In this article, we shared the DC generators objective questions and answers for electrical and electronics engineers.
DC Generators Objective Questions
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?
| A) | Shunt |
| B) | Compound |
| C) | Series |
| 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 |
| B) | E |
| C) | 2E |
| D) | E/2 |
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 |
| C) | 5m |
| D) | 0.5m |
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
| A) | Blv |
| B) | Blv2 |
| C) | Bl2v |
| D) | Bl2v2 |
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 |
| C) | rectifier |
| 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 |
| C) | poles |
| D) | slots |
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?
| A) | Flat-compound |
| B) | Over-compound |
| C) | Series |
| D) | Under-compound |
22. The ____ generator has the poorest voltage regulation.
| A) | over-compound |
| B) | series |
| C) | shunt |
| D) | compound |
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 |
| D) | electromagnets |
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 |
| B) | demagnetization |
| C) | none of these answers |
| D) | cross-magnetization |
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
| A) | load |
| B) | brushes |
| C) | armature |
| D) | field |
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
| A) | copper |
| B) | cast-iron |
| C) | non-ferrous material |
| D) | silicon steel |
39. In D.C. generators, current to the external circuit from armature is given through
| A) | commutator |
| 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 |
| C) | brazing |
| 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 |
| D) | two |
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
| A) | 0.1 |
| B) | 0.15 |
| C) | 0.025 |
| D) | 0.05 |
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
| A) | 4 |
| B) | 6 |
| C) | 2 |
| D) | 8 |
48. The material for commutator brushes is generally
| A) | copper |
| B) | cast iron |
| C) | mica |
| D) | carbon |
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
| A) | rotor |
| B) | field |
| C) | stator |
| D) | armature |
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
| A) | zero |
| 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
| A) | load |
| B) | speed |
| C) | voltage |
| 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 |
| B) | rivets |
| C) | welding |
| D) | brazing |
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 |
| B) | current |
| C) | speed |
| D) | voltage |
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
| A) | interpoles |
| 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 |
| D) | voltage |
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 |
| D) | Commutator |
75. In D.C. generators on no-load, the air gap flux distribution in space is
| A) | pulsating |
| B) | flat topped |
| C) | triangular |
| D) | sinusoidal |
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 |
| C) | carbon |
| 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
| A) | mica |
| B) | paper |
| C) | graphite |
| 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
| A) | 1 |
| B) | 0.95 |
| C) | 0.8 |
| D) | 0.6 |
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 |
| B) | magnetizing |
| C) | none of these answers |
| D) | demagnetizing |
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
| A) | load |
| B) | armature |
| C) | brushes |
| D) | field |
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
| A) | efficiency |
| B) | armature reactance |
| C) | regulation |
| 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 |
| C) | commutation |
| D) | armature resistance drop |
113. Laminations of core are generally made of
| A) | silicon steel |
| B) | carbon |
| 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
| A) | resistance |
| B) | ampere-turns |
| C) | reluctance |
| 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 |
| B) | high |
| C) | zero |
| D) | small |
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
| A) | 32 |
| B) | 16 |
| C) | 8 |
| D) | 4 |
124. In a D.C. generator in case the resistance of the field winding is increased, then the output voltage will
| A) | remain unaffected |
| B) | increase |
| C) | fluctuate heavily |
| D) | decrease |
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
| A) | 0.2 |
| B) | 0.7 |
| C) | 0.9 |
| D) | zero% |
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
| A) | carbon |
| B) | copper |
| C) | mica |
| 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
| A) | 2Z/P |
| B) | 2P/Z |
| C) | Z |
| D) | P |
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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