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Top 100 MCQ Transformer questions and answers

Transformer
Transformer

Transformer: [ ISRO,DRDO,DMRC,SAIL, ODNANCE, HAL, WBSEDCL, RAILWAY
& Others competitive]

1. Which of the following does not change in a transformer? (ISRO, ORDNANCE , DMRC , DRDO Repeated )

1.Current

2.Voltage

3.  Frequency

4.All of the above

2. In a transformer the energy is conveyed from primary to secondary ?      

1.though cooling coil        

2.through air                                     

3.by the flux

4.none of the above

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3.  Why are the transformer core are lamination ? (ISRO, ORDNANCE , DMRC , DRDO Repeated )                                                1.reduce hysteresis loss

2.reduce eddy current losses    

3.reduce copper losses 

4.reduce all the above losses

4. Which loss is not common between a transformer and rotating machines?

1.Eddy current loss

2.Copper loss

3.Windage loss

4.Hysteresis loss.

5. The degree of mechanical vibrations produced by the laminations of a transformer depends on

 1.tightness of clamping

2.gauge of laminations

3.size of laminations

4.all of the above.

6. The no-load current drawn by transformer is usually what percent of the full-load current? (ISRO, ORDNANCE , DMRC , DRDO Repeated )

1.0.2 to 0.5 per cent

2.   2 to 5 per cent

3.12 to 15 per cent

4.20 to 30 per cent

7. In case there are burrs on the edges of the laminations of the transformer, it is likely to result in…                    

1.vibrations

 2.noise

3.   higher eddy current loss

4.higher hysteresis loss

8. The path of a magnetic flux in a transformer should have….

1.high resistance

2.high reluctance

3.low resistance

4.   low reluctance.

9. No-load test on a transformer is carried out to determine (ISRO, ORDNANCE , DMRC , DRDO Repeated )

1.copper loss

2.magnetizing current

3.magnetiing current and lose 

4.efficiency of the transformer 

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10. The dielectric strength of transformer oil is expected to be… (ISRO, ORDNANCE , DMRC , DRDO Repeated )

1.1 kV

2.33 kV 

3.100 kV                                                                                                                                      

 4.330 kV

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ISRO Previous Years Question paper pdf technician- B (electrician)

Question Papers pdf  in Hindi & English language (ITI Electrical) 

Anyone want to buy full question sets so click below link . In this pdf file to developed

Previous Years Question Paper
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DC Motor MCQ Questions And Answers

DC Motor

 

D.C Motor: [ ISRO,DRDO,DMRC,SAIL, ODNANCE, HAL, WBSEDCL, RAILWAY & Others competitive] DC Motor MCQ Questions And Answers

1. Starters are used with D.C. motors because….

(a) these motors have high starting torque

(b) these motors are not self-starting

(c) back e.m.f. of these motors is zero initially

(d) to restrict armature current as there is no back e.m.f. while starting

Ans: d

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2. In D.C. shunt motors as load is reduced……

(a) the speed will increase abruptly

(b) the speed will increase in proportion to reduction in load 

(c) the speed will remain almost/constant

(d) the speed will reduce

Ans: c

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3. A D.C. series motor is that which  …….

(a) has its field winding consisting of thick wire and less turns

(b) has a poor torque

(c) can be started easily without load

(d) has almost constant speed

Ans: a

4. For starting a D.C. motor a starter is required because………

(a) it limits the speed of the motor

(b) it limits the starting current to a safe value

(c) it starts the motor

(d) none of the above

Ans: b

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5. The type of D.C. motor used for shears and punches is……….

(a) shunt motor

(b) series motor

(c) differential compound D.C. motor https://youtu.be/IknfOS2f4qA

(d) cumulative compound D.C. motor

Ans: d

6. If a D.C. motor is connected across the A.C. supply it will……….

(a) run at normal speed

(b) not run

(c) run at lower speed

(d) burn due to heat produced in the field winding by eddy currents

Ans: d

7. To get the speed of D.C, motor below the normal without wastage of electrical energy is used.……….

(a) Ward Leonard control

(b) rheostatic control

(c) any of the above method

(d) none of the above method

Ans: a

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8. When two D.C. series motors are connected in parallel, theresultant speed is……….

