Induction Motor : Stator, Rotor and Its Principle

0. Induction Motor

The induction motor is invented by the scientist Nikola Tesla and it is the most common motor type even today (Around 90%). About 50% of global electric power consumption is due to induction motors. The induction motor has basically two main parts: Stator and Rotor.

1) Stator: Stationary Part

The stator is the stationary part of an induction motor like Fig 1-2. It is made up of various stampings with slots to carry 3 phase windings. The windings are geometrically divided 120 degrees separated. It

does not require DC current to run the machine.

1. Induction Motor

2) Rotor: Rotating Part

2. :Various Rotors

The rotor is the rotating part of the induction motor. The rotor is simply a collection of conducting bars short-circuited by end rings. Its rotation is because of the interaction between the windings and magnetic fields producing a torque around the rotor's axis. There are many kinds of rotors: Squirrel-cage rotor, Wound rotor, Salient pole rotor, Cylindrical rotor and etc... In an induction rotor, we normally use a Squirrel-cage rotor and Wound rotor.

3) Its Principle

Fig. 3-1 is the picture that explains how induction motor works. The winding passes through the slots of the stator. The AC power(3-phase current) is supplied to the motor's stator creates a rotating magnetic field. This RMF is what causes the rotor to turn. Fig

3-1. 3 phase and RMF

3-2. Induced current in the loop

3-2 explains how 3 phase current through the winding of stator can make RMF. Assuming that a closed conductor is put inside it, according to the Lorentz Force law, an electromagnetic force is produced on the loop like Fig 3-2. In an induction motor, the rotor always lags behind the RMF. The same thing happens in the rotor part.

3-3. Rotor

Fig 3-3 explains how RMF can affect Rotor. According to the Lorentz Force law, the rotor got forced to the direction of the purple arrows and it makes the rotor turn.

Let's think about why induction motors rule both the industrial and domestic worlds! Induction motors don't need a permanent magnet. They do not have brushes, commutator rings, or position sensors. They are more simple than other electrical machines. The most advantage of induction motors is that their speed can be controlled easily by the input power frequency.

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