1. Which of the following is the major consideration to evolve a good design ?
Correct : D. All of the above
2. impose limitation on design.
Correct : D. All above
3. The efficiency of a machine should be as ______ as possible to reduce the operating
cost.
Correct : A. high
4. If an insulating material is operated beyond the maximum allowable temperature, its
life is
Correct : B. drastically reduced
5. The design of mechanical parts is particularly important in case of _____ speed
machines.
Correct : C. high
6. In induction motors, the length of air gap in kept as small as mechanically possible is
order to have
Correct : 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.
Correct : C. large
8. The length cf air gap to be provided in ______ is primarily determined by power factor
consideration.
Correct : C. induction motor
9. Electrical machines having a power output upto about 750 W may be
called_______machines.
Correct : A. small size
10. Electrical machines having power outputs ranging from a few kW upto approximately
250 kW may be classified as
Correct : B. medium size machines
11. Commercial available medium size machines have a speed range of ______ .
Correct : D. 2000 to 2500 r.p.m.
12. The action of electromagnetic machines can be related to which ofthe following basic
principles ?
Correct : D. All of the above
13. The change in flux linkages can be caused in which ofthe following ways ?
Correct : D. All ofthe above
14. is universally used for windings of electrical machines because it is easily workable
without any possibility of fracture.
Correct : D. Copper
15. Aluminium when adopted as a conductor material in ______ transformers, decreases the
overall cost of the transformer
Correct : 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 ?
Correct : D. Cast-iron
17. Materials exhibiting zero value of resistivity are known as ______ .
Correct : 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.
Correct : D. Cast iron
19. ______is extensively used for those portions of magnetic circuit which carry steady flux
and need superior mechanical properties ?
Correct : B. Cast steel
20. Hot rolled sheets have ______ value of permeability
Correct : B. low
21. The heated parts of an electrical machine dissipate heat into their surroundings by
which of the following modes of heat dissipation ?
Correct : D. All ofthe above
22. The heat dissipated by from a surface depends upon its temperature and its
characteristics like colour, roughness etc.
Correct : C. radiation
23. The mcrease in heat dissipation by air blasts is due to increase in
Correct : B. convection
24. On which of the following variables heat convected depends ?
Correct : D. All ofthe above
25. Which ofthe following methods is used for air cooling of turbo-alternators ?
Correct : D. All ofthe above
26. Multiple inlet system of air cooling of turbo-alternators can be used for machines of
rating upto
Correct : C. 60 MW
27. Which ofthe following is an advantage of hydrogen cooling ?
Correct : D. All ofthe above
28. The density of hydrogen is _____ times the density of air.
Correct : A. 0.07
29. Hydrogen has a heat transfer co-efficient _____ times that of air
Correct : A. 1.5
30. The thermal conductivity of hydrogen is ______ times that of air
Correct : D. 7
31. With conventional hydrogen cooling it is possible to increase the rating of a single unit
to
Correct : C. 200 MW
32. The noise produced by a ______ cooled machine is less as the rotor moves in a medium
of smaller density.
Correct : 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
Correct : A. Direct
34. Machines cooled by direct cooling method may be called
Correct : D. any of the above
35. In direct cooled system using hydrogen both stator and rotor conductors are made
Correct : B. hollow
36. With direct water cooling it is possible to have ratings of about
Correct : D. 600 MW
37. The resistivity of water should not be less than
Correct : D. 2000 Q m
38. Direct water cooling of rotor winding presents
Correct : C. greater mechanical difficulties
39. The time taken by the machine to attain 0.632 of its final steady temperature rise is
called
Correct : 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.
Correct : A. 2 to 3 times greater
41. By which of the following methods motor rating for variable load drives can be
determined ?
Correct : D. All of the above.
42. Which of the following methods does not take into account the maximum temperature
rise under variable load conditions ?
Correct : C. Method of average losses
43. Which of the following methods is most accurate ?
Correct : A. Equivalent current method
44. By which of the following methods the temperature rise of windings and other parts
may be determined ?
Correct : D. Any of the above
45. The slot leakage can be calculated by making which of the following assumptions ?
Correct : D. All of the above
46. The value of exciting or magnetizing current depends upon which of the following
factors ?