(a) more than the normal speed

(b) loss than the normal speed

(c) normal speed

(d) zero

Ans: c

9. The speed of a D.C. shunt motor more than its full-load speed can be obtained by……….

(a) decreasing the field current

(b) increasing the field current

(c) decreasing the armature current

(d) increasing the armature current

Ans: a

10. In a D.C. shunt motor, speed is……….

(a) independent of armature current

(b) directly proportional to the armature current

(c) proportional to the square of the current

(d) inversely proportional to the armature current

Ans: a 

 

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Top 100 MCQ Single Phase Induction motor

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Synchronous motor : [ ISRO,DRDO,DMRC,SAIL, ODNANCE, HAL, WBSEDCL, RAILWAY & Others competitive]

1. 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

 Ans :b

 

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2. 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

 Ans :d

3. 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
 Ans :c
4. 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
 Ans :a
5. 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
 Ans :c
6. 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
 Ans :b
7. 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
 Ans :a
8. 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
 Ans :d

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9. 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
Ans: d
10. Which of the following motors is used in mixtures ?
(a) Repulsion motor
(b) Reluctance motor
(c) Hysteresis motor
(d) Universal motor
Ans: d
11. Which of the following motors is inherently self starting ?
(a) Split motor
(b) Shaded-pole motor
(c) Reluctance motor                                                                                                                                                                                          (d) None of these

 Ans :b

 12. In a capacitor start motor, the phase displacement between starting and running winding can be nearly
(a) 10°
(b) 30°
(c) 60°
(d) 90°
Ans: d
13. 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
Ans: a
14. The rotor developed by a single-phase motor at starting is
(a) more than. the rated torque
(b) rated torque
(c) less than the rated torque
(d) zero
Ans: d
15. 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

 Ans :a
 16. 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
 Ans :a                                                                                                                                                                                                         17. 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 inductance
 Ans :b
18. 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.
 Ans :a
19. 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
 Ans :a
20. 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
 Ans :a                                                                                                                                                                                                           21. 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
 Ans :b
22. 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
 Ans :a
23. 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 

 Ans :a
24. Which of the following motors is used in tape-recorders ?
(a) Hysteresis motor
(b) Reluctance motor
(c) Capacitor-run motor
(d) Universal motor
 Ans :a

25. 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
 Ans :a
26. To reverse the direction of rotation of capacitor 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
 Ans :a
28. 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
 Ans :d
29. 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
 Ans :b
30. A shaded pole motor does not possess
(a) centrifugal switch
(b) capacitor
(c) commutator

(d) all of the above
 Ans :d
31. In a A.C. series motor armature coils are usually connected to commutator
(a) through resistance
(b) through reactance’s
(c) through capacitors
(d) solidly
 Ans :a
32. 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 unsymmetrical magnetic construction in order to vary reluctance path between stator and rotor
 Ans :a
33. 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
 Ans :a

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34. A repulsion motor is equipped with
(a) slip rings
(b) commutator
(c) both (a) and (b)
(d) none of the above
 Ans :b
35. The capacitors used in single-phase capacitor motors have no
(a) voltage rating
(b) dielectric medium
(c) polarity marking
(d) definite value
 Ans :c
36. 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
 Ans :d

37. 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
 Ans :b
38. 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
 Ans :c
39. 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
 Ans :d
40. 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
41. 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
 Ans :c
42. 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
 Ans :d

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43. A reluctance motor
(a) is self-starting
(b) is constant speed motor
(c) needs no D.C. excitation
(d) all of the above
 Ans :d
44. In a hysteresis motor, the rotor must have
(a) retentivity
(b) resistivity
(c) susceptibility
(d) none of the above
 Ans :a
45. The rotor of a hysteresis motor is made of
(a) aluminium
(b) cast iron
(c) chrome steel
(d) copper
 Ans :c
46. The electric motor used in portable drills is
(a) capacitor run motor
(b) hysteresis motor
(c) universal motor
(d) repulsion motor
 Ans :c
47. 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
 Ans :c

