Category: Electrical Engineering Multiple Choice Questions

Electromagnetic Induction Multiple Choice Questions :-

1. The property of coil by which a counter e.m.f. is induced in it when the current through the coil changes is known as
(a) self-inductance
(b) mutual inductance
(c) series aiding inductance
(d) capacitance
Answer: a

2. As per Faraday’s laws of electromagnetic induction, an e.m.f. is induced in a conductor whenever it
(a) lies perpendicular to the magnetic flux
(b) lies in a magnetic field
(e) cuts magnetic flux
(d) moves parallel to the direction of the magnetic field
Answer: c

3. Which of the following circuit element stores energy in the electromagnetic field ?
(a) Inductance
(b) Condenser
(c) Variable resistor
(d) Resistance
Answer: a

4. The inductance of a coil will increase under all the following conditions except
(a) when more length for the same number of turns is provided
(6) when the number of turns of the coil increase
(c) when more area for each turn is provided
(d) when permeability of the core increases
Answer: a

5. Higher the self-inductance of a coil,
(a) lesser its weber-turns
(b) lower the e.m.f. induced
(c) greater the flux produced by it
(d) longer the delay in establishing steady current through it
Answer: d

6. In an iron cored coil the iron core is removed so that the coil becomes an air cored coil. The inductance of the coil will
(a) increase
(b) decrease
(c) remain the same
(d) initially increase and then decrease
Answer: b

7. An open coil has
(a) zero resistance and inductance
(b) infinite resistance and zero inductance
(c) infinite resistance and normal inductance
(d) zero resistance and high inductance
Answer: b

8. Both the number of turns and the core length of an inductive coil are doubled.
Its self-inductance will be
(a) unaffected
(b) doubled
(c) halved
(d) quadrupled
Answer: b

9. If current in a conductor increases then according to Lenz’s law self-induced voltage will
(a) aid the increasing current
(b) tend to decrease the amount of cur-rent
(c) produce current opposite to the in-creasing current
(d) aid the applied voltage
Answer: c

10. The direction of induced e.m.f. can be found by
(a) Laplace’s law
(b) Lenz’s law
(c) Fleming’s right hand rule
(d) Kirchhoff s voltage law
Answer: b

11. Air-core coils are practically free from
(a) hysteresis losses
(b) eddy current losses
(c) both (a) and (b)
(d) none of the above
Answer: c

12. The magnitude of the induced e.m.f. in a conductor depends on the
(a) flux density of the magnetic field
(b) amount of flux cut
(c) amount of flux linkages
(d) rate of change of flux-linkages
Answer: d

13. Mutually inductance between two magnetically-coupled coils depends on
(a) permeability of the core
(b) the number of their turns
(c) cross-sectional area of their common core
(d) all of the above
Answer: d

14. A laminated iron core has reduced eddy-current losses because
(a) more wire can be used with less D.C. resistance in coil
(b) the laminations are insulated from each other
(c) the magnetic flux is concentrated in the air gap of the core
(d) the laminations are stacked vertfcally
Answer: b

15. The law that the induced e.m.f. and current always oppose the cause producing them is due to
(a) Faraday
(b) Lenz
(c) Newton
(d) Coulomb
Answer: b

16. Which of the following is not a unit of inductance ?
(a) Henry
(b) Coulomb/volt ampere
(c) Volt second per ampere
(d) All of the above
Answer: b

17. In case of an inductance, current is proportional to
(a) voltage across the inductance
(b) magnetic field
(c) both (a) and (b)
(d) neither (a) nor (b)
Answer: b

18. Which of the following circuit elements will oppose the change in circuit current ?
(a) Capacitance
(b) Inductance
(c) Resistance
(d) All of the above
Answer: b

19. For a purely inductive circuit which of the following is true ?
(a) Apparent power is zero
(b) Relative power is.zero
(c) Actual power of the circuit is zero
(d) Any capacitance even if present in the circuit will not be charged
Answer: c

20. Which of the following is unit of inductance ?
(a) Ohm
(b) Henry
(c) Ampere turns
(d) Webers/metre
Answer: b

21. An e.m.f. of 16 volts is induced in a coil of inductance 4H. The rate of change of current must be
(a) 64 A/s
(b) 32 A/s
(c) 16 A/s
(d) 4 A/s
Answer: d

22. The core of a coil has a length of 200 mm. The inductance of coil is 6 mH. If the core length is doubled, all other quantities, remaining the same, the inductance will be
(a) 3 mH
(b) 12 mH
(c) 24mH
(d)48mH
Answer: a

23. The self inductances of two coils are 8 mH and 18 mH. If the co-efficients of coupling is 0.5, the mutual inductance of the coils is
(a) 4 mH
(b) 5 mH
(c) 6 mH
(d) 12 mH
Answer: c

24. Two coils have inductances of 8 mH and 18 mH and a co-efficient of coupling of 0.5. If the two coils are connected in series aiding, the total inductance will be
(a) 32 mH
(b) 38 mH
(c) 40 mH
(d) 48 mH
Answer: b

25. A 200 turn coil has an inductance of 12 mH. If the number of turns is increased to 400 turns, all other quantities (area, length etc.) remaining the same, the inductance will be
(a) 6 mH
(b) 14 mH
(c) 24 mH
(d) 48 mH
Answer: d

26. Two coils have self-inductances of 10 H and 2 H, the mutual inductance being zero. If the two coils are connected in series, the total inductance will be
(a) 6 H
(b) 8 H
(c) 12 H
(d) 24 H
Answer: c

27. In case all the flux from the current in coil 1 links with coil 2, the co-efficient of coupling will be
(a) 2.0
(b) 1.0
(c) 0.5
(d) zero
Answer: b

28. A coil with negligible resistance has 50V across it with 10 mA. The inductive reactance is
(a) 50 ohms
(b) 500 ohms
(c) 1000 ohms
(d) 5000 ohms
Answer: d

29. A conductor 2 meters long moves at right angles to a magnetic field of flux density 1 tesla with a velocity of 12.5 m/s. The induced e.m.f. in the conductor will be
(a) 10 V
(6) 15 V
(c) 25V
(d) 50V
Answer: c

30. Lenz’s law is a consequence of the law of conservation of
(a) induced current
(b) charge
(c) energy
(d) induced e.m.f.
Answer: c

31. A conductor carries 125 amperes of current under 60° to a magnetic field of 1.1 tesla. The force on the conductor will be nearly
(a) 50 N
(b) 120 N
(c) 240 N
(d) 480 N
Answer: b

32. Find the force acting on a conductor 3m long carrying a current of 50 amperes at right angles to a magnetic field having a flux density of 0.67 tesla.
(a) 100 N
(b) 400 N
(c) 600 N
(d) 1000 N
Answer: a

33. The co-efficient of coupling between two air core coils depends on
(a) self-inductance of two coils only
(b) mutual inductance between two coils only
(c) mutual inductance and self inductance of two coils
(d) none of the above
Answer: c

34. An average voltage of 10 V is induced in a 250 turns solenoid as a result of a change in flux which occurs in 0.5 second. The total flux change is
(a) 20 Wb
(b) 2 Wb
(c) 0.2 Wb
(d) 0.02 Wb
Answer: d

35. A 500 turns solenoid develops an average induced voltage of 60 V. Over what time interval must a flux change of 0.06 Wb occur to produce such a voltage ?
(a) 0.01 s
(b) 0.1 s
(c) 0.5 s
(d) 5 s
Answer: c

36. Which of the fpllowing inductor will have the least eddy current losses ?
(a) Air core
(b) Laminated iron core
(c) Iron core
(d) Powdered iron core
Answer: a

37. A coil induces 350 mV when the current changes at the rate of 1 A/s. The value of inductance is
(a) 3500 mH
(b) 350 mH
(c) 250 mH
(d) 150 mH
Answer: b

38. Two 300 uH coils in series without mutual coupling have a total inductance of
(a) 300 uH
(b) 600 uH
(c) 150 uH
(d) 75 uH
Answer: b

39. Current changing from 8 A to 12 A in one second induced 20 volts in a coil. The value of inductance is
(a) 5 mH
(b) 10 mH
(c) 5 H
(d) 10 H
Answer: c

40. Which circuit element(s) will oppose the change in circuit current ?
(a) Resistance only
(b) Inductance only
(c) Capacitance only
(d) Inductance and capacitance
Answer: b

41. A crack in the magnetic path of an inductor will result in
(a) unchanged inductance
(b) increased inductance
(c) zero inductance
(d) reduced inductance
Answer: d

42. A coil is wound on iron core which carries current I. The self-induced voltage in the coil is not affected by
(a) variation in coil current
(b) variation in voltage to the coil
(c) change of number of turns of coil
(d) the resistance of magnetic path
Answer: b

43. A moving magnetic field will produce the same effect as a conductor that is moving.
(a) Yes
(b) No
Ans:

44. The polarity of the induced voltage can be determined by using the left-hand generator rule.
(a) Yes
(b) No
Answer: a

45. Increasing the field or increasing the current will decrease the force on the conductor.
(a) Yes
(b) No
Answer: b

46. Reversing the field or the current will reverse the force on the conductor.
(a) Yes
(b) No
Answer: a

49. When a conductor moves in the field, so that it makes an angle 8 with the lines of flux, the force F is given as : F = Bl sin2 0.
(a) Yes
(b) No
Answer: b

50. The self-inductance of the coil may be defined as equal to the e.m.f. induced in volts when the current in the circuit changes at the rate of unit Weber turns.
(a) Yes
(b) No
Answer: b

SINGLE PHASE INDUCTION MOTORS Multiple Choice Questions :-

1. In a split phase motor, the running winding should have

A. high resistance and low inductance
B. low resistance and high inductance
C. high resistance as well as high inductance
D. low resistance as well as low inductiance

Answer: B

2. If the capacitor of a single-phase motor is short-circuited

A. the motor will not start
B. the motor will run
C. the motor will run in reverse direction
D. the motor will run in the same direction at reduced r.p.m.

Answer: A

3. In capacitor start single-phase motors

A. current in the starting winding leads the voltage
B. current in the starting winding lags the voltage
C. current in the starting winding is in phase with voltage in running winding
D. none of the above

Answer: A

4. In a capacitor start and run motors the function of the running capacitor in series with the auxiliary winding is to

A. improve power factor
B. increase overload capacity
C. reduce fluctuations in torque
D. to improve torque

Answer: A

5. In a capacitor start motor, the phase displacement between starting and running winding can be nearly

A. 10°
B. 30°
C. 60°
D. 90°

Answer: D

6. In a split phase motor

A. the starting winding is connected through a centrifugal switch
B. the running winding is connected through a centrifugal switch
C. both starting and running windings are connected through a centrifugal switch
D. centrifugal switch is used to control supply voltage

Answer: A

7. The rotor developed by a single-phase motor at starting is

A. more than i.he rated torque
B. rated torque
C. less than the rated torque
D. zero

Answer: D

8. Which of the following motor will give relatively high starting torque ?

A. Capacitor start motor
B. Capacitor run motor
C. Split phase motor
D. Shaded pole motor

Answer: A

9. Which of the following motor will have relatively higher power factor ?

A. Capacitor run motor
B. Shaded pole motor
C. Capacitor start motor
D. Split phase motor

Answer: A

10. In a shaded pole motor, the shading coil usually consist of

A. a single turn of heavy wire which is in parallel with running winding
B. a single turn of heavy copper wire which is short-circuited and carries only induced current
C. a multilayer fine gauge copper wire in parallel with running winding
D. none of the above

Answer: B

11. In a shaded pole single-phase motor, the revolving field is produced by the use of

A. inductor
B. capacitor
C. resistor
D. shading coils

Answer: D

12. A centrifugal switch is used to dis- connect ‘starting winding when motor has

A. run for about 1 minute
B. run for about 5 minutes
C. picked up about 50 to 70 per cent of rated speed
D. picked up about 10 to 25 per cent of rated speed

Answer: C

13. If a particular application needs high speed and high starting torque, then which of the following motor will be preferred ?

