Construction, working principle and types of DC generator – motor Single phase transformer - single phase and three phase Induction motor -Applications

Construction, working principle and types of DC generator – motor
Single phase transformer - single phase and three phase
Induction motor -Applications�

1. UNIT II ELECTRICAL MACHINES Construction, working principle and types of DC generator – motor Single phase transformer - single phase and three phase Induction motor -Applications 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

2. DC GENERATOR A dc generator is an electrical machine which converts mechanical energy into direct current electricity . This energy conversion - dynamically induced EMF . 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

3. Working Principle of a DC Generator According to Faraday’s laws of electromagnetic induction “ whenever a conductor is placed in a varying magnetic field (OR a conductor is moved in a magnetic field) an EMF (electromotive force) is induced in the conductor ”. The magnitude of induced EMF can be calculated from the EMF equation of dc generator. If the conductor is provided with a closed path , the induced current will circulate within the path. In a DC generator - field coils produce an electromagnetic field and the armature conductors are rotated into the field . Thus, an electromagnetically induced EMF is generated in the armature conductors. The direction of induced current is given by Fleming’s right hand rule. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

4. Working Principle of a DC Generator Fleming’s right hand rule states that: Stretch the forefinger, middle finger and thump of the right hand mutually perpendicular to each other. If the forefinger shows the direction of magnetic field , thumb shows the direction of motion of conductor then middle finger shows the direction of emf induced. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

5. Working Principle of a DC Generator 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

6. Construction of a DC Machine Constructional details of a simple 4-pole DC machine 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

7. Construction of a DC Machine A DC machine consists of two basic parts. Stator Rotor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

8. Construction of a DC Machine Yoke: The outer frame of a dc machine is called as yoke. It is made up of cast iron or steel . It not only provides mechanical strength to the whole assembly but also carries the magnetic flux produced by the field winding. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

9. Construction of a DC Machine Poles and pole shoes Poles are joined to the yoke with the help of bolts or welding . They carry field winding and pole shoes are attached to them. Pole shoes serve two purposes . (i) They support field coils (ii) Spread out the flux in air gap uniformly . 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

10. Construction of a DC Machine Field winding: They are usually made of copper . Field coils are prior wound and placed on each pole and are connected in series . They are wound in such a way that when energized they form alternate North and South poles. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

11. Construction of a DC Machine Armature core - keyed to the shaft Armature core is the rotor of a dc machine . It is cylindrical in shape with slots to carry armature winding . The armature is built up of thin laminated circular steel disks for reducing eddy current losses. It may be provided with air ducts for the axial air flow for cooling purposes. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

12. Construction of a DC Machine Armature winding: It is usually a previous wound copper coil which is kept in armature slots . The armature conductors are insulated - each other and - armature core. Armature winding can be wound by one of the two methods, Lap winding or Wave winding. ( Double layer is generally used) Double layer - each armature slot will carry two different coils. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

13. Construction of a DC Machine Commutator and brushes: Physical connection to the armature winding is commutator-brush arrangement. The function of a commutator A dc generator is to collect the current generated in armature conductors . A dc motor commutator helps in providing current to the armature conductors. A commutator consists of a set of copper segments which are insulated from each other. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

14. Construction of a DC Machine Commutator and brushes: A commutator consists of a set of copper segments which are insulated from each other. The number of segments is equal to the number of armature coils. Each segment is connected to an armature coil and the commutator is keyed to the shaft . Brushes are usually made from carbon or graphite . They rest on commutator segments and slide on the segments when the commutator rotates keeping the physical contact and collect the current. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

15. Construction of a DC Machine 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

16. Construction of a DC Machine According to Fleming’s right hand rule “the direction of induced current changes whenever the direction of motion of the conductor changes”. Let’s consider an armature is rotating clockwise and the conductor at the left (conductor AB) is moving upward and the conductor CD is moving downwards. During this process conductor AB is in contact with commutator segment F and conductor CD is in contact with commutator segment F, Now the current flow is from Y to X. When the armature completes a half rotation, the direction of motion of that particular conductor will be reversed. Hence, the direction of current in every armature conductor will be alternating. But with a split ring commutator the direction of current remains same in the load (Y to X). Hence the direction of current in the load is unidirectional. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

17. DC Generator Watch video: https://youtu.be/x78mi794b8k?si=qYR0Ngq2cet2ytW4 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

18. TYPES OF DC GENERATORS Classified according to their methods of field excitation 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

