Question 187Electricity & Electronics - QMED

The correct answer is D) the circuit breaker can be closed. When the synchronizing lamps grow dim and are totally darkened as the synchroscope pointer approaches the 0° position, it indicates that the voltages and frequencies of the two alternators are closely matched, and it is safe to close the circuit breaker to parallel the alternators. The other options are incorrect because: A) the voltages being 180° apart would not result in the lamps dimming; B) the incoming alternator running too slowly would cause the lamps to remain bright; and C) a defective or broken synchroscope would not provide the necessary indication for paralleling the alternators.