electrical machine design Mcqs
51. The heat dissipated by from a surface depends upon its temperature and its characteristics like colour, roughness etc?
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A. convection

B. conduction

C. radiation

D. any of the above

52. In D.C. machines the number of slots per pole usually lies___________?
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A. between 2 to 4

B. between 9 to 16

C. between 6 to 8

D. between 20 to 30

53. With conventional hydrogen cooling it is possible to increase the rating of a single unit to___________?
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A. 200 MW

B. 50 MW

C. 100 MW

D. none of the above

54. Which of the following methods does not take into account the maximum temperature rise under variable load conditions ?
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A. Equivalent power method

B. Method of average losses

C. Equivalent torque method

D. Equivalent current method

55. Helical windings are used in________________?
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A. shell type transformers

B. none of the above

C. power transformers

D. distribution transformers

56. The high voltage winding is usually which of the following type ?
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A. Continuous disc type winding with rectangular conductors

B. Cross-over winding with either circular or small rectangular conductors

C. Cylindrical winding with circular conductors

D. All of the above types
57. The weight of copper of both armature and field windings decreases with __________ in number of poles?
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A. none of the above

B. decrease

C. either of the above

D. increase
58. The winding where dummy coils are used is sometimes called______________?
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A. triplex winding

B. none of the above

C. duplex winding

D. forced winding
59. The time taken by the machine to attain 0.632 of its final steady temperature rise is called_____________?
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A. cooling time constant

B. heating time constant

C. none of the above

D. either A. or B.

60. The cold rolled grain oriented steel has _________ permeability in the direction of the grain orientation?
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A. maximum

B. minimum

C. none of the above

D. nil

61. Which of the following is the commonly used type of electromagnets ?
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A. All of the above

B. Horse shoe type

C. Flat-faced armature type

D. Flat-faced plunger type

62. The operation of a D.C. machine with large air gap lengths is comparatively_____________?
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A. quiet

B. either of the above

C. noisy

D. none of the above

63. The stator of a D.C. machine comprises of_____________?
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A. interpoles

B. frame

C. main poles

D. all of the above
64. is usually used for brush rockers____________?
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A. Aluminium

B. Cast-iron

C. Mild steel

D. Copper

65. By which of the following methods motor rating for variable load drives can be determined ?
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A. Equivalent power method

B. Equivalent torque method

C. Equivalent current method

D. Method of average losses

E. All of the above
66. In D.C. machines, the ________ in field mmf results in increase in size and cost of machines?
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A. either of the above

B. decrease

C. increase

D. none of the above

67. Which of the following is the basic consideration in the design of insulation ?
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A. Electrical considerations

B. Thermal considerations

C. All of the above

D. Mechanical considerations

68. Cylindrical windings using circular conductors, employed in transformers, are_____________?
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A. double layered

B. single layered

C. none of the above

D. multi-layered
69. Which of the following brushes can be used for high values of current density ?
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A. Electro-graphitic brushes

B. Natural graphite brushes

C. Hard carbon brushes

D. Metal graphite brushes
70. The resistivity of water should not be less than_____________?
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A. 2000 Q m

B. 10 Q m

C. 1000 Q m

D. 100 Q m

71. Which of the following is the major consideration to evolve a good design?
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A. Cost

B. Durability

C. Compliance with performance criteria as laid down in specifications

D. All of the above
72. In transformers using hot rolled steel, the cross-section of the yoke is made about __________ greater than that of the core?
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A. 5 percent

B. 30 percent

C. 15 percent

D. 10 percent

E. none of the above

73. Power transformers have rating_______________?
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A. none of the above

B. equal to 100 kVA

C. equal to 50 kVA

D. above 200 kVA
74. In induction motors, the length of air gap in kept as small as mechanically possible is order to have____________?
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A. any of the above

B. high power factor

C. low power factor

D. high over load capacity

75. ____________are used for construction of core of electromagnets?
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A. None of the above

B. Soft magnetic materials

C. Either A. or B.

D. Hard magnetic materials

76. The density of hydrogen is __________ times the density of air?
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A. 2.5

