MCQOPTIONS
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MCQOPTIONS
This section includes 100 Mcqs, each offering curated multiple-choice questions to sharpen your NTPC (Technical Ability) knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
The noise resulting from vibrations of laminations set by magnetic forces, is termedas |
| A. | magnetostrication |
| B. | boo |
| C. | hum |
| D. | zoom |
| Answer» D. zoom | |
| 2. |
As a result of armature reaction, the reduction in the total mutual air gap fluxin aD.C. generator is approximately |
| A. | 40 percent |
| B. | 25 percent |
| C. | 10 percent |
| D. | 5 percent |
| Answer» E. | |
| 3. |
N atural air coo ling is generally restricted for transformers up to |
| A. | 1.5 MVA |
| B. | 5 MVA |
| C. | 15 MVA |
| D. | 50 MVA |
| Answer» B. 5 MVA | |
| 4. |
Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make useof |
| A. | D.C. series motor |
| B. | D.C. shunt motor |
| C. | induction motor |
| D. | all of above motors |
| Answer» B. D.C. shunt motor | |
| 5. |
For the parallel operation of single phase transformers it is necessary that they shouldhave |
| A. | same efficiency |
| B. | same polarity |
| C. | same kVA rating |
| D. | same number of turns on the secondary side. |
| Answer» C. same kVA rating | |
| 6. |
No-load speed of which of the following motor will be highest ? |
| A. | Shunt motor |
| B. | Series motor |
| C. | Cumulative compound motor |
| D. | Differentiate compound motor |
| Answer» C. Cumulative compound motor | |
| 7. |
In case-the conditions for maximum power for a D.C. motor are established,theefficiency of the motor will be |
| A. | 100% |
| B. | around 90% |
| C. | anywhere between 75% and 90% |
| D. | less than 50% |
| Answer» E. | |
| 8. |
Which of the following parts of a transformer is visible from outside ? |
| A. | Bushings |
| B. | Core |
| C. | Primary winding |
| D. | Secondary winding |
| Answer» B. Core | |
| 9. |
Which of the following is the most likely source of harmonics in a transformer ? |
| A. | poor insulation |
| B. | Overload |
| C. | loose connections |
| D. | Core saturation |
| Answer» E. | |
| 10. |
The no-load current drawn by transformer is usually what per cent of the full-loadcurrent ? |
| A. | 0.2 to 0.5 per cent |
| B. | 2 to 5 per cent |
| C. | 12 to 15 per cent |
| D. | 20 to 30 per cent |
| Answer» C. 12 to 15 per cent | |
| 11. |
Where D.C. motor of H.P. 12 or more requires frequent starting, stopping,reversingand speed control |
| A. | drum type controller is used |
| B. | three point starter is used |
| C. | four point starter is used |
| D. | all above can be used |
| Answer» B. three point starter is used | |
| 12. |
Which D.C. motor will be suitable alongwith flywheel for intermittent light andheavyloads? |
| A. | Series motor |
| B. | Shunt motor |
| C. | Cumulatively compounded motor |
| D. | Differentially compounded motor |
| Answer» D. Differentially compounded motor | |
| 13. |
Which of the following statements regarding an idel single-phase transformerhaving aturn ratio of 1 : 2 and drawing a current of 10 A from 200 V A.C. supply is incorrect ? |
| A. | Its secondary current is 5 A |
| B. | Its secondary voltage is 400 V |
| C. | Its rating is 2 kVA |
| D. | Its secondary current is 20 A |
| Answer» E. | |
| 14. |
In a D.C. shunt motor, under the conditions of maximum power, the current inthearmature will be |
| A. | almost negligible |
| B. | rated full-load current |
| C. | less than full-load current |
| D. | more than full-load current |
| Answer» E. | |
| 15. |
To achieve sparkless commutation brushes of a D.C. generator are rockedmahead 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» B. in magnetic neutral axis | |
| 16. |
For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f. ? |
| A. | Lap winding |
| B. | Wave winding |
| C. | Either of (a) and (b) above |
| D. | Depends on other features of design |
| Answer» C. Either of (a) and (b) above | |
| 17. |
In a given transformer for a given applied voltage, losses which remainconstantirrespective of load changes are |
