MCQOPTIONS
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MCQOPTIONS
This section includes 47 Mcqs, each offering curated multiple-choice questions to sharpen your Design Electrical Machines knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
How much does the addition iron losses relate with the supplied power? |
| A. | additional iron losses = 0.5% of supplied power |
| B. | additional iron losses = 0.6% of supplied power |
| C. | additional iron losses = 0.8% of supplied power |
| D. | additional iron losses = 0.9% of supplied power |
| Answer» B. additional iron losses = 0.6% of supplied power | |
| 2. |
The pulsation losses are caused by the direct axis pulsation of magnetic flux. |
| A. | true |
| B. | false |
| Answer» B. false | |
| 3. |
How many types are the additional losses in iron classified into? |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 5 |
| Answer» B. 3 | |
| 4. |
What is the use of skin effects in the induction motor? |
| A. | it helps in improving the efficiency |
| B. | it helps in improving the stopping characteristics |
| C. | it helps in improving the starting characteristics |
| D. | it helps in improving the running characteristics |
| Answer» D. it helps in improving the running characteristics | |
| 5. |
The additional losses owing to the higher order mmf harmonics occur mainly in windings of squirrel cage rotor. |
| A. | true |
| B. | false |
| Answer» B. false | |
| 6. |
The hydroelectric plants in the industry are best suited with _________ |
| A. | closed circuit air cooling |
| B. | hydrogen gas |
| C. | direct water |
| D. | all of the mentioned |
| Answer» B. hydrogen gas | |
| 7. |
A peaky voltage supply is given to the 3 phase power transformer of the connection power system. These results in _________ |
| A. | reduction in iron losses |
| B. | reduction in copper losses |
| C. | increase in iron losses |
| D. | reduction in noise |
| Answer» B. reduction in copper losses | |
| 8. |
A three phase induction motor is connected to the infinite bus operating at the normal conditions. There occurs an unbalancing in the supply, leading to _________ |
| A. | unequal heating losses |
| B. | stopping of motor |
| C. | increase in lower |
| D. | none of the mentioned |
| Answer» B. stopping of motor | |
| 9. |
If one of the phases of RYB supply gets broken, then the temperature rise of the induction motor _________ |
| A. | remains same as before |
| B. | reduces as compared to the normal operating temperature |
| C. | reduces to temperature rise of corresponding single phase induction motor |
| D. | increases |
| Answer» B. reduces as compared to the normal operating temperature | |
| 10. |
If one of the phases of the supply breaks down, then the connected three phase induction motor _________ |
| A. | continues to run as a single phase induction motor, provided load does does not increase beyond 57.7% |
| B. | stops operating after few seconds |
| C. | continues to run as single phase induction motor |
| D. | continues to run as two phase induction motor |
| Answer» B. stops operating after few seconds | |
| 11. |
For squirrel cage and slip ring induction motor, cooling methods is efficient in _________ |
| A. | squirrel cage induction motor |
| B. | slip ring induction motor |
| C. | both of the motors |
| D. | none of the mentioned |
| Answer» B. slip ring induction motor | |
| 12. |
In dc machine iron losses cause _________ |
| A. | heating in core |
| B. | loss in efficiency |
| C. | rise in temperature of ventilating air |
| D. | all of the mentioned |
| Answer» B. loss in efficiency | |
| 13. |
If two series motors are identically coupled. One is running as motor while other as generator. For this combination, the iron losses and frictional losses are found identical for _________ |
| A. | identical speed and excitation |
| B. | identical speed |
| C. | identical rating and construction |
| D. | none of the mentioned |
| Answer» B. identical speed | |
| 14. |
For the given traction application using a dc series motor for a starting time ’t’ is applied. If this method is replaced by a series-parallel control, giving 50% time for each series and parallel. The saving in the starting energy of _________ |
| A. | 25% |
| B. | zero |
| C. | 50% |
| D. | 75% |
| Answer» B. zero | |
| 15. |
THE_PULSATION_LOSSES_ARE_CAUSED_BY_THE_DIRECT_AXIS_PULSATION_OF_MAGNETIC_FLUX??$ |
| A. | true |
| B. | false |
| Answer» B. false | |
| 16. |
WHICH_OF_THE_GIVEN_LOSSES_ARE_DIRECTLY_PROPORTIONAL_TO_SQUARE_OF_SPEED??$ |
| A. | Windage loss |