19. Separately Excited DC Generators A dc generator whose field winding is supplied from an independent external dc source (e.g., a battery etc.) is called a separately excited generator . The voltage output depends upon the speed of rotation of armature and the field current . The greater the speed and field current, greater is the generated EMF. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

20. Separately Excited DC Generators Armature current, I a = I L Voltage generated by armature, E g = V + I a R a Electric power developed in the armature = E g I a Power delivered to load = VI L 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

21. Self-Excited DC Generators A dc generator whose field winding is supplied from the output of the generator itself is called a self-excited generator. There are three types of self-excited generators depending on the manner in which the field winding is connected to the armature. Series generator Shunt generator Compound generator 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

22. Series generator In a series wound generator the field winding is connected in series with armature winding so that whole armature current flows through the field winding as well as the load . Since the field winding carries the whole of load current it has a few turns of thick wire having low resistance . 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

23. Series generator Armature current, I a = I se = I L  Voltage generated by the armature, E g = V + I a (R a + R se )  Power developed in armature = E g I a     4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

24. Shunt generator In a shunt generator the field winding is connected in parallel with the armature winding. The shunt field winding has many turns of fine wire having high resistance. Therefore, only a part of armature current flow through shunt field winding and the rest flows through the load . 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

25. Shunt generator Shunt field current, I sh = V/R sh Armature current, I a = I L + I sh Voltage generated in the armature, E g = V + I a R a Power developed in armature = E g I a Power delivered to load = VI L 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

26. Compound generator In a compound-wound generator there are two sets of field windings on each pole ; one is in series and the other in parallel with the armature. A compound wound generator may be: 1. Short shunt 2. Long shunt 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

27. Short shunt compound generator Short Shunt compound generator is one which has a shunt field winding in parallel with the armature winding . This combination is in series with series winding. Armature current, I a = I L + I sh Shunt field current I sh = (V+ I se R se )/R sh Voltage generated in the armature, E g = V + I a R a + I se R se Power developed in armature = E g I a Power delivered to load = VI L 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

28. Long shunt compound generator Long shunt compound generator is one in which the series winding is connected in series with armature winding and this combination is connected in parallel with the shunt field winding. Armature current, I se = I a = I L + I sh Shunt field current, I sh = V/R sh Voltage generated in the armature, E g = V + I a R a + I se R se Power developed in armature = E g I a Power delivered to load = VI L   4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

29. MOTOR An electric motor is an electrical machine which converts electrical energy into mechanical energy. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

30. Working Principle of a DC Motor "Whenever a current carrying conductor is placed in a magnetic field , it experiences a mechanical force ". The direction of this force is given by Fleming's left-hand rule and its magnitude is given by F = BILsinθ. Where, B = magnetic flux density, 3I = current, L = length of the conductor within the magnetic field θ is the angle between flux and conductor. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

31. Working Principle of a DC Motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

32. Fleming's left hand rule Stretch the fore finger, middle finger and thumb of the left hand mutually perpendicular to each other, if the direction of magnetic field is represented by the fore finger , direction of the current is represented by the middle finger, then thumb shows direction of the force experienced by the current carrying conductor . 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

33. Working Principle of a DC Motor When the stator poles of the motor is excited by a dc supply the poles becomes an electromagnet . The magnetic lines of force between the poles is shown in figure A. When armature windings are connected to a DC supply , an electric current sets up in the armature winding . Due to the current flow in the armature conductors a flux is developed in the form of concentric circles around the conductor (as shown in figure B). Due to the interaction of main field and armature field the armature conductors experience a force and the rotor rotates . 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

34. Working Principle of a DC Motor Magnetic neutral axis - MNA 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

35. Working Principle of a DC Motor   Commutator and carbon brushes arrangement is used to provide DC supply to the armature. The commutator segments provide unidirectional current flow in the armature conductors on one side of magnetic neutral axis (as shown above). The current flow in the conductors on the left hand side of MNA is opposite to that in the right side, so that torque is unidirectional.   4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

36. Construction 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

37. Yoke The outer frame of a dc machine is called as yoke . It is made up of cast iron or steel . It not only provides mechanical strength to the whole assembly but also carries the magnetic flux produced by the field winding. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

38. Poles and pole shoes Poles are joined to the yoke with the help of bolts or welding . They carry field winding and pole shoes are fastened to them. Pole shoes serve two purposes; (i) They support field coils (ii) Spread out the flux in air gap uniformly. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

39. Field winding They are usually made of copper . Field coils are previously wound and placed on each pole and are connected in series. They are wound in such a way that, when energized , they form alternate North and South poles . 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

