Which motor type requires two sources of power, one AC and one DC, to operate?

Which motor type requires two sources of power, one AC and one DC, to operate?

• A. Induction Motor.
• B. Squirrel-Cage Motor.
• C. Synchronous Motor.
• D. Wound-Rotor Motor.

Answer: (C)

Synchronous motors use two power sources: AC on the stator to create the rotating magnetic field, and DC on the rotor to establish a fixed magnetic field. This DC excitation makes the rotor’s magnetic polarity constant, so the rotor can lock in with the rotating stator field and run at synchronous speed. Without the DC rotor excitation, the rotor would not maintain a steady field and would slip relative to the stator field. Induction motors, including squirrel-cage and wound-rotor types, rely on AC in the stator and obtain rotor currents by induction; they do not require a DC supply for rotor operation. A wound-rotor configuration does allow rotor circuit adjustments for starting and torque control, but it still operates from AC on the stator and does not need a DC source for normal operation. Thus, the motor that inherently requires both AC and DC supplies is the synchronous motor.

Synchronous motors use two power sources: AC on the stator to create the rotating magnetic field, and DC on the rotor to establish a fixed magnetic field. This DC excitation makes the rotor’s magnetic polarity constant, so the rotor can lock in with the rotating stator field and run at synchronous speed. Without the DC rotor excitation, the rotor would not maintain a steady field and would slip relative to the stator field.

Induction motors, including squirrel-cage and wound-rotor types, rely on AC in the stator and obtain rotor currents by induction; they do not require a DC supply for rotor operation. A wound-rotor configuration does allow rotor circuit adjustments for starting and torque control, but it still operates from AC on the stator and does not need a DC source for normal operation. Thus, the motor that inherently requires both AC and DC supplies is the synchronous motor.