Quiz  /  Dc Generators Electrical Engineering MCQ Questions and Answers PDF

  • 1. 
    Lamination’s of core are generally made of

  • case iron
  • carbon
  • silicon steel
  • stainless steel

  • 2. 
    Which of the following could be lamina-proximately the thickness of lamination’s of a D.C. machine ?

  • 0.005 mm
  • 0.05 mm
  • 0.5 m
  • 5 m

  • 3. 
    The armature of D.C. generator is laminated to

  • reduce the bulk
  • provide the bulk
  • insulate the core
  • reduce eddy current loss

  • 4. 
    The resistance of armature winding depends on

  • length of conductor
  • cross-sectional area of the conductor
  • number of conductors
  • all of the above

  • 5. 
    The field coils of D.C. generator are usually made of

  • mica
  • copper
  • cast iron
  • carbon

  • 6. 
    The commutator segments are connected to the armature conductors by means of

  • copper lugs
  • resistance wires
  • insulation pads
  • brazing

  • 7. 
    In a commutator

  • copper is harder than mica
  • mica and copper are equally hard
  • mica is harder than copper
  • none of the above

  • 8. 
    In D.C. generators the pole shoes are fastened to the pole core by

  • rivets
  • counter sunk screws
  • brazing
  • welding

  • 9. 
    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

  • motion of conductor
  • lines of force
  • either of the above
  • none of the above

  • 10. 
    Fleming’s right-hand rule regarding direction of induced e.m.f., correlates

  • magnetic flux, direction of current flow and resultant force
  • magnetic flux, direction of motion and the direction of e.m.f. induced
  • magnetic field strength, induced voltage and current
  • magnetic flux, direction of force and direction of motion of conductor

  • 11. 
    While applying Fleming’s right-hand rule to And the direction of induced e.m.f., the thumb points towards

  • direction of induced e.m.f.
  • direction of flux
  • direction of motion of the conductor if forefinger points in the direction of generated e.m.f.
  • direction of motion of conductor, if forefinger points along the lines of flux

  • 12. 
    The bearings used to support the rotor shafts are generally

  • ball bearings
  • bush bearings
  • magnetic bearmgs
  • needle bearings

  • 13. 
    In D.C. generators, the cause of rapid brush wear may be

  • severe sparking
  • rough commutator surface
  • imperfect contact
  • any of the above

  • 14. 
    In lap winding, the number of brushes is always

  • double the number of poles
  • same as the number of poles
  • half the number of poles
  • two

  • 15. 
    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. ?

  • Lap winding
  • Wave winding
  • Either of (a) and (b) above
  • Depends on other features of design

  • 16. 
    In a four-pole D.C. machine

  • all the four poles are north poles
  • alternate poles are north and south
  • all the four poles are south poles
  • two north poles follow two south poles

  • 17. 
    Copper brushes in D.C. machine are used

  • where low voltage and high currents are involved
  • where high voltage and small cur-rents are involved
  • in both of the above cases
  • in none of the above cases

  • 18. 
    A separately excited generator as compared to a self-excited generator

  • is amenable to better voltage control
  • is more stable
  • has exciting current independent of load current
  • has all above features

  • 19. 
    In case of D.C. machines, mechanical losses are primary function of

  • current
  • voltage
  • speed
  • none of above

  • 20. 
    Iron losses in a D.C. machine are independent of variations in

  • speed
  • load
  • voltage
  • speed and voltage

  • 21. 
    In D.C. generators, current to the external circuit from armature is given through

  • commutator
  • solid connection
  • slip rings
  • none of above

  • 22. 
    Brushes of D.C. machines are made of

  • carbon
  • soft copper
  • hard copper
  • all of above

  • 23. 
    If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by

  • Blv
  • Blv2
  • Bl2v
  • Bl2v2

  • 24. 
    In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be

  • 4
  • 8
  • 16
  • 32

  • 25. 
    The material for commutator brushes is generally

  • mica
  • copper
  • cast iron
  • carbon

  • 26. 
    The insulating material used between the commutator segments is normally

