McqMate
| 1. |
Which of the following is the major consideration to evolve a good design ? |
| A. | Cost |
| B. | Durability |
| C. | Compliance with performance criteria as laid down in specifications |
| D. | All of the above |
| Answer» D. All of the above | |
| 2. |
impose limitation on design. |
| A. | Saturation |
| B. | Temperature rise |
| C. | Efficiency |
| D. | All above |
| Answer» D. All above | |
| 3. |
The efficiency of a machine should be as ______ as possible to reduce the operating cost. |
| A. | high |
| B. | low |
| C. | either of the above |
| D. | none of the above |
| Answer» A. high | |
| 4. |
If an insulating material is operated beyond the maximum allowable temperature, its life is |
| A. | drastically increased |
| B. | drastically reduced |
| C. | unaffected |
| D. | none of the above |
| Answer» B. drastically reduced | |
| 5. |
The design of mechanical parts is particularly important in case of _____ speed machines. |
| A. | low |
| B. | medium |
| C. | high |
| D. | any of the above |
| Answer» C. high | |
| 6. |
In induction motors, the length of air gap in kept as small as mechanically possible is order to have |
| A. | low power factor |
| B. | high power factor |
| C. | high over load capacity |
| D. | any of the above |
| Answer» B. high power factor | |
| 7. |
In ______ machines, the size of the shaft is decided by the critical speed which depends on the deflection of the shaft. |
| A. | small |
| B. | medium |
| C. | large |
| D. | any of the above. |
| Answer» C. large | |
| 8. |
The length cf air gap to be provided in ______ is primarily determined by power factor consideration. |
| A. | d.c. series motor . |
| B. | d.c. shunt motor |
| C. | induction motor |
| D. | synchronous motor |
| Answer» C. induction motor | |
| 9. |
Electrical machines having a power output upto about 750 W may be called_______machines. |
| A. | small size |
| B. | medium size |
| C. | large size |
| D. | any of the above |
| Answer» A. small size | |
| 10. |
Electrical machines having power outputs ranging from a few kW upto approximately 250 kW may be classified as |
| A. | small size machines |
| B. | medium size machines |
| C. | large size machines |
| D. | any ofthe above |
| Answer» B. medium size machines | |
| 11. |
Commercial available medium size machines have a speed range of ______ . |
| A. | 200 to 400 r.p.m. |
| B. | 600 to 1000 r.p.m. |
| C. | 1000 to 1500 r.p.m. |
| D. | 2000 to 2500 r.p.m. |
| Answer» D. 2000 to 2500 r.p.m. | |
| 12. |
The action of electromagnetic machines can be related to which ofthe following basic principles ? |
| A. | Induction |
| B. | Interaction |
| C. | Alignment |
| D. | All of the above |
| Answer» D. All of the above | |
| 13. |
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» D. All ofthe above | |
| 14. |
is universally used for windings of electrical machines because it is easily workable without any possibility of fracture. |
| A. | Silver |
| B. | Steel |
| C. | Aluminium |
| D. | Copper |
| Answer» D. Copper | |
| 15. |
Aluminium when adopted as a conductor material in ______ transformers, decreases the overall cost of the transformer |
| A. | small size |
| B. | medium size |
| C. | large size |
| D. | any of the above size |
| Answer» A. small size | |
| 16. |
Which ofthe following materials is used in the manufacture of resistance grids to be used in the starters of large motors ? |
| A. | Copper |
| B. | Aluminium |
| C. | Steel |
| D. | Cast-iron |
| Answer» D. Cast-iron | |
| 17. |
Materials exhibiting zero value of resistivity are known as ______ . |
| A. | conductors |
| B. | semiconductors |
| C. | insulators |
| D. | superconductors |
| Answer» D. superconductors | |
| 18. |
________ has a lowrelative permeability and is used principally in field frames when cost is of primary importance and extra weight is not objectionable. |
| A. | Cast steel |
| B. | Aluminium |
| C. | Soft steel |
| D. | Cast iron |
| Answer» D. Cast iron | |
| 19. |
______is extensively used for those portions of magnetic circuit which carry steady flux and need superior mechanical properties ? |
| A. | Grey cast-iron |
| B. | Cast steel |
| C. | High carbon steel |
| D. | Stainless steel |
| Answer» B. Cast steel | |
| 20. |
