How do you reverse a 3-phase induction motor?

How do you reverse a 3-phase induction motor?

• A. Swap any two of the three power leads (T1, T2, T3).
• B. Swap the rotor windings.
• C. Change the supply frequency.
• D. Reverse the direction of the DC offset in the input.

Answer: (A)

Swapping the direction of rotation comes from changing the phase sequence of the stator supply. A three-phase motor relies on three voltages that are 120 degrees apart to create a rotating magnetic field. The direction of that field depends on the order in which the phases reach their peaks. If you swap two of the supply leads, the phase sequence changes (for example from ABC to ACB), which makes the rotating magnetic field spin the other way. The rotor simply follows this field, so the motor runs in the opposite direction. The rotor windings aren’t the method here, especially for a typical squirrel‑cage motor where you can’t practically swap rotor connections. Changing the supply frequency would change speed (via Ns = 120f/p) but not the rotation direction. A DC offset in the input isn’t part of a standard three‑phase AC supply, so it won’t reverse direction. So the correct action is to swap any two of the three power leads.

Swapping the direction of rotation comes from changing the phase sequence of the stator supply. A three-phase motor relies on three voltages that are 120 degrees apart to create a rotating magnetic field. The direction of that field depends on the order in which the phases reach their peaks. If you swap two of the supply leads, the phase sequence changes (for example from ABC to ACB), which makes the rotating magnetic field spin the other way. The rotor simply follows this field, so the motor runs in the opposite direction.

The rotor windings aren’t the method here, especially for a typical squirrel‑cage motor where you can’t practically swap rotor connections. Changing the supply frequency would change speed (via Ns = 120f/p) but not the rotation direction. A DC offset in the input isn’t part of a standard three‑phase AC supply, so it won’t reverse direction.

So the correct action is to swap any two of the three power leads.