What provides the rotating magnetic field in an AC induction motor?

• A. Stator currents
• B. Rotor currents
• C. Capacitor bank
• D. Slip rings

Answer: (A)

In an AC induction motor, the rotating magnetic field is produced by the stator windings fed with a three-phase AC supply. Each phase’s winding creates a magnetic field that is 120 degrees apart in space and time, and the combination of these three fields sweeps around the stator, forming a rotating field that travels at synchronous speed. This rotating field is what induces currents in the rotor (whether shorted-cage or wound), and those rotor currents interact with the rotating field to produce torque. A capacitor bank is used in some single-phase motors to create a phase-shifted current, but it does not provide the rotating field in a standard induction motor. Slip rings are part of the rotor circuit in wound-rotor machines, not the source of the rotating field.