Quiz  /  Electrical Machine Design Electrical Engineering MCQ Interview Questions and Answers PDF

  • 1. 
    Which of the following is the major consideration to evolve a good design ?

  • Cost
  • Durability
  • Compliance with performance criteria as laid down in specifications
  • All of the above

  • 2. 
    mpose limitation on design.

  • Saturation
  • Temperature rise
  • Efficiency
  • Power factor
  • All above

  • 3. 
    The efficiency of a machine should be as ______ as possible to reduce the operating cost.

  • high
  • low
  • either of the above
  • none of the above

  • 4. 
    If an insulating material is operated beyond the maximum allowable temperature, its life is

  • drastically increased
  • drastically reduced
  • unaffected
  • none of the above

  • 5. 
    The design of mechanical parts is particularly important in case of _____ speed machines.

  • low
  • medium
  • high
  • any of the above

  • 6. 
    In induction motors, the length of air gap in kept as small as mechanically possible is order to have

  • low power factor
  • high power factor
  • high over load capacity
  • any of the above

  • 7. 
    In ______ machines, the size of the shaft is decided by the critical speed which depends on the deflection of the shaft.

  • small
  • medium
  • large
  • any of the above.

  • 8. 
    The length cf air gap to be provided in ______ is primarily determined by power factor consideration.

  • d.c. series motor .
  • d.c. shunt motor
  • induction motor
  • synchronous motor

  • 9. 
    Electrical machines having a power output up to about 750 W may be called_______machines.

  • small size
  • medium size
  • large size
  • any of the above

  • 10. 
    Electrical machines having power outputs ranging from a few kW up to approximately 250 kW may be classified as

  • small size machines
  • medium size machines
  • large size machines
  • any of the above

  • 11. 
    Commercial available medium size machines have a speed range of ______ .

  • 200 to 400 r.p.m.
  • 600 to 1000 r.p.m.
  • 1000 to 1500 r.p.m.
  • 2000 to 2500 r.p.m.

  • 12. 
    The action of electromagnetic machines can be related to which of the following basic principles ?

  • Induction
  • Interaction
  • Alignment
  • All of the above

  • 13. 
    The change in flux linkages can be caused in which of the following ways ?

  • The flux is constant with respect to time and is stationary and the coil moves through it
  • The coil is stationary with respect to flux and the flux varies in magnitude with respect to time
  • Both the changes mentioned above occur together, i.e., the coil moves through a time varying field
  • All of the above

  • 14. 
    is universally used for windings of electrical machines because it is easily workable without any possibility of fracture.

  • Silver
  • Steel
  • Aluminium
  • Copper

  • 15. 
    Aluminium when adopted as a conductor material in ______ transformers, decreases the overall cost of the transformer

  • small size
  • medium size
  • large size
  • any of the above size

  • 16. 
    Which of the following materials is used in the manufacture of resistance grids to be used in the starters of large motors ?

  • Copper
  • Aluminium
  • Steel
  • Cast-iron

  • 17. 
    Materials exhibiting zero value of resistivity are known as ______ .

  • conductors
  • semiconductors
  • insulators
  • 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.

  • Cast steel
  • Aluminium
  • Soft steel
  • Cast iron

  • 19. 
    ______is extensively used for those portions of magnetic circuit which carry steady flux and need superior mechanical properties ?

  • Grey cast-iron
  • Cast steel
  • High carbon steel
  • Stainless steel

  • 20. 
    Hot rolled sheets have ______ value of permeability

  • zero
  • low
  • high
  • none of the above

  • 21. 
    The heated parts of an electrical machine dissipate heat into their surroundings by which of the following  odes of heat dissipation ?

  • Conduction
  • Convection
  • Radiation
  • All of the above

  • 22. 
    The heat dissipated by from a surface depends upon its temperature and its characteristics like colour, roughness etc.

  • conduction
  • convection
  • radiation
  • any of the above

  • 23. 
    The mcrease in heat dissipation by air blasts is due to increase in

  • conduction
  • convection
  • radiation
  • any ofthe above

  • 24. 
    On which of the following variables heat convected depends ?

  • Power density
  • Temperature difference between heated surface and coolant
  • Thermal resistivity, density, specific heat
  • Gravitational constant
  • All of the above

  • 25. 
    Which of the following methods is used for air cooling of turbo-alternators ?

  • One sided axial ventilation
  • Two sided axial ventilation
  • Multiple inlet system
  • All of the above

  • 26. 
    Multiple inlet system of air cooling of turbo-alternators can be used for machines of rating upto

  • 10 MW
  • 30 MW
  • 60 MW
  • 150 MW

  • 27. 
    Which of the following is an advantage of hydrogen cooling ?

