Electrical Engineering – Past Papers PPSC

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1. : The main purpose of using a transformer is to: (PPSC Electrical Engineer – 2021)
(A) Convert AC to DC
(B) Step up or step down AC voltage
(C) Increase frequency
(D) Decrease current losses only

2. : The core of a transformer is laminated to: (WAPDA Electrical Engineer – 2020)
(A) Reduce copper losses
(B) Reduce eddy current losses
(C) Increase efficiency
(D) Reduce hysteresis losses

3. : In a transformer, the voltage per turn is: (LESCO Electrical Engineer – 2021)
(A) Same for both primary and secondary windings
(B) Different for primary and secondary windings
(C) Greater in primary winding
(D) Greater in secondary winding

4. : Which type of transformer is used for measuring high voltages? (NTDC Electrical Engineer – 2023)
(A) Potential transformer
(B) Power transformer
(C) Distribution transformer
(D) Isolation transformer

5. : The efficiency of a transformer is maximum when: (PESCO Sub Engineer Electrical – 2022)
(A) Iron losses = Copper losses
(B) Copper losses are minimum
(C) Load is full
(D) Iron losses are zero

6. : What is the purpose of oil in a transformer? (WAPDA Electrical Engineer – 2019)
(A) Cooling and insulation
(B) Power factor correction
(C) Voltage regulation
(D) Current control

7. : The open-circuit test on a transformer gives: (PPSC Electrical Engineer – 2021)
(A) Copper losses
(B) Iron losses
(C) Efficiency
(D) Voltage regulation

8. : The short-circuit test on a transformer gives: (NTDC Electrical Engineer – 2022)
(A) Iron losses
(B) Hysteresis losses
(C) Copper losses
(D) Dielectric losses

9. : The auto-transformer is more efficient because: (LESCO Engineer Recruitment Test – 2021)
(A) It has one winding partly common to both primary and secondary
(B) It has more copper loss
(C) It has more leakage reactance
(D) It uses less magnetic material

10. : Which of the following is not a type of transformer loss? (PESCO Electrical Engineer – 2023)
(A) Copper loss
(B) Iron loss
(C) Stray loss
(D) Corona loss

11. : In an induction motor, the speed of the rotor is always: (PPSC Electrical Engineer – 2021)
(A) Equal to synchronous speed
(B) Less than synchronous speed
(C) Greater than synchronous speed
(D) Zero

12. : The rotating magnetic field in a 3-phase induction motor rotates at: (NTDC Electrical Engineer – 2023)
(A) Rotor speed
(B) Synchronous speed
(C) Slip speed
(D) Zero speed

13. : The slip in an induction motor is given by: (WAPDA Electrical Engineer – 2020)
(A) (Ns – Nr) / Ns
(B) (Nr – Ns) / Nr
(C) Ns / Nr
(D) Nr / Ns

14. : The torque developed by an induction motor is maximum when: (LESCO Engineer Recruitment Test – 2022)
(A) Rotor resistance = Rotor reactance
(B) Rotor resistance < Rotor reactance
(D) Slip = 0

15. : The starting torque of a squirrel cage induction motor is: (PESCO Electrical Engineer – 2021)
(A) Very high
(B) Moderate
(C) Very low
(D) Infinite

16. : Which method is commonly used to start a three-phase induction motor? (PPSC Sub Engineer Electrical – 2022)
(A) Direct-on-line starter
(B) Resistance starter
(C) Inductive starter
(D) Rotor start method

17. : In a synchronous motor, the rotor speed is: (NTDC Electrical Engineer – 2023)
(A) Equal to synchronous speed
(B) Less than synchronous speed
(C) Greater than synchronous speed
(D) Independent of frequency

18. : The excitation of a synchronous motor is provided by: (WAPDA Electrical Engineer – 2020)
(A) Induction effect
(B) DC source
(C) Alternating current
(D) Capacitor

19. : The main advantage of a synchronous motor over an induction motor is: (LESCO Sub Engineer Electrical – 2022)
(A) It is cheaper
(B) It can operate at unity power factor
(C) It requires no excitation
(D) It has higher slip

