What could cause voltage fluctuations after synchronization that stabilize slowly?

• A. Faulty AVR response, faulty excitation system, or governor instability or load transients.
• B. Weather changes.
• C. Ambient light level changes.
• D. A loose mechanical belt.

Answer: (A)

After synchronization, a generator must hold both voltage and frequency by coordinating the excitation system and the prime mover. The automatic voltage regulator senses terminal voltage and adjusts excitation to keep that voltage near the setpoint. If the AVR response is faulty, it won’t correct voltage errors promptly or may overshoot, so the voltage pops up and down and only settles slowly as the loop finally damps out.

If the excitation system itself is faulty, the generator can’t supply the needed reactive power to support the terminal voltage. That creates voltage swings as the system fights to find a new balance, and the settling is slow because the excitation path isn’t providing the proper reactive support.

Governor instability or load transients affect the same stabilization process from the mechanical side. An unstable governor can cause speed (and thus frequency) fluctuations, which feed back into voltage regulation, while sudden load changes change the reactive and real power balance the AVR must respond to. Both situations produce voltage fluctuations that take time to damp as the control systems work to restore steady operation.

Weather changes, ambient light, or a loose mechanical belt don’t address the electrical regulation loop in the same direct way. Weather and light don’t directly alter the generator’s voltage control after synchronization, and while a loose belt can affect mechanical drive, it’s not the primary mechanism for slowly stabilizing voltage once the generator is tied to the bus.