What is Induction Motor: Types, Working Principles and Applications

Introduction of induction motor:

The induction motors are basically ac motors.
They need an alternating voltage as the source of energy for their operation.

They operate on single phase or three phase ac supply

Types of Induction Motors

1. Slip ring
2. Squirrel Cage

Advantages

1. Low maintenance requirement.
2. Smaller in size.
3. Low cost.
4. Operate at higher speed.
5. It runs at constant speed

Disadvantages

1. Efficiency of motors varies with speed.
2. In induction motors the flux and armature current cannot be controlled separately, as there is only stator winding and rotor is not accessible for the user.
3. They have low starting torque
4. They have lagging and low power factor

Application

1. Fans
2. Pumps
3. Conveyors
4. Food and chemical industries
5. Paper and sugar industries.

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Construction of 3-Phsae Induction Motor

There are two main parts of a 3-phase induction motor

1. Stator
2. Rotor

Stator:

It is the stationary part of the motor. This part is made of silicon steel stampings thin sheets). The stampings are slotted.

The slots may be open type, semi-open type or closed type. In these slots, a 3-phase winding is accommodated.

The stator windings, stator and the AC. supply connected to the stator winding.

Fig.4.1 Induction Motor

Rotor

There are two types of induction motors depending upon the construction of the rotor:
1. Squirrel cage type

2. Wound rotor type

This is the simplest and most rugged construction. The rotor consists of a cylindrical laminated core with bronze and there are three brushes resting on them.
skewed rotor slots.
The rotor conductors which are thick copper bars, are placed in these slots and are brazed or welded to and rings.
Thus, the rotor conductors are permanently circuited. short- Therefore it is not possible
resistance to add any external in the rotor circuit.

The rotor body is made of silicon steel stampings. construction The of the rotor
and hence looks like a cage of "squirrel" called as "squirrel cage type motor"

Fig.4.2. Squirrel cage rotor

Fig.4.3. Slip-Ring type motor rotor

Induction Motor Parts and their Functions

Part	Material	Function
Stator frame	Case iron	Supports the core, protects inner parts.
Stator core	Silicon steel	Houses stator winding.
Stator winding	Copper and insulated	Produces rotating magnetic field.
Rotor core	Silicon steel	Houses rotor winding.
Rotor winding	Copper and insulated	To produces rotor cureent.
Air gap	_	To provide gap in rotor and stator.
Air inlet-outlet	_	For air circulation.
Cooling fan	Aluminium	For air circulation.
Slip-rings	Phosphorus broze	Connects resistance to rotor ciruit via- brushes.
Brushes	Carbon	To provides connection between residtance and slip-rings.
Shaft	M.S.	Supports rotor.

Rotor

There are two types of induction motors depending upon the construction of the rotor:
1. Squirrel cage type

2. Wound rotor type

This is the simplest and most rugged construction. The rotor consists of a cylindrical laminated core with bronze and there are three brushes resting on them.
skewed rotor slots.
The rotor conductors which are thick copper bars, are placed in these slots and are brazed or welded to and rings.
Thus, the rotor conductors are permanently circuited. short- Therefore it is not possible
resistance to add any external in the rotor circuit.