How is overvoltage protection implemented in an aircraft electrical system?

• A. Through sensing relays or regulators that disconnect or regulate the source when voltage exceeds preset limit.
• B. By fuses that blow with high voltage.
• C. By automatically increasing generator speed.
• D. By dimming cabin lights.

Answer: (A)

Overvoltage protection is achieved by monitoring the system voltage and taking action to prevent damage when it rises above a preset value. In aircraft electrical systems, sensing relays or voltage regulators continuously monitor bus voltage and, if an overvoltage condition is detected, they either disconnect the generator from the electrical bus or regulate its output to bring voltage back into the safe range. This is typically done by opening a contactor to isolate the source or by adjusting excitation to reduce generator output. Fuses protect against excessive current, not overvoltage, so they aren’t the primary means of overvoltage protection. Automatically increasing generator speed would worsen the condition, and dimming cabin lights is simply load control, not protective action. Therefore, the sensing relays or regulators that disconnect or regulate the source are the correct mechanism.