When a compound wound DC motor is differentially compounded, what does this mean?

Correct Answer: Option C — The current flow direction in each series-field coil is in the opposite direction as the current flow direction in its corresponding shunt-field coil, in which case the field fluxes are subtractive.

Differential compounding means the series field winding opposes the shunt field winding, causing their magnetic fluxes to act subtractively. As load increases, motor flux decreases, potentially causing unstable speed characteristics or dangerous motor runaway under heavy loads.