40. Armature core Armature core is the rotor of a dc machine . It is cylindrical in shape with slots to carry armature winding. The armature is built up of thin laminated circular steel disks for reducing eddy current losses. It may be provided with air ducts for the axial air flow for cooling purposes. Armature is keyed to the shaft. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

41. Armature winding It is usually a previous wound copper coil which is kept in armature slots. The armature conductors are insulated - each other and - armature core. Armature winding can be wound by one of the two methods , Lap winding or Wave winding. (Double layer is generally used) Double layer - each armature slot will carry two different coils. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

42. Commutator and brushes Physical connection to the armature winding is made through a commutator-brush arrangement . The function - to provide current to the armature conductors. A commutator consists of a set of copper segments which are insulated from each other. The number of segments is equal to the number of armature coils. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

43. Commutator and brushes Each segment is connected to an armature coil and the commutator is keyed to the shaft . Brushes are usually made from carbon or graphite . They rest on commutator segments and slide on the segments when the commutator rotates keeping the physical contact and provide the current. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

44. Back EMF When the armature of a motor is rotating , the conductors are also cutting the magnetic flux lines and hence according to the Faraday's law of electromagnetic induction, an emf induces in the armature conductors. The direction of this induced emf is such that it opposes the armature current (I a ). The circuit diagram below illustrates the direction of the back emf and armature current. E b = PNФZ/60A P-Number of poles, N-Speed of rotor, A-Number of parallel paths in armature, Ф -magnetic flux, Z- number of armature conductors 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

45. TYPES OF DC MOTORS Generally classified according to their methods of field excitation . 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

46. Separately Excited DC motor A dc motor whose field winding and armature winding are supplied from independent dc source (e.g., a battery etc.) is called a separately excited motor. The speed of motor depends upon the supply voltage and field current . (Eb =PØ ZN/60A). Armature current, I a = I L Line voltage, V = E b + I a R a + V brush Power supplied by source = VI L 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

47. Self-Excited DC motor A dc motor whose field winding is supplied from the same excitation is called a self-excited motor. There are three types of self-excited motor depending on the manner in which the field winding is connected to the armature. Series motor Shunt motor Compound motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

48. Series Motor In series wound motor the field winding is connected in series with the armature. Since the current passing through a series field winding is the same as the armature current series field windings must be designed with much fewer turns. A series field winding has a relatively small number of turns of thick wire and therefore will possess a low resistance. Armature current, I a = I se = I L Line voltage, V = E b + I a (R a + R se ) + V brush 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

49. Shunt Motor In shunt wound motor the field winding is connected in parallel with armature winding. The current through the shunt field winding is not the same as the armature current. Shunt field windings are designed to produce the necessary EMF by means of a relatively large number of turns of wire having high resistance. Therefore, shunt field current is relatively small compared with the armature current. Shunt field current, I sh = V/R sh Line current, I L = I a + I sh Line voltage, V = E b + I a R a + V brush 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

50. Compound motor In a compound-wound motor, there are two sets of field windings on each pole, one is in series and the other in parallel with the armature winding. A compound wound motor may be: Short shunt Long shunt 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

51. Short shunt compound motor Short Shunt compound motor is one which has a shunt field winding in parallel with the armature winding. This combination is in series with series field winding. Line current, I L = I se = I a + I sh Shunt field current, I sh = (V- I se R se )/R sh Line voltage, V = E b + I a R a + I se R se + V brush Power supplied = VI L 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

52. Long shunt compound motor Long shunt compound motor is one in which the series field winding is connected in series with armature winding and this combination is connected in parallel with the shunt field winding 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

53. Long shunt compound motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

54. TYPES OF SINGLE PHASE INDUCTION MOTOR (BASED ON STARTING METHODS) The single-phase induction motor has no starting torque . In a single-phase induction motor - auxiliary winding in stator & main winding - angle of 90 degree (electrical) - starting torque is produced. The currents main and auxiliary stator windings - 90 degree ( maximum starting torque ). Split-phase motor Capacitor-start motor Capacitor-start and capacitor-run motor Permanent capacitor motor Shaded-pole induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

55. SPLIT-PHASE MOTOR 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› In split phase motor - auxiliary winding is added along with the main winding in the stator. This winding has higher resistance and low reactance. The phasor diagram of the currents in two windings and the input voltage is shown in Fig. The current in the main winding - lags - current in auxiliary winding by an angle θ. This results in a small amount of starting torque . The centrifugal switch is in series with the auxiliary winding .

