Shreeji International

An AC Induction Motor (IM), also called an Asynchronous Motor, is the most widely used type of AC electric motor. It operates based on electromagnetic induction to create the current and subsequent torque in the rotor, meaning the rotor receives its power without a direct electrical connection.

Induction motors are favored for their simple construction, ruggedness, low maintenance, high reliability, and low cost, making them the workhorse of both industrial and domestic applications.

The operation of an induction motor relies on the principle of magnetic induction and the necessity of slip.

1. Rotating Magnetic Field (RMF): When an AC voltage is applied to the stator windings, it generates a magnetic field that rotates around the stator at a speed called the Synchronous Speed ($N_s$).

   $$N_s = \frac{120 \times f}{P} \quad (\text{in RPM})$$

    

   (Where $f$ is the supply frequency and $P$ is the number of poles.)

2. Induction: This RMF cuts across the conductors of the rotor (which are initially stationary or moving slowly). According to Faraday's Law, this induces an electromotive force (EMF) and a high current in the rotor conductors (as they form a closed circuit).

3. Torque Production: The induced current creates its own magnetic field in the rotor. The interaction between the rotor's magnetic field and the stator's RMF produces a torque, causing the rotor to rotate in the same direction as the RMF.

4. Slip: For current to be induced, the rotor's speed ($N_r$) must always be slightly slower than the synchronous speed ($N_s$). This essential difference is called slip ($s$). If the rotor ran at the exact synchronous speed, there would be no relative movement between the conductors and the RMF, thus no induced current, and no torque.