What causes the rotor to turn in a typical induction motor?

What causes the rotor to turn in a typical induction motor?

• A. The stator iron becomes a permanent magnet
• B. The rotor is pre-energized before starting
• C. The phase windings align to produce a single rotating field
• D. Each phase is wrapped around the poles in a way that creates opposite magnetic polarities on the poles when energized

Answer: (D)

A rotating magnetic field created by the stator windings is what drives the rotor. When three-phase power energizes the stator, the windings are arranged around the circumference with phase shifts so the poles alternate N and S as you move around the stator. This arrangement makes the magnetic field sweep around the stator, i.e., rotate. The rotor, typically a squirrel-cage conductor, then has currents induced in it by the changing flux. The interaction of those rotor currents with the stator’s rotating field produces torque, so the rotor begins to turn (never exactly at synchronous speed, due to slip). So the key is the distributed, phase-shifted windings that create opposite poles around the stator to form a rotating field, which in turn causes rotation.

A rotating magnetic field created by the stator windings is what drives the rotor. When three-phase power energizes the stator, the windings are arranged around the circumference with phase shifts so the poles alternate N and S as you move around the stator. This arrangement makes the magnetic field sweep around the stator, i.e., rotate. The rotor, typically a squirrel-cage conductor, then has currents induced in it by the changing flux. The interaction of those rotor currents with the stator’s rotating field produces torque, so the rotor begins to turn (never exactly at synchronous speed, due to slip). So the key is the distributed, phase-shifted windings that create opposite poles around the stator to form a rotating field, which in turn causes rotation.