DC Generators Objective Questions and Answers

In this article, we shared the DC generators objective questions and answers for electrical and electronics engineers.

DC Generators Objective Questions

DC Generators Objective Questions and Answers

The below list provides all the multiple-choice questions related to DC generators.

Answers are available at the bottom of the article.

1. The following constitute short-circuit in the armature winding.

A)Insulation failure between two turns of a coil
B)Option Insulation failure between two commutator bars
C)Two or more turns of the same coil getting grounded
D)All of these answers

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

A)load current
B)shunt current
C)armature current
D)external current

3. Requirement of speed at which machine is driven is

A)more critical in the case of D.C. generators
B)more critical in the case of alternators
C)none of these answers
D)equally critical in the case of alternators as well as D.C. generators

4. Which one of the following generators is used for charging the batteries?

D)Any of these answers

5. The resistance of armature winding depends on

A)number of conductors
B)all of these answers
C)length of conductor
D)the cross-sectional area of the conductor

6. 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)slightly less than E

7. 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

8. In the case of a flat compounded generator

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

9. In a D.C. machine, short-circuited field coil will result in

A)the odor of burning insulation
B)unbalanced magnetic pull producing vibrations
C)reduction of generated voltage for which excitation has to be increased to maintain the voltage
D)all of these answers

10. While applying Fleming’s right-hand rule to find 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 conductor, if forefinger points along the lines of flux
D)direction of motion of the conductor if forefinger points in the direction of generated e.m.f.

11. Following energized winding of a D.C. machine should not be opened as it would produce a high inductive voltage which may be dangerous to personnel and may cause its own insulation failure.

A)Inter pole field
B)Compensating field
C)Series field
D)Shunt field

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


13. In over compounded generator, full load terminal voltage is

A)less than no-load terminal voltage
B)almost zero
C)more than no-load terminal voltage
D)equal to no-load terminal voltage

14. A series generator can self-excite

A)irrespective of the value of load current
B)only if the load current is not zero
C)none of these answers
D)only if the load current is zero

15. A D.C. generator can be considered as

A)rotating amplifier
B)prime mover
D)power pump

16. A shunt generator can self-excite

A)irrespective of the value of the resistance in the field circuit
B)only if the resistance of the field circuit is less than critical value
C)only if the resistance of the field circuit is greater than critical value
D)none of these answers

17. 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

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

A)armature conductors
B)winding elements

19. The purpose of providing dummy coils in a generator is

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

20. 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 these answers

21. Which one of the following types of generators does not need equalizers for satisfactory parallel operation?


22. The ____ generator has the poorest voltage regulation.


23. Magnetic field in a D.C. generator is produced by

A)none of these answers
B)permanent magnets
C)both electromagnets and permanent magnets

24. In D.C. generator, on no load

A)magnetic neutral axis moves from the geometrical neutral axis in the direction of rotation
B)none of these answers
C)magnetic neutral axis moves from geometrical neutral axis in the opposite direction of rotation
D)magnetic neutral axis coincides with geometrical neutral axis

25. 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

26. In a D.C. generator in case the brushes are moved so as to bring them in magnetic neutral axis, then, there will be

A)cross-magnetization as well as demagnetization
C)none of these answers

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

A)using carbon brushes of superior quality
B)using commutator with a large number of segments
C)using conductor of annealed copper
D)using equalizer rings

28. Fleming’s right-hand rule regarding the direction of induced e.m.f., co-relates

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 flux, direction of force and direction of motion of conductor
D)magnetic field strength, induced voltage and current

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

A)to avoid sudden loading of the prime mover
B)to avoid burning of switch contacts
C)all of these answers
D)to avoid mechanical jerk to the shaft

30. Flashing the field of the D.C. generator means

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

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

A)oscillating magnetic field
B)all of these answers
C)relative rotation between field and armature
D)pulsating magnetic flux

32. 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)Depends on other features of the design
B)Lap winding
C)Wave winding
D)Either of Lap winding and Wave winding

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


34. 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)greater than 150 V
B)150 V
C)less than 150 V
D)none of these answers

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

A)Shunt generator
B)None of these answers
C)Series generator
D)Compound generator

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

A)iron loss and mechanical loss
B)shunt field copper loss and mechanical loss
C)armature copper loss and iron loss
D)total copper loss and mechanical loss

