1. Motors
3 phase Induction Motor

2. 3 Phase Induction Motor Introduction to 3 Induction Motors
Dept of E & E, MIT Manipal
3 Phase Induction Motor
Introduction to 3 Induction Motors
Applications
Classification
Constructional Features
Summary
References
Edward Hughes, Chapter
Nagasarkar & Sukhija, Chapter 8
Nagrath & Kothari, Chapter 12

3. Introduction Invented by Nikola Tesla, 1888
Dept of E & E, MIT Manipal
Introduction
Nikola Tesla
( )
Invented by Nikola Tesla, 1888
Converts electrical power into mechanical power
Energy transfer by means of electromagnetic induction
Widely used for commercial & industrial applications

4. Applications Industrial & Commercial Applications Pumping Systems
Dept of E & E, MIT Manipal
Applications
Industrial & Commercial Applications
Pumping Systems
Refrigeration Systems
Compressors
Fans & Blowers
Industrial Drives

5. Rotating Magnetic Field
3 phase supply is given to a balanced 3 phase winding of stator.
3 alternating magnetic fluxes displaced mutually at 120 deg. Is produced.

6. Rotating Magnetic Field
Considering different instances of time (i) At wt = 0 The instantaneous fluxes are The resultant magnetic flux is 1.5 times peak value and acting at 90 deg. to axis of reference.

7. Rotating Magnetic Field
Similarly (ii) At wt = 60 The instantaneous fluxes are The resultant magnetic flux is 1.5 times peak value and acting at 30 deg. to axis of reference. i.e., rotated by 60 deg w.r.t. previous angle

8. Rotating Magnetic Field
Similarly if various instances are considered upto 360 deg. It is seen that the resultant always has a magnitude of 1.5 times peak value and pointing in a direction at the angle of consideration. For every 360 deg the resultant magnetic field completes one rotation. Inference: When 3 phase currents flows in a balanced 3 phase winding, a rotating magnetic field is created which has constant magnitude, but rotates in synchronism with supply frequency. This speed of rotating magnetic field is SYNCHRONOUS SPEED

9. Classification Construction Connection Squirrel Cage, Slip Ring
Dept of E & E, MIT Manipal
Classification
Construction
Squirrel Cage, Slip Ring
Connection
Stator : Star, Delta
Rotor : Cage, Wound

10. Dept of E & E, MIT Manipal
Construction – Stator
Stator frame: Cast Iron, Mechanical Support to stator core
Stator core: Stack of cylindrical steel laminations
Stator Slots: Inner periphery, Windings
Laminations
Slots
Stator Conductors

11. Construction – Stator Stator support Outer frame Stator Core
Dept of E & E, MIT Manipal
Construction – Stator
Stator support
Outer frame
Stator Core
Stator Slots
Stator insulation
Stator windings

12. Construction – Rotor Types on the basis of rotor construction
Dept of E & E, MIT Manipal
Construction – Rotor
Types on the basis of rotor construction
Squirrel Cage Rotor
Slip Ring Rotor
Cylindrical Laminated core
Slots cutout on outer periphery
Conductors placed in slots

13. Construction – Squirrel cage Rotor
Dept of E & E, MIT Manipal
Construction – Squirrel cage Rotor
Rotor bars
Skewed arrangement
Copper or Aluminum Bars
Conductors shorted by end rings
Closed rotor circuit
End rings

14. Construction – Slip ring rotor
Dept of E & E, MIT Manipal
Construction – Slip ring rotor
One end of Rotor conductors connected to each other
Other ends connected to slip rings
External resistance
Slip rings in contact with brushes
Brushes connected to external resistance
Brush
Rotor
Shaft
Slip rings
Rotor Conductors

15. Construction – Squirrel cage Rotor
Dept of E & E, MIT Manipal

16. Construction – Slip Ring Rotor
Dept of E & E, MIT Manipal
Construction – Slip Ring Rotor
Slip rings

17. Cross Sectional View Terminal Box Stator Cage Rotor Shaft
Dept of E & E, MIT Manipal
Cross Sectional View
Terminal Box
Stator
Cage Rotor
Shaft
Ball Bearings
Outer Frame
Supporting Base

18. Induction motor setup
Dept of E & E, MIT Manipal

19. Representation Stator Core Stator Slots 3Ø Supply Stator conductors
Dept of E & E, MIT Manipal
Stator Core
3Ø Supply
Stator Slots
Stator conductors
Rotor Core
Shaft
Rotor Slots
Rotor conductors

20. Air gap Uniform over stator & rotor periphery
Dept of E & E, MIT Manipal
Uniform over stator & rotor periphery
Must be as small as possible
usually of the order 0.5 mm to 1 mm
Reduce the leakage flux between stator and rotor
Leads to better operating power factor
Necessary to facilitate free rotor movement

21. Lecture 1 Summary Applications, Classifications
Dept of E & E, MIT Manipal
L1 – 17
Applications, Classifications
Main Parts : Stator, Rotor
Rotor
Squirrel cage : Skewed arrangement, End rings
Wound rotor : Slip rings, external resistance
Air gap
Provided to enable free rotor rotation
Rotating magnetic field
Rotating nature with resultant of constant magnitude