A. Universal motor
B. Shaded pole type motor
C. Capacitor start motor
D. Capacitor start and run motor

Answer: A

14. The value of starting capacitor of a fractional horse power motor will be

A. 100 uF
(6) 200 uF
C. 300 uF
D. 400 uF

Answer: C

15. In repulsion motor direction of rotation of motor

A. is opposite to that of brush shift
B. is the same as that of brush shift
C. is independent of brush shift

Answer: B

16. In a single phase motor the centrifugal switch

A. disconnects auxiliary winding of the motor
B. disconnects main winding of the motor
C. reconnects the main winding the motor
D. reconnects the auxiliary winding of the motor

Answer: A

17. The running winding of a single phase motor on testing with meggar is found to be ground. Most probable location of the ground will be

A. at the end connections
B. at the end terminals
C. anywhere on the winding inside a slot
D. at the slot edge where coil enters or comes out of the slot

Answer: D

18. A capacitor-start single phase induction motor is switched on to supply with its capacitor replaced by an inductor of equivalent reactance value. It will

A. start and then stop
B. start and run slowly
C. start and run at rated speed
D. not start at all

Answer: D

19. Which of the following motors is used in mixies ?

A. Repulsion motor
B. Reluctance motor
C. Hysteresis motor
D. Universal motor

Answer: D

20. Which of the following motors is inherently self starting ?

A. Split motor
B. Shaded-pole motor
C. Reluctance motor
D. None of these

Answer: B

21. The direction of rotation of an hysteresis motor is determined by

A. interchanging the supply leads
B. position of shaded pole with respect to main pole
C. retentivity of the rotor material
D. none of these

Answer: B

22. Burning out of winding is due to

A. short circuited capacitor
B. capacitor value hiving changed
C. open circuiting of capacitor
D. none of the above

Answer: A

23. Direction of rotation of a split phase motor can be reversed by reversing the connection of

A. running winding only
B. starting winding only
C. either
A. or (b)
D. both
A. and (b)

Answer: C

24. Short-circuiter is used in

A. repulsion induction motor
B. repulsion motor
C. repulsion start induction run motor
D. none of the above

Answer: C

25. The range of efficiency for shaded pole motors is

A. 95% to 99%
B. 80% to 90%
C. 50% to 75%
D. 5% to 35%

Answer: D

26. In a capacitor start single-phase motor, when capacitor is replaced by a resistance

A. torque will increase
B. the motor will consume less power
C. motor will run in reverse direction
D. motor will continue to run in same direction

Answer: D

27. The power factor of a single-phase induction motor is usually

A. lagging
B. always leading
C. unity
D. unity to 0.8 leading

Answer: A

28. A shaded pole motor can be used for

A. toys
B. hair dryers
C. circulators
D. any of the above

Answer: D

29. A hysteresis motor works on the principle of

A. hysteresis loss
B. magnetisation of rotor
C. eddy current loss
D. electromagnetic induction

Answer: A

30. Which of the following motor will give the highest starting torque ?

A. D.C. shunt motor
B. Schrage motor
C. Repulsion start and induction run motor
D. Universal motor

Answer: B

31. For which of the applications a reluctance motor is preferred ?

A. Electric shavers
B. Refrigerators
C. Signalling and timing devices
D. Lifts and hoists

Answer: C

32. The motor used on small lathes is usually

A. universal motor
B. D.C. shunt motor
C. single-phase capacitor run motor
D. 3-phase synchronous motor

Answer: C

33. Which of the following motors is preferred for tape-recorders ?

A. Shaded pole motor
B. Hysteresis motor
C. Two value capacitor motor
D. Universal motor

Answer: B

34. A single-phase induction motor is

A. inherently self-starting with high torque
B. inherently self-starting with low torque
C. inherently non-self-starting with low torque
D. inherently non-self-starting with high torque

Answer: C

35. A schrage motor can run on

A. zero slip
B. negative slip
C. positive slip
D. all of the above

Answer: D

36. A universal motor can run on

A. A.C. only
B. D.C. only
C. either A.C. or D.C.
D. none of the above

Answer: C

37. Which of the following single-phase motors is suitable for timing and control purposes ?

A. Reluctance motor
B. Series motor
C. Repulsion motor
D. Universal motor

Answer: A

38. Single phase induction motor usually operates on

A. 0.6 power factor lagging
B. 0.8 power factor lagging
C. 0.8 power factor leading
D. unity power factor

Answer: A

39. In split-phase motor auxiliary winding is of

A. thick wire placed at the bottom of the slots
B. thick wire placed at the top of the slots
C. thin wire placed at the top of the slots
D. thin wire placed at the bottom of the slots

Answer: C

40. Which of the following motors will operate at high power factor ?

A. Shaped pole motor
B. Split phase motor
C. Capacitor start motor
D. Capacitor run motor

Answer: D

41. In a two value capacitor motor, the capacitor used for running purposes is

A. air capacitor
B. paper spaced oil filled type
C. ceramic type
D. a.c. electrolytic type

Answer: B

42. Which of the following motors can be run on AC. as well as D.C. supply ?

A. Universal motor
B. Repulsion motor
C. Synchronous motor
D. Reluctance motor

Answer: A

43. In A.C. series motor compensating winding is employed to

A. reduce the effects of armature reaction
B. increase the torque
C. reduce sparking at the brushes
D. none of the above

Answer: C

44. Which of the following single-phase induction motors is generally used in time phonographs ?

A. Resistance start
B. Capacitor start capacitor run
C. Shaded pole
D. Universal

Answer: C

45. Which of the following motors has highest starting torque ?

A. Repulsion motor
B. Shaped pole motor
C. Capacitor-start motor
D. Split-phase motor

Answer: C

46. The repulsion-start induction-run motor is used because of

A. good power factor
B. high efficiency
C. minimum cost
D. high starting torque

Answer: D

47. In case of a shaded pole motor the direction of rotation of the motor is

A. from main pole to shaded pole
B. from shaded pole to main pole
C. either of the above depending on voltage
D. either of the above depending on power factor

Answer: A

48. In case of high speed universal motor which of the following needs more attention ?

A. End play
B. Air gap
C. Insulation in rotor
D. Balancing of rotor

Answer: D

49. The wattage rating for a ceiling fan motor will be in the range

A. 200 to 250 W
B. 250 to 500 W
C. 50 to 150 W
D. 10 to 20 W

Answer: C

50. The wattage of motor for driving domestic sewing machine will be around

A. 100 to 150 W
B. 40 to 75 W
C. 10 to 30 W
D. 5 to 10 W

Answer: A

51. Which of the following single-phase motors has relatively poor starting torque ?

A. Universal motor
B. Repulsion motor
C. Capacitor motor
D. All single phase motors have zero starting torque

Answer: C

52. Which type of load is offered by cranes and hoists ?

A. Gradually varying load
B. Non-reversing, no-load start
C. Reversing, light start
D. Reversing, heavy start

Answer: D

53. The speed of a universal motor is generally reduced by using

A. gear trains
B. V-belts
C. brakes
D. chains

Answer: A

54. Which of the following motors can be used for unity power factor ?

A. Capacitor run motor
B. Shaded pole motor
C. Hysteresis motor
D. Schrage motor

Answer: D

55. When a D.C. series motor is connected to A.C. supply, the power factor will be low because of

A. high inductance of field and armature circuits
B. induced current in rotor due to variations of flux
C. fine copper wire winding
D. none of the above

Answer: A

56. The direction of rotation of universal motor can be reversed the by reversing the flow of current through

A. armature winding
B. field winding
C. either armature winding or field winding
D. none of the above

Answer: C

57. In which single-phase motor, the rotor has no teeth or winding ?

A. Split phase motor
B. Reluctance motor
C. Hysteresis motor
D. Universal motor

Answer: C

58. Which motor is normally free from mechanical and magnetic vibrations ?

A. Split phase motor
B. Universal motor
C. Hysteresis motor
D. Shaded pole motor

Answer: C

59. As hysteresis motors are free from mechanical and magnetic vibrations therefore these are considered as suitable for

A. fans
B. blowers
C. sound equipment
D. mixer grinders

Answer: C

60. A reluctance motor

A. is self-starting
B. is constant speed motor
C. needs no D.C. excitation
D. all of the above

Answer: D

61. In a hysteresis motor, the rotor must have

A. retentivity
B. resistivity
C. susceptibility
D. none of the above

Answer: A

62. The rotor of a hysteresis motor is made of

A. aluminium
B. cast iron
C. chrome steel
D. copper

Answer: C

63. The electric motor used in portable drills is

A. capacitor run motor
B. hysteresis motor
C. universal motor
D. repulsion motor

Answer: C

64. Which of the following applications always have some load whenever switched on ?

A. Vacuum cleaners
B. Fan motors
C. Pistol drills
D. All of the above

Answer: C

65. The speed control of universal motor used for sewing machines is by

A. friction
B. varying the resistance
C. tapping the field
D. centrifugal mechanism

Answer: B

66. Torque developed by a single phase induction motor at starting is

A. pulsating
B. uniform
C. none of the above
D. nil

Answer: D

67. In split phase motor main winding is of

A. thin wire placed at the top of the slots
B. thin wire placed at the bottom of the slots
C. thick wire placed at the bottom of the slots
D. thick wire placed at the top of the” slots

Answer: C

68. In repulsion motor, maximum torque is developed when

A. brush axis is at 45° electrical to the field axis
B. brush axis coincides with the field axis
C. brush axis is at 90° electrical to the field axis
D. none of the above

Answer: A

69. If the centrifugal switch does not open at 70 to 80 percent of synchronous speed of motor, it would result in

A. damage to the starting winding
B. damage to the centrifugal switch
C. overloading of running winding
D. none of the above

Answer: A

70. Speed torque characteristic of a repulsion induction motor is similar to that of a D.C.

A. shunt motor
B. series motor
C. compound motor
D. separately excited motor

Answer: C

71. In a ceilingfan employing capacitor run motor

A. secondary winding surrounds the primary winding
B. primary winding surrounds the secondary winding
C. both are usual arrangements
D. none of the above

Answer: A

72. The shaded pole motor is used for

A. high starting torque
B. low starting torque
C. medium starting torque
D. very high starting torque

Answer: B

73. The rotor slots, in an induction motor, are usually not quite parallel to the shaft because it

A. improves the efficiency
B. helps the rotor teeth to remain under the stator teeth
C. helps in reducing the tendency of the rotor teeth to remain under the stator teeth
D. improves the power factor

Answer: C

74. The speed/load characteristics of a universal motor is same as that of

A. A.C. motor
B. D.C. shunt motor
C. D.C. series motor
D. none of the above

Answer: C

75. The purpose of stator winding in the compensated repulsion motor is to

A. provide mechanical balance
B. improve power factor and provide better speed regulation
C. prevent hunting in the motor
D. eliminate armature reaction

Answer: B

76. Which of the following motors is used for unity power factor ?

A. Hysteresis motor
B. Schrage motor
C. Universal motor
D. Reluctance motor

Answer: B

77. The motor used for the compressors is

A. d.c. series motor
B. shaded pole motor
C. capacitor-start capacitor-run motor
D. reluctance motor

Answer: C

78. Which of the following motors is used in a situation where load increases with speed ?

A. Induction motor
B. Three-phase series motor
C. Schrage motor
D. Hysteresis motor

Answer: B

79. In repulsion motor, zero torque is developed when

A. brush axis is 45° electrical to field axis
B. brush axis coincides with the field axis
C. brush axis is 90° electrical to field axis
D. both B. and (c)

Answer: D

80. Centrifugal switch disconnects the auxiliary winding of the motor at about ____ percent of synchronous speed

A. 30 to 40
B. 70 to 80
C. 80 to 90
D. 100

Answer: B

81. Starting winding of a single phase motor of a refrigerator is disconnected from the circuit by means of a

A. magnetic relay
B. thermal relay
C. centrifugal switch
D. none of the above

Answer: A

82. If a single phase induction motor runs slower than normal, the most likely defect is

A. worn bearings
B. short-circuit in the winding
C. open-circuit in the winding
D. none of the above

Answer: A

83. Which of the following motors is used in tape-recorders ?

A. Hysteresis motor
B. Reluctance motor
C. Capacitor-run motor
D. Universal motor

Answer: A

84. Which of the following statements regarding two value capacitor motor is incorrect ?

A. It is a reversing motor
B. It is preferred to permanent-split single-value capacitor motor where frequent reversals are required
C. It has low starting as well as rushing currents
D. It has high starting torque

Answer: B

85. Two-value capacitor motor finds increased application as compressor motor in small home air-conditioners
because

A. it is comparatively cheaper
B. it has almost non-destructible capacitor
C. it has low starting as well as running currents at relatively high power factor
D. it is quiet in operation

Answer: C

86. If the centrifugal switch of a two-value capacitor motor using two capacitors fails to open then

A. motor will not come up to speed
B. motor will not carry the load
C. current drawn by the motor will be excessively high
D. electrolytic capacitor will, in all probability, suffer break down