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

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

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

C)non-ferrous material
D)silicon steel

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

B)slip rings
C)none of these answers
D)solid connection

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

A)lines of force
B)either motion of conductor or lines of force
C)motion of conductor
D)none of these answers

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

A)unequal series field resistances
B)unequal number of turns in their series field windings
C)unequal speed regulation of their prime movers
D)their rising voltage characteristics

42. The rapid wear of brushes takes place due to

A)rough commutator bars
B)abrasion from dust
C)excessive spring pressure
D)high mica insulation between commutation bars
E)all of these answers

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

A)copper lugs
B)resistance wires
D)insulation pads

44. In lap winding, the number of brushes is always

A)half the number of poles
B)same as the number of poles
C)double the number of poles

45. If the no-load voltage of a certain generator is 210 V and the rated voltage is 200 V, then the voltage regulation is


46. 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)175 V
B)150 V
C)240 V
D)290 V

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


48. The material for commutator brushes is generally

B)cast iron

49. In a separately excited generator supplying rated load the armature reaction

A)is always present
B)is always absent
C)none of these answers
D)may be sometimes present

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


51. Which of the following statements is incorrect in D.C. shunt generators about hysteresis loss?

A)None of these answers
B)It depends upon the supply frequency
C)It is independent of lamination thickness
D)It can be minimize by laminating the armature

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

B)about 2 V
C)about 50V
D)220 V

53. Lap winding is composed of

A)any even number of conductors
B)that even number which is exact multiple of poles
C)that even number which is exact multiple of poles + 2
D)any odd number of conductors

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

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

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

A)rotary converter
B)synchronous motor D.C. generator set
C)induction motor D.C. generator set
D)mercury are rectifier

56. Number of tappings for each equalizer ring is equal to

A)number of parallel paths
B)number of poles
C)number of pole pairs
D)number of parallel paths

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

D)speed and voltage

58. In a D.C. machine, fractional pitch winding is used

A)to save the copper because of shorter end connections
B)to reduce sparking
C)due to reduce sparking and to save the copper because of shorter end connections
D)to increase the generated voltage

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

A)will be of 5 Hz
B)will be of N/5 Hz
C)will be zero
D)will be of 5 x N Hz

60. Drop in the speed of a D.C. generator due to an increase in load can be compensated by

A)increasing the armature resistance
B)cooling the armature
C)increasing the input to the prime mover
D)reducing the load voltage

61. Interpole flux should be sufficient to

A)none of these answers
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)neutralise the commutating self-induced e.m.f.

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

A)more than no-load terminal voltage
B)equal to no-load terminal voltage
C)less than no-load terminal voltage
D)negligibly low

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

A)counter sunk screws

64. In D.C. generators the polarity of the interpoles

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

65. In the case of D.C. generators, the armature voltage control is considered suitable if the machine is driven

A)at constant VA
B)at constant load
C)at constant torque
D)at constant current

66. In the case of D.C. machines, mechanical losses are the primary function of

A)none of these answers

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

A)100% regulation
B)infinite regulation
C)1% regulation
D)50% regulation

68. In the case of D.C. machine winding, the number of commutator segments is equal to

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

69. Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohms 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)267.5 V
B)265 V
C)257.4 V
D)270 V

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

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

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

B)compensating winding
C)dummy coils
D)shifting of axis of brushes

72. The number of brushes in a commutator depends on

A)type of winding
B)amount of current to be collected
C)speed of armature

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

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

74. Which of the following components of a D.C. generator plays a vital role in providing direct current of a D.C. generator?

A)Dummy coils
B)Equalizer rings
C)Eye bolt

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

B)flat topped

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

A)10 percent
B)40 percent
C)25 percent
D)5 percent

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

A)cross magnetization as well as magnetization
B)demagnetization only
C)cross-magnetization as well as demagnetizing
D)cross magnetization only

78. To achieve sparkless commutation brushes of a D.C. generator are rocked ahead so as to bring them

A)just ahead of the magnetic neutral axis
B)in the magnetic neutral axis
C)just behind the magnetic neutral axis
D)none of these answers

79. D.C. generator generates

A)a.c. voltage in the armature
B)none of these answers
C)a.c. superimposed over d.c.
D)d.c. voltage in the armature