B. 0.07

C. 3.5

D. 1.5

77. Which of the following methods may be adopted to reduce the effects of armature reaction ?
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A. Increasing reluctance of pole tips

B. Increase in length of air gap at pole tips

C. All of the above

D. Interpoles

E. Compensating windings

78. Power transformers should be designed to have maximum efficiency________________?
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A. any of the above

B. at or near full load

C. at one-half load

D. at one-fourth load

79. The cylindrical windings using circular conductors are used for current rating of____________?
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A. upto 20 A

B. upto 80 A

C. upto 40 A

D. upto 60 A

80. The forced oil and air circulation method is usual one for transformers of capacities____________?
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A. upto 5 MVA

B. upto 10 MVA

C. 30 MVA upwards

D. upto 20 MVA

81. The change in flux linkages can be caused in which of the following ways ?
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A. The flux is constant with respect to time and is stationary and the coil moves through it

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 occur together, i.e., the coil moves through a time varying field

D. All of the above
82. Hydrogen has a heat transfer co-efficient __________ times that of air?
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A. 3.5

B. 4.5

C. 2.5

D. 1.5
83. ____________ is the common method of applying brushes to the commntator?
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A. Reaction

B. Trailing

C. Radial

D. All of the above
84. In direct cooled system using hydrogen both stator and rotor conductors are made____________?
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A. solid

B. hollow

C. perforated

D. any ofthe above

85. Multi-layer helical windings are commonly used in the transformers as high voltage windings_______________?
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A. upto 80 kV

B. upto 20 kV

C. upto 50 kV

D. for 110 kV and above
86. The mcrease in heat dissipation by air blasts is due to increase in______________?
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A. any ofthe above

B. convection

C. conduction

D. radiation

87. The heated parts of an electrical machine dissipate heat into their surroundings by which of the following modes of heat dissipation ?
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A. Conduction

B. All of the above

C. Radiation

D. Convection

88. electromagnets generally function as holding magnets ?
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A. None of the above

B. Portative

C. Either of the above

D. Tractive

89. The design of mechanical parts is particularly important in case of __________ speed machines?
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A. any of the above

B. high

C. medium

D. low

90. Multiple inlet system of air cooling of turbo-alternators can be used for machines of rating upto_______________?
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A. 60 MW

B. 10 MW

C. 150 MW

D. 30 MW

91. cooling is the process of dissipating the armature and field winding losses to a cooling medium circulating within the winding insulation wall______________?
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A. Indirect

B. Any of the above

C. Direct

D. Conventional

92. ___________ brushes are fragile and cause excessive wear of commutator?
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A. Electro graphitic

B. Hard carbon

C. Natural graphite

D. Metal graphite

93. D.C. servomotors are used in______________?
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A. purely D.C. control systems

B. purely AC. control systems

C. both D.C. and AC. control systems

D. none of the above

94. In self cooled motors the cooling time constant is about ___________ than the heating time constant because cooling conditions are worse at standstill?
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A. 4 to 5 times greater

B. none of the above

C. 3 to 4 times greater

D. 2 to 3 times greater
95. The efficiency of a machine should be as ____________ as possible to reduce the operating cost?
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A. high

B. none of the above

C. either of the above

D. low

96. Aluminium when adopted as a conductor material in __________ transformers, decreases the overall cost of the transformer?
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A. large size

B. any of the above size

C. medium size

D. small size
97. For large power transformers, self oil cooled type or air blast type which of the following values of current density may be used?
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A. 2.2 to 3.2 A/mm2

B. 1.5 to 2.0 A/mm2

C. 3.2 to 4.2 A/mm2

D. 1.0 to 1.2 A/mm2

98. Dummy coil should not be used in_________________?
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A. small machines

B. none of the above

C. large machines

D. either A. or B.

99. The usual values of maximum flux densities for distribution transformers using hot rolled silicon steel are______________?
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A. 0.8 to 1.0 Wb/m2

B. 0.5 to 0.8 Wb/m2

C. 1.4 to 1.8 Wb/m2

D. 1.1 to 1.35 Wb/m2
100. Which of the following is the major consideration to evolve a good design ?
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A. Durability

B. All of the above

C. Compliance with performance criteria as laid down in specifications

D. Cost