| A. | hysteresis and eddy current losses |
| B. | friction and windage losses |
| C. | copper losses |
| D. | none of the above |
| Answer» B. friction and windage losses | |
| 18. |
What will happen if the transformers working in parallel are not connected withregard to polarity ? |
| A. | The power factor of the two trans-formers will be different from the power factor of common load |
| B. | Incorrect polarity will result in dead short circuit |
| C. | The transformers will not share load in proportion to their kVA ratings |
| D. | none of the above |
| Answer» C. The transformers will not share load in proportion to their kVA ratings | |
| 19. |
Which of the following protection is normally not provided on smalldistributiontransformers ? |
| A. | Overfluxing protection |
| B. | Buchholz relay |
| C. | Overcurrent protection |
| D. | All of the above |
| Answer» C. Overcurrent protection | |
| 20. |
Which of the following generating machine will offer constant voltage on allloads ? |
| A. | Self-excited generator |
| B. | Separately excited generator |
| C. | Level compounded generator . |
| D. | All of the above |
| Answer» D. All of the above | |
| 21. |
If the supply voltage for a D.C. motor is increased, which of the following willdecrease? |
| A. | Starting torque |
| B. | Operating speed |
| C. | Full-load current |
| D. | All of the above |
| Answer» D. All of the above | |
| 22. |
Natural oil cooling is used for transformers upto a rating of |
| A. | 3000 kVA |
| B. | 1000 kVA |
| C. | 500 kVA |
| D. | 250 kVA |
| Answer» B. 1000 kVA | |
| 23. |
Which of the following could be lamina-proximately the thickness of laminations of aD.C. machine ? |
| A. | 0.005 mm |
| B. | 0.05 mm |
| C. | 0.5 m |
| D. | 5 m |
| Answer» D. 5 m | |
| 24. |
The transformer oil should have volatility and viscosity. |
| A. | low,low |
| B. | high,high |
| C. | low,high |
| D. | high,low |
| Answer» B. high,high | |
| 25. |
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» B. Shunt generator | |
| 26. |
Which winding of the transformer has less cross-sectional area ? |
| A. | Primary winding |
| B. | Secondary winding |
| C. | Low voltage winding |
| D. | High voltage winding |
| Answer» E. | |
| 27. |
If B is the flux density, I the length of conductor and v the velocity of conductor,then induced e.m.f. is given by |
| A. | Blv |
| B. | Blv2 |
| C. | Bl2v |
| D. | Bl2v2 |
| Answer» B. Blv2 | |
| 28. |
In a step-down transformer, there is a change of 15 A in the load current. This results inchange of supply current of |
| A. | less than 15 A |
| B. | more than 15 A |
| C. | 15 A |
| D. | none of the above |
| Answer» B. more than 15 A | |
| 29. |
Which of the following acts as a protection against high voltage surges due tolightning and switching ? |
| A. | Horn gaps |
| B. | Thermal overload relays |
| C. | Breather |
| D. | Conservator |
| Answer» B. Thermal overload relays | |
| 30. |
Which of the following generators will be preferred if they are required to berun in parallel ? |
| A. | Shunt generators |
| B. | Series generators |
| C. | Compound generators |
| D. | None of the above |
| Answer» B. Series generators | |
| 31. |
Which of the following is the main advantage of an auto-transformer over a twowinding transformer ? |
| A. | Hysteresis losses are reduced |
| B. | Saving in winding material |
| C. | Copper losses are negligible |
| D. | Eddy losses are totally eliminated |
| Answer» C. Copper losses are negligible | |
| 32. |
The full-load copper loss of a trans¬former is 1600 W. At half-load, the copper loss will be |
| A. | 6400 W |
| B. | 1600 W |
| C. | 800 W |
| D. | 400 W |
| Answer» E. | |
| 33. |
A 220 V D.C. generator is run at full speed without any excitation. Theopen circuit voltage will be |
| A. | zero |
| B. | about 2 V |
| C. | about 50 V |
| D. | 220V |
| Answer» C. about 50 V | |
| 34. |
As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent aheavy current from flowing though the armature circuit |
| A. | a resistance is connected in series with armature |
