1. INDUCTION MACHINES M ODULE 1 Prepared by: Aswathy Mohandas P

2. I NTRODUCTION Three-phase induction motors are the most common and frequently encountered machines in industry simple design, rugged, low-price, easy maintenance run essentially as constant speed from no-load to full load called as asynchronous motors described as ―transformer type a.c machine in which electrical energy is converted into mechanical energy. Its speed depends on the frequency of the power source not easy to have variable speed control requires a variable-frequency power-electronic drive for optimal speed control 2

3. Advantages It has simple and rugged construction. It is relatively cheap. It requires little maintenance. It has high efficiency, good speed regulation and reasonably good power factor. It has self starting torque. Disadvantages It is essentially a constant speed motor and its speed cannot be changed easily. Its starting torque is inferior to d.c motors. 3

4. P ARTS OF INDUCTION MOTOR 4

5. C ONSTRUCTION Frame: It is the outer body of the motor. Its function are to support the stator core and winding, to protect the inner parts of the machine and serve as a ventilating housing or means of guiding the coolant into effective channels. Stator: It consists of a steel frame which encloses a hollow, cylindrical core made up of thin laminations of silicon steel. A number of evenly spaced slots are provided on the inner periphery of the laminations. 5

6. Rotor: The rotor consists of a laminated core, with slots cut on its outer periphery where windings are placed. The windings may be either of squirrel cage type or wound rotor type. The core is mounted on a steel shaft, provided with bearings on both sides and is supported on end covers attached to the main frame of the motor Shaft and bearings: The rotor shaft is supported by bearings housed in the end shield. 6

7. T YPES OF ROTOR 7

8. Squirrel cage rotorWound rotor 8

9. R OTATING M AGNETIC F IELD D UE TO 3-P HASE C URRENTS 9

10. At instant 1, ωt = 0°. Therefore, the three fluxes are given by, 10

11. At instant 2, ωt = 30°. Therefore, the three fluxes are given by, 11

12. At instant 3, ωt = 60°. Therefore, the three fluxes are given by, 12

13. At instant 4, ωt = 90°. Therefore, the three fluxes are given by, 13

14. SLIP 14

15. ROTOR CURRENT FREQUENCY 15

16. EQUATION FOR STATOR AND ROTOR EMF S 16

17. ROTOR CURRENT 17

18. 18

19. 19

20. ROTOR TORQUE 20

21. STARTING TORQUE 21

22. 22

23. CONDITION FOR MAXIMUM STARTING TORQUE 23

24. TORQUE UNDER RUNNING CONDITION 24

25. 25

26. 26

27. MAXIMUM TORQUE UNDER RUNNING CONDITION 27

28. 28

29. FULL LOAD, S TARTING AND M AXIMUM TORQUES 29

30. T ORQUE - SLIP CHARACTERISTICS 30

31. 31

32. TORQUE – SPEED CHARACTERISTICS 32

33. EFFECT OF ROTOR RESISTANCE UPON TORQUE - SLIP OR TORQUE - SPEED CHARACTERISTIC 33

34. EFFECT OF CHANGE IN SUPPLY VOLTAGE ON TORQUE – SPEED CHARACTERISTIC 34

35. 35

36. POWER STAGES IN AN INDUCTION MOTOR 36

37. 37

38. 38

39. I NDUCTION M OTOR T ORQUE 39

40. R OTOR O UTPUT 40

41. 41

42. I NDUCTION M OTOR T ORQUE E QUATION 42

43. 43

44. 44

45. 45

46. P HASOR D IAGRAM 46

47. 47

48. 48

49. 49

50. 50

51. C IRCLE D IAGRAM 51

52. 52

53. 53