USCG Exam PracticeHand/power tools, measuring instruments, and maintenance
A wattmeter on the main switchboard shows a negative power reading immediately after an incoming generator's breaker is closed to parallel with the bus. This indication means the incoming generator is:
- A. Supplying excess reactive power and must have its excitation reduced
- B. Running above synchronous speed and must have its governor advanced
- ✓ Being motored by the bus, and the breaker must be tripped to protect the prime moverCorrect
- D. Experiencing a phase-sequence reversal that will correct itself as speed stabilizes
Why C is correct
NEETS Mod. 3 §1-4 states that a wattmeter reading that swings negative warns of reverse power, in which a generator is being motored by the bus. The generator must be tripped to protect its prime mover from damage caused by being driven as a motor.
Cited:NEETS Mod. 3 §1-4