Correct : D. All of the above
47. Tractive magnets are operated from
Correct : C. either a.c. or d.c. supply
48. electromagnets generally function as holding magnets.
Correct : B. Portative
49. Which of the following is the commonly used type of electromagnets ?
Correct : D. All of the above
50. are used for construction of core of electromagnets.
Correct : A. Soft magnetic materials
51. The design of electromagnets is based upon which of the following fundamental
equations ?
Correct : 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
Correct : B. full pitch
53. are always double layer type.
Correct : A. Closed windings
54. The distance between the starts of two consecutive coils measured in terms of coil
sides is called
Correct : B. winding pitch
55. The winding where dummy coils are used is sometimes called
Correct : C. forced winding
56. Dummy coil should not be used in
Correct : B. large machines
57. Power transformers have rating
Correct : C. above 200 kVA
58. Power transformers should be designed to have maximum efficiency
Correct : 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
Correct : C. 15 percent
60. Yokes with rectangular cross-section are used for
Correct : A. small capacity transformers
61. The cold rolled grain oriented steel has ______ permeability in the direction of the
grain orientation.
Correct : B. maximum
62. Cylindrical windings using circular conductors, employed in transformers, are
Correct : C. multi-layered
63. Helical windings are used in
Correct : B. power transformers
64. Multi-layer helical windings are commonly used in the transformers as high voltage
windings
Correct : D. for 110 kV and above
65. Disc windings are primarily used in
Correct : 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 ?
Correct : D. All of the above
67. Transformers with a capacity of upto _____ have a cooling radiator system with natural
cooling
Correct : D. 10 MVA
68. The forced oil and air circulation method is usual one for transformers of capacities
Correct : D. 30 MVA upwards
69. The flash point of transformer oil should be higher than
Correct : D. 104°C
70. The voltage control in electric supply networks in required on account of which of the following reasons ?
Correct : D. All of the above
71. D.C. windings are
Correct : C. always 2-layer type
72. The usual values of maximum flux densities for distribution transformers using hot
rolled silicon steel are
Correct : 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?
Correct : 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 ?
Correct : 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
Correct : D. 5.4 to 6.2 A/mm2
76. The high voltage winding is usually which of the following type ?
Correct : D. All of the above types
77. Which of the following is the basic consideration in the design of insulation ?
Correct : D. All of the above
78. A practical formula for determining the thickness of insulation between low voltage
and high voltage windings is
Correct : 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
Correct : B. major insulation
80. The cylindrical windings using circular conductors are used for current rating of
Correct : D. upto 80 A
81. The surge phenomenon is particularly important in case of
Correct : C. high voltage transformers
82. Which of the following in an application of D.C. motors?
Correct : D. All of the above
83. D.C. servomotors are used in
Correct : A. purely D.C. control systems
84. The stator of a D.C. machine comprises of
Correct : D. all of the above
85. The laminations of the armature of a D.C. machine are usually _____ thick.
Correct : D. 0.4 to 0.5 mm
86. is usually used for brush rockers
Correct : D. Cast-iron
87. ______ brushes are fragile and cause excessive wear of commutator,
Correct : A. Natural graphite
88. Which of the following brushes can be used for high values of current density ?
Correct : A. Metal graphite brushes
89. ________ is the common method of applying brushes to the commntator.
Correct : D. All of the above
90. Which of the following problem arises in D.C. motors which are fed from thyristor
bridge circuits ?
Correct : D. All of the above
91. The weight of copper of both armature and field windings decreases with _____ in
number of poles.
Correct : A. increase
92. In a D.C. machine the number of brush arms is _____ the number of poles.
Correct : B. equal to
93. In a D.C. machine the current per brush arm should not be more than
Correct : D. 400 A
94. In a D.C. machine, the value of peripheral speed should not, normally, exceed
Correct : C. 30 m/s
95. In D.C. machines the width of the duct is usually
Correct : D. 10 mm
96. D.C. machines designed with a large value of air gap length have
Correct : 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
Correct : 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.
Correct : A. increase
99. The operation of a D.C. machine with large air gap lengths is comparatively
Correct : A. quiet
100. Which of the following methods may be adopted to reduce the effects of armature
reaction ?