| B. | Eddy current loss |
| C. | Both Windage and eddy current loss |
| D. | Hysteresis loss and brush loss |
| Answer» D. Hysteresis loss and brush loss | |
| 17. |
A_PEAKY_VOLTAGE_SUPPLY_IS_GIVEN_TO_THE_3_PHASE_POWER_TRANSFORMER_OF_THE_CONNECTION_POWER_SYSTEM._THESE_RESULTS_INTO?$ |
| A. | reduction in iron losses |
| B. | reduction in copper losses |
| C. | increase in iron losses |
| D. | reduction in noise |
| Answer» B. reduction in copper losses | |
| 18. |
HOW_MANY_TYPES_ARE_THE_ADDITIONAL_LOSSES_IN_IRON_CLASSIFIED_INTO??$ |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 5 |
| Answer» B. 3 | |
| 19. |
The electromechanical energy conversion devices used in power systems are never operated to deliver maximum power output, because at maximum power output, _____________$ |
| A. | Efficiency is less than 50% |
| B. | Temperature of the power devices is much more than the specified allowable temperature rise |
| C. | Half of the power input appears as losses |
| D. | Any of the mentioned |
| Answer» C. Half of the power input appears as losses | |
| 20. |
The hydroelectric plants in the industry are best suited with$ |
| A. | closed circuit air cooling |
| B. | hydrogen gas |
| C. | direct water |
| D. | any of the mentioned. |
| Answer» B. hydrogen gas | |
| 21. |
How much does the addition iron losses relate with the supplied power ?$ |
| A. | additional iron losses = 0.5% of supplied power |
| B. | additional iron losses = 0.6% of supplied power |
| C. | additional iron losses = 0.8% of supplied power |
| D. | additional iron losses = 0.9% of supplied power |
| Answer» B. additional iron losses = 0.6% of supplied power | |
| 22. |
Consider the following statements regarding efficiency of electrical machines:$ |
| A. | efficiency should be calculated by measuring output and input |
| B. | efficiency is maximum when constant losses = variable losses |
| C. | electrical machines are designed to have maximum efficiency at full load |
| D. | electrical machines are designed to have maximum efficiency at near about full load |
| Answer» C. electrical machines are designed to have maximum efficiency at full load | |
| 23. |
The_iron_losses_in_a_saturated_three_phase_alternator_is_lesser_than_the_non-saturated_three_phase_alternator.$ |
| A. | True |
| B. | False |
| Answer» B. False | |
| 24. |
No load rotational losses in electrical machine consists of _____________ |
| A. | Friction and windage losses |
| B. | Stator core, friction and windage losses |
| C. | Rotor core, friction and windage losses |
| D. | No load core, friction and windage losses |
| Answer» E. | |
| 25. |
For the same rating machines, which of the following statement is correct regarding the efficiency (η)?$ |
| A. | η of low speed machine > η of high speed machine |
| B. | η of low speed machine < η of high speed machine |
| C. | η of low speed machine = η of high speed machine |
| D. | Any of the mentioned |
| Answer» C. ‚âà√≠‚Äö√†√´ of low speed machine = ‚âà√≠‚Äö√†√´ of high speed machine | |
| 26. |
What percentage of the rated output for DC machine and synchronous machine is taken as stray load losses respectively? |
| A. | 1% and 0.5% |
| B. | 0.5% and 1% |
| C. | 3% and 0.1% |
| D. | 0.1% and 5% |
| Answer» B. 0.5% and 1% | |
| 27. |
A three phase induction motor is connected to the infinite bus operating at the normal conditions. There occurs an unbalancing in the supply, leading t? |
| A. | unequal heating losses |
| B. | stopping of motor |
| C. | increase in lower |
| D. | None of the mentioned |
| Answer» B. stopping of motor | |
| 28. |
What should be the maximum permissible level for frequency in normal operating conditions? |
| A. | < 2 Hz |
| B. | > 3 Hz |
| C. | < 4 Hz |
| D. | > 3 Hz |
| Answer» C. < 4 Hz | |
| 29. |
The pole shoes in DC and synchronous machines are laminated to reduce _____________ |
| A. | Resistance losses |
| B. | Pulsation or pole-face losses |
| C. | Mechanical losses |
| D. | None of the mentioned |
| Answer» C. Mechanical losses | |
| 30. |
If one of the phases of RYB supply gets broken, then the temperature rise of the induction motor |
| A. | remains same as before |
| B. | reduces as compared to the normal operating temperature |
| C. | reduces to temperature rise of corresponding single phase induction motor |
| D. | increases |
| Answer» B. reduces as compared to the normal operating temperature | |
| 31. |
What is the use of skin effect in the induction motor? |
| A. | it helps in improving the efficiency |
| B. | it helps in improving the stopping characteristics |
