What is an Induction Motor (Asynchronous Motor)

An Induction Motor or Asynchronous Motor is the most basic and common type of electric motor which has only Armortisseur winding which means auxiliary winding only on the armature. In an Induction Motor (or Asynchronous motor), the Stator part of the motor provides electromagnetic field with its winding, to the Rotor part of the motor. This generates an electric current in the Rotor. The electric current produces the torque which results in motion.

Fig. 1 – Introduction to Induction Motor (Asynchronous Motor)

It is referred to as “ Asynchronous Motor ” as it will always run at a speed less than it’ssynchronous speed. Synchronous speed is defined as the speed of the magnetic field of a rotary machine which is again determined by the number of poles and frequency in the machine.

Since in this type of Motor, Rotor gets it flux and rotation by the magnetic field in the Stator, there is a lag between the currents in Stator and Rotor. Due to this, the Rotor never reaches its synchronous speed. Hence the term “Asynchronous Motor”. Fig. 2 shows parts of Asynchronous Motor.

Fig. 2 – Parts of Induction Motor (Asynchronous Motor)

Construction of Induction Motor (Asynchronous Motor)

It consists of mainly two parts namely:

• Stator
• Rotor

Stator

It is the stationary part of an electric motor. This part provides the electromagnetic field required to drive the rotating part of the motor. It is made up of a number of stampings with slots to carry three-phase winding. Each winding is separated by 120 degrees from the other winding.

Rotor

It is the rotating part of the motor. The more common type of Rotor in Induction Motors (or Asynchronous Motor) is the squirrel cage one. The Rotor is shaped as an anchor with a core which is cylindrical in shape. Around the core are parallel slots which carry the conduction. The core has a bar made of aluminum, copper, or alloy.

Fig. 3 – Basic Rotor and Stator

Types of Induction Motor (Asynchronous Motor)

It is classified into two types:

• SinglePhaseInductionMotor
• ThreePhaseInductionMotor

SinglePhaseInductionMotor

Single Phase Induction Motor is not a self-starting motor. Here motor is connected to a single-phase power supply which carries an AC current to the main winding. Since AC supply is a sinusoidal wave, it produces a pulsating magnetic field in the Stator winding.

Pulsating magnetic fields are two magnetic fields rotating in opposite directions; hence no torque is generated.So after supplying the current, Rotor has to be moved in either direction externally for the motor to start running. Single Phase inductor hence; can have different varieties depending on the device that is used to start the motor and they are:

• SplitPhaseMotor
• ShadedPoleMotor
• CapacitorStartMotor
• Capacitor Start and Capacitor Run Motor

Fig. 4 – Schematic Diagram of (a) Single Phase (b) Three Phase Induction Motor