The voltage regulator controls which parameter to regulate the alternator's voltage?

• A. The generator field current
• B. The rotor speed
• C. The air flow
• D. The terminal resistance

Answer: (A)

Voltage regulation is achieved by controlling the generator’s field current. The voltage regulator watches the output voltage and adjusts the current in the generator’s field winding to keep the terminal voltage within limits. A stronger field (more current) increases the generated EMF and raises the output voltage; reducing the field current lowers the EMF and the voltage. This direct control of the magnetic field is how the system maintains a steady voltage even as load or temperature changes.

The other factors aren’t used to regulate voltage. Rotor speed affects the generator’s frequency and, to a small degree, the generated EMF, but the regulator’s job isn’t to set rotor speed. Air flow is unrelated to voltage control in this context, and terminal resistance varies with wiring and connections but isn’t what the regulator adjusts to regulate voltage.