McqMate
1. |
Laminations of core are generally made of |
A. | case iron |
B. | carbon |
C. | silicon steel |
D. | stainless steel |
Answer» C. silicon steel |
2. |
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» C. 0.5 m |
3. |
The armature of D.C. generator is laminated to |
A. | reduce the bulk |
B. | provide the bulk |
C. | insulate the core |
D. | reduce eddy current loss |
Answer» D. reduce eddy current loss |
4. |
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» D. all of the above |
5. |
The field coils of D.C. generator are usually made of |
A. | mica |
B. | copper |
C. | cast iron |
D. | carbon |
Answer» B. copper |
6. |
The commutator segments are connected to the armature conductors by means of |
A. | copper lugs |
B. | resistance wires |
C. | insulation pads |
D. | brazing |
Answer» A. copper lugs |
7. |
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» C. mica is harder than copper |
8. |
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» B. counter sunk screws |
9. |
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» D. all of the above |
10. |
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» B. magnetic flux, direction of motion and the direction of e.m.f. induced |
11. |
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» D. direction of motion of conductor, if forefinger points along the lines of flux |
12. |
The bearings used to support the rotor shafts are generally |
A. | ball bearings |
B. | bush bearings |
C. | magnetic bearmgs |
D. | needle bearings |
Answer» A. ball bearings |
13. |
In D.C. generators, the cause of rapid brush wear may be |
A. | severe sparking |
B. | rough commutator surface |
C. | imperfect contact |
D. | any of the above |
Answer» D. any of the above |
14. |
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» B. same as the number of poles |
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. ? |
A. | Lap winding |
B. | Wave winding |
C. | Either of (a) and (b) above |
D. | Depends on other features of design |
Answer» B. Wave winding |
16. |
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» B. alternate poles are north and south |
17. |
Copper brushes in D.C. machine are used |
A. | where low voltage and high currents are involved |
B. | where high voltage and small cur-rents are involved |
C. | in both of the above cases |
D. | in none of the above cases |
Answer» A. where low voltage and high currents are involved |
18. |
A separately excited generator as compared to a self-excited generator |
A. | is amenable to better voltage con-trol |
B. | is more stable |
C. | has exciting current independent of load current |
D. | has all above features |
Answer» D. has all above features |
19. |
In case of D.C. machines, mechanical losses are primary function of |
A. | current |
B. | voltage |
C. | speed |
D. | none of above |
Answer» C. speed |
20. |
Iron losses in a D.C. machine are independent of variations in |
A. | speed |
B. | load |
C. | voltage |
D. | speed and voltage |
Answer» B. load |
21. |
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» A. commutator |
22. |
Brushes of D.C. machines are made of |
A. | carbon |
B. | soft copper |
C. | hard copper |
D. | all of above |
Answer» A. carbon |
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 |
A. | Blv |
B. | Blv2 |
C. | Bl2v |
D. | Bl2v2 |
Answer» A. Blv |
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 |
A. | 4 |
B. | 8 |
C. | 16 |
D. | 32 |
Answer» B. 8 |
25. |
The material for commutator brushes is generally |
A. | mica |
B. | copper |
C. | cast iron |
D. | carbon |
Answer» D. carbon |
26. |
The insulating material used between the commutator segments is normally |
A. | graphite |
B. | paper |
C. | mica |
D. | insulating varnish |
Answer» C. mica |
27. |
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» C. lie under interpolar region |
28. |
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. | crossmagnetisation as well as demagnetising |
D. | cross magnetisation only |
Answer» C. crossmagnetisation as well as demagnetising |
29. |
Armature reaction of an unsaturated D.C. machine is |
A. | crossmagnetising |
B. | demagnetising |
C. | magnetising |
D. | none of above |
Answer» A. crossmagnetising |
30. |
D.C. generators are connected to the busbars or disconnected from them only under the floating condition |
A. | to avoid sudden loading of the primemover |
B. | to avoid mechanicaljerk to the shaft |
C. | to avoid burning of switch contacts |
D. | all above |
Answer» D. all above |
31. |
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» C. relative rotation between field and armature |
32. |
Equilizer rings are required in case armature is |
A. | wave wound |
B. | lap wound |
C. | delta wound |
D. | duplex wound |
Answer» B. lap wound |
33. |
Welding generator will have |
A. | lap winding |
B. | wave winding |
C. | delta winding |
D. | duplex wave winding |
Answer» A. lap winding |
34. |
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» A. number of armature coils |
35. |
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» C. induction motor D.C. generator set |
36. |
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» D. to discharge all the above functions |
37. |
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» D. difference of front and back pitches |
38. |
A D.C. welding generator has |
A. | lap winding |
B. | wave moving |
C. | duplex winding |
D. | any of the above |
Answer» A. lap winding |
39. |
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. | Equilizing bus bars are used with parallel running of D.C. shunt generators |
Answer» D. Equilizing bus bars are used with parallel running of D.C. shunt generators |
40. |
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» A. reduces generator e.m.f. |
41. |
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» A. electromagnets |
42. |
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» D. amount of current to be collected |
43. |
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» C. to neutralise the cross-magnetising effect of the armature reaction |
44. |
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. | Equilizer rings |
Answer» B. Commutator |
45. |
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 equiliser rings |
Answer» C. using carbon brushes of superior quality |
46. |
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» B. low voltage, high 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 |
A. | 2 : 3 |
B. | 3 : 1 |
C. | 3 : 2 |
D. | 1 : 3 |
Answer» B. 3 : 1 |
48. |
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» C. Metal graphite brushes |
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 |
A. | E/2 |
B. | 2E |
C. | slightly less than E |
D. | E |
Answer» B. 2E |
50. |
The armature core of a D.C. generator is usually made of |
A. | silicon steel |
B. | copper |
C. | non-ferrous material |
D. | cast-iron |
Answer» A. silicon steel |