56. SPLIT-PHASE MOTOR 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

57. SPLIT-PHASE MOTOR 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› It automatically cuts out the auxiliary winding when the motor attains a speed close to 75% of rated load speed . The motor has a starting torque of 100−200% of full load torque & starting current as 5-7 times the full load current . The direction of rotation is reversed by reversing the terminals of any one of two windings. This motor is used in applications, such as fan, saw, small lathe, centrifugal pump, blower, office equipment, washing machine, etc.

58. CAPACITOR-START MOTOR 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› A capacitor along with a centrifugal switch is connected in series with the auxiliary winding (starting winding). The function of the centrifugal switch is open the auxiliary winding when 75% of rated speed has been achieved . The phasor diagram of two currents and the torque-speed characteristics of the motor with/without auxiliary winding, are shown in Fig. The starting torque is much better the phase difference is close to 90 o . This motor is used in applications, such as compressor, conveyor, machine tool drive, refrigeration and air-conditioning equipment, etc.

59. CAPACITOR-START MOTOR 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

60. Capacitor - start and Capacitor - run Motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› In this motor two capacitors − Cs for starting and Cr for running . The first capacitor is rated for intermittent duty , being used only for starting . A centrifugal switch is also needed here. The second one is to be rated for continuous duty , as it is used for running . The phase difference between the starting and running winding (90 o ) provides the starting torque. The efficiency of the motor under this condition is higher . Using two capacitors, the performance of the motor improves both at the time of starting and then running. This motor is used in applications, such as compressor, refrigerator, etc.

61. Capacitor-start and Capacitor-run Motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

62. Permanent Capacitor Motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› Permanent Capacitor Motor does not use a centrifugal switch . The same capacitor is utilized for both starting and running . The power factor - when running is high . The operation is also quiet and smooth . This motor is used in applications, such as ceiling fans, air circulator, blower, etc.

63. Permanent Capacitor Motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

64. Shaded-pole induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› The stator has salient or projected poles . A small portion of each pole is covered with a short-circuited , copper coil called the shading coil . The sinusoidally varying flux created by single-phase ac excitation of the main winding induces EMF in the shading coil . Induced currents flow in the shading coil producing their own flux in the shaded portion of the pole.

65. Shaded-pole induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› Shaded-pole motor is single-winding (no auxiliary winding) self-starting one. Less costly and results in rugged construction . The motor has low efficiency and a range of 1/300 to 1/20 kW. It is used for domestic fans, record players and tape recorders, humidifiers, slide projectors, small business machines, etc.

66. Shaded-pole induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

67. Shaded-pole induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

68. Shaded-pole induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› During the portion OA of the alternating-current cycle [Fig 1], the flux begins to increase and an EMF is induced in the shading coil . The resulting current in the shading coil will be in such a direction ( Lenz’s law ) so as to oppose the change in flux . Thus the flux in the shaded portion of the pole is weakened while that in the unshaded portion is strengthened (figure 2). During the portion AB of the alternating-current cycle, the flux has reached the almost maximum value and is not changing. Consequently, the flux distribution across the pole is uniform [See Fig 3] since no current is flowing in the shading coil.

69. Shaded-pole induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› During the portion AB of the alternating-current cycle, the flux has reached the almost maximum value and is not changing . Consequently, the flux distribution across the pole is uniform [See Fig 3] since no current is flowing in the shading coil .

70. Shaded-pole induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› As the flux decreases (portion BC of the alternating current cycle), current is induced in the shading coil so as to oppose the decrease in current . Thus the flux in the shaded portion of the pole is strengthened while that in the unshaded portion is weakened as shown in Fig 4. The effect of the shading coil is to cause the field flux to shift across the pole face from the unshaded to the shaded portion .

71. Shaded-pole induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› This shifting flux - a rotating weak field moving in the direction from unshaded portion to the shaded portion of the pole . The rotor is of the squirrel- cage type and is under the influence of this moving field - a small starting torque is developed. This torque starts to revolve the rotor , additional torque is produced by induction . The motor accelerates to a speed slightly below the synchronous speed and runs as a single-phase induction motor .

72. Three phase induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› It is a rotating electric machine that is designed to operate on a three-phase supply. The 3 phase motor is also called as an asynchronous motor . These AC motors are of two types: squirrel and slip-ring type induction motors. The principle of operation of this motor is based on the production of a rotating magnetic field .