Answer: D

87. In a universal motor, the most common cause of brush sparking is

A. open armature winding
B. shorted armature winding
C. shorted field winding”
D. high commutator mica
(e) all of the above
Ans: e

88. If starting winding of a single-phase induction motor is left in the circuit, it will

A. run faster
B. spark at light loads
C. draw excessive current and overheat
D. run slower

Answer: C

89. Most of the fractional horsepower motors have either

A. hard and annealed bearings
B. ball or roller bearings
C. soft and porous bearings
D. plain or sleeve bearings

Answer: D

90. Which of the following statements regarding reluctance-start motor is incorrect ?

A. It is similar to reluctance motor
B. It is basically an induction motor and not a synchronous one
C. So far as its basic working principle is concerned, it is similar to shaded pole motor
D. the air-gap between rotor and salient poles is non- uniform

Answer: A

91. To reverse the direction of rotation of acapacitor start motor while it is running we should

A. disconnect motor from the supply till it stops then reconnect it to supply with reversed connection of main or auxiliary winding
B. disconnect motor from supply and immediately reconnect it to supply with reversed connections of the main winding
C. reverse the direction of connection of the auxiliary winding and after motor comes to rest then connect auxiliary winding to the supply
D. reverse the direction of connections of the auxiliary winding and immediately connect it to supply

Answer: A

92. In case of a reluctance motor, when the load is increased so that it cannot maintain synchronous speed the motor will

A. become unstable
B. draw excessive armature current and may burn out
C. fall out of synchronism and come to stand still
D. run as induction motor

Answer: D

93. Which of the following motors has two separate windings on the motor ?

A. Repulsion motor
B. Repulsion induction motor
C. Repulsion start induction run motor
D. None of the above

Answer: B

94. A shaded pole motor does not possess

A. centrifugal switch
B. capacitor
C. commutator
D. all of the above

Answer: D

95. In a A.C. series motor armature coils are usually connected to commutator

A. through resistance
B. through reactances
C. through capacitors
D. solidly

Answer: A

96. Which of the following statements regarding a reluctance motor is incorrect ?

A. It cannot be reversed, ordinarily
B. It requires no D.C. field excitation for its operation
C. It is nothing else but a single-phase, salient pole synchronous-induction motor
D. Its squirrel cage-rotor is of unsym-metrical magnetic construction in order to vary reluctance path between stator and rotor

Answer: A

97. A universal motor is one which

A. can be operated either on D.C. or A.C. supply at approximately the same speed and output
B. can be marketed internationally
C. runs at dangerously high speed on no-load

Answer: A

98. A repulsion motor is equipped with

A. slip rings
B. commutator
C. both
A. and (b)
D. none of the above

Answer: B

99. The capacitors used in single-phase capacitor motors have no

A. voltage rating
B. dielectric medium
C. polarity marking
D. definite value

Answer: C

100. If a D.C. series motor is operated on A.C. supply, it will

A. spark excessively
B. have poor efficiency
C. have poor power factor
D. all of the above

Answer: D

101. After the starting winding of a single phase induction motor is disconnected from supply, it continues to run only on

A. running winding
B. rotor winding
C. field winding
D. compensating winding

Answer: A

102. Which of the following statements regarding repulsion-start induction motor is incorrect ?

A. It requires more maintenance of commutator and other mechanical devices
B. It makes quite a bit of noise on starting
C. In fractional horse power motors, it has replaced the capacitor motors
D. It is not easily reversed

Answer: C

103. A.C. series motor as compared to D.C. series motor has

A. smaller brush width
B. less number of field turns
C. more number of armature turns
D. less air gap
(e) all of the above
Ans: e

104. Locked rotor current of a shaded pole motor is

A. equal to full load current
B. less than full load current
C. slightly more than full load current
D. several times the full load current

Answer: C

105. Speed control of a universal motor is achieved by

A. varying field flux with tapped field windings
B. connecting rheostat in series
C. applying variable voltage by means of silicon controlled rectifier
D. applying variable voltage by means of variable auto-transformer
(e) all of the above methods
Ans: e

116. Hysteresis motor is particularly useful for high-quality record players and tape-recorders because

A. it revolves synchronously
B. it is not subject to any magnetic or mechanical vibrations
C. it can be easily manufactured in extremely small sizes of up to 1 W output
D. it develops hysteresis torque which is extremely steady both in amplitude and phase

Answer: D

117. Which of the following statements regarding hysteresis motor is in incorrect ?

A. It is extremely sensitive to fluctuations in supply voltage
B. Its high starting torque is due to its high rotor hysteresis loss
C. It is extremely quiet in operation
D. It accelerates from rest to full-speed almost instantaneously

Answer: A

118. Which of the following statements regarding single-phase induction motoris correct ?

A. It requires only one winding
B. It can rotate in one direction only
C. It is self-starting
D. It is not self-starting

Answer: D

119. The starting winding of a single-phase motor is placed in

A. armature
B. field
C. rotor
D. stator

Answer: D

120. The speed of a universal motor is usually reduced by using

A. gearing
B. belts
C. brakes
D. chains

Answer: A

Synchronous Motors Questions :-

1. Synchronous motors are generally not self-starting because
A. the direction of rotation is not fixed
B. the direction of instantaneous torque reverses after half cycle
C. startes cannot be used on these machines
D. starting winding is not provided on the machines
Answer: B

2. In case one phase of a three-phase synchronous motor is short-circuited the motor will
A. not start
B. run at 2/3 of synchronous speed
C. run with excessive vibrations
D. take less than the rated load
Answer: A

3. A pony motor is basically a
A. small induction motor
B. D.C. series motor
C. D.C. shunt motor
D. double winding A.C./D.C. motor
Answer: A

4. A synchronous motor can develop synchronous torque
A. when under loaded
B. while over-excited
C. only at synchronous speed
D. below or above synchronous speed
Answer: C

5. A synchronous motor can be started by
A. pony motor
B. D.C. compound motor
C. providing damper winding
D. any of the above
Answer: D

6. A three-phase synchronous motor will have
A. no slip-rings
B. one slip-ring
C. two slip-rings
D. three slip-rings
Answer: C

7. Under which of the following conditions hunting of synchronous motor is likely to occur ?
A. Periodic variation of load
B. Over-excitation
C. Over-loading for long periods
D. Small and constant load
Answer: A

8. When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected
A. the motor stops
B. it runs as a reluctance motor at the same speed
C. it runs as a reluctance motor at a lower speed
D. none of the above
Answer: A

9. When V is the applied voltage, then the breakdown torque of a synchronous motor varies as
A. V
B. V312
C. V2
D. 1/V
Answer: A

10. The power developed by a synchronous motor will be maximum when the load angle is
A. zero
B. 45°
C. 90°
D. 120°
Answer: C

11. A synchronous motor can be used as a synchronous capacitor when it is
A. under-loaded
B. over-loaded
C. under-excited
D. over-excited
Answer: D

12. A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased
A. power factor as well as armature current will decrease
B. power factor as well as armature current will increase
C. power factor will increase but armature current will decrease
D. power factor will decrease and armature current will increase
Answer: D

13. Mostly, synchronous motors are of
A. alternator type machines
(6) induction type machines
C. salient pole type machines
D. smooth cylindrical type machines
Answer: C

14. The synchronous motor is not inherently self-starting because
A. the force required to accelerate the rotor to the synchronous speed in an instant is absent
B. the starting device to accelerate the rotor to near synchronous speed is absent
C. a rotating magnetic field does not have enough poles
D. the rotating magnetic field is produced by only 50 Hz frequency currents
Answer: A

15. As the load is applied to a synchronous motor, the motor takes more armature current because
A. the increased load has to take more current
B. the rotor by shifting its phase backward causes motor to take more current
C. the back e.m.f. decreases causing an increase in motor current
D. the rotor strengthens the rotating field casuing more motor current
Answer: B

16. Synchronous motor always runs at
A. the synchronous speed
B. less than synchronous speed
C. more than synchronous speed
D. none of the above
Answer: A

17. An over-excited synchronous motor takes
A. leading current
B. lagging current
C. both A. and B.
D. none of the above
Answer: A

18. The working of a synchronous motor is similar to
A. gear train arrangement
B. transmission of mechancial power by shaft
C. distribution transformer
D. turbine
E. none of the above
Answer: B

19. The minimum armature current of the synchronous motor corresponds to operation at
A. zero power factor leading
B. unity power factor
C. 0.707 power factor lagging
D. 0.707 power factor leading
Answer: B

20. In a synchronous motor, the magnitude of stator back e.m.f. £& depends on
A. d.c. excitation only
B. speed of the motor
C. load on the motor
D. both the speed and rotor flux
Answer: A

21. If load (or torque) angle of a 4-pole synchronous motor is 6° electrical, its value in mechanical degrees is
A. 2
B. 3
C. 4
D. 6
Answer: B

22. For V-curves for a synchronous motor the graph is drawn between
A. field current and armature current
B. terminal voltage and load factor
C. power factor and field current
D. armature current and power factor
Answer: A

23. The back e.m.f. of a synchronous motor depends on
A. speed
B. load
C. load angle
D. all of the above
Answer: C

24. A synchronous motor can operate at
A. lagging power factor only
(6) leading power factor only
C. unity power factor only
D. lagging, leading and unity power factors
Answer: D

25. In a synchronous motor which loss varies with load ?
A. Windage loss
B. Bearing friction loss
C. Copper loss
D. Core loss
Answer: C

26. A synchronous motor can be made self starting by providing
A. damper winding on rotor poles
B. damper winding on stator
C. damper winding on stator as well as rotor poles
D. none of the above
Answer: A

27. The oscillations in a synchronous motor can be damped out by
A. maintaining constant excitation
B. running the motor on leading power factors
C. providing damper bars in the rotor pole faces
D. oscillations cannot be damped
Answer: C

28. The shaft of synchronous motor is made of
A. mild steel
B. chrome steel
C. alnico
D. stainless steel
Answer: A

29. When the field of a synchronous motor is under-excited, the power factor will be
A. leading
B. lagging
C. unity
D. zero
Answer: B

30. The speed regulation of a synchronous motor is always
A. 1%
B. 0.5%
C. positive
D. zero
Answer: D

31. The percentage slip in case of a synchronous motor is
A. 1%
B. 100%
C. 0.5%
D. zero
Answer: D

32. The operating speed of a synchronous motor can be changed to new fixed value by
A. changing the load
B. changing the supply voltage
C. changing frequency
D. using brakes
Answer: C

33. A synchronous motor will always stop when
A. supply voltage fluctuates
B. load in motor varies
C. excitation winding gets disconnected
D. supply voltage frequency changes9885859805
Answer: C

34. riunting in a synchronous motor takes place
A. when supply voltage fluctuates
B. when load varies
C. when power factor is unity
D. motor is under loaded
Answer: B

35. When load on an over-excited or under excited synchronous*motor is increased, rate of change of its armature current as compared with that of power factor is
A. more
B. less
C. equal
D. twice
Answer: B

36. The rotor copper losses, in a synchronous motor, are met by
A. d.c. source
B. armature input
C. motor input
D. supply lines
Answer: A

37. The maximum power developed in a synchronous motor occurs at a coupling angle of
A. 30°
B. 60°
C. 90°
D. 180°
Answer: C

38. When the stator windings are connected in such a fashion that the number of poles are made half, the speed of the rotor of a synchronous motor
A. remains same as the original value
B. decreases to half the original value
C. tends to becomes zero
D. increases to two times the original value
Answer: D

39. In which of the following motors the stator and rotor magnetic field rotate at the same speed ?
A. Universal motor
B. Synchronous motor
C. Induction motor
D. Reluctance motor
Answer: B

40. Synchronsizingpower of a synchronous machine is
A. direcly proportional to the synchronous reactance
(6) inversely proportional to the synchronous reactance
A. equal to the synchronous reactance
D. none of the above
Answer: B

41. Synchronous motors are
A. not-self starting
B. self-starting
C. essentially self-starting
D. none of the above
Answer: A

42. The standard full-load power factor ratings for synchronous motors are
A. zero or 0.8 leading
B. unity or 0.8 lagging
C. unity or 0.8 leading
D. unity or zero
Answer: C

43. A synchronous motor running with normal excitation adjusts to load increases essentially by increase in
A. back e.m.f.
B. armature current
C. power factor
D. torque angle
Answer: B

44. A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because
A. synchronous motor has no slip
B. stator supply is not required to produce magnetic field
C. mechanical load on the rotor remains constant
D. synchronous motor has large airgap
Answer: B