48. 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
 Ans :a
49. 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
 Ans :c
50. 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
 Ans :d
51. The speed of a universal motor is generally reduced by using
(a) gear trains
(b) V-belts
(c) brakes
(d) chains
 Ans :a
52. 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
 Ans :d
53. 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
 Ans :a
54. 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
 Ans :c
55. 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
 Ans :c

56. Which motor is normally free from mechanical and magnetic vibrations ?
(a) Split phase motor
(b) Universal motor
(c) Hysteresis motor
(d) Shaded pole motor
 Ans :c
57. 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
Ans :c  

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58. 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
 Ans :b
59. Torque developed by a single phase induction motor at starting is
(a) pulsating
(b) uniform
(c) none of the above
(d) nil
 Ans :d
60. 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
 Ans :c
61. 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
 Ans :a
62. 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
 Ans :a
63. 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
 Ans :c
64. In a ceiling fan 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
 Ans :a
65. The shaded pole motor is used for
(a) high starting torque
(b) low starting torque
(c) medium starting torque
(d) very high starting torque
 Ans :b
66. 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
 Ans :c
67. 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
 Ans :c
68. 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
 Ans :b
69. Which of the following motors is used for unity power factor ?
(a) Hysteresis motor
(b) Schrage motor
(c) Universal motor
(d) Reluctance motor
 Ans :b
70. 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
 Ans :c
71. 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
 Ans :b
72. 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)
 Ans :d

73. 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
 Ans :b
74. Burning out of windings is due to
(a) short circuited capacitor
(b) capacitor value hiving changed
(c) open circuiting of capacitor
(d) none of the above
 Ans :a
75. 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)
 Ans :c
76. Short-circuiter is used in
(a) repulsion induction motor
(b) repulsion motor
(c) repulsion start induction run motor
(d) none of the above
 Ans :c
77. 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%
 Ans :d
78. 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
 Ans :d
79. The power factor of a single-phase induction motor is usually
(a) lagging
(b) always leading
(c) unity
(d) unity to 0.8 leading
 Ans :a
80. A shaded pole motor can be used for
(a) toys
(b) hair dryers
(c) circulators
(d) any of the above
 Ans :d
81. A hysteresis motor works on the principle of
(a) hysteresis loss
(b) magnetisation of rotor
(c) eddy current loss
(d) electromagnetic induction
 Ans :a
82. 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
 Ans :b

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83. 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
 Ans :d
84. 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
 Ans :b
85. 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
 Ans :a
86. 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
 Ans :c
87. 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
 Ans :c
88. Which of the following motors has highest starting torque ?
(a) Repulsion motor
(b) Shaped pole motor

(c) Capacitor-start motor
(d) Split-phase motor
 Ans :c
89. The repulsion-start induction-run motor is used because of
(a) good power factor
(b) high efficiency
(c) minimum cost
(d) high starting torque
 Ans :d
90. 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
 Ans :a
91. 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
 Ans :d
92. 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
 Ans :c

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93. For which of the applications a reluctance motor is preferred ?
(a) Electric shavers
(b) Refrigerators
(c) Signaling and timing devices
(d) Lifts and hoists
 Ans :c
94. 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
 Ans :c

95. 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
 Ans :b
96. 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
 Ans :c
97. A Schrage motor can run on
(a) zero slip
(b) negative slip
(c) positive slip
(d) all of the above
 Ans :d
98. 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
 Ans :c
99. 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
 Ans :a
100. 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
 Ans :a

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Top 100 MCQ Synchronous motor

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Synchronous motor : [ ISRO,DRDO,DMRC,SAIL, ODNANCE, HAL, WBSEDCL, RAILWAY & Others competitive]

 
1. The power developed by a synchronous motor will be maximum when the load angle is…….

(a) zero

(b) 45°

(c) 90°

(d) 120°

Ans: c

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2. 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

Ans: d

3. 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

Ans: d 

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4. Mostly, synchronous motors are of…….