73. Three phase induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

74. Three phase induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› Consist of stator and rotor and between which no electrical connection exists. These stator and rotors are constructed with the use of high-magnetic core materials in order to reduce hysteresis and eddy current losses. Stator frame can be constructed using cast iron, aluminum, or rolled steel.

75. Three phase induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› The stator frame provides - mechanical protection and support for stator laminated core, windings, and other arrangements for ventilation. The stator is wounded with three-phase windings which are overlapped with one another at a 120-degree phase shift fitted into slotted laminations. The six ends of the three windings are brought out and connected to the terminal box so that these windings are excited by three-phase main supply .

76. Three phase induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› These windings are of copper wire insulated with varnish fitted into insulated slotted laminations. These windings have high-insulation resistance and high resistance to the saline atmosphere, moisture, alkaline fumes, oil, and grease, etc. these windings are connected in either star or delta connections.

77. Three phase induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

78. Three phase induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› The rotor - different for slip-ring and squirrel-cage induction motors . The rotor in the slip-ring type consists of heavy aluminium or copper bars shorted on both ends of the cylindrical rotor . The shaft of the induction motor is supported on two bearings at each ends to ensure free rotating within the stator and to reduce the friction. It consists of a stack of steel laminations evenly spaced slots that are punched around of its circumference into which un-insulated heavy aluminium or copper bars are placed.

79. Three phase induction motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› A slip-ring-type rotor - are internally starred at one end and the other ends are brought outside and connected to the slip rings mounted on the rotor shaft. Developing a high-starting torque - windings are connected to rheostat with the help of carbon brushes . This external resistor or rheostat is used at the starting period only. Once the motor attains the normal speed the brushes are short-circuited and the wound rotor works as a squirrel cage rotor.

80. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› Three phase induction motor

81. Principle of Operation of 3-Phase Induction Motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› RMF: Rotating Magnetic Field

82. Principle of Operation of 3-Phase Induction Motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› Stator is excited with a three-phase supply. Three-phase stator winding produces a rotating magnetic field with 120 o displacements at a constant magnitude which rotates at synchronous speed. This changing magnetic field cuts the rotor conductors and induces a current in them according to the principle of Faraday’s laws of electromagnetic induction . As these rotor conductors are shorted , the current starts to flow through these conductors.

83. Principle of Operation of 3-Phase Induction Motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› In the presence of the magnetic field of the stator , rotor conductors are placed - according - Lorenz force principle , “ a mechanical force acts on the rotor conductor”. This rotor conductor’s - by Lenz’s law “Induced currents in the rotor oppose the cause for its production, here this opposition is rotating magnetic field”. This result the rotor starts rotating in the same direction of the stator rotating magnetic field.

84. Principle of Operation of 3-Phase Induction Motor 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› If the rotor speed more than the stator speed , then no current will induce in the rotor because the reason for rotor rotation is the relative speed of the rotor and stator magnetic fields . Stator and the rotor field difference are called slip. A 3-phase motor is called an asynchronous machine due to this relative speed difference between the stator and the rotors. Relative speed between the stator field and the rotor conductors causes to rotate the rotor in a particular direction. The rotor speed Nr must always be less than the stator field speed Ns , and the difference between these two parameters depends on the load on the motor.

85. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#› The difference of speed or the slip of the AC induction motor is given as When the stator is stationary, Nr=0; so the slip becomes 1 or 100% When, Nr is at synchronous speed, the slip becomes zero; The slip in the 3 phase induction motor from no load to full load is about 0.1% to 3%; that’s why the induction motors are called as constant-speed motors.

86. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

87. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

88. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

89. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

90. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

91. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

92. Core Type Transformer

93. Shell Type Transformer

94. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

95. Basic Principle 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

96. Basic Principle The ac primary current produces an alternating flux (Ф) in the core. Most of this changing flux gets linked with the secondary winding through the core. The varying flux will induce voltage into the secondary winding according to the faraday’s laws of electromagnetic induction. Voltage level change but frequency i.e. time period remains same. There is no electrical contact between the two winding, an electrical energy gets transferred from primary to the secondary.

97. Basic Principle A simple transformer consists of two electrical conductors called the primary winding and the secondary winding. Energy is coupled between the windings by the time varying magnetic flux that passes through( links) both primary and secondary windings.

98. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

99. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

100. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

101. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

102. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

103. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›

104. 4/4/2024 SXCCE/MECH-B/BEEE/CO2: Understand the working principles and applications of electrical machines. ‹#›