Question 190Electricity & Electronics - QMED

The correct answer is D) the generators are out of phase sequence and one lamp is burned out. When paralleling generators, the synchronizing lamps and synchroscope are used to ensure the incoming generator is in phase with the running generator(s). If the synchroscope pointer is at the noon position and one synchronizing lamp is bright while the other is dark, this indicates the generators are out of phase sequence. The bright lamp signifies the voltages are in phase, while the dark lamp indicates they are 180 degrees out of phase. This out of phase condition would lead to a large circulating current if the breaker was closed, potentially damaging the generators. The other options are incorrect because A) low voltage would cause both lamps to be dim, B) a closed breaker would cause the synchroscope to indicate an in-phase condition, and C) a burned out lamp would cause both lamps to be dark, not one bright and one dark.