Which of the following motors can be connected across a single-phase AC supply?

• A. Differential compound motor
• B. Cumulative compound motor
• C. DC shunt motor
• D. DC Series Motor

Answer: (D)

A DC motor can be operated from a single-phase AC supply.
The direction of the torque produced by a DC machine is determined by the direction of current flow in the armature conductors and by the polarity of the field.
Torque is developed in a DC machine because the commutator arrangement permits the field and armature currents to remain in phase, thus producing torque in a constant direction.
A similar result can be obtained by using an AC supply, and by connecting the armature and field windings in series.