20. : If the load on a synchronous motor increases, the motor’s: (PPSC Electrical Engineer – 2021)
(A) Speed increases
(B) Speed decreases
(C) Power factor changes
(D) Frequency increases

21. : Power factor of an AC circuit is defined as: (PPSC Electrical Engineer – 2021)
(A) Ratio of active power to apparent power
(B) Ratio of reactive power to active power
(C) Ratio of voltage to current
(D) Ratio of apparent power to active power

22. : A lagging power factor is caused by: (WAPDA Electrical Engineer – 2020)
(A) Capacitive load
(B) Inductive load
(C) Resistive load
(D) Short circuit

23. : The main purpose of power factor correction is to: (NTDC Electrical Engineer – 2023)
(A) Reduce voltage
(B) Reduce current and losses
(C) Increase frequency
(D) Reduce power

24. : Synchronous capacitors are used in power systems to: (LESCO Electrical Engineer – 2022)
(A) Supply reactive power and improve power factor
(B) Reduce voltage
(C) Increase frequency
(D) Reduce harmonics

25. : An alternator converts: (PESCO Electrical Engineer – 2021)
(A) Mechanical energy into DC electrical energy
(B) Mechanical energy into AC electrical energy
(C) Electrical energy into mechanical energy
(D) Heat energy into electrical energy

26. : The synchronous speed of a 6-pole alternator operating at 50 Hz is: (PPSC Sub Engineer Electrical – 2022)
(A) 1000 rpm
(B) 500 rpm
(C) 1500 rpm
(D) 3000 rpm

27. : The voltage induced in an alternator is proportional to: (NTDC Electrical Engineer – 2023)
(A) Speed and flux per pole
(B) Load current only
(C) Frequency only
(D) Armature resistance

28. : In an alternator, the efficiency is maximum when: (WAPDA Electrical Engineer – 2020)
(A) Load is zero
(B) Copper losses = Iron losses
(D) Iron losses = 0

29. : The voltage regulation of an alternator is: (LESCO Sub Engineer Electrical – 2022)
(A) Ratio of no-load voltage to full-load voltage
(B) Ratio of full-load voltage to no-load voltage
(C) Change in voltage from no-load to full-load at constant speed
(D) Ratio of reactive power to active power

30. : Which of the following affects the voltage regulation of an alternator? (PESCO Electrical Engineer – 2021)
(A) Load power factor
(B) Excitation
(C) Internal impedance
(D) All of these

31. : The efficiency of a transformer depends mainly on: (NTDC Electrical Engineer – 2023)
(A) Load and copper losses
(B) Core material only
(C) Frequency only
(D) Voltage regulation

32. : In a 3-phase induction motor, the direction of rotation can be reversed by: (PESCO Electrical Engineer – 2022)
(A) Swapping any two phases of supply
(B) Changing the rotor resistance
(C) Increasing the supply voltage
(D) Changing the frequency

33. : The rotor of a squirrel cage induction motor has: (LESCO Electrical Engineer – 2021)
(A) Wound rotor with slip rings
(B) Laminated rotor with bars short-circuited at ends
(C) Solid copper rotor
(D) Ferrite core rotor

34. : The synchronous speed of a 4-pole, 50 Hz induction motor is: (PPSC Electrical Engineer – 2021)
(A) 1000 rpm
(B) 1500 rpm
(C) 1200 rpm
(D) 1800 rpm

35. : The primary purpose of a protective relay in a power system is to: (WAPDA Electrical Engineer – 2020)
(A) Measure current
(B) Detect faults and initiate circuit breaker operation
(C) Regulate voltage
(D) Control frequency

36. : A Buchholz relay is primarily used in: (NTDC Electrical Engineer – 2023)
(A) Transmission lines
(B) Transformers
(C) Generators
(D) Synchronous motors

