Which device is used to excite a three-phase alternator to achieve stable operation?

• A. PMG
• B. AVR
• C. Battery
• D. Rectifier

Answer: (A)

The excitation source for keeping a three-phase alternator stable is provided by a permanent magnet generator. This device supplies a steady source of excitation energy that the automatic voltage regulator uses to control the field current of the main alternator. By feeding the regulator with a reliable excitation signal, the main generator can maintain a consistent output voltage even as engine speed and electrical load change. In brushless aviation systems, the PMG’s output is what enables the AVR to regulate the field effectively, ensuring stable operation. The AVR sets how much DC current reaches the rotor, but without the PMG’s excitation reference, the regulator wouldn’t have a dependable source to work from. The battery and rectifier are important parts of the electrical system, but the PMG specifically provides the dedicated excitation to keep the generator stable.