45. A synchronous motor working at leading power factor can be used as
A. voltage booster
B. phase advancer
C. noise generator
D. mechanical synchronizer
Answer: B

46. Slip rings are usually made of
A. carbon or graphite
B. brass or steel
C. silver or gold
D. copper or aluminium
Answer: B

47. An over excited synchronous motor is used for
A. fluctuating loads
B. variable speed loads
C. low torque loads
D. power factor corrections
Answer: D

48. When the voltage applied to a synchronous motor is increased, which of the following will reduce ?
A. Stator flux
B. Pull in torque
C. Both A. and B.
D. None of the above
Answer: D

51. The efficiency of a properly designed synchronous motor will usually fall in range
A. 60 to 70%
(6) 75 to 80%
C. 85 to 95%
D. 99 to 99.5%
Answer: C

52. To limit the operating temperature an electrical machine should have proper
A. voltage rating
B. current rating
C. power factor
D. speed
Answer: B

53. Slip-rings in a synchronous motor carry
A. direct current
B. alternating current
C. no current
D. all of the above
Answer: A

54. A synchronous machine with large air gap has
A. a higher value of stability limit
(6) a small value of inherent regulation
C. a higher synchronizing power which makes the machine less sensitive to load variations
D. all of the above
Answer: D

55. The armature current of the synchronous motor has higher values for
A. high excitation only
B. low excitation only
C. both A. and B.
D. none of the above
Answer: C

56. In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately
A. one-third
B. twice
C. thrice
D. six times
E. nine times
Answer: C

57. The angle between the rotating stator flux and rotor poles is called _____ angle.
A. torque
B. obtuse
C. synchronizing
D. power factor
Answer: A

58. Which of the following methods is used to start a synchronous motor ?
A. Damper winding
B. Star-delta starter
C. Damper winding in conjunction with star-delta starter
D. Resistance starter in the armature circuit
Answer: C

59. When the rotor speed, in a synchronous machine, becomes more than the synchronous speed during hunting, the damper bars develop
A. inductor motor torque
B. induction generator torque
C. synchronous motor torque
D. d.c. motor toque
E. none of the above
Answer: B

60. An important advantage of a synchronous motor over wound round induction motor is that
A. its power factor may be varied at will
B. its speed is independent of supply frequency
C. its speed may be controlled more easily
D. none of the above
Answer: A

61. The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motors running at full load, is of the order of
A. zero degree
B. two degrees
C. five degrees
D. ten degrees
Answer: C

62. Power factor of a synchronous motor is unity when
A. the armature current is maximum
B. the armature current is minimum
C. the armature current is zero
D. none of the above
Answer: B

63. Change of D.C. excitation of a synchronous motor changes
A. applied voltage of the motor
B. motor speed
C. power factor of power drawn by the motor
D. any of the above
E. all of the above
Answer: C

64. While starting a synchronous motor by induction motor action, field winding is usually
A. connected to D.C. supply
B. short-circuited by low resistance
C. kept open-circuited
D. none of the above
Answer: B

65. Which of the following motors will be used in electric clocks ?
A. D.C. shunt motor
B. D.C. series motor
C. A.C. induction motor
D. A.C. synchronous motor
Answer: D

SYNCHRONOUS MOTORS Multiple Choice Questions and Answers

66. If in a synchronous motor, driving mechanical load and drawing current at lagging power factor from constant voltage supply, its field excitation is increased, then its power factor
A. become more
B. become less
C. remain constant
D. none of the above
Answer: B

67. A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will
A. remain same
B. go down
C. improve
D. none of the above
Answer: C

68. While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerting torque is produced by
A. induction motor torque in field winding
B. induction motor torque in damper winding
C. eddy current and hysteresis torque in pole faces
D. reHetance motor torque due to saliency of the rotor
E. all of the above methods
Answer: E

69. Armature of a synchronous machine is
A. of reducing number of slip rings on the rotor
B. armature is associated with large power as compared to the field circuits
C. of difficulty of providing high voltage insulation on rotor
D. all of the above reasons
Answer: D

70. If excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to
A. increase in both armature current and power factor angle
B. increase in back e.m.f. but decrease in armature current
C. increase in both armature current and power factor which is lagging
D. increase in torque angle but decrease in back e.m.f.
Answer: A

71. When a 3-phase synchronous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way
A. augments it directly
B. directly opposes it
C. cross-magnetises it
D. none of the above
Answer: B

72. Stability of a synchronous machine
A. decreases with increase in its excitation
B. increases with increase in its excitation
C. remains unaffected with increase in excitation
D. any of the above
Answer: B

73. The power factor of a synchronous motor is better than that of induction motor because
A. stator supply is relieved of responsibility of producing magnetic field
B. mechanical load on the motor can be adjusted
C. synchronous motor runs at synchronous speed
D. synchronous motor has large air gap
Answer: A

74. If in a synchronous motor, driving a given mechanical load and drawing current at a leading power factor from constant voltage supply its field excitation is increased, its power factor
A. will become more
B. will become less
C. will remain unchanged
D. none of the above.
Answer: B

75. A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because
A. speed of the motor is reduced
B. power factor is decreased
C. Eb (back e.m.f.) becomes less than V (applied voltage)
D. Er (net resultant voltage) in armature is increased
E. none of the above
Answer: D

76. If one-phase of a 3-phase synchronous motor is short-circuited, motor
A. will refuse to start
B. will overheat in spots
C. will not come upto speed
D. will fail to pull into step
Answer: A

77. If the field circuit of an unloaded salientpole synchronous motor gets suddenly open-circuited, then
A. it runs at a slower speed
B. the motor stops
C. it continues to run at the same speed
D. it runs at a very high speed
Answer: B

78. In which of the following motors the stator and rotor fields rotate simultaneously ?
A. D.C. motor
B. Reluctance motor
C. Universal motor
D. Synchronous motor
E. Induction motor
Answer: D

79. The speed of a synchronous motor
A. increases as the load increases
B. decreases as the load decreases
C. always remains constant
D. none of the above
Answer: C

80. A rotory converter can also be run as a
A. d.c. shunt motor
B. d.c. series motor
C. d.c. compound motor
D. induction motor
E. synchronous motor
Answer: E

81. The maximum speed variation in a 3-phase synchronous motor is
A. 10 per cent
B. 6 per cent
C. 4 per cent
D. 2. per cent
E. zero
Answer: E

82. Which of the following resistances can be measured by conducting insulation resistance test on a synchronous motor ?
A. Phase to phase winding resistance
B. Stator winding to earthed frame
C. Rotor winding to earthed shaft
D. All of the above
Answer: D

83. Due to which of the following reasons a synchronous motor fails to pull into synchronism after applying D.C. field current ?
A. High field current
B. Low short circuit ratio
C. High core losses
D. Low field current
Answer: D

84. In a synchronous motor, the maximum power developed depends on all of the following except
A. rotor excitation
B. maximum value of coupling angle
C. direction of rotation
D. supply voltage
Answer: C

85. In a 3-phase synchronous motor, the negative phase sequence exists when the motor is
A. supplied with unbalanced voltage
B. under-loaded
C. over-loaded
D. none of the above
Answer: A

86. In a synchronous motor, damper windings are provided on
A. stator frame
B. rotor shaft
C. pole faces
D. none of the above
Answer: C

87. The induced e.m.f. in a synchronous motor working on leading power factor will be
A. more than the supply voltage
B. less than the supply voltage
C. equal to the supply voltage
Answer: A

88. The effect of increasing the load on a synchronous motor running with normal excitation is to
A. decrease both armature current and power factor
(6) decrease armature current but increase power factor
C. increase armature current but decrease power factor
D. increase both its armature current and power factor
Answer: C

89. The net armature voltage of a synchronous motor is equal to the
A. vector sum of Eb and V
B. arithmetic sum of Eb and V
C. arithmetic difference of Eb and V
D. vector difference of Eh and V
Answer: D

90. The ratio of starting torque to running torque in a synchronous motor is
A. zero
B. one
C. two
D. infinity
Answer: A

91. In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on
A. load on the motor
B. d.c. excitation only
C. both the speed and rotor flux
D. none of the above
Answer: B

92. A 3-phase synchronous motor is running clockwise. If the direction of its field current is reversed
A. the motor will stop
B. the motor continue to run in the same direction
C. the winding of the motor will burn
D. the motor will run in the reverse direction
E. none of the above
Answer: B

93. The magnitude of field flux in a 3-phase synchronous motor
A. remains constant at all loads
B. varies with speed
C. varies with the load
D. varies with power factor
Answer: A

94. The torque angle, in a synchronous motor, is the angle between
A. the supply voltage and the back e.m.f.
B. magnetising current and back e.m.f.
C. the rotating stator flux and rotor poles
D. none of the above
Answer: C

95. Hunting in a synchronous motor cannot be due to
A. windage friction
B. variable load
C. variable frequency
D. variable supply voltage
Answer: A

96. By which of the following methods the constant speed of a synchronous motor can be changed to new fixed value ?
A. By changing the supply frequency
B. By interchanging any two phases
C. By changing the applied voltage
D. By changing the load.
Answer: A

97. In a synchronous motor, V-curves represent relation between
A. armature current and field current
B. power factor and speed
C. field current and speed
D. field current and power factor
Answer: A

98. In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be
A. 3000 r.p.m.
B. 1500 r.p.m.
C. 750 r.p.m.
D. none of the above
Answer: B

99. A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have
A. no change of power factor
B. lagging power factor with over-excitation
C. leading power factor with under-excitation
D. leading power factor with over-excitation
Answer: D

100. Which of the following motors is non-self starting ?
A. D.C. series motor
B. synchronous motor
C. Squirrel cage induction motor
D. Wound round induction motor
Answer: B

101. In a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then
A. the motor is said to be fully loaded
B. the torque generated is maximum
C. the excitation is said to be zero per cent
D. the excitation is said to be hundred per cent
Answer: D

102. In a synchronous motor, the damping winding is generally used to
A. prevent hunting and provide the starting torque
B. reduce the eddy currents
C. provide starting torque only
D. reduce noise level
E. none of the above
Answer: A

103. If the field of a synchronous motor is underexcited, the power factor will be
A. zero
B. unity
C. lagging
D. leading
Answer: C

104. The back e.m.f. in the stator of a synchronous motor depends on
A. number of poles
B. flux density
C. rotor speed
D. rotor excitation
E. none of the above
Answer: D

105. The maximum value of torque that a synchronous motor can develop without losing its synchronism, is known as
A. slip torque
B. pull-out torque
C. breaking torque
D. synchronising torque
Answer: D

106. In a synchronous motor, the armature current has large values for
A. high excitation only
B. low excitation only
C. both high and low excitation
D. none of the above
Answer: C

107. Which of the following losses, in a synchronous motor, does not vary with load?
A. Windage loss
B. Copper losses
C. Any of the above
D. None of the above
Answer: A

108. The size of a synchronous motor decreases with the increase in
A. flux density
B. horse power rating
C. speed
D. all of the above
Answer: A

109. Which of the following losses is not dissipated by the stator core surface in a synchronous motor ?
A. Eddy current losses in the conductors
B. Iron losses in the stator
C. Copper losses in the slot portion of the conductors
D. Windage losses
E. None of the above
Answer: D

110. The duration of sudden snort-circuit test on a synchronous motor is usually about
A. one hour
B. one minute
C. one second
D. none of the above
Answer: C

111. The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as
A. pull-up torque
B. pull-in torque
C. pull-out torque
D. none of the above
Answer: B

112. A synchronous machine with low value of short-circuit ratio has
A. lower stability limit
(6) high stability limit
C. good speed regulation
D. good voltage regulation
E. none of the above
Answer: A

113. The construction of a synchronous motor resembles
A. a series motor
B. an induction motor
C. an alternator
D. a rotary converter
Answer: C

114. If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will
A. stop
B. run as induction motor
C. function as static condenser
D. burn with dense smoke
Answer: A

115. For power factor correction, synchronous motors operate at
A. no-load and greatly over-excited fields
B. no-load and under-excited fields
C. normal load with minimum excitation
D. normal load with zero excitation
Answer: A

116. The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as
A. locked-rotor torque
B. synchronous torque
C. pull up torque
D. reluctance torque
Answer: A

117. Exciters of synchronous machines are
A. d.c. shunt machines
B. d.c. series machines
C. d.c. compound machines
D. any of the above
Answer: A

118. The coupling angle or load angle of synchronous motor is defined as the angle between the
A. rotor and stator teeth
B. rotor and the stator poles of opposite polarity
C. rotor and the stator poles of the same polarity
D. none of the above
Answer: B

