1. STATE STAFF TRAINING AND RESEARCH CENTRE
ALIGANJ LUCKNOW
PRESENTATION
ON
THREE PHASE INDUCTION MOTOR
Submitted by:
Name : Noorul Amin
Trade : Electrician

2. Overview
 Introduction
 Components
 Construction
 Rotating Magnetic Field
 Working Principle
 Application
 Advantages
 Disadvantages

3. Introduction
 Electrical Machine are Electromechanical Energy conversion devices.
 Electrical Motor converts Electrical Energy into Mechanical Energy and electrical
generators are vice versa.
 An induction motor works on transforming action.
 The stator works as the primary while the rotor works as the secondary.
 It is also called asynchronous motor.
 Most of the industrial load are inductive, especially 3- phase induction motor are
widely used in industrial applications for continuous operation.

4. Components
 Frame
 Stator
 Stator Winding
 Rotor
 Rotor Winding
 Cooling Fan
 Bearings

5. Construction
 A three-phase induction motor
consists of two major parts:
1. A Stator: It is the stationary part of
the motor.
2. A Rotor: It is the rotating part of the
motor.

6. Stator has three main parts:
 Outer Frame – It is the outer body of the motor.
It protects the inner part of the machine.
 Stator Core – Built up of high grade Silicon Steel.
Carries the alternating magnetic field.
 Stator Winding – Has a three phase winding.

7. Rotor
 There are two types of rotors which are employed in 3 – phase induction motor.
 Squirrel Cage Rotor.
 Phase Wound/ Slip Ring Rotor.

8. Squirrel Cage Rotor
 It consists of a laminated cylindrical core having
semi closed circular slots at the outer periphery.
 Copper or aluminium bar conductors are placed in
these slots and short circuited at each end by
copper or aluminium rings called short circuiting
rings.
 The rotor winding is permanently short circuited
and it is not possible to add any external
resistance.

9. Phase Wound/ Slip Ring Rotor
 Consists of a laminated core having semi closed
slots at the outer periphery and carries a 3-phase
insulated winding.
 The rotor is wound for the same number of poles as
that of stator.
 The three finish terminals are connected together
forming a star point and the three star terminals are
connected to three slip rings fixed on the shaft.

11. Rotating Magnetic Field
 When a 3 phase stator winding is connected to a 3 phase voltage supply, 3 phase
current will flow in the windings, which also will induced 3 phase flux in the stator.
 These flux will rotate at a speed called a synchronous speed (Ns). The flux is called
as rotating magnetic field.
 Synchronous Speed: Speed of rotating flux
Ns =
120 f
p

12. Working Principle
 When 3 phase supply is given to the
resulting current generates a magnetic
flux “Φ”.
 According to Faraday’s law, Emf is
induced in the Copper bar and due to
this, current flows in the rotor.
 The direction of the rotor can be given
by Lenz law.

13. Slip
 Induction motor rotor always rotate at a speed less than synchronous speed.
 The difference between the flux (Ns) and the rotor Speed (N) is called Slip.
% Slip =
(Ns – N)
Ns
∗ 100
Slip Speed = (Ns – N)

14. Application
 Pumps and submersible
 Pressure machine
 Lathe machine
 Grinding machine
 Conveyor
 Flour mills
 Compressor

15. Advantages
 The construction of motor is very simple and robust.
 The working of an induction motor is very simple.
 It can operate in any environment condition.
 The efficiency of the motor is very high.
 The maintenance of an induction motor is less compared to other motors.

16. Disadvantages
 During light load condition, the power factor is very less and it draws more
current. So, the copper loss is more which reduce the efficiency during light load
condition.
 The induction motor is a constant speed motor. For the application where variable
speed requires, this motor is not used.
 Speed control of this motor is difficult.
 The induction motor has a high starting inrush current. This causes a reduction in
voltage at the time of starting.

17. Thank you
NEXT LESSON: Testing of Transformers