80. A D.C. generator that fails to build up the probable cause could not be

A)field resistance less than the critical resistance
B)faulty shunt connections tending to reduce the residual magnetism
C)no residual magnetism in the generator
D)imperfect brush contact

81. Brushes of D.C. machines are made of

A)hard copper
B)soft copper
D)all of these answers

82. Wave winding is composed of

A)that even number which is exact multiple of poles
B)that even number which is exact multiple of poles + 2
C)any even number of conductors
D)any odd number of conductors

83. D.C. generator generally preferred for charging automobile batteries is

A)shunt generator
B)series generator
C)long shunt compound generator
D)any of these answers

84. 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

85. Armature reaction in generator results in

A)magnetizing the center of all poles
B)demagnetizing the center of all poles
C)demagnetization of leading pole tip and magnetization of trailing pole tip
D)demagnetization of trailing pole tip and magnetization of leading pole tip

86. A simple method of increasing the voltage of a D.C. generator is

A)to decrease the speed of rotation
B)to increase the length of the armature
C)any of these answers
D)to decrease the length of the armature
E)to increase the speed of rotation

87. The insulating material used between the commutator segments is normally

D)insulating varnish

88. Armature coil is short-circuited by brushes when it lies

A)along field axis
B)any of these answers
C)none of these answers
D)along neutral axis

89. If a self-excited D.C. generator after being installed, fails to build upon its first trial run, the first thing to do is to

A)check armature insulation resistance
B)increase the speed of prime mover
C)increase the field resistance
D)reverse the field connections

90. Welding generator will have

A)duplex wave winding
B)delta winding
C)wave winding
D)lap winding

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

A)Separately excited generator
B)All of these answers
C)Self-excited generator
D)Level compounded generator

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

A)Graphite brushes
B)None of these answers
C)Metal graphite brushes
D)Carbon brushes

93. The demagnetizing component of armature reaction in a D.C. generator

A)reduces generator e.m.f.
B)results in sparking trouble
C)increases armature speed
D)reduces interpoles flux density

94. In the case of lap winding resultant pitch is

A)sum of front and back pitches
B)multiplication of front and back pitches
C)difference of front and back pitches
D)division of front pitch by back pitch

95. An exciter for a turbo generator is a

A)separately excited generator
B)series generator
C)compound generator
D)shunt generator

96. D.C. series generator is used

A)none of these answers
B)as a booster to maintain constant voltage at the load end of the feeder
C)to supply industrial load at constant voltage
D)to supply traction load

97. A properly designed D.C. generator can have an overall efficiency of


98. In a shunt generator the voltage build-up is generally restricted by

A)insulation restrictions
B)saturation of iron
C)speed limitation
D)armature heating

99. Armature reaction of an unsaturated D.C. machine is

A)cross magnetizing
C)none of these answers

100. Which generator cannot start if there is no residual magnetism?

A)Shunt generator
B)Separately excited generator
C)All of these answers
D)Series generator

101. In a D.C. generator, the actual flux distribution depends upon

A)clearance between tips of the adjacent pole shoes
B)all of these answers
C)size of air gap
D)shape of the pole shoe

102. The critical resistance of the D.C. generator is the resistance of


103. In a D.C. generator the change in voltage when the load is reduced from rated value to zero, expressed as a percentage of rated load voltage, is known as

B)armature reactance
D)loss factor

104. A separately excited generator as compared to a self-excited generator

A)has exciting current independent of load current
B)is more stable
C)is amenable to better voltage control
D)all of these answers

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

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

106. If the residual magnetism of a shunt generator is destroyed accidentally, it may be restored by connecting its shunt field

A)in reverse
B)to an alternator
C)to a battery
D)to earth

107. Compensating windings are used in D.C. generators

A)to neutralize the cross-magnetising effect of the armature reaction
B)none of these answers
C)to provide a path for the circulation of cooling air
D)mainly to reduce the eddy currents by providing local short-circuits

108. Satisfactory commutation of D.C. machines requires

A)brushes should smoothly run in the holders
B)smooth, concentric commutator properly undercut
C)all of these answers
D)brushes should be of proper grade and size

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

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

110. In D.C. generators, the brushes remain in contact with conductors which

A)lie in the inter-polar gaps
B)lie under north pole
C)lie under south pole
D)none of these answers