| C. | it helps in improving the starting characteristics |
| D. | it helps in improving the running characteristics |
| Answer» D. it helps in improving the running characteristics | |
| 32. |
In an induction motor, which of the following is correct: |
| A. | Stator core loss < rotor core loss |
| B. | Stator core loss = rotor core loss |
| C. | Stator core loss > rotor core loss |
| D. | Any of the mentioned |
| Answer» D. Any of the mentioned | |
| 33. |
If one of the phases of the supply breaks down, then the connected three phase induction motor |
| A. | continues to run as a single phase induction motor, provided load does does not increase beyond 57.7% |
| B. | stops operating after few seconds |
| C. | continues to run as single phase induction motor |
| D. | continues to run as two phase induction motor |
| Answer» B. stops operating after few seconds | |
| 34. |
How can the additional losses be decreased in the induction motor? |
| A. | chording the stator winding |
| B. | skewing the rotor |
| C. | having a proper slot combination |
| D. | chording the stator winding, skewing the rotor, having a proper slot combination. |
| Answer» E. | |
| 35. |
The usual lamination thickness selected to minimize the eddy current loss in rotor is _____________ |
| A. | 0.1 mm to 0.2 mm |
| B. | 0.3 mm to 0.4 mm |
| C. | 0.4 mm to 0.5 mm |
| D. | 0.9 mm to 0.10 mm |
| Answer» D. 0.9 mm to 0.10 mm | |
| 36. |
For squirrel cage and slip ring induction motor, cooling methods is efficient in |
| A. | squirrel cage induction motor |
| B. | slip ring induction motor |
| C. | both of the motors |
| D. | none of the mentioned |
| Answer» B. slip ring induction motor | |
| 37. |
The additional losses owing to the higher order mmf harmonics occur mainly in windings of squirrel cage rotor? |
| A. | true |
| B. | false |
| Answer» B. false | |
| 38. |
In rotating electrical machines, when the armature rotates, there are continuous magnetic reversals and power required for their reversals is called _____________ |
| A. | Eddy current loss |
| B. | Hysteresis loss |
| C. | Resistance or ohmic losses |
| D. | Mechanical loss |
| Answer» C. Resistance or ohmic losses | |
| 39. |
In dc machine iron losses cause |
| A. | heating in core |
| B. | loss in efficiency |
| C. | rise in temperature of ventilating air |
| D. | all of the mentioned |
| Answer» B. loss in efficiency | |
| 40. |
What factor does the additional copper losses depend upon? |
| A. | skin effect |
| B. | mmf harmonics |
| C. | machine design |
| D. | mmf harmonics and skin effect |
| Answer» E. | |
| 41. |
Which of the following statements are correct regarding brush contact losses? |
| A. | In DC machine: proportional to armature current |
| B. | In synchronous machine: neglected |
| C. | In induction machine: neglected |
| D. | Any of the mentioned |
| Answer» E. | |
| 42. |
Hysteresis loss in a dc machine is _____ of rate of flow of air and _____ on frequency of _____ |
| A. | independent, dependent, magnetic reversal |
| B. | independent, dependent, operation |
| C. | dependent, independent, magnetic reversal |
| D. | None of the mentioned |
| Answer» B. independent, dependent, operation | |
| 43. |
How many types of additional losses are present? |
| A. | 1 |
| B. | 4 |
| C. | 2 |
| D. | 3 |
| Answer» D. 3 | |
| 44. |
To determine the efficiency of the machine, direct load test is not advantageous because of which of the following reasons? |
| A. | Cost of providing large inputs |
| B. | Difficulty of dissipating the large outputs |
| C. | Both cost of providing large inputs and difficulty in dissipating the large outputs |
| D. | None of the mentioned |
| Answer» D. None of the mentioned | |
| 45. |
If two series motors are identically coupled. One is running as motor while other as generator. For this combination,the iron losses and frictional losses are found identical for |
| A. | identical speed and excitation. |
| B. | identical speed. |
| C. | identical rating and construction |
| D. | None of the mentioned. |
| Answer» B. identical speed. | |
| 46. |
What is the formula for efficiency at full load? |
| A. | efficiency at full load = output / output + losses |
| B. | efficiency at full load = output / output – losses |
| C. | efficiency at full load = output / output * losses |
| D. | efficiency at full load = output * output + losses |
| Answer» B. efficiency at full load = output / output ‚Äö√Ñ√∂‚àö√ë‚àö¬® losses | |
| 47. |
How many losses are present in induction motors? |
| A. | 4 |
| B. | 3 |
| C. | 5 |
| D. | 2 |
| Answer» D. 2 | |