MCQOPTIONS
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MCQOPTIONS
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 | |