119. If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then
A. the stator current will be zero
B. the stator current will be very small
C. the stator current will be very high
D. the back e.m.f. will be more than the supply voltage
E. none of the above
Answer: A

120 The armature current of the synchronous motor
A. has large values for low excitation i niy
B. has large values for high excitation only
C. has large values for low and high excitation
D. any of the above
Answer: C

121. The maximum power developed in a synchronous motor will depend on
A. the rotor excitation only
B. the supply voltage only
C. the rotor excitation and supply volt-age both
D. the rotor excitation, supply voltage and maximum value of coupling angle (90°)
E. none of the above
Answer: D

122. A synchronous motor which works on a leading power factor and does not drive a mechanical load is called as
A. static condenser
B. condenser
C. synchronous condenser
D. none of the above
Answer: C

129. A synchronous motor develops maximum power when load angle is
A. 45°
B. 60°
C. 90°
D. 120°
Answer: C

130. In a synchronous motor, the breakdown torque is
A. directly proportional to applied voltage
B. directly proportional to the square of the applied voltage
C. inversely proportional to applied voltage
D. none of the above
Answer: A

RECTIFIERS & CONVERTERS Questions and Answers

1. Which of the following are the applications of D.C. system ?
(a) Battery charging work
(b) Arc welding
(c) Electrolytic and electro-chemical processes
(d) Arc lamps for search lights
(e) All of the above

Answer: e

2. Which of the following methods may be used to convert A.C. system to D.C. ?
(a) Rectifiers
(b) Motor converters
(c) Motor-generator sets
(d) Rotary converters
(e) All of the above

Answer: e

3. In a single phase rotary converter the number of slip rings will be
(a) two
(b) three
(c) four
(d) six
(e) none

Answer: a

4. A synchronous converter can be started
(a) by means of a small auxiliary motor
(b) from AC. side as induction motor
(c) from D.C. side as D.C. motor
(d) any of the above methods
(e) none of the above methods

Answer: d

5. A rotary converter is a single machine with
(a) one armature and one field
(b) two armatures and one field
(c) one armature and two fields
(d) none of the above

Answer: a

6. A rotary converter combines the function of
(a) an induction motor and a D.C. generator
(b) a synchronous motor and a D.C. generator.
(c) a D.C. series motor and a D.C. generator
(d) none of the above

Answer: b

7. Which of the following is reversible in action ?
(a) Motor generator set
(b) Motor converter
(c) Rotary converter
(d) Any of the above
(e) None of the above

Answer: c

8. Which of the following metals is generally manufactured by electrolysis process ?
(a) Load
(b) Aluminium
(c) Copper
(d) Zinc
(e) None of the above

Answer: b

9. With a motor converter it is possible to obtain D.C. voltage only upto
(a) 200-100 V
(6) 600—800 V
(c) 1000—1200 V
(d) 1700—2000 V

Answer: d

10. Normally, which of the following is used, when a large-scale conversion from AC. to D.C. power is required ?
(a) Motor-generator set
(b) Motor converter
(c) Rotary converter
(d) Mercury arc rectifier

Answer: d

11. A rotary converter in general construction and design, is more or less like
(a) a transformer
(b) an induction motor
(c) an alternator
(d) any D.C. machine

Answer: d

12. A rotary converter operates at a
(a) low power factor
(6) high power factor
(c) zero power factor
(d) none of the above

Answer: b

13. In which of the following appUcations, direct current is absolutely essential ?
(a) Illumination
(b) Electrolysis
(c) Variable speed operation
(d) Traction

Answer: b

14. Which of the following AC. motors is usually used in large motor-generator sets?
(a) Synchronous motor
(b) Squirrel cage induction motor
(c) Slip ring induction motor
(d) Any of the above

Answer: a

15. In a rotary converter armature currents are
(a) d.c. only
(b) a.c. only
(c) partly a.c. and partly d.c.

Answer: c

16. In which of the following equipment direct current is needed ?
(a) Telephones
(b) Relays
(c) Time switches
(d) All of the above

Answer: d

17. In a rotary converter I2R losses as compared to a D.C. generator of the same size will be
(a) same
(b) less
(c) double
(d) three times

Answer: b

18. In a mercury arc rectifier positive ions are attracted towards
(a) anode
(b) cathode
(c) shell bottom
(d) mercury pool

Answer: b

19. Mercury, in arc rectifiers, is chosen for cathode because
(a) its ionization potential is relatively low
(b) its atomic weight is quite high
(c) its boiling point and specific heat are low
(d) it remains in liquid state at ordi¬nary temperature
(e) all of the above

Answer: e

20. The ionization potential of mercury is approximately
(a) 5.4 V
(b) 8.4 V
(c) 10.4 V
(d) 16.4 V

Answer: c

21. The potential drop in the arc, in a mercury arc rectifier, varies
(a) 0.05 V to 0.2 V per cm length of the arc
(b) 0.5 V to 1.5 V per cm length of the arc
(c) 2 V to 3.5 V per cm length of the arc
(d) none of the above

Answer: d

22. The voltage drop between the anode and cathode, of a mercury arc rectifier comprises of the following
(a) anode drop and cathode drop
(b) anode drop and arc drop
(c) cathode drop and arc drop
(d) anode drop, cathode drop and arc drop

Answer: d

23. Glass rectifiers are usually made into units capable of D.C. output (maximum continuous rating) of
(a) 100 A at 100 V
(b) 200 A at 200 V
(c) 300 A at 300 V
(d) 400 A at 400 V
(e) 500 A at 500 V

Answer: e

24. The voltage drop at anode, in a mercury arc rectifier is due to
(a) self restoring property of mercury
(b) high ionization potential
(c) energy spent in overcoming the electrostatic field
(d) high temperature inside the rectifier

Answer: c

25. The internal efficiency of a mercury arc rectifier depends on
(a) voltage only
(b) current only
(c) voltage and current
(d) r.m.s. value of current
(e) none of the above

Answer: a

26. If cathode and anode connections in a mercury arc rectifier are inter changed
(a) the rectifier will not operate
(b) internal losses will be reduced
(c) both ion and electron streams will move in the same direction
(d) the rectifier will operate at reduced efficiency

Answer: a

27. The cathdde voltage drop, in a mercury arc rectifier, is due to
(a) expenditure of energy in ionization
(b) surface resistance
(c) expenditure of energy in overcoming the electrostatic field
(d) expenditure of energy in liberating electrons from the mercury

Answer: d

28. To produce cathode spot in a mercury arc rectifier
(a) anode is heated
(b) tube is evacuated
(c) an auxiliary electrode is used
(d) low mercury vapour pressures are used

Answer: c

29. The advantage of mercury arc rectifier is that
(a) it is light in weight and occupies small floor space
(b) it has high efficiency
(c) it has high overload capacity
(d) it is comparatively noiseless
(e) all of the above

Answer: e

30. In a mercury pool rectifier, the voltage drop across its electrodes
(a) is directly proportional to load
(b) is inversely proportional to load
(c) varies exponentially with the load current
(d) is almost independent of load current

Answer: d

RECTIFIERS & CONVERTERS Multiple Choice Questions and Answers

31. In a three-phase mercury arc rectifiers each anode conducts for
(a) one-third of a cycle
(b) one-fourth of a cycle
(c) one-half a cycle
(d) two-third of a cycle

Answer: a

32. In a mercury arc rectifier characteristic blue luminosity is due to
(a) colour of mercury
(b) ionization
(c) high temperature
(d) electron streams

Answer: b

33. Which of the following mercury arc rectifier will deliver least undulating current?
(a) Six-phase
(b) Three-phase
(c) Two-phase
(d) Single-phase

Answer: a

34. In a glass bulb mercury arc rectifier the maximum current rating is restricted to
(a) 2000 A
(b) 1500 A
(c) 1000 A
(d) 500 A

Answer: d

35. In a mercury arc rectifier______ flow from anode to cathode
(a) ions
(b) electrons
(c) ions and electrons
(d) any of the above

Answer: a

36. When a rectifier is loaded which of the following voltage drops take place ?
(a) Voltage drop in transformer reactance
(6) Voltage drop in resistance of transformer and smoothing chokes
(c) Arc voltage drop
(d) All of the above

Answer: d

37. On which of the following factors the number of phases for which a rectifier should be designed depend ?
(a) The voltage regulation of the rec¬tifier should be low
(b) In the output circuit there should be no harmonics
(c) The power factor of the system should be high
(d) The rectifier supply transformer should be utilized to the best ad-vantage
(e) all of the above

Answer: e

38. A mercury arc rectifier possesses ________ regulation characteristics
(a) straight line
(b) curved line
(c) exponential
(d) none of the above

Answer: d

39. It is the_______of the transformer on which the magnitude of angle of overlap depends.
(a) resistance
(b) capacitance
(c) leakage reactance
(d) any of the above

Answer: c

41. In a grid control of mercury arc rectifiers when the grid is made positive relative to cathode, then it the electrons on their may to anode.
(a) accelerates
(b) decelerates
(c) any of the above
(d) none of the above

Answer: a

42. In mercury arc rectifiers having grid, the arc can be struck between anode and cathode only when the grid attains a certain potential, this potential being known as
(a) maximum grid voltage
(b) critical grid voltage
(c) any of the above
(d) none of the above

Answer: b

43. In phase-shift control method the control is carried out by varying the of grid voltage.
(a) magnitude
(b) polarity
(c) phase
(d) any of the above
(e) none of the above

Answer: c

44. In a phase-shift control method, the phase shift between anode and grid voltages can be achieved by means of
(a) shunt motor
(6) synchronous motor
(c) induction regulator
(d) synchronous generator

Answer: c

45. The metal rectifiers are preferred to valve rectifiers due to which of the following advantages ?
(a) They are mechanically strong
(b) They do not require any voltage for filament heating
(c) Both (a) and (b)
(d) None of the above

Answer: c

46. Which of the following statement is incorrect ?
(a) Copper oxide rectifier is a linear device
(b) Copper oxide rectifier is not a perfect rectifier
(c) Copper oxide rectifier has a low efficiency
(d) Copper oxide rectifier finds use in control circuits
(e) Copper oxide rectifier is not stable during early life

Answer: a

47. The efficiency of the copper oxide rectifier seldom exceeds
(a) 90 to 95%
(b) 85 to 90%
(c) 80 to 85%
(d) 65 to 75%

Answer: d

48. Copper oxide rectifier is usually designed not to operate above
(a) 10°C
(b) 20°C
(c) 30°C
(d) 45°C

Answer: d

49. Selenium rectifier can be operated at temperatures as high as
(a) 25°C
(b) 40°C
(c) 60°C
(d) 75°C

Answer: d

50. In selenium rectifiers efficiencies ranging from ______ to ______ percent are attainable
(a) 25, 35
(b) 40, 50
(c) 60, 70
(d) 75, 85

Answer: d

51. Ageing of a selenium rectifier may change the output voltage by
(a) 5 to 10 per cent
(b) 15 to 20 per cent
(c) 25 to 30 per cent
(d) none of the above

Answer: a

52. The applications of selenium rectifiers are usually limited to potential of
(a) 10 V
(b) 30 V
(c) 60 V
(d) 100 V
(e) 200 V

Answer: d

53. Which of the following rectifiers have been used extensively in supplying direct current for electroplating ?
(a) Copper oxide rectifiers
(b) Selenium rectifiers
(c) Mercury arc rectifiers
(d) Mechanical rectifiers
(e) None of the above

Answer: b

54. A commutating rectifier consists of commutator driven by
(a) an induction motor
(b) a synchronous motor
(c) a D.C. series motor
(d) a D.C. shunt motor

Answer: b

55. Which of the following rectifiers are primarily used for charging of low voltage batteries from AC. supply ?
(a) Mechanical rectifiers
(b) Copper oxide rectifiers
(c) Selenium rectifiers
(d) Electrolytic rectifiers
(e) Mercury arc rectifiers

Answer: d

56. The efficiency of an electrolytic rectifier is nearly
(a) 80%
(b) 70%
(c) 60%
(d) 40%

Answer: c

57. Which of the following is the loss within the mercury arc rectifier chamber ?
(a) Voltage drop in arc
(6) Voltage drop at the anode
(c) Voltage drop at the cathode
(d) All of the above

Answer: d

58. The metal rectifiers, as compared to mercury arc rectifiers
(a) operate on low temperatures
(b) can operate on high voltages
(c) can operate on heavy loads
(d) give poor regulation
(e) none of the above

