USCG Exam PracticeAC circuits and theory
A wattmeter on the switchboard suddenly shows a negative (reverse) reading for one of the ship's alternators. What does this indicate?
- A. The alternator's voltage regulator has failed and output voltage has collapsed.
- ✓ The alternator is being motored by the bus and must be tripped to protect its prime mover.Correct
- C. The power factor of the load has shifted from lagging to leading.
- D. The frequency of the incoming machine is higher than the bus frequency.
Why B is correct
Per NEETS Mod. 3 §1-4, a wattmeter reading that swings negative warns of reverse power, meaning the machine is being driven as a motor by the bus rather than generating. The machine must be tripped to protect its prime mover from damage.
Cited:NEETS Mod. 3 §1-4