MCQOPTIONS
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MCQOPTIONS
This section includes 120 Mcqs, each offering curated multiple-choice questions to sharpen your ENGINEERING SERVICES EXAMINATION (ESE) knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
By which of the following methods the temperature rise of windings and other partsmay be determined ? |
| A. | Thermometer method |
| B. | Resistance method |
| C. | Embedded temperature detector method |
| D. | Any of the above |
| Answer» E. | |
| 2. |
______is extensively used for those portions of magnetic circuit which carry steady fluxand need superior mechanical properties ? |
| A. | Grey cast-iron |
| B. | Cast steel |
| C. | High carbon steel |
| D. | Stainless steel |
| Answer» C. High carbon steel | |
| 3. |
The thermal conductivity of hydrogen is ______ times that of air |
| A. | 2 |
| B. | 3 |
| C. | 5 |
| D. | 7 |
| Answer» E. | |
| 4. |
Electrical machines having power outputs ranging from a few kW upto approximately250 kW may be classified as |
| A. | small size machines |
| B. | medium size machines |
| C. | large size machines |
| D. | any ofthe above |
| Answer» C. large size machines | |
| 5. |
________ has a lowrelative permeability and is used principally in field frames when costis of primary importance and extra weight is not objectionable. |
| A. | Cast steel |
| B. | Aluminium |
| C. | Soft steel |
| D. | Cast iron |
| Answer» E. | |
| 6. |
Which of the following methods does not take into account the maximum temperaturerise under variable load conditions ? |
| A. | Equivalent power method |
| B. | Equivalent current method |
| C. | Method of average losses |
| D. | Equivalent torque method |
| Answer» D. Equivalent torque method | |
| 7. |
In induction motors, the length of air gap in kept as small as mechanically possible isorder to have |
| A. | low power factor |
| B. | high power factor |
| C. | high over load capacity |
| D. | any of the above |
| Answer» C. high over load capacity | |
| 8. |
The efficiency of a machine should be as ______ as possible to reduce the operatingcost. |
| A. | high |
| B. | low |
| C. | either of the above |
| D. | none of the above |
| Answer» B. low | |
| 9. |
The heat dissipating capability of transformers of ratings higher than 30 kVA inincreased by providing which of the following ? |
| A. | Corrugations |
| B. | Fins |
| C. | Tubes |
| D. | All of the above |
| Answer» E. | |
| 10. |
Which of the following methods may be adopted to reduce the effects of armaturereaction ? |
| A. | Increase in length of air gap at pole tips |
| B. | Increasing reluctance of pole tips |
| C. | Compensating windings |
| D. | All of the above |
| Answer» E. | |
| 11. |
The change in flux linkages can be caused in which ofthe following ways ? |
| A. | The flux is constant with respect to time and is stationary and the coil moves throughnit |
| B. | The coil is stationary with respect to flux and the flux varies in magnitude with respect to time |
| C. | Both the changes mentioned above occure together, i.e., the coil moves through a time varying field |
| D. | All ofthe above |
| Answer» E. | |
| 12. |
In self cooled motors the cooling time constant is about ______ than the heating timeconstant because cooling conditions are worse at standstill. |
| A. | 2 to 3 times greater |
| B. | 3 to 4 times greater |
| C. | 4 to 5 times greater |
| D. | none of the above |
| Answer» B. 3 to 4 times greater | |
| 13. |
The design of mechanical parts is particularly important in case of _____ speedmachines. |
| A. | low |
| B. | medium |
| C. | high |
| D. | any of the above |
| Answer» D. any of the above | |
| 14. |
The length cf air gap to be provided in ______ is primarily determined by power factorconsideration. |
| A. | d.c. series motor . |
| B. | d.c. shunt motor |
| C. | induction motor |
| D. | synchronous motor |
| Answer» D. synchronous motor | |
| 15. |
Multiple inlet system of air cooling of turbo-alternators can be used for machines ofrating upto |
| A. | 10 MW |
| B. | 30 MW |
| C. | 60 MW |
| D. | 150 MW |
| Answer» D. 150 MW | |