Answer: a

59. In a mercury arc rectifier, the anode is usually made of
(a) copper
(b) aluminium
(c) silver
(d) graphite
(e) tungsten

Answer: d

60. The ignited or auxiliary anode in mercury arc rectifier is made of
(a) graphite
(b) boron carbide
(c) aluminium
(d) copper

Answer: b

TRANSMISSION & DISTRIBUTION Multiple Choice Questions :-

1. By which of the following systems electric power may be transmitted ?
(a) Overhead system
(b) Underground system
(c) Both (a) and (b)
(d) None of the above
Answer: c

2. are the conductors, which connect the consumer’s terminals to the distribution
(a) Distributors
(b) Service mains
(c) Feeders
(d) None of the above
Answer: b

3. The underground system cannot be operated above
(a) 440 V
(b) 11 kV
(c) 33 kV
(d) 66 kV
Answer: d

4. Overhead system can be designed for operation up to
(a) 11 kV
(b) 33 kV
(c) 66 kV
(d) 400 kV
Answer: c

5. If variable part of annual cost on account of interest and depreciation on the capital outlay is equal to the annual cost of electrical energy wasted in the conductors, the total annual cost will be minimum and the corresponding size of conductor will be most economical. This statement is known as
(a) Kelvin’s law
(b) Ohm’s law
(c) Kirchhoffs law
(d) Faraday’s law
(e) none of the above
Answer: a

6. The wooden poles well impregnated with creosite oil or any preservative compound have life
(a) from 2 to 5 years
(b) 10 to 15 years
(c) 25 to 30 years
(d) 60 to 70 years
Answer: c

7. Which of the following materials is not used for transmission and distribution of electrical power ?
(a) Copper
(b) Aluminium
(c) Steel
(d) Tungsten
Answer: d

8. Galvanised steel wire is generally used as
(a) stay wire
(b) earth wire
(c) structural components
(d) all of the above
Answer: d

9. The usual spans with R.C.C. poles are
(a) 40—50 meters
(b) 60—100 meters
(c) 80—100 meters
(d) 300—500 meters
Answer: c

10. The corona is considerably affected by which of the following ?
(a) Size of the conductor
(b) Shape of the conductor
(c) Surface condition of the conductor
(d) All of the above
Answer: d

11. Which of the following are the constants of the transmission lines ?
(a) Resistance
(b) Inductance
(c) Capacitance
(d) All of the above
Answer: d

12. 310 km line is considered as
(a) a long line
(b) a medium line
(c) a short line
(d) any of the above
Answer: a

13. The phenomenon qf rise in voltage at the receiving end of the open-circuited or lightly loaded line is called the
(a) Seeback effect
(b) Ferranti effect
(c) Raman effect
(d) none of the above
Answer: b

14. The square root of the ratio of line impedance and shunt admittance is called the
(a) surge impedance of the line
(b) conductance of the line
(c) regulation of the line
(d) none of the above
Answer: a

15. Which of the following is the demerit of a ‘constant voltage transmission system’ ?
(a) Increase of short-circuit current of the system
(b) Availability of steady voltage at all loads at the line terminals
(c) Possibility of better protection for the line due to possible use of higher terminal reactants
(d) Improvement of power factor at times of moderate and heavy loads
(e) Possibility of carrying increased power for a given conductor size in case of long-distance heavy power transmission
Answer: a

16. Low voltage cables are meant for use up to
(a)l.lkV
(b)3.3kV
(c)6.6kV
(d)llkV
Ans: e

17. The operating voltage of high voltage cables is up to
(a)l.lkV
(b)3.3kV
(c)6.6kV
(d)llkV
Answer: d

18. The operating voltage of supertension cables is up to
(a) 3.3 kV
(b) 6.6 kV
(c) 11 kV
(d) 33 kV
Answer: d

19. The operating voltage of extra high tension cables is upto
(a) 6.6 kV
(b) 11 kV
(c) 33 kV
(d) 66 kV
(e) 132 kV
Answer: d

20. Which of the following methods is used for laying of underground cables ?
(a) Direct laying
(b) Draw-in-system
(c) Solid system
(d) All of the above
Answer: d

21. Which of the following is the source of heat generation in the cables ?
(a) Dielectric losses in cable insulation
(b) losses in the conductor
(c) Losses in the metallic sheathings and armourings
(d) All of the above
Answer: d

22. Due to which of the following reasons the cables should not be operated too hot ?
(a) The oil may loose its viscosity and it may start drawing off from higher levels
(b) Expansion of the oil may cause the sheath to burst
(c) Unequal expansion may create voids in the insulation which will lead to ionization
(d) The thermal instability may rise due to the rapid increase of dielectric losses with temperature
(e) All of the above
Answer: e

23. Which of the following D.C. distribution system is the simplest and lowest in first cost ?
(a) Radial system
(b) Ring system
(c) Inter-connected system
(d) None of the above
Answer: a

24. A booster is a
(a) series wound generator
(b) shunt wound generator
(c) synchronous generator
(d) none of the above
Answer: a

25. Besides a method of trial and error, which of the following methods is employed for solution of network problems in interconnected system ?
(a) Circulating current method
(b) Thevenin’s theorem
(c) Superposition of currents
(d) Direct application of Kirehhoffs laws
(e) All of the above
Ans: e

26. Which of the following faults is most likely to occur in cables ?
(a) Cross or short-circuit fault
(b) Open circuit fault
(c) Breakdown of cable insulation
(d) All of the above
Answer: d

27. The cause of damage to the lead sheath of a cable is
(a) crystallisation of the lead through vibration
(b) chemical action on the lead when buried in the earth
(c) mechanical damage
(d) all of the above
Answer: d

28. The voltage of the single phase supply to residential consumers is
(a) 110 V
(b) 210 V
(c) 230 V
(d) 400 V
Answer: c

29. Most of the high voltage transmission lines in India are
(a) underground
(b) overhead
(c) either of the above
(d) none of the above
Answer: b

30. The distributors for residential areas are
(a) single phase
(b) three-phase three wire
(c) three-phase four wire
(d) none of the above
Answer: c

31. The conductors of the overhead lines are
(a) solid
(b) stranded
(c) both solid and stranded
(d) none of the above
Answer: b

32. High voltage transmission lines use
(a) suspension insulators
(b) pin insulators
(c) both (a) and (b)
(d) none of the above
Answer: a

33. Multicore cables generally use
(a) square conductors
(b) circular conductors
(c) rectangular conductors
(d) sector-shaped conductors
(e) none of the above
Answer: d

34. Distribution lines in India generally use
(a) wooden poles
(b) R.C.C. poles
(c) steel towers
(d) none of the above
Answer: b

35. The material commonly used for insulation in high voltage cables is
(a) lead
(b) paper
(c) rubber
(d) none of the above
Answer: b

36. The loads on distributors systems are generally
(a) balanced
(b) unbalanced
(c) either of the above
(d) none of the above
Answer: b

37. The power factor of industrial loads is generally
(a) unity
(b) lagging
(c) leading
(d) zero
Answer: b

38. Overhead lines generally use
(a) copper conductors
(b) all aluminium conductors
(c) A.C.S.R. conductors
(d) none of these
Answer: c

39. In transmission lines the cross-arms are made of
(a) copper
(b) wood
(c) R.C.C.
(d) steel
Answer: d

40. The material generally used for armour of high voltage cables is
(a) aluminium
(b) steel
(c) brass
(d) copper
Answer: b

41. Transmission line insulators are made of
(a) glass
(b) porcelain
(c) iron
(d) P.V.C.
Answer: b

42. The material commonly used for sheaths of underground cables is
(a) lead
(b) rubber
(c) copper
(d) iron
Answer: a

43. The minimum clearance between the ground and a 220 kV line is about
(a) 4.3 m
(b) 5.5 m
(c) 7.0 m
(d) 10.5 m
Answer: c

44. The spacing between phase conductors of a 220 kV line is approximately equal to
(a) 2 m
(b) 3.5 m
(c) 6 m
(d) 8.5 m
Answer: c

45. Large industrial consumers are supplied electrical energy at
(a) 400 V
(b) 11 kV
(c) 66 kV
(d) 400 kV
Answer: c

46. In a D.C. 3-wire distribution system, balancer fields are cross-connected in order to
(a) boost the generated voltage
(b) balance loads on both sides of the neutral
(c) make both machine^ run as unloaded motors
(d) equalize voltages on the positive and negative outers
Answer: d

47. In a D.C. 3-wire distributor using balancers and having unequal loads on the two sides
(a) both balancers run as generators
(b) both balancers run as motors
(c) balancer connected to lightly- loaded side runs as a motor
(d) balancer connected to heavily- loaded side runs as a motor
Answer: c

48. Transmitted power remaining the same, if supply voltage of a D.C. 2-wire feeder is increased 100 percent, saving in copper is
(a) 25 percent
(b) 50 percent
(c) 75 percent
(d) 100 percent
Answer: b

49. A uniformly-loaded D.C. distributor is fed at both ends with equal voltages. As compared to a similar distributor fed at one end only, the drop at the middle point is
(a) one-fourth
(b) one-third
(c) one-half
(d) twice
(e) none of the above
Answer: a

50. As compared to a 2-wire D.C. distributor, a 3-wire distributor with same maximum voltage to earth uses only
(a) 31.25 percent of copper
(b) 33.3 percent of copper
(c) 66.7 percent of copper
(d) 125 percent of copper
Answer: a

51. Which of the following is usually not the generating voltage ?
(a) 6.6 kV
(b) 8.8 kV
(c) 11 kV
(d) 13.2 kV
Answer: b

52. For an overhead line, the surge impedance is taken as
(a) 20-30 ohms
(b) 70—80 ohms
(c) 100—200 ohms
(d) 500—1000 ohms
(e) none of the above
Answer: c

53. The presence of ozone due to corona is harmful because it
(a) reduces power factor
(b) corrodes the material
(c) gives odour
(d) transfer energy to the ground
(e) none of the above
Answer: b

54. A feeder, in a transmission system, feeds power to
(a) distributors
(b) generating stations
(c) service mains
(d) all of the above
Answer: a

55. The power transmitted will be maximum when
(a) corona losses are minimum
(b) reactance is high
(c) sending end voltage is more
(d) receiving end voltage is more
Answer: c

56. A 3-phase 4 wire system is commonly used on
(a) primary transmission
(b) secondary transmission
(c) primary distribution
(d) secondary distribution
Answer: d

57. Which of the following materials is used for overhead transmission lines ?
(a) Steel cored aluminium
(b) Galvanised steel
(c) Cadmium copper
(d) Any of the above
Answer: d

58. Which of the following is not a constituent for making porcelain insulators ?
(a) Quartz
(b) Kaolin
(c) Felspar
(d) Silica
Answer: d

59. There is a greater possibility of occurence of corona during
(a) dry weather
(b) winter
(c) summer heat
(d) humid weather
(e) none of the above
Answer: d

60. Which of the following relays is used on long transmission lines ?
(a) Impedance relay
(b) Mho’s relay
(c) Reactance relay
(d) None of the above
Answer: b

61. The steel used in steel cored conductors is usually
(a) alloy steel
(b) stainless steel
(c) mild steel
(d) high speed steel
(e) all of the above
Answer: c

62. Which of the following distribution systems is more reliable ?
(a) Radial system
(b) Tree system
(c) Ring main system
(d) All are equally reliable
Answer: c

63. Which of the following characteristics should the line supports for transmission lines possess ?
(a) Low cost
(b) High mechanical strength
(c) Longer life
(d) All of the above
Answer: d

64. Transmission voltage of ll kV is normally used for distances upto
(a) 20—25 km
(b) 40—50 km
(c) 60—70 km
(d) 80—100 km
Answer: a

65. Which of the following regulations is considered best?
(a) 50%
(b) 20%
(c) 10%
(d) 2%
Answer: d

66. Skin effect is proportional to
(a) (conductor diameter)
(b) (conductor diameter)
(c) (conductor diameter)
(d) (conductor diameter)
(e) none of the above
Answer: c

67. A conductor, due to sag between two supports, takes the form of
(a) semi-circle
(b) triangle
(c) ellipse
(d) catenary
Answer: d

68. In AC.S.R. conductors, the insulation between aluminium and steel conductors is
(a) insulin
(b) bitumen
(c) varnish
(d) no insulation is required
Answer: d

69. Which of the following bus-bar schemes has the lowest cost ?
(a) Ring bus-bar scheme
(b) Single bus-bar scheme
(c) Breaker and a half scheme
(d) Main and transfer scheme
Answer: b

