: These systems monitor and adjust the engine speed to ensure the alternator output frequency remains at 400 Hz.
2. Synchronization: Multiple alternators are synchronized together to maintain a consistent output frequency.
3. Governor Systems: These systems regulate the fuel flow to the engine, which in turn affects the engine speed and alternator output frequency.