Hot rolled sheets have ______ value of permeability |
| A. | zero |
| B. | low |
| C. | high |
| D. | none ofthe above |
| Answer» B. low | |
| 21. |
The heated parts of an electrical machine dissipate heat into their surroundings by which of the following modes of heat dissipation ? |
| A. | Conduction |
| B. | Convection |
| C. | Radiation |
| D. | All ofthe above |
| Answer» D. All ofthe above | |
| 22. |
The heat dissipated by from a surface depends upon its temperature and its characteristics like colour, roughness etc. |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | any ofthe above |
| Answer» C. radiation | |
| 23. |
The mcrease in heat dissipation by air blasts is due to increase in |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | any ofthe above |
| Answer» B. convection | |
| 24. |
On which of the following variables heat convected depends ? |
| A. | Power density |
| B. | Temperature difference between heated surface and coolant |
| C. | Thermal resistivity, density, specific heat |
| D. | All ofthe above |
| Answer» D. All ofthe above | |
| 25. |
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» D. All ofthe above | |
| 26. |
Multiple inlet system of air cooling of turbo-alternators can be used for machines of rating upto |
| A. | 10 MW |
| B. | 30 MW |
| C. | 60 MW |
| D. | 150 MW |
| Answer» C. 60 MW | |
| 27. |
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» D. All ofthe above | |
| 28. |
The density of hydrogen is _____ times the density of air. |
| A. | 0.07 |
| B. | 1.5 |
| C. | 2.5 |
| D. | 3.5 |
| Answer» A. 0.07 | |
| 29. |
Hydrogen has a heat transfer co-efficient _____ times that of air |
| A. | 1.5 |
| B. | 2.5 |
| C. | 3.5 |
| D. | 4.5 |
| Answer» A. 1.5 | |
| 30. |
The thermal conductivity of hydrogen is ______ times that of air |
| A. | 2 |
| B. | 3 |
| C. | 5 |
| D. | 7 |
| Answer» D. 7 | |
| 31. |
With conventional hydrogen cooling it is possible to increase the rating of a single unit to |
| A. | 50 MW |
| B. | 100 MW |
| C. | 200 MW |
| D. | none ofthe above |
| Answer» C. 200 MW | |
| 32. |
The noise produced by a ______ cooled machine is less as the rotor moves in a medium of smaller density. |
| A. | air |
| B. | hydrogen |
| C. | either (a) or (b) |
| D. | none of the above |
| Answer» B. hydrogen | |
| 33. |
cooling is the process of dissipating the armature and field winding losses to a cooling medium circulating within the winding insulation wall |
| A. | Direct |
| B. | Indirect |
| C. | Conventional |
| D. | Any ofthe above |
| Answer» A. Direct | |
| 34. |
Machines cooled by direct cooling method may be called |
| A. | "supercharged" |
| B. | "inner cooled" |
| C. | "conductor cooled" |
| D. | any of the above |
| Answer» D. any of the above | |
| 35. |
In direct cooled system using hydrogen both stator and rotor conductors are made |
| A. | solid |
| B. | hollow |
| C. | perforated |
| D. | any ofthe above |
| Answer» B. hollow | |
| 36. |
With direct water cooling it is possible to have ratings of about |
| A. | 200 MW |
| B. | 300 MW |
| C. | 400 MW |
| D. | 600 MW |
| Answer» D. 600 MW | |
| 37. |
The resistivity of water should not be less than |
| A. | 10 Q m |
| B. | 100 Q m |
| C. | 1000 Q m |
| D. | 2000 Q m |
| Answer» D. 2000 Q m | |
| 38. |
Direct water cooling of rotor winding presents |
| A. | no mechanical difficulties |
| B. | lesser mechanical difficulties |
| C. | greater mechanical difficulties |
| D. | none of the above |
| Answer» C. greater mechanical difficulties | |
| 39. |
The time taken by the machine to attain 0.632 of its final steady temperature rise is called |
| A. | heating time constant |
| B. | cooling time constant |
| C. | either (a) or (b) |
| D. | none of the above |
| Answer» A. heating time constant | |
| 40. |
In self cooled motors the cooling time constant is about ______ than the heating time constant 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» A. 2 to 3 times greater | |
| 41. |
By which of the following methods motor rating for variable load drives can be determined ? |
| A. | Method of average losses |
| B. | Equivalent current method |
| C. | Equivalent torque method |
| D. | All of the above. |
| Answer» D. All of the above. | |
| 42. |