  • graphite
  • paper
  • mica
  • insulating varnish

  • 27. 
    In D.C. generators, the brushes on commutator remain in contact with conductors which

  • lie under south pole
  • lie under north pole
  • lie under interpolar region
  • are farthest from the poles

  • 28. 
    If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be

  • demagnetisation only
  • cross magnetisation as well as mag¬netisation
  • crossmagnetisation as well as demagnetising
  • cross magnetisation only

  • 29. 
    Armature reaction of an unsaturated D.C. machine is

  • crossmagnetising
  • demagnetising
  • magnetising
  • none of above

  • 30. 
    D.C. generators are connected to the busbars or disconnected from them only under the floating condition

  • to avoid sudden loading of the primemover
  • to avoid mechanicaljerk to the shaft
  • to avoid burning of switch contacts
  • all above

  • 31. 
    Eddy currents are induced in the pole shoes of a D.C. machine due to

  • oscillating magnetic field
  • pulsating magnetic flux
  • relative rotation between field and armature
  • all above

  • 32. 
    Equilizer rings are required in case armature is

  • wave wound
  • lap wound
  • delta wound
  • duplex wound

  • 33. 
    Welding generator will have

  • lap winding
  • wave winding
  • delta winding
  • duplex wave winding

  • 34. 
    In case of D.C. machine winding, number of commutator segments is equal to

  • number of armature coils
  • number of armature coil sides
  • number of armature conductors
  • number of armature turns

  • 35. 
    For a D.C. machines laboratory following type of D.C. supply will be suitable

  • rotary converter
  • mercury are rectifier
  • induction motor D.C. generator set
  • synchronous motor D.C. generator set

  • 36. 
    The function of pole shoes in the case of D.C. machine is

  • to reduce the reluctance of the mag¬netic path
  • to spread out the flux to achieve uniform flux density
  • to support the field coil
  • to discharge all the above functions

  • 37. 
    In the case of lap winding resultant pitch is

  • multiplication of front and back pitches
  • division of front pitch by back pitch
  • sum of front and back pitches
  • difference of front and back pitches

  • 38. 
    A D.C. welding generator has

  • lap winding
  • wave moving
  • duplex winding
  • any of the above

  • 39. 
    Which of the following statement about D.C. generators is false ?

  • Compensating winding in a D.C. machine helps in commutation
  • In a D. C. generator interpoles winding is connected in series with the armature winding
  • Back pitch and front pitch are both odd and approximately equal to the pole pitch
  • Equilizing bus bars are used with parallel running of D.C. shunt gen¬erators

  • 40. 
    The demagnetising component of armature reaction in a D.C. generator

  • reduces generator e.m.f.
  • increases armature speed
  • reduces interpoles flux density
  • results in sparking trouble

  • 41. 
    Magnetic field in a D.C. generator is produced by

  • electromagnets
  • permanent magnets
  • both (a) and (b)
  • none of the above

  • 42. 
    The number of brushes in a commutator depends on

  • speed of armature
  • type of winding
  • voltage
  • amount of current to be collected

  • 43. 
    Compensating windings are used in D.C. generators

  • mainly to reduce the eddy currents by providing local short-circuits
  • to provide path for the circulation of cooling air
  • to neutralise the cross-magnetising effect of the armature reaction
  • none of the above

  • 44. 
    Which of the following components of a D.C, generator plays vital role for providing direct current of a D.C. generator ?

  • Dummy coils
  • Commutator
  • Eye bolt
  • Equilizer rings

  • 45. 
    In a D.C. generator the ripples in the direct e.m.f. generated are reduced by

  • using conductor of annealed copper
  • using commutator with large number of segments
  • using carbon brushes of superior quality
  • using equiliser rings

  • 46. 
    In D.C. generators, lap winding is used for

  • high voltage, high current
  • low voltage, high current
  • high voltage, low current
  • low voltage, low current

  • 47. 
    Two generators A and B have 6-poles 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

  • 2 : 3
  • 3 : 1
  • 3 : 2
  • 1 : 3

  • 48. 
    The voltage drop for which of the following types of brush can be expected to be least ?

