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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