Three Phase Induction Motor.pptx

three phase induction motor

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: A Stator: It is the stationary part of the motor. 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.

10. 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 (N s ). The flux is called as rotating magnetic field. Synchronous Speed: Speed of rotating flux N s =  

11. 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.

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

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

14. 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.

15. 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.

16. Thank you NEXT LESSON: Testing of Transformers