| 16. |
A practical formula for determining the thickness of insulation between low voltageand high voltage windings is |
| A. | 1 + 0.2 kVmm |
| B. | 2 + 0.5 kVmm |
| C. | 4 + 0.7 kV mm |
| D. | 5 + 0.9 kV mm |
| Answer» E. | |
| 17. |
The design of electromagnets is based upon which of the following fundamentalequations ? |
| A. | Force equation |
| B. | Magnetic circuit equation |
| C. | Heating equation |
| D. | All of the above |
| Answer» E. | |
| 18. |
When the two coil sides forming a coil are spaced exactly one pole pitch apart they aresaid to be of |
| A. | short pitch |
| B. | full pitch |
| C. | either of the above |
| D. | none of the above |
| Answer» C. either of the above | |
| 19. |
Electrical machines having a power output upto about 750 W may becalled_______machines. |
| A. | small size |
| B. | medium size |
| C. | large size |
| D. | any of the above |
| Answer» B. medium size | |
| 20. |
The heat dissipated by from a surface depends upon its temperature and itscharacteristics like colour, roughness etc. |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | any ofthe above |
| Answer» D. any ofthe above | |
| 21. |
The noise produced by a ______ cooled machine is less as the rotor moves in a mediumof smaller density. |
| A. | air |
| B. | hydrogen |
| C. | either (a) or (b) |
| D. | none of the above |
| Answer» C. either (a) or (b) | |
| 22. |
With conventional hydrogen cooling it is possible to increase the rating of a single unitto |
| A. | 50 MW |
| B. | 100 MW |
| C. | 200 MW |
| D. | none ofthe above |
| Answer» D. none ofthe above | |
| 23. |
Which ofthe following materials is used in the manufacture of resistance grids to beused in the starters of large motors ? |
| A. | Copper |
| B. | Aluminium |
| C. | Steel |
| D. | Cast-iron |
| Answer» E. | |
| 24. |
The time taken by the machine to attain 0.632 of its final steady temperature rise iscalled |
| A. | heating time constant |
| B. | cooling time constant |
| C. | either (a) or (b) |
| D. | none of the above |
| Answer» B. cooling time constant | |
| 25. |
The weight of copper of both armature and field windings decreases with _____ innumber of poles. |
| A. | increase |
| B. | decrease |
| C. | either of the above |
| D. | none of the above |
| Answer» B. decrease | |
| 26. |
In D.C. machines, ir order to prevent excessive distortion of field form by the armaturereaction, the field mmf must be made |
| A. | equal to that of armature mmf |
| B. | less in comparison with the arma¬ture mmf |
| C. | large in comparison with the arma-ture mmf |
| D. | none of the above |
| Answer» D. none of the above | |
| 27. |
The heated parts of an electrical machine dissipate heat into their surroundings bywhich of the following modes of heat dissipation ? |
| A. | Conduction |
| B. | Convection |
| C. | Radiation |
| D. | All ofthe above |
| Answer» E. | |
| 28. |
In D.C. machines, the ____ in field mmf results in increase in size and cost of machines. |
| A. | increase |
| B. | decrease |
| C. | either of the above |
| D. | none of the above |
| Answer» B. decrease | |
| 29. |
Which ofthe following methods is used for air cooling of turbo-alternators ? |
| A. | One sided axial ventilation |
| B. | Two sided axial ventilation |
| C. | Multiple inlet system |
| D. | All ofthe above |
| Answer» E. | |
| 30. |
is universally used for windings of electrical machines because it is easily workablewithout any possibility of fracture. |
| A. | Silver |
| B. | Steel |
| C. | Aluminium |
| D. | Copper |
| Answer» E. | |
| 31. |
The value of exciting or magnetizing current depends upon which of the followingfactors ? |
| A. | Total m.m.f. required |
| B. | The number of turns in the exciting winding |
| C. | The way in which the winding is distributed |
| D. | All of the above |
| Answer» E. | |
| 32. |
For 275 kV transformers, using cold rolled grain oriented steel, which of the followingvalues of flux density may be used? |
| A. | 1.0 Wb/m2 |
| B. | 1.1 Wb/m2 |
| C. | 1.3 Wb/m2 |
| D. | 1.6 Wb/m2 |
| Answer» E. | |
| 33. |