37. : The slip of an induction motor is zero when: (PESCO Electrical Engineer – 2022)
(A) Motor is running at synchronous speed
(B) Motor is at start
(C) Motor is at half load
(D) Rotor is stationary

38. : In a DC shunt motor, the speed decreases with: (LESCO Electrical Engineer – 2021)
(A) Increase in load
(B) Decrease in load
(C) Increase in supply voltage
(D) Decrease in armature resistance

39. : The main advantage of a synchronous motor is: (PPSC Electrical Engineer – 2021)
(A) Constant speed operation
(B) High starting torque
(C) Simple starting method
(D) Self-excitation

40. : In power factor correction, capacitors are used to: (WAPDA Electrical Engineer – 2020)
(A) Improve power factor
(B) Reduce active power
(C) Reduce frequency
(D) Increase line losses

41. : The main cause of low power factor in an industrial AC circuit is: (PESCO Electrical Engineer – 2022)
(A) Resistive load
(B) Inductive load
(C) Capacitive load
(D) High voltage

42. : Synchronous capacitors are primarily used to: (NTDC Electrical Engineer – 2023)
(A) Supply reactive power and improve power factor
(B) Reduce active power
(C) Increase frequency
(D) Reduce harmonics

43. : The voltage regulation of a transformer depends mainly on: (WAPDA Electrical Engineer – 2020)
(A) Load current and power factor
(B) Frequency only
(C) Core material
(D) Cooling method

44. : The efficiency of a transformer is maximum when: (LESCO Electrical Engineer – 2021)
(A) Copper losses = Iron losses
(C) Iron losses = 0
(D) Load is zero

45. : The primary and secondary windings of a transformer are: (PPSC Electrical Engineer – 2021)
(A) Electrically connected
(B) Magnetically coupled
(C) Short-circuited
(D) Isolated with no magnetic coupling

46. : A step-up transformer increases: (NTDC Electrical Engineer – 2023)
(A) Current
(B) Voltage
(C) Frequency
(D) Resistance

47. : The main purpose of using a starter in a DC motor is to: (PESCO Electrical Engineer – 2022)
(A) Limit starting current
(B) Increase speed
(C) Reduce torque
(D) Control temperature

48. : In a DC series motor, the speed is inversely proportional to: (LESCO Electrical Engineer – 2021)
(A) Armature current
(B) Field flux
(C) Supply voltage
(D) Load torque

49. : The back EMF in a DC motor is proportional to: (PPSC Electrical Engineer – 2021)
(A) Armature current
(B) Speed of the motor
(C) Supply voltage
(D) Torque

50. : The main function of a Buchholz relay is to: (WAPDA Electrical Engineer – 2020)
(A) Detect overheating in alternator
(B) Detect internal faults in transformers
(C) Measure power factor
(D) Protect induction motor

51. : The primary winding of a transformer is connected to: (NTDC Electrical Engineer – 2023)
(A) AC supply
(B) DC supply
(C) Load
(D) Ground

52. : The secondary winding of a transformer delivers: (PESCO Electrical Engineer – 2022)
(A) AC voltage
(B) DC voltage
(C) Constant current
(D) Variable frequency

53. : The main losses in a transformer are: (WAPDA Electrical Engineer – 2020)
(A) Copper and iron losses
(B) Dielectric and leakage losses
(C) Friction and windage losses
(D) Corona and hysteresis losses

54. : The efficiency of a transformer increases when: (LESCO Electrical Engineer – 2021)
(A) Load increases to full load
(B) Load decreases
(C) Core material is removed
(D) Voltage is decreased

55. : In a DC shunt motor, the field winding is connected: (PPSC Electrical Engineer – 2021)
(A) In parallel with the armature
(B) In series with the armature
(C) Across the supply with resistor only
(D) Between supply and ground

56. : In a DC series motor, the field winding is connected: (NTDC Electrical Engineer – 2023)
(A) In parallel with the armature
(B) In series with the armature
(C) Across the supply with resistor
(D) Between supply and ground

57. : The speed of a DC shunt motor is: (PESCO Electrical Engineer – 2022)
(A) Almost constant
(B) Highly variable with load
(C) Zero at full load
(D) Infinite at no load