Which of the following methods does not take into account the maximum temperature rise under variable load conditions ? |
| A. | Equivalent power method |
| B. | Equivalent current method |
| C. | Method of average losses |
| D. | Equivalent torque method |
| Answer» C. Method of average losses | |
| 43. |
Which of the following methods is most accurate ? |
| A. | Equivalent current method |
| B. | Equivalent power method |
| C. | Equivalent torque method |
| D. | Method of average losses |
| Answer» A. Equivalent current method | |
| 44. |
By which of the following methods the temperature rise of windings and other parts may be determined ? |
| A. | Thermometer method |
| B. | Resistance method |
| C. | Embedded temperature detector method |
| D. | Any of the above |
| Answer» D. Any of the above | |
| 45. |
The slot leakage can be calculated by making which of the following assumptions ? |
| A. | The current in the slot conductors is uniformly distributed over their cross-section |
| B. | The leakage path is straight across the slot and around the iron at the bottom |
| C. | The permanence of air paths is only considered. The reluctance of iron paths is assumed as zero |
| D. | All of the above |
| Answer» D. All of the above | |
| 46. |
The value of exciting or magnetizing current depends upon which of the following factors ? |
| 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» D. All of the above | |
| 47. |
Tractive magnets are operated from |
| A. | a.c. supply |
| B. | d.c. supply |
| C. | either a.c. or d.c. supply |
| D. | none of the above |
| Answer» C. either a.c. or d.c. supply | |
| 48. |
electromagnets generally function as holding magnets. |
| A. | Tractive |
| B. | Portative |
| C. | Either of the above |
| D. | None of the above |
| Answer» B. Portative | |
| 49. |
Which of the following is the commonly used type of electromagnets ? |
| A. | Flat-faced armature type |
| B. | Horse shoe type |
| C. | Flat-faced plunger type |
| D. | All of the above |
| Answer» D. All of the above | |
| 50. |
are used for construction of core of electromagnets. |
| A. | Soft magnetic materials |
| B. | Hard magnetic materials |
| C. | Either (a) or (b) |
| D. | None of the above |
| Answer» A. Soft magnetic materials | |
| 51. |
The design of electromagnets is based upon which of the following fundamental equations ? |
| A. | Force equation |
| B. | Magnetic circuit equation |
| C. | Heating equation |
| D. | All of the above |
| Answer» D. All of the above | |
| 52. |
When the two coil sides forming a coil are spaced exactly one pole pitch apart they are said to be of |
| A. | short pitch |
| B. | full pitch |
| C. | either of the above |
| D. | none of the above |
| Answer» B. full pitch | |
| 53. |
are always double layer type. |
| A. | Closed windings |
| B. | Open windings |
| C. | Either of the above |
| D. | None of the above |
| Answer» A. Closed windings | |
| 54. |
The distance between the starts of two consecutive coils measured in terms of coil sides is called |
| A. | front pitch |
| B. | winding pitch |
| C. | commutator pitch |
| D. | back pitch |
| Answer» B. winding pitch | |
| 55. |
The winding where dummy coils are used is sometimes called |
| A. | duplex winding |
| B. | triplex winding |
| C. | forced winding |
| D. | none of the above |
| Answer» C. forced winding | |
| 56. |
Dummy coil should not be used in |
| A. | small machines |
| B. | large machines |
| C. | either (a) or (b) |
| D. | none of the above |
| Answer» B. large machines | |
| 57. |
Power transformers have rating |
| A. | equal to 50 kVA |
| B. | equal to 100 kVA |
| C. | above 200 kVA |
| D. | none of the above |
| Answer» C. above 200 kVA | |
| 58. |
Power transformers should be designed to have maximum efficiency |
| A. | at one-fourth load |
| B. | at one-half load |
| C. | at or near full load |
| D. | any of the above |
| Answer» C. at or near full load | |
| 59. |
In transformers using hot rolled steel, the cross-section of the yoke is made about _____ greater than that of the core |
| A. | 5 percent |
| B. | 10 percent |
| C. | 15 percent |
| D. | 30 percent |
| Answer» C. 15 percent | |
| 60. |
Yokes with rectangular cross-section are used for |
| A. | small capacity transformers |