51. |
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» C. both (a) and (b) |
52. |
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 equilizer connection |
D. | series fields of all generators should be either on positive side or negative side of the armature |
Answer» D. series fields of all generators should be either on positive side or negative side of the armature |
53. |
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» C. voltage at the toad end of the feeder |
54. |
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» D. self-excited generator |
55. |
Interpole 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» C. neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil |
56. |
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» C. long shunt compound generator |
57. |
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» D. number of poles is 2 |
58. |
Permeance is the reciprocal of |
A. | flux density |
B. | reluctance |
C. | ampere-turns |
D. | resistance |
Answer» B. reluctance |
59. |
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» A. is the same as that of the main pole ahead |
60. |
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» B. speed of armature |
61. |
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» B. dummy coils |
62. |
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» D. flat topped |
63. |
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» C. 240 V |
64. |
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» D. to provide mechanical balance for the rotor |
65. |
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» B. field resistance less than the critical resistance |
66. |
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» B. creating residual magnetism by a D.C. source |
67. |
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» D. 580 V |
68. |
In a D.C. generator the critical resistance refers to the resistance of |
A. | brushes |
B. | field |
C. | armature |
D. | load |
Answer» B. field |
69. |
To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them |
A. | just ahead of magnetic neutral axis |
B. | in magnetic neutral axis |
C. | just behind the magnetic neutral axis |
Answer» A. just ahead of magnetic neutral axis |
70. |
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» A. along neutral axis |
71. |
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» B. differentially compounded long shunt |
72. |
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 |
Answer» A. the brushes of opposite polarity should track each other |
73. |
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» D. all of the above factors |
74. |
Number of tappings for each equilizer ring is equal to |
A. | number of pole pairs |
B. | number of poles |
C. | number of parallel paths |
D. | number of commutator segments |
Answer» A. number of pole pairs |
75. |
A D.C. generator can be considered as |
A. | rectifier |
B. | primemover |
C. | rotating amplifier |
D. | power pump |
Answer» C. rotating amplifier |
76. |
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» D. armature |
77. |
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» D. iron loss and mechanical loss |
78. |
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» A. any even number of conductors |
79. |
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» B. decrease |
80. |
An exciter for a turbo generator is a |
A. | separately excited generator |
B. | shunt generator |
C. | series generator |
D. | compound generator |
Answer» B. shunt generator |
81. |
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 irrespec¬tive of the load |
D. | speed varies in proportion to the load on the generator |
Answer» C. voltage remains constant irrespec¬tive of the load |
82. |
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» A. Series generator |
83. |
Which of the following D.C. generators 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. | None of the above |
Answer» D. None of the above |
84. |
In over compounded generator, full load terminal voltage is |
A. | almost zero |
B. | less than noload terminal voltage |
C. | more than noload terminal voltage |
D. | equal to no-load terminal voltage |
Answer» C. more than noload terminal voltage |
85. |
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» B. equal to 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 |
A. | armature reaction |
B. | armature resistance drop |
C. | field weakening due to armature reaction and armature |
D. | commutation |
Answer» D. commutation |
87. |
In a D.C. generator |
A. | external resistance = internal char-acteristic - armature reaction |
B. | internal characteristic = magnetisation characteristic - ohmic drop |
C. | external characteristic = magnetisation characteristic - ohmic drop - armature reaction |
D. | magnetisation characteristic = external characteristic |
Answer» C. external characteristic = magnetisation characteristic - ohmic drop - armature reaction |
88. |
A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armature voltage wave |
A. | will be zero |
B. | will be of 5 Hz |
C. | willbeof5xiVHz |
D. | will be of v Hz 5 |
Answer» B. will be of 5 Hz |
89. |
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» B. about 2 V |
90. |
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» A. is always present |
91. |
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» A. zero |
92. |
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. | damagnetising the centre of all poles |
D. | magnetising the centre of all poles |
Answer» A. demagnetisation of leading pole tip and magnetisation of trailing pole tip |
93. |
Following energized winding of a D.C. machine should not be opened as it would produce high inductive voltage which may be dangerous to personnel and may cause its own insulation failure. |
A. | Series field |
B. | Compensating field |
C. | Inter pole field |
D. | Shunt field |
Answer» D. Shunt field |
94. |
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» C. that even number which is exact multiple of poles + 2 |
95. |
The critical resistance of the D.C. generator is the resistance of |
A. | field |
B. | brushes |
C. | armature |
D. | load |
Answer» A. field |
96. |
When two D.C. series generators are running in parallel, an equilizer 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 ar-mature reaction of both machines |
Answer» C. so that two similar machines will pass approximately equal currents to the load |
97. |
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» C. Level compounded generator . |
98. |
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» A. Shunt generators |
99. |
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» D. That generator takes large share of loads |
100. |
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» C. Faraday's law of electromagnetic induction |
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