58. : The speed of a DC series motor is: (LESCO Electrical Engineer – 2021)
(A) Constant
(B) Varies with load
(C) Always zero at start
(D) Independent of load

59. : The back EMF of a DC motor opposes: (PPSC Electrical Engineer – 2021)
(A) Supply voltage
(B) Armature current
(C) Torque
(D) Rotor speed

60. : The main purpose of a starter in a DC motor is: (WAPDA Electrical Engineer – 2020)
(A) Limit high starting current
(B) Increase speed
(C) Reduce torque
(D) Control power factor

61. : The slip of a 3-phase induction motor is defined as: (NTDC Electrical Engineer – 2023)
(A) (Ns – Nr) / Ns
(B) (Nr – Ns) / Nr
(C) Ns / Nr
(D) Nr / Ns

62. : The starting torque of a squirrel cage induction motor is: (PESCO Electrical Engineer – 2022)
(A) Very high
(B) Moderate
(C) Very low
(D) Infinite

63. : The direction of rotation of a 3-phase induction motor can be reversed by: (WAPDA Electrical Engineer – 2020)
(A) Swapping any two supply phases
(B) Changing rotor resistance
(C) Increasing supply voltage
(D) Changing frequency

64. : The rotor of a squirrel cage induction motor consists of: (LESCO Electrical Engineer – 2021)
(A) Laminated core with bars short-circuited at ends
(B) Solid copper rotor
(C) Ferrite core rotor
(D) Wound rotor with slip rings

65. : The synchronous speed of a 6-pole induction motor at 50 Hz is: (PPSC Electrical Engineer – 2021)
(A) 500 rpm
(B) 1000 rpm
(C) 1500 rpm
(D) 3000 rpm

66. : In a synchronous motor, the rotor rotates at: (NTDC Electrical Engineer – 2023)
(A) Synchronous speed
(B) Less than synchronous speed
(C) Greater than synchronous speed
(D) Independent of supply frequency

67. : The excitation of a synchronous motor is provided by: (PESCO Electrical Engineer – 2022)
(A) DC supply
(B) AC supply
(C) Capacitor bank
(D) Induction effect

68. : The main advantage of a synchronous motor over an induction motor is: (LESCO Electrical Engineer – 2021)
(A) Ability to operate at unity power factor
(B) Simpler construction
(C) Lower cost
(D) No excitation required

69. : In a DC shunt motor, if the field winding is opened while running, the motor will: (PPSC Electrical Engineer – 2021)
(A) Run at dangerously high speed
(B) Stop immediately
(C) Reverse direction
(D) Continue at same speed

70. : The purpose of power factor correction is to: (WAPDA Electrical Engineer – 2020)
(A) Reduce current and losses
(B) Reduce voltage
(C) Increase frequency
(D) Control torque

71. : The main function of a relay in a power system is to: (NTDC Electrical Engineer – 2023)
(A) Measure voltage
(B) Detect faults and operate circuit breakers
(C) Regulate frequency
(D) Increase efficiency

72. : A Buchholz relay is used in: (PESCO Electrical Engineer – 2022)
(A) Generators
(B) Transformers
(C) Transmission lines
(D) Synchronous motors

73. : The surge impedance of a transmission line is: (LESCO Electrical Engineer – 2021)
(A) Ratio of voltage to current under surge conditions
(B) Product of voltage and current
(C) Ratio of current to resistance
(D) None of these

74. : The Ferranti effect in a transmission line causes: (WAPDA Electrical Engineer – 2020)
(A) Voltage drop at receiving end
(B) Voltage rise at receiving end during light load
(C) Increase in current
(D) Decrease in power factor

75. : The skin effect in transmission lines causes: (PPSC Electrical Engineer – 2021)
(A) Uniform current distribution
(B) Decrease in current density near conductor surface
(C) Increase in current density near conductor surface
(D) Current flow in the center only