| B. | medium capacity transformers |
| C. | large capacity transformers |
| D. | any of the above |
| Answer» A. small capacity transformers | |
| 61. |
The cold rolled grain oriented steel has ______ permeability in the direction of the grain orientation. |
| A. | minimum |
| B. | maximum |
| C. | nil |
| D. | none of the above |
| Answer» B. maximum | |
| 62. |
Cylindrical windings using circular conductors, employed in transformers, are |
| A. | single layered |
| B. | double layered |
| C. | multi-layered |
| D. | none of the above |
| Answer» C. multi-layered | |
| 63. |
Helical windings are used in |
| A. | distribution transformers |
| B. | power transformers |
| C. | shell type transformers |
| D. | none of the above |
| Answer» B. power transformers | |
| 64. |
Multi-layer helical windings are commonly used in the transformers as high voltage windings |
| A. | upto 20 kV |
| B. | upto 50 kV |
| C. | upto 80 kV |
| D. | for 110 kV and above |
| Answer» D. for 110 kV and above | |
| 65. |
Disc windings are primarily used in |
| A. | short capacity transformers |
| B. | medium capacity transformers |
| C. | high capacity transformers |
| D. | any of the above |
| Answer» C. high capacity transformers | |
| 66. |
The heat dissipating capability of transformers of ratings higher than 30 kVA in increased by providing which of the following ? |
| A. | Corrugations |
| B. | Fins |
| C. | Tubes |
| D. | All of the above |
| Answer» D. All of the above | |
| 67. |
Transformers with a capacity of upto _____ have a cooling radiator system with natural cooling |
| A. | 2 MVA |
| B. | 5 MVA |
| C. | 7.5 MVA |
| D. | 10 MVA |
| Answer» D. 10 MVA | |
| 68. |
The forced oil and air circulation method is usual one for transformers of capacities |
| A. | upto 5 MVA |
| B. | upto 10 MVA |
| C. | upto 20 MVA |
| D. | 30 MVA upwards |
| Answer» D. 30 MVA upwards | |
| 69. |
The flash point of transformer oil should be higher than |
| A. | 40°C |
| B. | 60°C |
| C. | 80°C |
| D. | 104°C |
| Answer» D. 104°C | |
| 70. |
The voltage control in electric supply networks in required on account of which of the following reasons ? |
| A. | Adjustment of voltage at consumers premises within statutory limits |
| B. | Control of active and reactive power |
| C. | Adjustment of short period daily and seasonal voltage variations in accordance with variations of load |
| D. | All of the above |
| Answer» D. All of the above | |
| 71. |
D.C. windings are |
| A. | sometimes 2-layer type |
| B. | never 2-layer type |
| C. | always 2-layer type |
| D. | none of the above |
| Answer» C. always 2-layer type | |
| 72. |
The usual values of maximum flux densities for distribution transformers using hot rolled 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» C. 1.1 to 1.35 Wb/m2 | |
| 73. |
For 275 kV transformers, using cold rolled grain oriented steel, which of the following values 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» D. 1.6 Wb/m2 | |
| 74. |
For large power transformers, self oil cooled type or air blast type which of the following 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» C. 2.2 to 3.2 A/mm2 | |
| 75. |
A current density of _____ is ilsed for large power transformers with forced circulation of 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» D. 5.4 to 6.2 A/mm2 | |
| 76. |
The high voltage winding is usually which of the following type ? |
| A. | Cylindrical winding with circular conductors |
| B. | Cross-over winding with either circular or small rectangular conductors |
| C. | Continuous disc type winding with rectangular conductors |
| D. | All of the above types |
| Answer» D. All of the above types | |
| 77. |
Which of the following is the basic consideration in the design of insulation ? |
| A. | Electrical considerations |
| B. | Mechanical considerations |
| C. | Thermal considerations |
| D. | All of the above |
| Answer» D. All of the above | |
| 78. |
A practical formula for determining the thickness of insulation between low voltage and 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» D. 5 + 0.9 kV mm | |
| 79. |
The insulation between windings and grounded core and the insulation between the windings of the same phase is called |
| A. | minor insulation |
