If any two phases are reversed, rotation will change.

If any two phases are reversed, rotation will change.

• A. The machine stops
• B. Rotation will change
• C. The speed doubles
• D. The torque reverses but continues

Answer: (B)

The direction of rotation in a three-phase machine is set by the order of the phase voltages, the phase sequence. The three phase currents create a rotating magnetic field that turns in a specific direction based on that sequence. If you swap any two phases, the phase sequence is reversed, so the rotating magnetic field also reverses its rotation. The speed and the torque magnitude stay essentially the same for a given supply and load, so you don’t get a stop, a doubled speed, or a torque reversal with continued forward rotation. The result is simply that the rotation direction changes.

The direction of rotation in a three-phase machine is set by the order of the phase voltages, the phase sequence. The three phase currents create a rotating magnetic field that turns in a specific direction based on that sequence. If you swap any two phases, the phase sequence is reversed, so the rotating magnetic field also reverses its rotation. The speed and the torque magnitude stay essentially the same for a given supply and load, so you don’t get a stop, a doubled speed, or a torque reversal with continued forward rotation. The result is simply that the rotation direction changes.