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What is Induction Motor?

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An induction motor is a type of an AC (alternating current) motor and is also called as a squirrel-cage motor or asynchronous motor. In an induction motor, electric current is given to the rotor, to produce torque, by means of an electromagnetic induction. Thus an induction motor works without any mechanical commutation and excitation of the energy. Now we will first throw some light on the history of Induction motor, after that we will check different types of Induction motors and at the end we will check their limitations. This tutorial is throwing lights on the basics of Induction motor which are very essential for an engineer to learn.

History

Francois Arago, a French physicist, described the presence of rotating magnetic fields, the Arago's rotations, in 1824. In 1885, a working motor model was presented by Galileo Ferraris and then Nikola Tesla invented the AC induction motor in 1887.

Types of induction motor

There are three types of induction motor:

• Single Phase Induction Motor

Single phase induction motors are used with the single power supply. It is the simplest induction motor and is used commonly. Here torque is produced by a wire loop on a frame through alternating current. These are used extensively for smaller loadslike household appliances.

• Two phase Induction Motor

A two phase induction motor used as servomotor in control system and is high speed, low torque machine that produce reversible torque. It consists of a squirrel cage rotor and a two windings’ (AC) field that are:

1. A constant voltage main winding.
2. A control voltage winding in quadrature with the main winding.

• Three Phase Induction Motor

A three phase induction motor operates through a three phase source of AC. It can be of two types:

1. Squirrel cage three phase induction motor.
2. Wound three phase induction motor.

Out of these, squirrel cage three phase induction motor is used commonly. It contains a three phase stator through which AC is passed to create rotor current which in turn generates torque and rotating magnetic field.

Applications of Induction Motor

Single phase and three phase induction motors are used commonly in domestic appliances and industries because these are

• Reliable
• Easy to start
• Less expensive
• Require less maintenance
• Rugged
• Economical.

These motors have no need of any slip ring, commutator or brush like DC motors.

• Single phase induction motors produce fractional horsepower and are commonly used in household appliances like blenders, washing machines, fans and juice mixtures etc.
• Three phase induction motors produce tens or hundreds of horsepower and are used in cranes, pumps, compressors, lifts, large capacity exhaust fans, hoists, crushers, in paper mills, textile and in oil extracting mills etc.

Limitations of Induction Motor

Although there are a lot of applications of induction motor but still it has some limitations that are as follows:

• It has low starting torque as compared to Dc motor.
• If the load is increased, speed of the motor is decreased.
• Its speed cannot be changed until frequency is reduced.

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