70. Owing to skin effect
(a) current flows through the half cross-section of the conductor
(b) portion of the conductor near the surface carries more current and core of the conductor carries less current
(c) portion of the conductor near the surface carries less current and core of the conductor carries more cur¬rent
(d) any of the above
(e) none of the above
Answer: b

71. By which of the following methods string efficiency can be improved ?
(a) Using a guard ring
(b) Grading the insulator
(c) Using long cross arm
(d) Any of the above
(e) None of the above
Answer: d

72. In aluminium conductors, steel core is provided to
(a) compensate for skin effect
(b) neutralise proximity effect
(c) reduce line inductance
(d) increase the tensile strength
Answer: d

73. By which of the following a bus-bar is rated ?
(a) Current only
(b) Current and voltage
(c) Current, voltage and frequency
(d) Current, voltage, frequency and short time current
Answer: d

74. A circuit is disconnected by isolators when
(a) line is energized
(b) there is no current in the line
(c) line is on full load
(d) circuit breaker is not open
Answer: b

75. For which of the following equipment current rating is not necessary ?
(a) Circuit breakers
(b) Isolators
(c) Load break switch
(d) Circuit breakers and load break switches
Answer: b

76. In a substation the following equipment is not installed
(a) exciters
(b) series capacitors
(c) shunt reactors
(d) voltatre transformers
Answer: a

77. jCorona usually occurs when the electrostatic stress in air around the conductor exceeds
(a) 6.6 kV (r.m.s. value)/cm
(b) 11 kV (r.m.s. value)/cm
(c) 22 kV (maximum value)/cm
(d) 30 kV (maximum value)/cm
Answer: d

78. The voltage drop, for constant voltage transmission is compensated by installing
(a) inductors
(b) capacitors
(c) synchronous motors
(d) all of above
(e) none of the above
Answer: c

79. The use of strain type insulators is made where the conductors are
(a) dead ended
(b) at intermediate anchor towers
(c) any of the above
(d) none of the above
Answer: c

80. The current drawn by the line due to corona losses is
(a) non-sinusoidal
(b) sinusoidal
(c) triangular
(d) square
Answer: a

81. Pin type insulators are generally not used for voltages beyond
(a) 1 kV
(b) 11 kV
(c) 22 kV
(d) 33 kV
Answer: d

82. Aluminium has a specific gravity of
(a) 1.5
(b) 2.7
(c) 4.2
(d) 7.8
Answer: b

83. For transmission of power over a distance of 200 km, the transmission voltage should be
(a) 132 kV
(b) 66 kV
(c) 33 kV
(d) 11 kV
Answer: a

84. For aluminium, as compared to copper, all the following factors have higher values except
(a) specific volume
(6) electrical conductivity
(c) co-efficient of linear expansion
(d) resistance per unit length for same cross-section
Answer: b

85. Which of the following equipment, for regulating the voltage in distribution feeder, will be most economical ?
(a) Static condenser
(b) Synchronous condenser
(c) Tap changing transformer
(d) Booster transformer
Answer: d

86. In a tap changing transformer, the tappings are provided on
(a) primary winding
(b) secondary winding
(c) high voltage winding
(d) any of the above
Answer: c

87. Constant voltage transmission entails the following disadvantage
(a) large conductor area is required for same power transmission
(b) short-circuit current of the system is increased
(c) either of the above
(d) none of the above
Answer: b

88. On which of the following factors skin effect depends ?
(a) Frequency of the current
(b) Size of the conductor
(c) Resistivity of the conductor material
(d) All of the above
Answer: d

89. The effect of corona can be detected by
(a) presence of ozone detected by odour
(b) hissing sound
(c) faint luminous glow of bluish colour
(d) all of the above
Answer: d

90. For transmission of power over a distance of 500 km, the transmission voltage should be in the range
(a) 150 to 220 kV
(b) 100 to 120 kV
(c) 60 to 100 kV
(d) 20 to 50 kV
Answer: a

91. In the analysis of which of the following lines shunt capacitance is neglected ?
(a) Short transmission lines
(b) Medium transmission lines
(c) Long transmission lines
(d) Medium as well as long transmission lines
Answer: a

92. When the interconnector between two stations has large reactance
(a) the transfer of power will take place with voltage fluctuation and noise
(b) the transfer of power will take place with least loss
(c) the stations will fall out of step be¬cause of large angular displacement between the stations
(d) none of the above
Answer: c

93. The frequency of voltage generated, in case of generators, can be increased by
(a) using reactors
(b) increasing the load
(c) adjusting the governor
(d) reducing the terminal voltage
(e) none of the above
Answer: c

94. When an alternator connected to the bus-bar is shut down the bus-bar voltage will
(a) fall
(b) rise
(c) remain unchanged
(d) none of the above
Answer: c

95. The angular displacement between two interconnected stations is mainly due to
(a) armature reactance of both alternators
(b) reactance of the interconnector
(c) synchronous reactance of both the alternators
(d) all of the above
Answer: a

96. Electro-mechanical voltage regulators are generally used in
(a) reactors
(b) generators
(c) transformers
(d) all of the above
Answer: b

97. Series capacitors on transmission lines are of little use when the load VAR requirement is
(a) large
(b) small
(b) fluctuating
(d) any of the above
Answer: b

98. The voltage regulation in magnetic amplifier type voltage regulator is effected by
(a) electromagnetic induction
(b) varying the resistance
(c) varying the reactance
(d) variable transformer
Answer: c

99. When a conductor carries more current on the surface as compared to core, it is due to
(a) permeability variation
(b) corona
(c) skin effect
(d) unsymmetrical fault
(e) none of the above
Answer: c

100. The following system is not generally used
(a) 1-phase 3 wire
(b) 1-phase 4 wire
(c) 3-phase 3 wire
(d) 3-phase 4 wire
Answer: b

101. The skin effect of a conductor will reduce as the
(a) resistivity of conductor material increases
(b) permeability of conductor material increases
(c) diameter increases
(d) frequency increases
Answer: a

110. When a live conductor of public electric supply breaks down and touches the earth which of the following will happen ?
(a) Current will flow to earth
(b) Supply voltage will drop
(c) Supply voltage will increase
(d) No current will flow in the conductor
(e) None of the above
Answer: a

TRANSMISSION & DISTRIBUTION Mcqs Interview Questions Pdf ::

SWITCHGEAR & PROTECTION Multiple Choice Questions :-

1. The main function of a fuse is to
(a) protect the line
(b) open the circuit
(c) protect the appliance
(d) prevent excessive currents
(e) none of the above
Ans: d

2. On which of the following routine tests are conducted ?
(a) Oil circuit breakers
(b) Air blast circuit breakers
(c) Minimum oil circuit breakers
(d) All of the above
Ans: d

3. SF6 gas
(a) is yellow in colour
(b) is lighter than air
(c) is nontoxic
(d) has pungent small
(e) none of the above
Ans: c

4. The arcing contacts in a circuit breaker are made of
(a) copper tungsten alloy
(b) porcelain
(c) electrolytic copper
(d) aluminium alloy
Ans: a

5. Which of the following medium is employed for extinction of arc in air circuit breaker ?
(a) Water
(b) Oil
(c) Air
(d) SF6
Ans: c

6. With which of the following, a circuit breaker must be equipped for remote operation ?
(a) Inverse time trip
(b) Time-delay trip
(c) Shunt trip
(d) None of the above
(e) All of the above
Ans: c

7. Fault diverters are basically
(a) fuses
(b) relays
(c) fast switches
(d) circuit breakers
Ans: c

8. A thermal protection switch can protect against
(a) short-circuit
(b) temperature
(c) overload
(d) over voltage
Ans: c

9. Arc in a circuit behaves as
(a) a capackive reactance
(b) an inductive reactance
(c) a resistance increasing with voltage rise across the arc
(d) a resistance decreasing with voltage rise across the arc
Ans: d

10. Thermal circuit breaker has
(a) delayed trip action
(b) instantaneous trip action
(c) both of the above
(d) none of the above
Ans: a

11. Relays can be designed to respond to changes in
(a) resistance, reactance or impedance
(b) voltage and current
(c) light intensity
(d) temperature
(e) all above
Ans: e

12. Overload relays are of…… type.
(a) induction
(b) solid state
(c) thermal
(d) electromagnetic
(e) all above
Ans: e

13. Thermal overload relays are used to protect the motor against over current due to
(a) short-circuits
(b) heavy loads
(c) grounds
(d) all of the above
Ans: b

14. Magnetic circuit breaker has ______ trip action.
(a) delayed
(b) instantaneous
(c) both of the above
(d) none of the above
Ans: b

15. D.C. shunt relays are made of
(a) few turns of thin wire
(b) few turns of thick wire
(c) many turns of thin wire
(d) many turns of thick wire
Ans: c

16. The relay operating speed depends upon
(a) the spring tension
(b) the rate of flux built up
(c) armature core air gap
(d) all of the above
Ans: d

17. In order that current should flow without causing excessive heating or voltage drop, the relay contacts should
(a) have low contact resistance
(b) be clean and smooth
(c) be of sufficient size and proper shape
(d) have all above properties
Ans: d

18. Circuit breakers usually operate under
(a) transient state of short-circuit current
(b) sub-transient state of short-circuit current
(c) steady state of short-circuit current
(d) after D.C. component has ceased
Ans: a

19. Circuit breakers are essentially
(a) current carrying contacts called electrodes
(b) arc extinguishers
(c) circuits to break the system
(d) transformers to isolate the two systems
(e) any of the above
Ans: a

20. The current zero interruption, in oil and air blast circuit breakers, is achieved by
(a) lengthening of the gap
(b) cooling and blast effect
(c) both (a) and (b)
(d) deionizing the oil with forced air
(e) none of the above
Ans: c

21. Air blast circuit breaker is used for
(a) over currents
(b) short duty
(c) intermittant duty
(d) repeated duty
Ans: d

22. An efficient and a well designed protective relaying should have
(a) good selectivity and reliability
(b) economy and simplicity
(c) high speed and selectivity
(d) all of the above
Ans: d

23. Burden of a protective relay is the power
(a) required to operate the circuit breaker
(b) absorbed by the circuit of relay
(c) developed by the relay circuit
(d) none of the above
Ans: b

24. Directional relays are based on flow of
(a) power
(b) current
(c) voltage wave
(d) all of the above
Ans: a

25. A differential relay measures the vector difference between
(a) two currents
(b) two voltages
(c) two or more similar electrical quantities
(d) none of the above
Ans: c

26. A transmission line is protected by
(a) inrush protection
(b) distance protection
(c) time graded and current graded over current protection
(d) both (b) and (c)
(e) none of the above
Ans: d

27. Large internal faults are protected by
(a) merz price percentage differential protection
(b) mho and ohm relays
(c) horn gaps and temperature relays
(d) earth fault and positive sequence relays
Ans: a

28. When a transmission line is energized, the wave that propagates on it is
(a) current wave only
(b) voltage wave only
(c) both (a) and (b)
(d) power factor wave only
Ans: c

29. Protective relays are devices that detect abnormal conditions in electrical circuits by measuring
(a) current during abnormal condition
(b) voltage during abnormal condition
(c) constantly the electrical quantities which differ during normal and abnormal conditions
(d) none of the above
Ans: c

30. The voltage appearing across the contacts after opening of the circuit breaker is called______voltage.
(a) recovery
(b) surge
(c) operating
(d) arc
(e) none of the above
Ans: a

31. Ionization in circuit breaker is facilitated by
(a) high temperature
(b) increase of mean free path
(c) increasing field strength
(d) all of the above
Ans: d

32. In a circuit breaker the basic problem is to
(a) maintain the arc
(b) extinguish the arc
(c) transmit large power
(d) emit the ionizing electrons
Ans: c

33. Overheating of relay contacts or contact born out is due to
(a) slow making and breaking of load circuit contacts
(b) foreign matter on the contact surface
(c) too low contact pressure
(d) all of the above
Ans: d

34. Interruption of large currents by relay requires
(a) arc suppressing blow out coils
(b) wide separation of the opened contacts
(c) high speed opening of contacts
(d) all of the above
Ans: d

35. Shunt capacitance is neglected while considering
(a) short transmission line
(b) medium transmission line
(c) long transmission line
(d) medium and long transmission lines
Ans: a

36. The arc voltage produced in A.C. circuit breaker is always
(a) in phase with the arc current
(b) lagging the arc current by 90″
(c) leading the arc current by 90°
(d) none of the above
Ans: a

37. The time of closing the cycle, in modern circuit breakers is
(a) 0.003 sec
(b) 0.001 sec
(c) 0.01 sec
(d) 0.10 sec
(e) none of the above
Ans: a