  • Graphite brushes
  • Carbon brushes
  • Metal graphite brushes
  • None of the above

  • 49. 
    The e.m.f. generated by a shunt wound D.C. generator isE. Now while pole flux remains constant, if the speed of the generator is doubled, the e.m.f. generated will be

  • E/2
  • 2E
  • slightly less than E
  • E

  • 50. 
    The armature core of a D.C. generator is usually made of

  • silicon steel
  • copper
  • non-ferrous material
  • cast-iron

  • 51. 
    Satisfactory commutation of D.C. machines requires

  • brushes should be of proper grade and size
  • brushes should smoothly run in the holders
  • smooth, concentric commutator properly undercut
  • all of the above

  • 52. 
    Open circuited armature coil of a D.C. machine is

  • identified by the scarring of the commutator segment to which open circuited coil is connected
  • indicated by a spark completely around the commutator
  • both (a) and (b)
  • none of the above

  • 53. 
    For the parallel operation of two or more D.C. compound generators, we should ensure that

  • voltage of the incoming generator should be same as that of bus bar
  • polarity of incoming generator should be same as that of bus bar
  • all the series fields should be run in parallel by means of equilizer connection
  • series fields of all generators should be either on positive side or negative side of the armature
  • all conditions mentioned above should be satisfied

  • 54. 
    D.C. series generator is used

  • to supply traction load
  • to supply industrial load at constant voltage
  • voltage at the toad end of the feeder
  • for none of the above purpose

  • 55. 
    Following D.C. generator will be in a position to build up without any residual magnetism in the poles

  • series generator
  • shunt generator
  • compound generator
  • self-excited generator

  • 56. 
    Interpole flux should be sufficient to

  • neutralise the commutating self induced e.m.f.
  • neutralise the armature reaction flux
  • neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil
  • perform none of the above functions

  • 57. 
    D.C. generator generally preferred for charging automobile batteries is

  • series generator
  • shunt generator
  • long shunt compound generator
  • any of’the above

  • 58. 
    In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when

  • r.p.m. is more than 300
  • r.p.m. is less than 300
  • number of poles is 4
  • number of poles is 2

  • 59. 
    Permeance is the reciprocal of

  • flux density
  • reluctance
  • ampere-turns
  • resistance

  • 60. 
    In D.C. generators the polarity of the interpoles

  • is the same as that of the main pole ahead
  • is the same as that of the immediately preceding pole
  • is opposite to that of the main pole ahead
  • is neutral as these poles do not play part in generating e.m.f.

  • 61. 
    The e.m.f. generated in a D.C. generator is directly proportional to

  • flux/pole
  • speed of armature
  • number of poles
  • all of the above

  • 62. 
    In a D.C. generator the magnetic neutral axis coincides with the geometrical neutral axis, when

  • there is no load on|he generator
  • the generator runs on full load
  • the generator runs on overload
  • the generator runs on designed speed

  • 63. 
    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

  • interpoles
  • dummy coils
  • compensating winding
  • shifting of axis of brushes

  • 64. 
    In D.C. generators on no-load, the air gap flux distribution in space is

  • sinusoidal
  • triangular
  • pulsating
  • flat topped

  • 65. 
    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

  • 150 V
  • 175 V
  • 240 V
  • 290 V

  • 66. 
    The purpose of providing dummy coils in a generator is

  • to reduce eddy current losses
  • to enhance flux density
  • to amplify voltage
  • to provide mechanical balance for the rotor

  • 67. 
    If a D.C. generator fails to build up the probable cause could not be

  • imperfect brush contact
  • field resistance less than the critical resistance
  • no residual magnetism in the generator
  • faulty shunt connections tending to reduce the residual magnetism

  • 68. 
    Flashing the field of D.C. generator means

  • neutralising residual magnetism
  • creating residual magnetism by a D.C. source
  • making the magnetic losses of forces parallel
  • increasing flux density by adding extra turns of windings on poles

  • 69. 
    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

  • 640 V
  • 620 V
  • 600 V
  • 580 V

  • 70. 
    In a D.C. generator the critical resistance refers to the resistance of