76. : Corona loss in transmission lines increases with: (NTDC Electrical Engineer – 2023)
(A) Decrease in conductor spacing
(B) Increase in frequency
(C) Both (A) and (B)
(D) Decrease in voltage

77. : Which type of insulator is used for very high voltage transmission lines? (PESCO Electrical Engineer – 2022)
(A) Pin type
(B) Suspension type
(C) Shackle type
(D) Strain type

78. : The efficiency of a transmission line is maximum when: (LESCO Electrical Engineer – 2021)
(A) Sending end voltage = Receiving end voltage
(B) Line losses are zero
(C) Variable loss = Constant loss
(D) Reactive power = Zero

79. : The dielectric strength of transformer oil should be at least: (NTDC Electrical Engineer – 2023)
(A) 5 kV
(B) 15 kV
(C) 30 kV
(D) 50 kV

80. : The synchronous speed of a 4-pole alternator operating at 50 Hz is: (PPSC Electrical Engineer – 2021)
(A) 1500 rpm
(B) 3000 rpm
(C) 1000 rpm
(D) 750 rpm

81. : The main function of a transmission line is to: (PPSC Lecturer Electrical Engineer – 2022)
(A) To generate power
(B) To transfer electric power from generating stations to substations
(C) To measure current
(D) To control voltage fluctuations

82. : The surge impedance of a transmission line is: (PPSC Instructor Electrical Engineer – 2021)
(A) Ratio of voltage to resistance
(B) Ratio of voltage to current under surge conditions
(C) Product of voltage and current
(D) None of these

83. : Which material is commonly used for overhead transmission lines? (PPSC Lecturer Electrical Engineer – 2020)
(A) Copper
(B) Aluminium
(C) Silver
(D) Iron

84. : The Ferranti effect occurs due to: (PPSC Instructor Electrical Engineer – 2019)
(A) Voltage drop along the line
(B) Voltage rise at the receiving end during light load
(C) Power loss due to corona
(D) Improvement of power factor

85. : Skin effect in transmission lines causes: (PPSC Lecturer Electrical Engineer – 2021)
(A) Uniform current distribution
(B) Increase in current at the conductor center
(C) Increase in current density near the surface of the conductor
(D) Decrease in current near surface

86. : Corona loss in transmission lines increases with: (PPSC Instructor Electrical Engineer – 2022)
(A) Decrease in line voltage
(B) Increase in frequency
(C) Decrease in conductor spacing
(D) Both (B) and (C)

87. : For very high voltage transmission lines, which type of insulator is commonly used? (PPSC Lecturer Electrical Engineer – 2021)
(A) Pin type
(B) Suspension type
(C) Shackle type
(D) Strain type

88. : The main purpose of a Buchholz relay in a transformer is to: (PPSC Instructor Electrical Engineer – 2020)
(A) Detect overheating in alternators
(B) Detect internal faults in transformers
(C) Measure power factor
(D) Protect induction motors

89. : The efficiency of a transmission line is maximum when: (PPSC Lecturer Electrical Engineer – 2021)
(A) Sending end voltage = Receiving end voltage
(B) Line losses are zero
(C) Total losses = Reactive power loss
(D) Variable loss = Constant loss

90. : The dielectric strength of transformer oil should be at least: (PPSC Instructor Electrical Engineer – 2023)
(A) 5 kV
(B) 15 kV
(C) 30 kV
(D) 50 kV

91. : The synchronous speed of a 4-pole alternator operating at 50 Hz is: (PPSC Instructor Electrical Engineer – 2021)
(A) 1500 rpm
(B) 3000 rpm
(C) 1000 rpm
(D) 750 rpm

92. : The main function of a transmission line is to: (PPSC Lecturer Electrical Engineer – 2022)
(A) To generate power
(B) To transfer electric power from generating stations to substations
(C) To measure current
(D) To control voltage fluctuations

93. : Which material is commonly used for overhead transmission lines? (PPSC Instructor Electrical Engineer – 2020)
(A) Copper
(B) Aluminium
(C) Silver
(D) Iron

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