| B. | major insulation |
| C. | either of the above |
| D. | none of the above |
| Answer» B. major insulation | |
| 80. |
The cylindrical windings using circular conductors are used for current rating of |
| A. | upto 20 A |
| B. | upto 40 A |
| C. | upto 60 A |
| D. | upto 80 A |
| Answer» D. upto 80 A | |
| 81. |
The surge phenomenon is particularly important in case of |
| A. | low voltage transformers |
| B. | medium voltage transformers |
| C. | high voltage transformers |
| D. | any of the above |
| Answer» C. high voltage transformers | |
| 82. |
Which of the following in an application of D.C. motors? |
| A. | Traction |
| B. | Drives for process industry |
| C. | Battery driven vehicles |
| D. | All of the above |
| Answer» D. All of the above | |
| 83. |
D.C. servomotors are used in |
| A. | purely D.C. control systems |
| B. | purely AC. control systems |
| C. | both D.C. and AC. control systems |
| D. | none of the above |
| Answer» A. purely D.C. control systems | |
| 84. |
The stator of a D.C. machine comprises of |
| A. | main poles |
| B. | interpoles |
| C. | frame |
| D. | all of the above |
| Answer» D. all of the above | |
| 85. |
The laminations of the armature of a D.C. machine are usually _____ thick. |
| A. | 0.1 to 0.2 mm |
| B. | 0.2 to 0.3 mm |
| C. | 0.3 to 0.4 mm |
| D. | 0.4 to 0.5 mm |
| Answer» D. 0.4 to 0.5 mm | |
| 86. |
is usually used for brush rockers |
| A. | Mild steel |
| B. | Copper |
| C. | Aluminium |
| D. | Cast-iron |
| Answer» D. Cast-iron | |
| 87. |
______ brushes are fragile and cause excessive wear of commutator, |
| A. | Natural graphite |
| B. | Hard carbon |
| C. | Electro graphitic |
| D. | Metal graphite |
| Answer» A. Natural graphite | |
| 88. |
Which of the following brushes can be used for high values of current density ? |
| A. | Metal graphite brushes |
| B. | Hard carbon brushes |
| C. | Electro-graphitic brushes |
| D. | Natural graphite brushes |
| Answer» A. Metal graphite brushes | |
| 89. |
________ is the common method of applying brushes to the commntator. |
| A. | Radial |
| B. | Trailing |
| C. | Reaction |
| D. | All of the above |
| Answer» D. All of the above | |
| 90. |
Which of the following problem arises in D.C. motors which are fed from thyristor bridge circuits ? |
| A. | Increased I R losses |
| B. | Increased core losses |
| C. | Poor commutation |
| D. | All of the above |
| Answer» D. All of the above | |
| 91. |
The weight of copper of both armature and field windings decreases with _____ in number of poles. |
| A. | increase |
| B. | decrease |
| C. | either of the above |
| D. | none of the above |
| Answer» A. increase | |
| 92. |
In a D.C. machine the number of brush arms is _____ the number of poles. |
| A. | less than |
| B. | equal to |
| C. | greater than |
| D. | none of the above |
| Answer» B. equal to | |
| 93. |
In a D.C. machine the current per brush arm should not be more than |
| A. | 100 A |
| B. | 200 A |
| C. | 300 A |
| D. | 400 A |
| Answer» D. 400 A | |
| 94. |
In a D.C. machine, the value of peripheral speed should not, normally, exceed |
| A. | 10 m/s |
| B. | 20 m/s |
| C. | 30 m/s |
| D. | 40 m/s |
| Answer» C. 30 m/s | |
| 95. |
In D.C. machines the width of the duct is usually |
| A. | 4 mm |
| B. | 6 mm |
| C. | 8 mm |
| D. | 10 mm |
| Answer» D. 10 mm | |
| 96. |
D.C. machines designed with a large value of air gap length have |
| A. | worst, ventilation |
| B. | poor ventilation |
| C. | better ventilation |
| D. | none of the above |
| Answer» C. better ventilation | |
| 97. |
In D.C. machines, ir order to prevent excessive distortion of field form by the armature reaction, 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» C. large in comparison with the arma-ture mmf | |
| 98. |
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» A. increase | |
| 99. |
The operation of a D.C. machine with large air gap lengths is comparatively |
| A. | quiet |
| B. | noisy |
| C. | either of the above |
| D. | none of the above |
| Answer» A. quiet | |
| 100. |
Which of the following methods may be adopted to reduce the effects of armature reaction ? |
| 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» D. All of the above | |
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