When testing the rotor of a synchronous motor for short circuits, a low voltage source is applied across the rotor coils through the collector rings. What would be the indication of a short- circuited coil?

Correct Answer: Option C — low or zero voltage drop reading, while the other coils will have higher readings

Applying a low-voltage DC source across rotor coils allows for a voltage drop test. A short-circuited coil will exhibit a significantly lower resistance than healthy coils, resulting in a near-zero voltage drop across the faulty coil compared to the higher voltage drops measured across the remaining healthy, intact coils.