  • brushes
  • field
  • armature
  • load

  • 71. 
    Armature coil is short circuited by brushes when it lies

  • along neutral axis
  • along field axis
  • in any of the above positions
  • in none of the above positions

  • 72. 
    A cumulatively compounded long shunt generator when operating as a motor would be

  • cumulatively compounded long shunt
  • differentially compounded long shunt
  • cumulatively compounded short shunt
  • differentially compounded short shunt

  • 73. 
    The rapid wear of brushes takes place due to

  • abrasion from dust
  • excessive spring pressure
  • rough commutator bars
  • high mica insulation between com-mutation bars
  • all of the above factors

  • 74. 
    Number of tappings for each equilizer ring is equal to

  • number of pole pairs
  • number of poles
  • number of parallel paths
  • number of commutator segments

  • 75. 
    A D.C. generator can be considered as

  • rectifier
  • primemover
  • rotating amplifier
  • power pump

  • 76. 
    In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called

  • rotor
  • stator
  • field
  • armature

  • 77. 
    In a D.C. machine stray loss is the sum of

  • total copper loss and mechanical loss
  • armature copper loss and iron loss
  • shunt field copper loss and mechanical loss
  • iron loss and mechanical loss

  • 78. 
    Lap winding is composed of

  • any even number of conductors
  • any odd number of conductors
  • that even number which is exact multiple of poles + 2
  • that even number which is exact multiple of poles

  • 79. 
    In a D.C. generator in case the resistance of the field winding is increased, then output voltage will

  • increase
  • decrease
  • remain unaffected
  • fluctuate heavily

  • 80. 
    An exciter for a turbo generator is a

  • separately excited generator
  • shunt generator
  • series generator
  • compound generator

  • 81. 
    In case of a flat compounded generator

  • voltage generated is less than the rated voltage
  • generated voltage is proportional to the load on the generator
  • voltage remains constant irrespective of the load
  • speed varies in proportion to the load on the generator

  • 82. 
    Which of the following generator will have negligible terminal voltage while running on no-load ?

  • Series generator
  • Shunt generator
  • Compound generator
  • Separately excited generator

  • 83. 
    Which of the following D.C. generators will be in a position to build up without any residual magnetism in the poles ?

  • Series generator
  • Shunt generator
  • Compound generator
  • None of the above

  • 84. 
    In over compounded generator, full load terminal voltage is

  • almost zero
  • less than no load terminal voltage
  • more than no load terminal voltage
  • equal to no-load terminal voltage

  • 85. 
    In a level compounded D.C. generator, full load terminal voltage is

  • negligibly low
  • equal to no-load terminal voltage
  • more than no-load terminal voltage
  • less than no-load terminal voltage

  • 86. 
    The terminal voltage of a D.C. shunt generator drops on load because of all of the following reasons except

  • armature reaction
  • armature resistance drop
  • field weakening due to armature reaction and armature
  • commutation

  • 87. 
    In a D.C. generator

  • external resistance = internal char-acteristic – armature reaction
  • internal characteristic = magnetisation characteristic – ohmic drop
  • external characteristic = magnetisation characteristic – ohmic drop – armature reaction
  • magnetisation characteristic = external characteristic

  • 88. 
    A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armature voltage wave

  • will be zero
  • will be of 5 Hz
  • will be of 5 xiVHz
  • will be of v Hz 5

  • 89. 
    A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be

  • zero
  • about 2 V
  • about 50 V
  • 220 V

  • 90. 
    In a separately excited generator supplying rated load the armature reaction ,

  • is always present
  • is always absent
  • may be sometimes present
  • none of the above

  • 91. 
    If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be

  • zero
  • small
  • the same as rated voltage
  • high

  • 92. 
    Armature reaction in a generator results in

  • demagnetization of leading pole tip and magnetization of trailing pole tip
  • demagnetization of trailing pole tip and magnetization of leading pole tip
  • demagnetizing the center of all poles
  • magnetizing the center of all poles

  • 93. 
    . Wave winding is composed of

  • any even number of conductors
  • any odd number of conductors
  • that even number which is exact multiple of poles + 2
  • that even number which is exact multiple of poles

  • 94. 
    . The critical resistance of the D.C. generator is the resistance of

  • field
  • brushes
  • armature
  • load

  • 95. 
    . When two D.C. series generators are running in parallel, an equalizer bar is used

  • to increase the speed and hence generated e.m.f.
  • to increase the series flux
  • so that two similar machines will pass approximately equal currents to the load
  • to reduce the combined effect of ar-mature reaction of both machines

  • 96. 
    . Which of the following generating machine will offer constant voltage on all loads ?

