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Q 1. In D.C. generators, the cause of rapid brush wear may be

DRex Electronics

(A) Severe sparking
(B) Rough commutator surface
(C) Imperfect contact
(D) Any of the above

Answer: Option D

Q 2. The insulating material used between the commutator segments is normally

(A) Graphite
(B) Paper
(C) Mica
(D) Insulating varnish

Answer: Option C

Q 3. Eddy currents are induced in the pole shoes of a D.C. machine due to

(A) Oscillating magnetic field
(B) Pulsating magnetic flux
(C) Relative rotation between field and armature
(D) All above

Answer: Option C

Q 4. Which of the following statement about D.C. generators is false?

(A) Compensating winding in a D.C. machine helps in commutation
(B)  In a D. C. generator interpoles winding is connected in series with the armature winding
(C)  Back pitch and front pitch are both odd and approximately equal to the pole pitch
(D) Equalizing bus bars are used with parallel running of D.C. shunt generators

Answer: Option D

Q 5. In a D.C. generator the ripples in the direct e.m.f. generated are reduced by

(A) Using conductor of annealed copper
(B) Using commutator with large number of segments
(C) Using carbon brushes of superior quality
(D) Using equaliser ring

Answer: Option C

Q 6. Satisfactory commutation of D.C. machines requires

(A) Brushes should be of proper grade and size
(B) Brushes should smoothly run in the holders
(C) Smooth, concentric commutator properly undercut
(D) All of the above

Answer: Option D

Q 7. In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when

(A) r.p.m. is more than 300
(B) r.p.m. is less than 300
(C) Number of poles is 4
(D) Number of poles is 2

Answer: Option D

Q 8. In D.C. generators on no-load, the air gap flux distribution in space is

(A) Sinusoidal
(B) Triangular
(C) Pulsating
(D) Flat topped

Answer: Option D

Q 9. Flashing the field of D.C. generator means

(A) Neutralising residual magnetism
(B) Creating residual magnetism by a D.C. source
(C) Making the magnetic losses of forces parallel
(D) Increasing flux density by adding extra turns of windings on poles

Answer: Option B

Q 10. The following constitute short-circuit in the armature winding.

(A) Insulation failure between two commutator bars
(B) Insulation failure between two turns of a coil
(C) Two of more turns of the same coil getting grounded
(D) All of the above

Answer: Option D

Q 11. In a D.C. machine stray loss is the sum of

(A) Total copper loss and mechanical loss
(B) Armature copper loss and iron loss
(C) Shunt field copper loss and mechanical loss
(D) Iron loss and mechanical loss

Answer: Option D

Q 12. Which of the following generator will have negligible terminal voltage while running on no-load?

(A) Series generator
(B) Shunt generator
(C) Compound generator
(D) Separately excited generator

Answer: Option A

Q 13. In a separately excited generator supplying rated load the armature reaction:

(A) Is always present
(B) Is always absent
(C) May be sometimes present
(D) None of the above

Answer: Option A

Q 14. When two D.C. series generators are running in parallel, an equalizer bar is used

(A) To increase the speed and hence generated e.m.f.
(B) To increase the series flux
(C)  So that two similar machines will pass approximately equal currents to the load
(D) To reduce the combined effect of armature reaction of both machines

Answer: Option C

Q 15. A D.C. generator works on the principle of

(A) Lenz’s law
(B) Ohm’s law
(C) Faraday’s law of electromagnetic induction
(D) None of the above

Answer: Option C

Q 16. Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the load circuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be

(A) 270 V
(B) 267.5 V
(C) 265 V
(D) 257.4 V

Answer: Option B

Q 17. In a D.C. generator the critical resistance can be increased by

(A) Increasing its field resistance
(B) Decreasing its field resistance
(C) Increasing its speed
(D) Decreasing its speed

Answer: Option C

Q 18. For both lap and wave windings, there are as many commutator bars as the number of

(A) Slots
(B) Armature conductors
(C) Winding elements
(D) Poles

Answer: Option C

Q 19. In case of D.C. machine winding, number of commutator segments is equal to

(A) Number of armature coils
(B) Number of armature coil sides
(C) Number of armature conductors
(D) Number of armature turns

Answer: Option A

Q 20. A D.C. welding generator has

(A) Lap winding
(B) Wave moving
(C) Duplex winding
(D) Any of the above

Answer: Option A

Q 21. A separately excited generator as compared to a self-excited generator

(A) Is amenable to better voltage control
(B) Is more stable
(C) Has exciting current independent of load current
(D) Has all above features

Answer: Option D

Q 22. In D.C. generators, the brushes on commutator remain in contact with conductors which