111. The polarity of a D.C. generator can be reversed by

A)increasing field current
B)reversing the field current
C)reversing field current as well as the direction of rotation
D)any of these answers

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

A)field weakening due to armature reaction and armature
B)armature reaction
D)armature resistance drop

113. Laminations of core are generally made of

A)silicon steel
C)case iron
D)stainless steel

114. Equilizer rings are required in case armature is

A)duplex wound
B)wave wound
C)delta wound
D)lap wound

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

A)all of these answers
B)series fields of all generators should be either on the positive side or negative side of the armature
C)all the series fields should be run in parallel by means of an equalizer connection
D)the polarity of incoming generator should be same as that of bus bar
E)the voltage of the incoming generator should be the same as that of the bus bar

116. 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

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

117. Permeance is the reciprocal of

D)flux density

118. Two generators A and B running in parallel are supplying power to a common load of 500 kW. Generator A has armature resistance equal to half that of B. Which of the following statements is correct?

A)Both generators will share the load equally
B)Generator A will take load less than the load taken by generator B
C)Generator B will take more load as compared to generator A
D)None of these answers

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

A)lie under north pole
B)lie under south pole
C)lie under interpolar region
D)are farthest from the poles

120. When the shunt field of a compound generator is connected across both the series field and armature. Such convection is known as

A)differential compounding
B)long shunt
C)cumulative compounding
D)short shunt

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

A)the same as rated voltage

122. For generating large currents on D.C. generators which winding is generally preferred?

A)Retrogressive wave winding
B)Lap winding
C)Current depends on the design
D)Progressive wave winding

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


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

A)remain unaffected
C)fluctuate heavily

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

A)self-excited generator
B)series generator
C)compound generator
D)shunt generator

126. The purpose of providing dummy coils in a generator is

A)to provide mechanical balance for the rotor
B)to reduce eddy currents
C)to amplify voltage
D)to enhance flux density

127. Open circuited armature coil of a D.C. machine is

A)identified by the scarring of the commutator segment to which the open-circuited coil is connected
B)both identified by the scarring of the commutator segment to which the open-circuited coil is connected and indicated by a spark completely around the commutator
C)indicated by a spark completely around the commutator
D)none of these answers

128. In a D.C. generator

A)external characteristic = magnetisation characteristic ohmic drop armature reaction
B)external resistance = internal characteristic armature reaction
C)internal characteristic = magnetisation characteristic ohmic drop
D)magnetiation characteristic = external characteristic

129. 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)maybe greater or less than 250 V
C)none of these answers
D)will always be 250 V

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

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

131. The slight curvature at the lower emf of the O.C.C. of a self-excited D.C. generator is due to

A)high armature speed
B)none of these answers
C)high field circuit resistance
D)residual pole flux
E)magnetic inertia

132. An ideal D.C. generator has a regulation of


133. In a four-pole D.C. machine

A)alternate poles are north and south
B)two north poles follow two south poles
C)all the four poles are north poles
D)all the four poles are south poles

134. In a D.C. generator, the critical resistance can be increased by

A)increasing its field resistance
B)increasing its speed
C)decreasing its speed
D)decreasing its field resistance

135. A D.C. welding generator has

A)lap winding
B)any of these answers
C)duplex winding
D)wave moving

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

A)Series generators
B)Compound generators
C)Shunt generators
D)None of these answers

137. The field coils of the D.C. generator are usually made of

D)cast iron

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

A)brush position has no effect on the commutator grooving
B)none of these answers
C)the brushes of same polarity should track each other
D)the brushes of opposite polarity should track each other

139. Copper brushes in D.C. machines are used

A)where low voltage and high currents are involved
B)none of the answers
C)both where low voltage and high currents are involved & where high voltage and small currents are involved cases
D)where high voltage and small currents are involved

140. In a D.C. generator, the armature reaction results in

A)demagnetization of the leading pole tip and magnetization of the trailing pole tip
B)magnetization of the leading tip and demagnetization of the trailing pole tip
C)demagnetisation of the centres of poles
D)magnetization of interpoles

141. In a commutator

A)copper is harder than mica
B)none of these answers
C)mica and copper are equally hard
D)mica is harder than copper

142. In a lap wound D.C. generator having p as the number of poles and Z as the number of conductors, the maximum number of equalizer rings will be


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

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

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