Induction motor starting direction

[John94N]

I have a question on induction motor starting direction. I understand the phase delay between the running winding and starting winding, but I don’t see why an induction motor should start in the same direction each time. Is there a directional bias on the stator or rotor coils that ensures the torque is always in one direction?

 

[Phrak]

The bias is obtained from the start winding used in conjunction with the run winding to start the motor.

Let's say the start winding induces a magnetic field in the armature so the north pole is at 12:00 o'clock. After a delay, the run winding peaks with it's south pole at 3:00 o'clock and north pole at 9:00. This will induce the armature to rotate clockwise.

 

[John94N]

That's makes sense. Thanks.

 

[Phrak]

You're welcome. Glad to help.

 

[PJC01]

Thank you for your question. The direction of an induction motor's starting rotation is determined by the design and construction of the motor itself. While the phase delay between the running and starting windings does play a role, it is not the only factor.

One of the main factors that determine the starting direction of an induction motor is the stator and rotor winding configuration. The stator winding is typically designed in such a way that it produces a rotating magnetic field. This field interacts with the rotor winding, causing it to rotate in a specific direction.

Additionally, the shape and placement of the rotor bars also contribute to the directional bias of the motor. The shape and placement of the rotor bars create a magnetic field that interacts with the stator field, resulting in a unidirectional torque.

Overall, it is the combination of these design elements that ensures the induction motor will start in the same direction each time. Any variations in the design or construction of the motor can affect the starting direction, but it is typically designed to start in a specific direction for optimal performance.