(a) alternator type machines

(b) induction type machines

(c) salient pole type machines

(d) smooth cylindrical type machines

Ans: c

5. 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

Ans: a

6. 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 causing more motor current

Ans: b

7. Synchronous motor always runs at…….

(a) the synchronous speed

(b) less than synchronous speed

(c) more than synchronous speed

(d) none of the above

Ans: a

8. An over-excited synchronous motor takes…….

(a) leading current

(b) lagging current

(c) both (a) and (b)

(d) none of the above

Ans: a

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9. The working of a synchronous motor is similar to…….

(a) gear train arrangement

(b) transmission of mechanical power by shaft

(c) distribution transformer

(d) turbine

Ans: b

10. 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

Ans: b

11. The maximum value of torque angel in a synchronous motor is ….

(a) 45

(b) 90

(c) between 45 and 90

(d) below 60

Ans:b                                                                                                                                                                     

12. A synchronous motor can be started by…….

(a) pony motor

(b) D.C. compound motor

(c) providing damper winding

(d) any of the above

Ans: d

13. A three-phase synchronous motor will have…….

(a) no slip-rings

(b) one slip-ring

(c) two slip-rings

(d) three slip-rings

Ans: c

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14. 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

Ans: a

15. 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

Ans: a

16. When V is the applied voltage, then the breakdown torque of a synchronous motor varies as…….

(a) V

(b) V3/2

(c) V2

(d) 1/V

Ans: a

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 17. 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) starter cannot be used on these machines

(d) starting winding is not provided on the machines

Ans: b

18. 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

Ans: a

19. 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

Ans: a

20. 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

Ans: c 
21. The maximum speed variation in a 3-phase synchronous motor is…….

(a) 10 percent

(b) 6 per cent

(c) 4 per cent

(d) zero

Ans: d                                                                                                                                                                                                           

22. 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

Ans: d

23. 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

Ans: d   

                                                                                                                                                       

24. The ratio of starting torque to running torque in a synchronous motor is…….

(a) zero

(b) one

(c) two

(d) infinity

Ans: a

25. 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

Ans: b

26. 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

Ans: b

27. 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

Ans: a


                                                                            https://www.electricaleducations.com                                                                                                                                                                               

 28. The torque angle, in a synchronous motor, is the angle between…….

(a) the supply voltage and the back e.m.f.

(b) magnetizing current and back e.m.f.

(c) the rotating stator flux and rotor poles

(d) none of the above

Ans: c

29. Hunting in a synchronous motor cannot be due to…….

(a) windage friction

(b) variable load

(c) variable frequency

(d) variable supply voltage

Ans: a

30. 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.

Ans: a

31. 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

Ans: a

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32. 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

Ans: b

33. 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

Ans: b                                                                                                                                                                                     

 34. 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

Ans: c

35. 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

Ans: a

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36. In a synchronous motor, damper windings are provided on…….

(a) stator frame

(b) rotor shaft

(c) pole faces

(d) none of the above

Ans: c

37. 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 tothe supply voltage 

(d) none of the above

Ans: a

38. The effect of increasing the load on a synchronous motor running with normal excitation is to…….

(a) decrease both armature current and power factor

(b) decrease armature current but increase power factor

(c) increase armature current but decrease power factor

(d) increase both its armature current and power factor

Ans: c

39. 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

Ans: d

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40. 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

Ans: a

41. 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

Ans: c

42. 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

Ans: b

43. In a synchronous motor, the rotor copper loss are met by …….

(a) rotor input

(b) armature input

(c) supply lines

(d) dc source

Ans: d

44. Synchronous capacitor is…….

(a) an ordinary static capacitor bank

(b) an over excited synchronous motor driving mechanical load

(c) an over excited synchronous motor running without mechanical load

(d) non of the above

Ans: c
45. 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%

Ans: c

46. To limit the operating temperature an electrical machine should have proper…….

(a) voltage rating

(b) current rating

(c) power factor

(d) speed

Ans: b

47. Slip-rings in a synchronous motor carry…….

(a) direct current

(b) alternating current

(c) no current

(d) all of the above

Ans: a

48. A synchronous machine with large air gap has…….

(a) a higher value of stability limit

(b) 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

Ans: d

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49. 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

Ans: c

50. 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

Ans: c      

 51. 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

Ans: b

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 52. The angle between the rotating stator flux and rotor poles is called _____ angle.

