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This section includes 15 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Machines knowledge and support exam preparation. Choose a topic below to get started.
1. |
If the magnetic circuit of the dc machine is in the saturation region, the armature reaction __________ |
A. | does not affect flux/pole |
B. | increases the flux/pole |
C. | decreases flux/pole |
D. | affects the flux/pole only when armature current is small |
Answer» B. increases the flux/pole | |
2. |
The compensating winding in dc generator is provided to __________ |
A. | neutralize cross-magnetizing flux |
B. | neutralize demagnetizing flux |
C. | neutralize armature mmf |
D. | maintain magnetizing mmf |
Answer» B. neutralize demagnetizing flux | |
3. |
The armature reaction is produced mainly by __________ |
A. | load current in armature |
B. | load current in field |
C. | all of the mentioned |
D. | none of the mentioned |
Answer» B. load current in field | |
4. |
The commutation process involves basically reversal of current in armature coil as it crosses MNA. |
A. | True |
B. | False |
Answer» B. False | |
5. |
Mark the most incorrect. In dc generator, commutation can be improved by __________ |
A. | using interpoles |
B. | using carbon brushes |
C. | shifting brush axis in direction of armature rotation |
D. | none of the mentioned |
Answer» B. using carbon brushes | |
6. |
Each of the following is valid for interpoles except __________ |
A. | they are connected in parallel with the armature so that they carry part of armature current |
B. | they are small yoke fixed poles spaced in between main poles |
C. | their polarity, in case of generator is same as that of main poles ahead |
D. | they automatically neutralize not only reactance voltage but cross-magnetization also |
Answer» B. they are small yoke fixed poles spaced in between main poles | |
7. |
A 400-V, 1000-A, lap wound dc machine has 10 poles, 860 armature conductors. The number of conductors in the pole face to give full compensation if pole face covers 70% of pole span is? |
A. | 3010 |
B. | 4300 |
C. | 2400 |
D. | 2800 |
Answer» B. 4300 | |
8. |
The number of compensating conductors/pole faces is _______ (where Z is the number of active armature conductors/pole; A is number of parallel paths; Ia is the armature current). |
A. | Z/A*Ia |
B. | 2*A*Ia/Z |
C. | Z*Ia/A |
D. | Z/2A*Ia |
Answer» B. 2*A*Ia/Z | |
9. |
The absence of compensating winding lead to __________ |
A. | statically induced emf in armature |
B. | fluctuations in supply |
C. | reduction in the flux |
D. | any of the mentioned |
Answer» B. fluctuations in supply | |
10. |
The principle contributors to magneto motive force is/are __________ |
A. | field current and armature current |
B. | field excitation |
C. | electromagnetic torque |
D. | all of the mentioned |
Answer» B. field excitation | |
11. |
The coil under going commutation lies along _____ while the coil getting short circuited lies along ____ for a practical dc machine. |
A. | gna, mna |
B. | mna, gna |
C. | gna, gna |
D. | mna, mna |
Answer» B. mna, gna | |
12. |
If the critical commutation time is 2 ms but it was observed that the practical commutation took 2.5 ms. This is the case of __________ |
A. | under commutation |
B. | over commutation |
C. | critical commutation |
D. | none of the mentioned |
Answer» B. over commutation | |
13. |
With no commutating poles used the brushes are given backward lead in the dc motor. |
A. | True |
B. | False |
Answer» B. False | |
14. |
The brushes should be shifted in _______ direction in generator for the satisfactory operation of commutation. |
A. | forward |
B. | reverse to rotation |
C. | all of the mentioned |
D. | none of the mentioned |
Answer» B. reverse to rotation | |
15. |
The brushes are placed __________ |
A. | along geometrical neutral axis |
B. | perpendicular to geometrical neutral axis |
C. | along magnetic neutral axis |
D. | perpendicular to magnetic neutral axis |
Answer» B. perpendicular to geometrical neutral axis | |