McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Electrical Engineering .
Chapters
| 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. | resis tance |
| 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 thespeed increases to 1200 r.p.m., the generated e.m.f. will be nearly |
| A. | 150 V |
| B. | 175 V |
| C. | 240 V |
| D. | 290V |
| 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. | 580V |
| Answer» D. 580V | |
| 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 soas to bring them |
| A. | just ahead of magnetic neutral axis |
| B. | in magnetic neutral axis |
| C. | just behind the magnetic neutral axis |
| D. | none |
| 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 following constitute short-circuit in the armature winding. |
| A. | Insulation failure between two com-mutator bars |
| B. | Insulation failure between two turns of a coil |
| C. | Two of more turns of the same coil getting grounded |
| D. | All of the above |
| Answer» D. All of the above | |
| 74. |
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 | |
| 75. |
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 | |
| 76. |
A D.C. generator can be considered as |
| A. | rectifier |
| B. | primemover |
| C. | rotating amplifier |
| D. | power pump |
| Answer» C. rotating amplifier | |
| 77. |
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 | |
| 78. |
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 | |
| 79. |
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 | |
| 80. |
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 | |
| 81. |
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 | |
| 82. |
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 | |
| 83. |
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 | |
| 84. |
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 | |
| 85. |
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 | |
| 86. |
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 | |
| 87. |
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. | commut ation |
| Answer» D. commut ation | |
| 88. |
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 | |
| 89. |
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 | |
| 90. |
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. | 220V |
| Answer» B. about 2 V | |
| 91. |
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 | |
| 92. |
If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speedwill be |
| A. | zero |
| B. | small |
| C. | the same as rated voltage |
| D. | high |
| Answer» A. zero | |
| 93. |
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 | |
| 94. |
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 | |
| 95. |
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 | |
| 96. |
The critical resistance of the D.C. generator is the resistance of |
| A. | field |
| B. | brushes |
| C. | armature |
| D. | load |
| Answer» A. field | |
| 97. |
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 | |
| 98. |
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 . | |
| 99. |
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 | |
| 100. |
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 | |
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