The action of electromagnetic machines can be related to which ofthe following basicprinciples ? |
| A. | Induction |
| B. | Interaction |
| C. | Alignment |
| D. | All of the above |
| Answer» E. | |
| 34. |
If an insulating material is operated beyond the maximum allowable temperature, itslife is |
| A. | drastically increased |
| B. | drastically reduced |
| C. | unaffected |
| D. | none of the above |
| Answer» C. unaffected | |
| 35. |
For large power transformers, self oil cooled type or air blast type which of thefollowing values of current density may be used ? |
| A. | 1.0 to 1.2 A/mm2 |
| B. | 1.5 to 2.0 A/mm2 |
| C. | 2.2 to 3.2 A/mm2 |
| D. | 3.2 to 4.2 A/mm2 |
| Answer» D. 3.2 to 4.2 A/mm2 | |
| 36. |
Which of the following problem arises in D.C. motors which are fed from thyristorbridge circuits ? |
| A. | Increased I R losses |
| B. | Increased core losses |
| C. | Poor commutation |
| D. | All of the above |
| Answer» E. | |
| 37. |
The distance between the starts of two consecutive coils measured in terms of coilsides is called |
| A. | front pitch |
| B. | winding pitch |
| C. | commutator pitch |
| D. | back pitch |
| Answer» C. commutator pitch | |
| 38. |
Which ofthe following is an advantage of hydrogen cooling ? |
| A. | Increase in efficiency |
| B. | Increase in ratings |
| C. | Increase in life |
| D. | All ofthe above |
| Answer» E. | |
| 39. |
The usual values of maximum flux densities for distribution transformers using hotrolled silicon steel are |
| A. | 0.5 to 0.8 Wb/m2 |
| B. | 0.8 to 1.0 Wb/m2 |
| C. | 1.1 to 1.35 Wb/m2 |
| D. | 1.4 to 1.8 Wb/m2 |
| Answer» D. 1.4 to 1.8 Wb/m2 | |
| 40. |
In ______ machines, the size of the shaft is decided by the critical speed which dependson the deflection of the shaft. |
| A. | small |
| B. | medium |
| C. | large |
| D. | any of the above. |
| Answer» D. any of the above. | |
| 41. |
______ brushes are fragile and cause excessive wear of commutator, |
| A. | Natural graphite |
| B. | Hard carbon |
| C. | Electro graphitic |
| D. | Metal graphite |
| Answer» B. Hard carbon | |
| 42. |
Aluminium when adopted as a conductor material in ______ transformers, decreases theoverall cost of the transformer |
| A. | small size |
| B. | medium size |
| C. | large size |
| D. | any of the above size |
| Answer» B. medium size | |
| 43. |
The cold rolled grain oriented steel has ______ permeability in the direction of thegrain orientation. |
| A. | minimum |
| B. | maximum |
| C. | nil |
| D. | none of the above |
| Answer» C. nil | |
| 44. |
Multi-layer helical windings are commonly used in the transformers as high voltagewindings |
| A. | upto 20 kV |
| B. | upto 50 kV |
| C. | upto 80 kV |
| D. | for 110 kV and above |
| Answer» E. | |
| 45. |
electromagnets generally function as holding magnets. |
| A. | Tractive |
| B. | Portative |
| C. | Either of the above |
| D. | None of the above |
| Answer» C. Either of the above | |
| 46. |
A current density of _____ is ilsed for large power transformers with forced circulationof oil or with water cooling coils |
| A. | 1.5 to 2.5 A/mm2 |
| B. | 3.5 to 4.5 A/mm2 |
| C. | 4.0 to 5.0 A/mm2 |
| D. | 5.4 to 6.2 A/mm2 |
| Answer» E. | |
| 47. |
By which of the following methods motor rating for variable load drives can bedetermined ? |
| A. | Method of average losses |
| B. | Equivalent current method |
| C. | Equivalent torque method |
| D. | All of the above. |
| Answer» E. | |
| 48. |
cooling is the process of dissipating the armature and field winding losses to a coolingmedium circulating within the winding insulation wall |
| A. | Direct |
| B. | Indirect |
| C. | Conventional |
| D. | Any ofthe above |
| Answer» B. Indirect | |
| 49. |
Transformers with a capacity of upto _____ have a cooling radiator system with naturalcooling |
| A. | 2 MVA |
| B. | 5 MVA |
| C. | 7.5 MVA |
| D. | 10 MVA |
| Answer» E. | |
| 50. |
The insulation between windings and grounded core and the insulation between thewindings of the same phase is called |
| A. | minor insulation |
| B. | major insulation |
| C. | either of the above |
| D. | none of the above |
| Answer» C. either of the above | |