Marine Electrical Systems USCG Question #1368 (Set 46)

As shown in the illustrated diagnostic setup for locating a shorted field coil of a ten- pole salient pole alternator, if 240 VAC 60-Hz is applied across the brushes, what would be the voltage drop across field coil #4 if that field coil had shorted turns and the other field coils were free of shorts? EL-0202

USCG Exam Illustration EL-0202
USCG Examination Diagram: Illustration EL-0202
Official USCG Answer & Rule Citation

Correct Answer: Option A — 17 VAC

When testing salient pole alternator field coils using an AC drop test, a shorted coil exhibits fewer turns and lower impedance. Applying 240 VAC across ten series coils results in a lower voltage drop across the shorted coil compared to healthy coils.

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