What device will cause the Generator to operate as a motor, potentially damaging its prime mover?

The reverse power relay is designed to detect when power flows in the opposite direction from what is intended, typically when a generator is inadvertently acting as a motor. This situation can occur if the generator's output does not meet the load demand, causing the generator to draw power from the grid or the prime mover instead of supplying it.

When a generator operates in this way, it can lead to excessive mechanical loads on the prime mover, which is the engine or turbine that drives the generator. If not addressed, this can result in serious damage to the prime mover due to overheating, excessive vibration, or loss of lubrication. The reverse power relay helps protect against this situation by disconnecting the generator from the grid or load when reverse power conditions are detected, ensuring that the generator operates correctly and safely.

In contrast, the other devices listed have different functions. An overload protection relay primarily safeguards against excessive current conditions, a voltage regulator maintains the voltage output of the generator, and a frequency monitor ensures that the generator operates within appropriate frequency ranges. While these devices are important, they do not specifically address the condition that leads to the generator operating as a motor like the reverse power relay does.