(A) Lie under South Pole
(B) Lie under North Pole
(C) Lie under interpolar region
(D) Are farthest from the poles

Answer: Option C

Q 23. For a D.C. machines laboratory following type of D.C. supply will be suitable

(A) Rotary converter
(B) Mercury are rectifier
(C) Induction motor D.C. generator set
(D) Synchronous motor D.C. generator set

Answer: Option C

Q 24. Compensating windings are used in D.C. generators

(A) Mainly to reduce the eddy currents by providing local short-circuits
(B) To provide path for the circulation of cooling air
(C) To neutralise the cross-magnetising effect of the armature reaction
(D) None of the above

Answer: Option C

Q 25. Open circuited armature coil of a D.C. machine is

(A)  Identified by the scarring of the commutator segment to which open circuited coil is connected
(B) Indicated by a spark completely around the commutator
(C) Both (A) and(B)
(D) None of the above

Answer: Option C

Q 26. Inter-pole flux should be sufficient to

(A) Neutralise the commutating self induced e.m.f.
(B) Neutralise the armature reaction flux
(C)  Neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil
(D) Perform none of the above functions

Answer: Option C

Q 27. In a D.C. generator the magnetic neutral axis coincides with the geometrical neutral axis, when

(A) There is no load on the generator
(B) The generator runs on full load
(C) The generator runs on overload
(D) The generator runs on designed speed

Answer: Option A

Q 28. In a D.C. generator the critical resistance refers to the resistance of

(A) Brushes
(B) Field
(C) Armature
(D) Load

Answer: Option B

Q 29. Lap winding is composed of

(A) Any even number of conductors
(B) Any odd number of conductors
(C) That even number which is exact multiple of poles + 2
(D) That even number which is exact multiple of poles

Answer: Option A

Q 30. In a D.C. generator

(A) External resistance = internal characteristic armature reaction
(B) Internal characteristic = magnetisation characteristic ohmic drop
(C) External characteristic = magnetisation characteristic ohmic drop armature reaction
(D) Magnetisation characteristic = external characteristic

Answer: Option C

Q 31. Which of the following generators will be preferred if they are required to be run in parallel?

(A) Shunt generators
(B) Series generators
(C) Compound generators
(D) None of the above

Answer: Option A

Q 32. When two D.C. generators are running in parallel an equalizer bar is used

(A) To increase the series flux
(B) To increase the generated e.m.f.
(C) To reduce the combined effect of armature reaction of both the machines
(D)  So that the two identical machines will pass approximately equal currents to the load

Answer: Option D

Q 33. Laminations of core are generally made of

(A) Case iron
(B) Carbon
(C) Silicon steel
(D) Stainless steel

Answer: Option C

Q 34. Fleming’s right-hand rule regarding direction of induced e.m.f., correlates

(A) Magnetic flux, direction of current flow and resultant force
(B) Magnetic flux, direction of motion and the direction of e.m.f. induced
(C) Magnetic field strength, induced voltage and current
(D) Magnetic flux, direction of force and direction of motion of conductor

Answer: Option B

Q 35. In a four-pole D.C. machine

(A) All the four poles are north poles
(B) Alternate poles are north and south
(C) All the four poles are south poles
(D) Two north poles follow two south poles

Answer: Option B

Q 36. In case of a 4pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be

(A) 4
(B) 8
(C) 16
(D) 32

Answer: Option B

Q 37. The demagnetising component of armature reaction in a D.C. generator

(A) Reduces generator e.m.f.
(B) Increases armature speed
(C) Reduces interpoles flux density
(D) Results in sparking trouble

Answer: Option A

Q 38. For the parallel operation of two or more D.C. compound generators, we should ensure that

(A)  Voltage of the incoming generator should be same as that of bus bar
(B) Polarity of incoming generator should be same as that of bus bar
(C)  All the series fields should be run in parallel by means of equalizer connection
(D)  Series fields of all generators should be either on positive side or negative side of the armature

Answer: Option D

Q 39. The e.m.f. generated in a D.C. generator is directly proportional to

(A) Flux/pole
(B) Speed of armature
(C) Number of poles
(D) All of the above

Answer: Option B

Q 40. A cumulatively compounded long shunt generator when operating as a motor would be

(A) Cumulatively compounded long shunt
(B) Differentially compounded long shunt
(C) Cumulatively compounded short shunt
(D) Differentially compounded short shunt

Answer: Option B

Q 41. In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called

(A) Rotor
(B) Stator
(C) Field
(D) Armature

Answer: Option D

Q 42. In over compounded generator, full load terminal voltage is

(A) Almost zero
(B) Less than no-load terminal voltage
(C) More than no-load terminal voltage
(D) Equal to no-load terminal voltage

Answer: Option C

Q 43. Wave winding is composed of

(A) Any even number of conductors
(B) Any odd number of conductors
(C) That even number which is exact multiple of poles + 2
(D) That even number which is exact multiple of poles

Answer: Option C

Q 44. The open circuit voltage of a compound generator is 250 V. At full load the terminal voltage

(A) Will be less than 250 V
(B) Will always be 250 V
(C) May be greater or less than 250 V
(D) None of the above

Answer: Option C

Q 45. Which of the following could be lamina proximately the thickness of laminations of a D.C. machine?