(a) torque

(b) obtuse

(c) synchronizing

(d) power factor

Ans: a

53. 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

Ans: c

54. 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

Ans: b                                                                                                                                                                       

55. 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

Ans: c

56. 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

Ans: b

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57. 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

Ans: d

58. 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

Ans: b

59. 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

Ans: c

60. While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerating 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) repentance motor torque due to saliency of the rotor

(e) all of the above methods

Ans: e

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61. 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

Ans: d

62. 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.

Ans:a
63. 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-magnetizes it

(d) none of the above

Ans: b

64. 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

Ans: b

65. 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

Ans: a

66. 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.

Ans: b

67. 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

Ans: d

68. 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 up to speed

(d) will fail to pull into step

Ans: a

69. If the field circuit of an unloaded salient pole 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

Ans: b

70. 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

Ans: d

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71. 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

Ans: c                                                                                                                                                                       

72. 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

Ans: b

73. 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

Ans: a

 74. The maximum power developed in a synchronous motor occurs at a coupling angle of…….

(a) 30°

(b) 60°

(c) 90°

(d) 180°

Ans: c

75. 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

Ans: d                                                                                                         
76. 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

Ans: b

77. The rotor copper losses, in a synchronous motor, are met by…….

(a) d.c. source

(b) armature input

(c) motor input

(d) supply lines

Ans: a

 

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78. The back e.m.f. of a synchronous motor depends on…….

(a) speed

(b) load

(c) load angle

(d) all of the above

Ans: c

79. A synchronous motor can operate at…….

(a) lagging power factor only

(b) leading power factor only

(c) unity power factor only

(d) lagging, leading and unity power factors

Ans: d

80. In a synchronous motor which loss varies with load ?

(a) Windage loss

(b) Bearing friction loss

(c) Copper loss

(d) Core loss

Ans: c

81. 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

Ans: d

82. 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

Ans: c

83. The shaft of synchronous motor is made of…….

(a) mild steel

(b) chrome steel

(c) alnico

(d) stainless steel

Ans: a

84. When the field of a synchronous motor is under-excited, the power factor will be…….

(a) leading

(b) lagging

(c) unity

(d) zero

Ans: b 

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85. The speed regulation of a synchronous motor is always…….

(a) 1%

(b) 0.5%

(c) positive

(d) zero

Ans: d 

86. ruining 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

Ans: b

87. Synchronizing power of a synchronous machine is…….

(a) directly proportional to the synchronous reactance

(b) inversely proportional to the synchronous reactance

(c) equal to the synchronous reactance

(d) none of the above

Ans: b

88. Synchronous motors are…….

(a) not-self starting

(b) self-starting

(c) essentially self-starting

(d) none of the above

Ans: a

89. 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

Ans: c

90. 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

Ans: b

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91. 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

Ans: b

92. A synchronous motor working at leading power factor can be used as…….
(a) voltage booster

(b) phase advancer

(c) noise generator

(d) mechanical synchronizer

Ans: b

93. Slip rings are usually made of…….

(a) carbon or graphite

(b) brass or steel

(c) silver or gold

(d) copper or aluminum

Ans: b

94. An over excited synchronous motor is used for…….

(a) fluctuating loads

(b) variable speed loads

(c) low torque loads

(d) power factor corrections

Ans: d

96. 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

Ans: d
97. The percentage slip in case of a synchronous motor is…….

(a) 1%

(b) 100%

(c) 0.5%

(d) zero

Ans: d

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98. 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

Ans: c

99. 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 changes

Ans: c

100. Synchronous motor is mainly used….

(a)in lift and hoist

(b) as power factor correction device

(c) in irrigation pump

(d) in electric traction

Ans: b

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