MCQOPTIONS
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MCQOPTIONS
This section includes 12 Mcqs, each offering curated multiple-choice questions to sharpen your Dc Machines knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
Each of the following statements regarding interpoles is true except______________________ |
| A. | They are small yoke-fixed poles spaced in between the main poles |
| B. | They are connected in parallel with the armature so that they carry part of the armature current |
| C. | Their polarity, in the case of generators is the same as that of the main pole ahead |
| D. | They automatically neutralize not only reactance voltage but cross-magnetisation as well |
| Answer» C. Their polarity, in the case of generators is the same as that of the main pole ahead | |
| 2. |
The most likely cause(s) of sparking at the brushes in a DC machine is /are ____________ |
| A. | Open coil in the armature |
| B. | Defective interpoles |
| C. | Incorrect brush spring pressure |
| D. | Open coil in armature, defective interpoles and incorrect brush spring pressure |
| Answer» E. | |
| 3. |
Why dummy coils are connected in DC machine? |
| A. | To reduce eddy current losses |
| B. | To enhance flux density |
| C. | To amplify voltage |
| D. | To provide mechanical balance for the rotor |
| Answer» E. | |
| 4. |
Function of interpole flux is_________ |
| A. | Neutralise the commutating self-induced emf |
| B. | Neutralise the armature reaction flux |
| C. | Neutralise both the armature reaction flux as well as commutating emf induced in the coil |
| D. | Perform none of the above functions |
| Answer» D. Perform none of the above functions | |
| 5. |
Exact purpose of compensating winding in a DC generator is _________ |
| 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. | Cannot be determined |
| Answer» D. Cannot be determined | |
| 6. |
What is the exact location of compensating winding? |
| A. | Across armature |
| B. | In series with armature |
| C. | Across armature or in series |
| D. | Cannot be determined |
| Answer» C. Across armature or in series | |
| 7. |
Which of the following method will completely neutralize the armature reaction in a DC machine? |
| A. | Only compensating winding |
| B. | Only interpoles |
| C. | Compensating winding and interpoles |
| D. | Cannot be determined |
| Answer» D. Cannot be determined | |
| 8. |
Inequality in brush arm currents caused due to different emf induced in different parallel paths may give rise to copper losses. These effects can be avoided by using _________ |
| A. | Compensating windings |
| B. | Interpoles |
| C. | Equalizer rings |
| D. | Cannot be determined |
| Answer» D. Cannot be determined | |
| 9. |
Where are no equalizer rings connected? |
| A. | Only wave winding |
| B. | Only lap winding |
| C. | Both wave winding and lap winding |
| D. | Cannot be determined |
| Answer» B. Only lap winding | |
| 10. |
What is the ampere turns per pole for compensating winding in DC machines? |
| A. | (pole arc / pole pitch) * armature ampere turns per pole |
| B. | (pole pitch / pole arc) * armature ampere turns per pole |
| C. | * armature ampere turns per polec) (pole arc / pole pitch) * total ampere conductors per pole |
| D. | Cannot be determined |
| Answer» B. (pole pitch / pole arc) * armature ampere turns per pole | |
| 11. |
In order to neutralize armature mmf perfectly under the pole shoe, the ampere-conductors of compensating winding must be (pole arc/pole pitch=1) _______ |
| A. | Not equal to the total armature ampere conductors under the pole shoe |
| B. | Equal to the total armature ampere conductors under the pole shoe |
| C. | Half of the total armature ampere conductors under the pole shoe |
| D. | Twice of the total armature ampere conductors under the pole shoe |
| Answer» C. Half of the total armature ampere conductors under the pole shoe | |
| 12. |
The armature reaction in a DC machine causes distortion in the main field flux. Effect of armature reaction can be reduced by_________ |
| A. | Increasing the length of air gap |
| B. | Decreasing the length of air gap |
| C. | Increasing the number of poles |
| D. | Decreasing the number of poles |
| Answer» C. Increasing the number of poles | |