(A) 0.005 mm
(B) 0.05 mm
(C) 0.5 m
(D) 5 m

Answer: Option C

Q 46. According to Fleming’s right-hand rule for finding the direction of induced e.m.f., when middle finger points in the direction of induced e.m.f., forefinger will point in the direction of

(A) Motion of conductor
(B) Lines of force
(C) Either of the above
(D) None of the above

Answer: Option B

Q 47. Brushes of D.C. machines are made of

(A) Carbon
(B) Soft copper
(C) Hard copper
(D) All of above

Answer: Option A

Q 48. The function of pole shoes in the case of D.C. machine is

(A) To reduce the reluctance of the magnetic path
(B) To spread out the flux to achieve uniform flux density
(C) To support the field coil
(D) To discharge all the above functions

Answer: Option D

Q 49. The voltage drop for which of the following types of brush can be expected to be least?

(A) Graphite brushes
(B) Carbon brushes
(C) Metal graphite brushes
(D) None of the above

Answer: Option C

Q 50. In D.C. generators the polarity of the interpoles

(A) Is the same as that of the main pole ahead
(B) Is the same as that of the immediately preceding pole
(C) Is opposite to that of the main pole ahead
(D) Is neutral as these poles do not play part in generating e.m.f.

Answer: Option A

Q 51. To avoid formation of grooves in the commutator of a D.C. machine

(A) The brushes of opposite polarity should track each other
(B) The brushes of same polarity should track each other
(C) Brush position has no effect on the commutator grooving
(D) All of the above

Answer: Option A

Q 52. In a level compounded D.C. generator, full load terminal voltage is

(A) Negligibly low
(B) Equal to no-load terminal voltage
(C) More than no-load terminal voltage
(D) Less than no-load terminal voltage

Answer: Option B

Q 53. Two generators are running in parallel. One of the generators may run as motor for which of the following reasons?

(A) The direction of that generator is reversed
(B) The speed of that generator is increased
(C) The field of that generator is weakened
(D) That generator takes large share of loads

Answer: Option D

Q 54. The number of armature parallel paths in a two-pole D.C. generator having duplex lap winding is

(A) 2
(B) 4
(C) 6
(D) 8

Answer: Option B

Q 55. The resistance of armature winding depends on

(A) Length of conductor
(B) Cross-sectional area of the conductor
(C) Number of conductors
(D) All of the above

Answer: Option D

Q 56. For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f.?

(A) Lap winding
(B) Wave winding
(C) Either of (A) and (B) above
(D) Depends on other features of design

Answer: Option B

Q 57. If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be

(A) Demagnetisation only
(B) Cross magnetisation as well as magnetisation
(C) Cross-magnetisation as well as demagnetising
(D) Cross magnetisation only

Answer: Option C

Q 58. In the case of lap winding resultant pitch is

(A) Multiplication of front and back pitches
(B) Division of front pitch by back pitch
(C) Sum of front and back pitches
(D) Difference of front and back pitches

Answer: Option D

Q 59. Two generators A and B have 6poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generator A and B will be

(A) 2 : 3
(B) 3 : 1
(C) 3 : 2
(D) 1 : 3

Answer: Option B

Q 60. In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralised by all of the following except

(A) Interpoles
(B) Dummy coils
(C) Compensating winding
(D) Shifting of axis of brushes

Answer: Option B

Q 61. The rapid wear of brushes takes place due to

(A) Abrasion from dust
(B) Excessive spring pressure
(C) Rough commutator bars
(D) All of the above factors

Answer: Option D

Q 62. A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be

(A) Zero
(B) About 2 V
(C) About 50 V
(D) 220 V

Answer: Option B

Q 63. The terminal voltage of a series generator is 150 V when the load current is 5 A. If the load current is increased to 10 A, the terminal voltage will be

