1. ELECTRICAL TECHNOLOGY (EET 103) PN HAZIAH ABDUL HAMID

2. SYLLABUSSYLLABUS – PART II

3. SYLLABUS TOPIC 4: THREE PHASE CIRCUIT TOPIC 5: TRANSFORMER TOPIC 6: ELECTRICAL MACHINES

4. TOPIC 4: THREE PHASE CIRCUIT

5. SINGLE PHASE TWO WIRE

6. SINGLE PHASE SYSTEM A generator connected through a pair of wire to a load – Single Phase Two Wire. V p is the magnitude of the source voltage, and  is the phase.

7. SINLGE PHASE THREE WIRE

8. SINGLE PHASE SYSTEM Most common in practice: two identical sources connected to two loads by two outer wires and the neutral: Single Phase Three Wire. Terminal voltages have same magnitude and the same phase.

9. POLYPHASE SYSTEM Circuit or system in which AC sources operate at the same frequency but different phases are known as polyphase.

10. TWO PHASE SYSTEM THREE WIRE

11. POLYPHASE SYSTEM Two Phase System: –A generator consists of two coils placed perpendicular to each other –The voltage generated by one lags the other by 90 .

12. POLYPHASE SYSTEM Three Phase System: –A generator consists of three coils placed 120  apart. –The voltage generated are equal in magnitude but, out of phase by 120 . Three phase is the most economical polyphase system.

13. THREE PHASE FOUR WIRE

14. IMPORTANCE OF THREE PHASE SYSTEM All electric power is generated and distributed in three phase. –One phase, two phase, or more than three phase input can be taken from three phase system rather than generated independently. –Melting purposes need 48 phases supply.

15. IMPORTANCE OF THREE PHASE SYSTEM Uniform power transmission and less vibration of three phase machines. –The instantaneous power in a 3  system can be constant (not pulsating). – High power motors prefer a steady torque especially one created by a rotating magnetic field.

16. IMPORTANCE OF THREE PHASE SYSTEM Three phase system is more economical than the single phase. –The amount of wire required for a three phase system is less than required for an equivalent single phase system. –Conductor: Copper, Aluminum, etc

17. THREE PHASE GENERATION

18. FARADAYS LAW Three things must be present in order to produce electrical current: a) Magnetic field b) Conductor c) Relative motion Conductor cuts lines of magnetic flux, a voltage is induced in the conductor Direction and Speed are important

19. GENERATING A SINGLE PHASE Motion is parallel to the flux. No voltage is induced. N S

20. x N S Motion is 45  to flux. Induced voltage is 0.707 of maximum. GENERATING A SINGLE PHASE

21. x N S Motion is perpendicular to flux. Induced voltage is maximum.

22. GENERATING A SINGLE PHASE Motion is 45  to flux. x N S Induced voltage is 0.707 of maximum.

23. GENERATING A SINGLE PHASE N S Motion is parallel to flux. No voltage is induced.

24. GENERATING A SINGLE PHASE x N S Notice current in the conductor has reversed. Induced voltage is 0.707 of maximum. Motion is 45  to flux.

25. GENERATING A SINGLE PHASE N S x Motion is perpendicular to flux. Induced voltage is maximum.

26. GENERATING A SINGLE PHASE N S x Motion is 45  to flux. Induced voltage is 0.707 of maximum.

27. GENERATING A SINGLE PHASE Motion is parallel to flux. N S No voltage is induced. Ready to produce another cycle.

28. THREE PHASE GENERATOR

29. GENERATOR WORK The generator consists of a rotating magnet (rotor) surrounded by a stationary winding (stator). Three separate windings or coils with terminals a-a’, b-b’, and c-c’ are physically placed 120  apart around the stator.

30. As the rotor rotates, its magnetic field cuts the flux from the three coils and induces voltages in the coils. The induced voltage have equal magnitude but out of phase by 120 .

31. GENERATION OF THREE-PHASE AC N xx S

32. THREE-PHASE WAVEFORM Phase 2 lags phase 1 by 120  Phase 2 leads phase 3 by 120  Phase 3 lags phase 1 by 240  Phase 1 lags phase 3 by 120  Phase 1Phase 2Phase 3 120  240  120  240 

33. Phase 1Phase 2Phase 3 GENERATION OF 3  VOLTAGES Phase 1 is ready to go positive. Phase 2 is going more negative. Phase 3 is going less positive. The algebraic sum of the instantaneous voltages of the three phases equals zero. N xx S

34. THREE PHASE QUANTITIES

35. BALANCED 3  VOLTAGES Balanced three phase voltages: –same magnitude (V M ) –120  phase shift

36. BALANCED 3  CURRENTS Balanced three phase currents: –same magnitude (I M ) –120  phase shift

37. PHASE SEQUENCE POSITIVE SEQUENCE NEGATIVE SEQUENCE

38. PHASE SEQUENCE

39. EXAMPLE Determine the phase sequence of the set voltages: Ans: Negative Sequence

40. BALANCED VOLTAGE AND LOAD Balanced Phase Voltage: all phase voltages are equal in magnitude and are out of phase with each other by 120 . Balanced Load: the phase impedances are equal in magnitude and in phase.