38. Insulation resistance of high voltage circuit breakers is more than
(a) 1 mega ohms
(b) 10 mega ohms
(c) 100 mega ohms
(d) 500 mega ohms
Ans: c

39. H.R.C. fuses provide best protection against
(a) overload
(b) reverse current
(c) open-circuits
(d) short-circuits
Ans: d

40. The ground wire should not be smaller than No ______ copper.
(a) 2
(b) 4
(c) 6
(d) 10
Ans: d

41. The delay fuses are used for the protection of ________ .
(a) motors
(b) power outlet circuits
(c) fluorescent lamps
(d) light circuits
Ans: a

42. Which of the following is the least expensive protection for overcurrent is low voltage system ?
(a) Rewireable fuse
(b) Isolator
(c) Oil circuit breaker
(d) Air break circuit breaker
(e) None of the above
Ans: a

43. Resistance grounding is used for voltage between
(a) 33kVto66kV
(b) HkVto33kV
(c) 3.3kVandllkV
(d) none of the above
Ans: c

44. The contacts of high voltage switches used in power system are submerged in oil. The main purpose of the oil is to
(a) lubricate the contacts
(b) insulate the contacts from switch body
(c) extinguish the arc
(d) all of the above
(e) none of the above
Ans: c

45. In Railway applications ______ circuit breaker is used.
(a) SFe
(b) bulk oil
(c) minimum oil
(d) air break
Ans:

46. To protect most of the electrical equipment handling low power, the types of relays used are
(a) thermocouple
(b) electronic and bimetallic
(c) both (a) and (b)
(d) none of the above
Ans: c

47. Wave trap is used to trap waves of
(a) power frequencies
(b) higher frequencies entering generator or transformer units
(c) either of the above
(d) none of the above
Ans: b

48. Ungrounded neutral transmission system is not recommended because of system
(a) insulation being overstressed due to over voltages
(b) insulation overstress may lead to failure and subsequent phase to phase faults
(c) being inadequately protected against ground fault
(d) all of the above
Ans: d

49. The reflection co-efficient at the open circuited end of a transmission line.
(a) zero
(b) infinity
(c) unity
(d) none of the above
Ans: c

50. For the protection of power station buildings against direct strokes the requirements are
(a) interception
(b) interception and conduction
(c) interception, conduction and dissipation
(d) interception, conduction, dissipation and reflection
(e) none of the above
Ans: c

51. The line insulation is the insulation level of the station equipment.
(a) less than
(b) same as
(c) more than
(d) proportional to
(e) not directly related with
Ans: e

52. The interaction between a transmission line and communication line is minimized by
(a) transposing transmission as well as communication lines
(b) increasing the height of the trans-mission line tower
(c) increasing the distance between the two lines
(d) all of the above
Ans: d

53. When a wave propagates on a transmission line, it suffers reflection several times at
(a) tapping
(b) load end
(c) sending end
(d) sending and other end
(e) all of the above
Ans: d

54. Which of the following statements is incorrect?
(a) Station batteries are used to operate relay only
(b) The lightning arresters are basically surge diverters
(c) An impedance relay has maximum fault current when fault occurs near the relay
(d) A high speed relay has an operation of 1 to 2 cycles
Ans: a

55. Discrimination between main and back up protection is provided by the use of relays which are
(a) fact
(b) sensitive
(c) slow
(d) none of the above
Ans: c

56. Induction cup relay is operated due to changes in
(a) current
(b) voltage
(c) impedance
(d) all of the above
Ans: d

57. A.C. network analyser is used to solve problems of
(a) load flow
(b) load flow and short-circuit
(c) load flow and stability
(d) load flow, short-circuit and stability
(e) none of the above
Ans: d

58. Which of the following statements is incorrect ?
(a) Lightning arrestors are used before the switchgear
(b) Shunt reactors are used as compensation reactors
(c) The peak short current is (1.8 xV2) times the A.C. component
(d) The MVA at fault is equal to base MVA divided by per unit equivalent fault reactance
Ans: a

59. Short-circuit currents are due to
(a) single phase to ground faults
(b) phase to phase faults
(c) two phase to ground faults
(d) three phase faults
(e) any of these
Ans: e

60. To reduce short circuit fault currents are used.
(a) reactors
(b) resistors
(c) capacitors
(d) none of the above
Ans: a

61. Bus coupler is very essential in arrangement
(a) single bus
(b) double bus, double breaker
(c) main and transfer bus
(d) all of the above
Ans: c

62. For cost and safety, the outdoor substations are installed for voltages above
(a) 11 kV
(b) 33 kV
(c) 60kV
(d) 110kV
Ans: b

63. The short circuit in any winding of the transformer is the result of
(a) mechanical vibration
(b) insulation failure
(c) loose connection
(d) impulse voltage
Ans: d

64. relays are used for phase faults on long line.
(a) Impedance
(b) Reactance
(c) Either of the above
(d) None of the above
Ans: a

65. For which of the following protection from negative sequence currents is provided ?
(a) Generators
(b) Motors
(c) Transmission line
(d) Transformers
Ans: a

66. relay is preferred for phase fault on short transmission line.
(a) Induction type
(b) Reactance
(c) Impedance
(d) None of the above
Ans: b

67. Distance relays are generally
(a) split-phase relays
(b) reactance relays
(c) impedance relays
(d) none of the above
Ans: d

68. For which of the following ratings of the transformer differential protection is recommended ?
(a) above 30 kVA.
(b) equal to and above 5 MVA
(c) equal to and above 25 MVA
(d) none of the above
Ans: b

69. A _______ is used to measure the stator % winding temperature of the generator.
(a) thermocouple
(b) pyrometer
(c) resistance thermometer
(d) thermometer
Ans: c

70. The under voltage relay can be used for
(a) generators
(b) busbars
(c) transformers
(d) motors
(e) all of the above
Ans: e

71. The relay with inverse time characteristic will operate within
(a) 1.5 sec
(b) 5 to 10 sec
(c) 5 to 20 sec
(d) 20 to 30 sec
(e) none of the above
Ans: b

72. The single phasing relays are used for the protection of
(a) single phase motors only
(b) two phase motors only
(c) two single phase motors running in parallel
(d) three phase motors
Ans: d

73. Which of the following devices will receive voltage surge first travelling on the transmission line ?
(a) Lightning arresters
(b) Relays
(c) Step-down transformer
(d) Switchgear
Ans: a

74. Which of the following parameter can be neglected for a short line ?
(a) Inductance
(b) Capacitance
(c) Resistance
(d) Reactance
Ans: b

75. Series reactors should have
(a) low resistance
(b) high resistance
(c) low impedance
(d) high impedance
Ans: a

76. Which of the following circuit breakers has high reliability and minimum maintenance ?
(a) Air blast circuit breakers
(b) Circuit breaker with SF6 gas
(c) Vacuum circuit breakers
(d) Oil circuit breakers
Ans: b

77. Arc in a circuit breaker is interrupted at
(a) zero current
(b) maximum current
(c) minimum voltage
(d) maximum voltage
Ans: a

78. transmission line has reflection coefficient as one.
(a) Open circuit
(b) Short-circuit
(e) Long
(d) None of the above
Ans: a

79. What will be the reflection co-efficient of the wave of load connected to transmission line if surge impedance of the line is equal to load ?
(a) Zero
(b) Unity
(c) Infinity
(d) None of the above
Ans: a

80. The inverse definite mean time relays are used for over current and earth fault protection of transformer against
(a) heavy loads
(b) internal short-circuits
(c) external short-circuits
(d) all of the above
Ans: b

81. Over voltage protection is recommended for
(a) hydro-electric generators
(b) steam turbine generators
(c) gas turbine generators
(d) all of the above
(e) none of the above
Ans: d

82. Air blast circuit breakers for 400 kV power system are designed to operate in
(a) 100 microsecond
(b) 50 millisecond
(c) 0.5 sec
(d) 0.1 sec
Ans: b

83. Overfluxing protection is recommended for
(a) distribution transformer
(b) generator transformer of the power plant
(c) auto-transformer of the power plant
(d) station transformer of the power plant
Ans: b

84. Series capacitors are used to
(a) compensate for line inductive reactance
(b) compensate for line capacitive reactance
(c) improve line voltage
(d) none of the above
Ans: a

85. Admittance relay is _______ relay.
(a) impedance
(b) directional
(c) non-directional
(d) none of the above
Ans: b

86. The material used for fuse must have
(a) low melting point and high specific resistance
(b) low melting point and -low specific resistance
(c) high melting point and low specific resistance
(d) low melting point and any specific resistance
Ans: a

87. If the fault occurs near the impedance relay, the VII ratio will be
(a) constant for all distances
(b) lower than that of if fault occurs away from the relay
(c) higher than that of if fault occurs away from the relay
(d) none of the above
Ans: b

88. The torque produced in induction type relay (shaded pole structure) is
(a) inversely proportional to the current
(b) inversely proportional to the square of the current
(c) proportional to the current
(d) proportional to square of the current
Ans: b

89. The steady state stability of the power system can be increased by
(a) connecting lines in parallel
(b) connecting lines in series
(e) using machines of high impedance
(d) reducing the excitation of machines
(e) none of the above
Ans: a

90. The inductive interference between power and communication line can be minimized by
(a) transposition of the power line
(b) transposition of the communication line
(c) both (a) and (b)
(d) increasing the distance between the conductors
Ans: c

91. The power loss is an important factor for the design of
(a) transmission line
(b) motor
(c) generator
(d) feeder
Ans: a

92. A fuse is connected
(a) in series with circuit
(b) in parallel with circuit
(c) either in series or in parallel with circuit
(d) none of the above
Ans: a

93. H.R.C. fuse, as compared to a rewirable fuse, has
(a) no ageing effect
(b) high speed of operation
(c) high rupturing capacity
(d) all of the above
Ans: d

94. The fuse rating is expressed in terms of
(a) current
(b) voltage
(c) VAR
(d) kVA
Ans: a

95. The fuse blows off by
(a) burning
(b) arcing
(c) melting
(d) none of the above
Ans: c

96. On which of the following effects of electric current a fuse operates ?
(a) Photoelectric effect
(b) Electrostatic effect
(c) Heating effect
(d) Magnetic effect
Ans: c

97. An isolator is installed
(a) to operate the relay of circuit breaker
(b) as a substitute for circuit breaker
(c) always independent of the position of circuit breaker
(d) generally on both sides of a circuit breaker
Ans: d

98. A fuse in a motor circuit provides protection against
(a) overload
(b) short-circuit and overload
(c) open circuit, short-circuit and overload
(d) none of the above
Ans: b

99. Protection by fuses is generally not used beyond
(a) 20 A
(b) 50 A
(c) 100 A
(d) 200 A
Ans: c

100. A fuse is never inserted in
(a) neutral wire
(b) negative of D.C. circuit
(c) positive of D.C. circuit
(d) phase dine
Ans: a

101. Oil switches are employed for
(a) low currents circuits
(b) low voltages circuits
(c) high voltages and large currents circuits
(d) all circuits
Ans: c

102. A switchgear is device used for
(a) interrupting an electrical circuit
(b) switching an electrical circuit 111.
(c) switching and controlling an electrical circuit
(d) switching, controlling and protecting the electrical circuit and equipment
Ans: d

103. The fuse wire, in D.C. circuits, is inserted in
(a) negative circuit only
(b) positive circuit only
(c) both (a) and (b)
(d) either (a) or (b)
Ans: c

104. By which of the following methods major portion of the heat generated in a H.R.C. fuse is dissipated ?
(a) Radiation
(b) Convection
(c) Conduction
(d) All of the above
Ans: c

105. A short-circuit is identified by
(a) no current flow
(b) heavy current flow
(c) voltage drop
(d) voltage rise
Ans: b

106. The information to the circuit breaker under fault conditions is provided by
(a) relay
(b) rewirable fuse
(c) H.R.C. only
(d) all of the above
Ans: a

107. To limit short-circuit current in a power system are used.
(a) earth wires
(b) isolators
(c) H.R.C. fuses
(d) reactors
Ans: d

109. A balanced 3-phase system consists of
(a) zero sequence currents only
(b) positive sequence currents only
(c) negative and zero sequence currents
(d) zero, negative and positive sequence currents
Ans: b

110. In a single bus-bar system there will be complete shut down when
(a) fault occurs on the bus itself
(b) fault occurs on neutral line
(c) two or more faults occur simultaneously
(d) fault occurs with respect to earthing
Ans: a

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