(A) 150 V
(B) Less than 150 V
(C) Greater than 150 V
(D) None of the above

Answer: Option C

Q 64. The field coils of D.C. generator are usually made of

(A) Mica
(B) Copper
(C) Cast iron
(D) Carbon

Answer: Option B

Q 65. In lap winding, the number of brushes is always

(A) Double the number of poles
(B) Same as the number of poles
(C) Half the number of poles
(D) Two

Answer: Option B

Q 66. In D.C. generators, current to the external circuit from armature is given through

(A) Commutator
(B) Solid connection
(C) Slip rings
(D) None of above

Answer: Option A

Q 67. Welding generator will have

(A) Lap winding
(B) Wave winding
(C) Delta winding
(D) Duplex wave winding

Answer: Option A

Q 68. D.C. series generator is used

(A) To supply traction load
(B) To supply industrial load at constant voltage
(C) Voltage at the toad end of the feeder
(D) For none of the above purpose

Answer: Option C

Q 69. The purpose of providing dummy coils in a generator is

(A) To reduce eddy current losses
(B) To enhance flux density
(C) To amplify voltage
(D) To provide mechanical balance for the rotor

Answer: Option D

Q 70. In a D.C. generator in case the resistance of the field winding is increased, then output voltage will

(A) Increase
(B) Decrease
(C) Remain unaffected
(D) Fluctuate heavily

Answer: Option B

Q 71. Armature reaction in a generator results in

(A) Demagnetisation of leading pole tip and magnetisation of trailing pole tip
(B) Demagnetisation of trailing pole tip and magnetisation of leading pole tip
(C) Demagnetizing the center of all poles
(D) Magnetising the center of all poles

Answer: Option A

Q 72. The essential condition for parallel operation of two D.C. generators is that they have

(A) Same kW rating
(B) The same operation r.p.m.
(C) The same drooping voltage characteristics
(D) Same percentage regulation

Answer: Option C

Q 73. The commutator segments are connected to the armature conductors by means of

(A) Copper lugs
(B) Resistance wires
(C) Insulation pads
(D) Brazing

Answer: Option A

Q 74. Copper brushes in D.C. machine are used

(A) Where low voltage and high currents are involved
(B) Where high voltage and small currents are involved
(C) In both of the above cases
(D) In none of the above cases

Answer: Option A

Q 75. Armature reaction of an unsaturated D.C. machine is

(A) Cross-magnetising
(B) Demagnetising
(C) Magnetising
(D) None of above

Answer: Option A

Q 76. In D.C. generators, lap winding is used for

(A) High voltage, high current
(B) Low voltage, high current
(C) High voltage, low current
(D) Low voltage, low current

Answer: Option B

Q 77. If a D.C. generator fails to build up the probable cause could not be

(A) Imperfect brush contact
(B) Field resistance less than the critical resistance
(C) No residual magnetism in the generator
(D) Faulty shunt connections tending to reduce the residual magnetism

Answer: Option B

Q 78. An exciter for a turbo generator is a

(A) Separately excited generator
(B) Shunt generator
(C) Series generator
(D) Compound generator

Answer: Option B

Q 79. The critical resistance of the D.C. generator is the resistance of

(A) Field
(B) Brushes
(C) Armature
(D) Load

Answer: Option A

Q 80. With a D.C. generator which of the following regulation is preferred?

(A) 100% regulation
(B) Infinite regulation
(C) 50% regulation
(D) 1% regulation

Answer: Option D

Q 81. A shunt generator can self-excite

(A)  Only if the resistance of the field circuit is less than critical value
(B)  Only if the resistance of the field circuit is greater than critical value
(C) Irrespective of the value of the resistance in the field circuit
(D) None of the above

Answer: Option A

Q 82. In a commutator

(A) Copper is harder than mica
(B) Mica and copper are equally hard
(C) Mica is harder than copper
(D) None of the above

Answer: Option C

Q 83. Iron losses in a D.C. machine are independent of variations in

(A) Speed
(B) Load
(C) Voltage
(D) Speed and voltage

Answer: Option B

Q 84. Magnetic field in a D.C. generator is produced by

(A) Electromagnets
(B) Permanent magnets
(C) Both (A) and (B)
(D) None of the above

Answer: Option A

Q 85. D.C. generator generally preferred for charging automobile batteries is

(A) Series generator
(B) Shunt generator
(C) Long shunt compound generator
(D) Any of the above

Answer: Option C

Q 86. In case of a flat compounded generator

(A) Voltage generated is less than the rated voltage
(B) Generated voltage is proportional to the load on the generator
(C) Voltage remains constant irrespective of the load
(D) Speed varies in proportion to the load on the generator