41. THREE PHASE CIRCUIT POWER –The instantaneous power is constant

42. THREE PHASE CIRCUIT Three Phase Power,

43. THREE PHASE QUANTITIES QUANTITYSYMBOL Phase currentII Line currentILIL Phase voltageVV Line voltageVLVL

44. PHASE VOLTAGES and LINE VOLTAGES Phase voltage is measured between the neutral and any line: line to neutral voltage Line voltage is measured between any two of the three lines: line to line voltage.

45. PHASE CURRENTS and LINE CURRENTS Line current (I L ) is the current in each line of the source or load. Phase current (I  ) is the current in each phase of the source or load.

46. THREE PHASE CONNECTION

47. SOURCE-LOAD CONNECTION SOURCELOADCONNECTION Wye Y-Y WyeDelta Y-  Delta  -  DeltaWye  -Y

48. SOURCE-LOAD CONNECTION Common connection of source: WYE –Delta connected sources: the circulating current may result in the delta mesh if the three phase voltages are slightly unbalanced. Common connection of load: DELTA –Wye connected load: neutral line may not be accessible, load can not be added or removed easily.

49. WYE CONNECTION

50. WYE CONNECTED GENERATOR

51. WYE CONNECTED LOAD OR

52. BALANCED Y-Y CONNECTION

53. PHASE CURRENTS AND LINE CURRENTS In Y-Y system:

54. PHASE VOLTAGES, V  Phase voltage is measured between the neutral and any line: line to neutral voltage V an V bn V cn

55. PHASE VOLTAGES, V 

56. LINE VOLTAGES, V L Line voltage is measured between any two of the three lines: line to line voltage. V ab V bc V ca

57. LINE VOLTAGES, V L

58. PHASE VOLTAGE (V  ) LINE VOLTAGE (V L )

59. PHASE DIAGRAM OF V L AND V 

60. PROPERTIES OF PHASE VOLTAGE All phase voltages have the same magnitude, Out of phase with each other by 120 

61. PROPERTIES OF LINE VOLTAGE All line voltages have the same magnitude, Out of phase with each other by 120 

62. RELATIONSHIP BETWEEN V  and V L 1.Magnitude 2.Phase - V L LEAD their corresponding V  by 30 

63. EXAMPLE Calculate the line currents

64. Single Phase Equivalent Circuit Phase ‘a’ equivalent circuit 5-j2

66. DELTA CONNECTION

67. DELTA CONNECTED SOURCES

68. DELTA CONNECTED LOAD OR

69. BALANCED  -  CONNECTION

70. PHASE VOLTAGE AND LINE VOLTAGE In  -  system, line voltages equal to phase voltages:

71. PHASE CURRENTS, I  Line voltages are equal to the voltages across the load impedances.

72. PHASE CURRENTS, I  The phase currents are obtained:

73. LINE CURRENTS, I L The line currents are obtained from the phase currents by applying KCL at nodes A,B, and C.

74. LINE CURRENTS, I L

75. PHASE CURRENTS (I  ) LINE CURRENTS (I L )

76. PHASE DIAGRAM OF I L AND I 

77. PROPERTIES OF PHASE CURRENT All phase currents have the same magnitude, Out of phase with each other by 120 

78. PROPERTIES OF LINE CURRENT All line currents have the same magnitude, Out of phase with each other by 120 

79. 1.Magnitude 2.Phase - V L LAG their corresponding V  by 30  RELATIONSHIP BETWEEN I  and I L

80. EXAMPLE A balanced delta connected load having an impedance 20-j15  is connected to a delta connected, positive sequence generator having V ab = 330  0  V. Calculate the phase currents of the load and the line currents.

81. Given Quantities

82. Phase Currents

83. Line Currents

84. BALANCED DELTA-WYE SYSTEM

85. EXAMPLE A balanced positive sequence Y- connected source with V an =100  10  V is connected to a  -connected balanced load (8+j4)  per phase. Calculate the phase and line currents.

86. Given Quantities Balanced WYE source –V an = 100  10  V Balanced DELTA load –Z  = 8+j4 

87. Phase Currents V AB = voltage across Z  = V ab = source line voltage

88. Phase Currents

89. Line Currents

90. DELTA TO WYE CONVERSION

91. THREE PHASE POWER MEASUREMENT

92. FOUR WIRE SYSTEM Each phase measured separately:

93. THREE PHASE THREE WIRE SYSTEM The three phase power is the sum of the two watt- meters reading

94. EXAMPLE Determine the total power (P), reactive power (Q), and complex power (S) at the source and at the load

95. Single Phase Equivalent Circuit Phase ‘a’ equivalent circuit 5-j2

96. Known Quantities V  =V an = 110  0  V Z Y = 10+j8  Z line =5-j2 

97. Line/Phase Currents

98. Source & Load Power

99. EXAMPLE A three phase motor can be regarded as a balanced Y-load. A three phase motor draws 5.6 kW when the line voltage is 220 V and the line current is 18.2 A. Determine the power factor of the motor

100. Known Quantities P Load =5600 W V L = 220 V I L = 18.2 A

101. Power factor Power factor = cos  |S| Q P 