Source of the initial excitation field

• A. PMG (AC) or Pilot Exciter (DC)
• B. Battery only
• C. Ground power unit
• D. External inertial spin

Answer: (A)

The generator starts producing electricity by first creating a magnetic field in its rotor, and that initial field must come from a dedicated excitation source. In aviation electrical systems, that job is handled by either a permanent magnet generator (PMG), which provides AC excitation to kick things off, or by a pilot exciter that supplies DC current to the rotor windings. Once the rotor is spinning and the main generator begins to generate, the system uses that output to sustain and regulate the excitation, keeping the generator charging smoothly. Other options don’t provide the specific excitation path: a battery can power devices or start systems but isn’t the dedicated initial excitation field source for the generator; a ground power unit can provide external power on the ground but isn’t the standard in-flight source for establishing the initial field; external inertial spin isn’t a recognized method for generating the initial excitation.