Electrical Engineering – Past Papers PPSC

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

Rotor reactance” onclick=”checkAnswer(‘q14’, ‘Rotor resistance = Rotor reactance’)”> (C) 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

Iron losses” onclick=”checkAnswer(‘q28’, ‘Copper losses = Iron losses’)”> (C) 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

Iron losses” onclick=”checkAnswer(‘q44’, ‘Copper losses = Iron losses’)”> (B) 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