| B. | a resistance is connected parallel to the armature |
| C. | armature is temporarily open circuited |
| D. | a high value resistor is connected across the fieldwinding |
| Answer» B. a resistance is connected parallel to the armature | |
| 35. |
Hysteresis loss in a transformer varies as CBmax = maximum flux density) |
| A. | Bmax |
| B. | Bmax1-6 |
| C. | Bmax1-83 |
| D. | B max |
| Answer» C. Bmax1-83 | |
| 36. |
The number of armature parallel paths in a two-pole D.C. generator havingduplexlap winding is |
| A. | 2 |
| B. | 4 |
| C. | 6 |
| D. | 8 |
| Answer» C. 6 | |
| 37. |
In a given transformer for given applied voltage, losses which remainconstantirrespective of load changes are |
| A. | friction and windage losses |
| B. | copper losses |
| C. | hysteresis and eddy current losses |
| D. | none of the above |
| Answer» D. none of the above | |
| 38. |
Which type of winding is used in 3phase shell-type transformer ? |
| A. | Circular type |
| B. | Sandwich type |
| C. | Cylindrical type |
| D. | Rectangular type |
| Answer» C. Cylindrical type | |
| 39. |
Which of the foJIowing is not a routine test on transformers ? |
| A. | Core insulation voltage test |
| B. | Impedance test |
| C. | Radio interference test |
| D. | Polarity test |
| Answer» D. Polarity test | |
| 40. |
Sumpner's test is conducted on trans-formers to determine |
| A. | temperature |
| B. | stray losses |
| C. | all-day efficiency |
| D. | none of the above |
| Answer» B. stray losses | |
| 41. |
In a D.C. series motor, if the armature current is reduced by 50%, the torque of themotor will be equal to |
| A. | 100% of the previous value |
| B. | 50% of the previous value |
| C. | 25% of the previous value |
| D. | 10% of the previous value |
| Answer» D. 10% of the previous value | |
| 42. |
Which of the following does not change in a transformer ? |
| A. | Current |
| B. | Voltage |
| C. | Frequency |
| D. | All of the above |
| Answer» D. All of the above | |
| 43. |
Which of the following law/rule can he used to determine the direction of rotationofD.C. motor ? |
| A. | Lenz's law |
| B. | Faraday's law |
| C. | Coloumb'slaw |
| D. | Fleming's left-hand rule |
| Answer» E. | |
| 44. |
If a D.C. shunt motor is working at full load and if shunt field circuit suddenlyopens |
| A. | this will make armature to take heavy current, possibly burning it |
| B. | this will result in excessive speed, possibly destroying armature due toexcessive centrifugal stresses |
| C. | nothing will happen to motor |
| D. | motor will come to stop |
| Answer» B. this will result in excessive speed, possibly destroying armature due toexcessive centrifugal stresses | |
| 45. |
In a D.C. generator the number of mechanical degrees and electrical degreeswill 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» E. | |
| 46. |
The efficiency of two identical transformers under load conditionscan bedetermined by |
| A. | short-circuit test |
| B. | back-to-back test |
| C. | open circuit test |
| D. | any of the above |
| Answer» C. open circuit test | |
| 47. |
While conducting short-circuit test on a transformer the following side is shortcircuited |
| A. | High voltage side |
| B. | Low voltage side |
| C. | Primary side |
| D. | Secondary side |
| Answer» C. Primary side | |
| 48. |
At the instant of starting when a D.C. motor is put on supply, it behaveslike |
| A. | a highly resistive circuit |
| B. | a low resistance circuit |
| C. | a capacitive circuit |
| D. | none of the above |
| Answer» C. a capacitive circuit | |
| 49. |
D.C. generators are connected to the busbars or disconnected from them only underthe floating condition |
| A. | to avoid sudden loading of the primemover |
| B. | to avoid mechanicaljerk to the shaft |
| C. | to avoid burning of switch contacts |
| D. | all above |
| Answer» E. | |
| 50. |
Auto-transformer makes effective saving on copper and copper losses, whenitstransformation ratio is |
| A. | approximately equal to one |
| B. | less than one |
| C. | great than one |
| D. | none of the above |
| Answer» B. less than one | |