Answer: Option C

Q 87. A series generator can self-excite

(A) Only if the load current is zero
(B) Only if the load current is not zero
(C) Irrespective of the value of load current
(D) None of the above

Answer: Option B

Q 88. In case of D.C. machines, mechanical losses are primary function of

(A) Current
(B) Voltage
(C) Speed
(D) None of above

Answer: Option C

Q 89. Equalizer rings are required in case armature is

(A) Wave wound
(B) Lap wound
(C) Delta wound
(D) Duplex wound

Answer: Option B

Q 90. Following D.C. generator will be in a position to build up without any residual magnetism in the poles

(A) Series generator
(B) Shunt generator
(C) Compound generator
(D) Self-excited generator

Answer: Option D

Q 91. The e.m.f. induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be

(A) 640 V
(B) 620 V
(C) 600 V
(D) 580 V

Answer: Option D

Q 92. If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be

(A) Zero
(B) Small
(C) The same as rated voltage
(D) High

Answer: Option A

Q 93. In D.C. generators the pole shoes are fastened to the pole core by

(A) Rivets
(B) Counter sunk screws
(C) Brazing
(D) Welding

Answer: Option B

Q 94. D.C. generators are connected to the bus-bars or disconnected from them only under the floating condition

(A) To avoid sudden loading of the prime mover
(B) To avoid mechanical jerk to the shaft
(C) To avoid burning of switch contacts
(D) All above

Answer: Option D

Q 95. The e.m.f. generated by a shunt wound D.C. generator is E. Now while pole flux remains constant, if the speed of the generator is doubled, the e.m.f. generated will be

(A) E/2
(B) 2E
(C) Slightly less than E
(D) E

Answer: Option B

Q 96. Armature coil is short circuited by brushes when it lies

(A) Along neutral axis
(B) Along field axis
(C) In any of the above positions
(D) In none of the above positions

Answer: Option A

Q 97. Which generator would you prefer for feeding long D.C. transmission lines?

(A) Series generator
(B) Shunt generator
(C) Over compound generator
(D) Flat compound generator

Answer: Option C

Q 98. Number of tapings for each equalizer ring is equal to

(A) Number of pole pairs
(B) Number of poles
(C) Number of parallel paths
(D) Number of commutator segments

Answer: Option A

Q 99. The number of brushes in a commutator depends on

(A) Speed of armature
(B) Type of winding
(C) Voltage
(D) Amount of current to be collected

Answer: Option D

Q 100. While applying Fleming’s right-hand rule to and the direction of induced e.m.f., the thumb points towards

(A) Direction of induced e.m.f.
(B) Direction of flux
(C)  Direction of motion of the conductor if forefinger points in the direction of generated e.m.f.
(D)  Direction of motion of conductor, if forefinger points along the lines of flux

Answer: Option D

Q 101. The bearings used to support the rotor shafts are generally

(A) Ball bearings
(B) Bush bearings
(C) Magnetic bearings
(D) Needle bearings

Answer: Option A

Q 102. The material for commutator brushes is generally

(A) Mica
(B) Copper
(C) Cast iron
(D) Carbon

Answer: Option D

Q 103. Which of the following components of a D.C, generator plays vital role for providing direct current of a D.C. generator?

(A) Dummy coils
(B) Commutator
(C) Eye bolt
(D) Equalizer rings

Answer: Option B

Q 104. The armature core of a D.C. generator is usually made of

(A) Silicon steel
(B) Copper
(C) Nonferrous material
(D) Cast-iron

Answer: Option A

Q 105. Permeance is the reciprocal of

(A) Flux density
(B) Reluctance
(C) Ampere turns
(D) Resistance

Answer: Option B

Q 106. A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If the speed increases to 1200 r.p.m., the generated e.m.f. will be nearly

(A) 150 V
(B) 175 V
(C) 240 V
(D) 290 V

Answer: Option C

Q 107. A D.C. generator can be considered as

(A) Rectifier
(B) Prime mover
(C) Rotating amplifier
(D) Power pump

Answer: Option C

Q 108. The terminal voltage of a D.C. shunt generator drops on load because of all of the following reasons except

(A) Armature reaction
(B) Armature resistance drop
(C) Field weakening due to armature reaction and armature
(D) Commutation

Answer: Option D

Q 109. Which of the following generating machine will offer constant voltage on all loads?

(A) Self-excited generator
(B) Separately excited generator
(C) Level compounded generator
(D) All of the above

Answer: Option C

Q 110. If B is the flux density, l the length of conductor and v the velocity of conductor, then induced e.m.f. is given by

(A) Blv
(B) Blv2
(C) Bl2v
(D) Bl2v2

Answer: Option A