What produces field current in an AC generator?

• A. Exciter generator
• B. Battery
• C. External power
• D. PMG

Answer: (A)

Field current in an AC generator is the DC current that creates the rotor’s magnetic field, which is necessary for producing voltage in the stator. The device that provides this excitation in a typical aircraft generator system is the exciter generator. It furnishes DC to the rotor windings (through slip rings, or via a rotating rectifier in brushless setups), and the regulator then controls this current to maintain proper output voltage. A battery only supplies initial excitation for starting or temporary boosts, not the normal ongoing field current; external power isn’t used to excite the field in normal operation. Some systems use a PMG as part of the excitation circuit, but the direct source of the field current for the main generator is the exciter.