  • Self-excited generator
  • Separately excited generator
  • Level compounded generator .
  • All of the above

  • 97. 
    . Which of the following generators will be preferred if they are required to be run in parallel ?

  • Shunt generators
  • Series generators
  • Compound generators
  • None of the above

  • 98. 
    . Two generators are running in parallel. One of the generators may run as motor for which of the following reasons ?

  • The direction of that generator is reversed
  • The speed of that generator is increased
  • The field of that generator is weakened
  • That generator takes large share of loads

  • 99. 
    . A D.C. generator works on the principle of

  • Lenz’s law
  • Ohm’s law
  • Faraday’s law of electromagnetic induction
  • none of the above

  • 100. 
    . A series generator can self-excite

  • only if the load current is zero
  • only if the load current is not zero
  • irrespective of the value of load current
  • none of the above

  • 101. 
    . 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

  • 150 V
  • less than 150 V
  • greater than 150 V
  • none of the above

  • 102. 
    . The open circuit voltage of a compound generator is 250 V. At full load the terminal voltage

  • will be less than 250 V
  • will always be 250 V
  • may be greater or less than 250 V
  • none of the above

  • 103. 
    . 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

  • 270 V
  • 267.5 V
  • 265 V
  • 257.4 V

  • 104. 
    . The essential condition for parallel operation of two D.C. generators is that they have ‘

  • same kW rating
  • the same operation r.p.m.
  • the same drooping voltage characteristics
  • same percentage regulation

  • 105. 
    . When two D.C. generators are running in parallel an equalizer bar is used

  • to increase the series flux
  • to increase the generated e.m.f.
  • to reduce the combined effect of AR-mature reaction of both the machines
  • so that the two identical machines will pass approximately equal cur¬rents to the load

  • 106. 
    . With a D.C. generator which of the following regulation is preferred ?

  • 100% regulation
  • infinite regulation
  • 50% regulation
  • 1% regulation

  • 107. 
    . Which generator would you prefer for feeding long D.C. transmission lines ?

  • Series generator
  • Shunt generator
  • Over compound generator
  • Flat compound generator

  • 108. 
    . In a D.C. generator the critical resistance can be increased by

  • increasing its field resistance
  • decreasing its field resistance
  • increasing its speed
  • decreasing its speed

  • 109. 
    . The number of armature parallel paths in a two-pole D.C. generator having duplex lap winding is

  • 2
  • 4
  • 6
  • 8

  • 110. 
    . For both lap and wave winding’s, there are as many commutator bars as the number of

  • slots
  • armature conductors
  • winding elements
  • poles

  • 111. 
    . The series field of a short-shunt D.C. generator is excited by

  • external current
  • armature current
  • shunt current
  • load current

  • 112. 
    . As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C. generator is approximately

  • 40 percent
  • 25 percent
  • 10 percent
  • 5 percent

  • 113. 
    . Shunt generators are most suited for stable parallel operation because of their

  • rising voltage characteristics
  • identical voltage characteristics
  • drooping voltage characteristics
  • linear voltage characteristics

  • 114. 
    . The main factor which leads to unstable parallel operation of flat and over compounded generators is

  • their rising voltage characteristics
  • unequal number of turns in their series field winding’s
  • unequal speed regulation of their prime movers
  • unequal series field resistances

  • 115. 
    . If a self excited D.C. generator after being installed, fails to build up on its first trial run, the first thing to do is to

  • reverse the field connections
  • increase the field resistance
  • increase the speed of prime mover
  • check armature insulation resistance
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