  • Increase in efficiency
  • Increase in ratings
  • Increase in life
  • Smaller size of coolers
  • All of the above

  • 28. 
    The density of hydrogen is _____ times the density of air.

  • 0.07
  • 1.5
  • 2.5
  • 3.5

  • 29. 
    Hydrogen has a heat transfer co-efficient _____ times that of air

  • 1.5
  • 2.5
  • 3.5
  • 4.5

  • 30. 
    The thermal conductivity of hydrogen is ______ times that of air

  • 2
  • 3
  • 5
  • 7

  • 31. 
    With conventional hydrogen cooling it is possible to increase the rating of a single unit to

  • 50 MW
  • 100 MW
  • 200 MW
  • none of the above

  • 32. 
    The noise produced by a ______ cooled machine is less as the rotor moves in a medium of smaller density.

  • air
  • hydrogen
  • either (a) or (b)
  • none of the above

  • 33. 
    cooling is the process of dissipating the armature and field winding losses to a cooling medium circulating within the winding insulation wall

  • Direct
  • Indirect
  • Conventional
  • Any of the above

  • 34. 
    Machines cooled by direct cooling method may be called

  • “supercharged”
  • “inner cooled”
  • “conductor cooled”
  • any of the above

  • 35. 
    In direct cooled system using hydrogen both stator and rotor conductors are made

  • solid
  • hollow
  • perforated
  • any ofthe above

  • 36. 
    With direct water cooling it is possible to have ratings of about

  • 200 MW
  • 300 MW
  • 400 MW
  • 600 MW

  • 37. 
    The resistivity of water should not be less than

  • 10 Q m
  • 100 Q m
  • 1000 Q m
  • 2000 Q m

  • 38. 
    Direct water cooling of rotor winding presents

  • no mechanical difficulties
  • lesser mechanical difficulties
  • greater mechanical difficulties
  • none of the above

  • 39. 
    The time taken by the machine to attain 0.632 of its final steady temperature rise is called

  • heating time constant
  • cooling time constant
  • either (a) or (b)
  • none of the above

  • 40. 
    In self cooled motors the cooling time constant is about ______ than the heating time constant because cooling conditions are worse at standstill.

  • 2 to 3 times greater
  • 3 to 4 times greater
  • 4 to 5 times greater
  • none of the above

  • 41. 
    By which of the following methods motor rating for variable load drives can be determined ?

  • Method of average losses
  • Equivalent current method
  • Equivalent torque method
  • Equivalent power method
  • All of the above.

  • 42. 
    Which of the following methods does not take into account the maximum temperature rise under variable load  onditions ?

  • Equivalent power method
  • Equivalent current method
  • Method of average losses
  • Equivalent torque method

  • 43. 
    Which of the following methods is most accurate ?

  • Equivalent current method
  • Equivalent power method
  • Equivalent torque method
  • Method of average losses

  • 44. 
    The slot leakage can be calculated by making which of the following assumptions ?

  • The current in the slot conductors is uniformly distributed over their cross-section
  • The leakage path is straight across the slot and around the iron at the bottom
  • The permanence of air paths is only considered. The reluctance of iron paths is assumed as zero
  • All of the above

  • 45. 
    The value of exciting or magnetizing current depends upon which of the following factors ?

  • Total m.m.f. required
  • The number of turns in the exciting winding
  • The way in which the winding is distributed
  • All of the above

  • 46. 
    Tractive magnets are operated from

  • a.c. supply
  • d.c. supply
  • either a.c. or d.c. supply
  • none of the above

  • 47. 
    electromagnets generally function as holding magnets.

  • Tractive
  • Portative
  • Either of the above
  • None of the above

  • 48. 
    Which of the following is the commonly used type of electromagnets ?

  • Flat-faced armature type
  • Horse shoe type
  • Flat-faced plunger type
  • All of the above

  • 49. 
    are used for construction of core of electromagnets.

  • Soft magnetic materials
  • Hard magnetic materials
  • Either (a) or (b)
  • None of the above

  • 50. 
    The design of electromagnets is based upon which of the following fundamental equations ?

  • Force equation
  • Magnetic circuit equation
  • Heating equation
  • Voltage equation
  • All of the above

  • 51. 
    When the two coil sides forming a coil are spaced exactly one pole pitch apart they are said to be of

  • short pitch
  • full pitch
  • either of the above
  • none of the above

  • 52. 
    are always double layer type.

  • Closed windings
  • Open windings
  • Either of the above
  • None of the above

  • 53. 
    The distance between the starts of two consecutive coils measured in terms of coil sides is called

  • front pitch
  • winding pitch
  • commutator pitch
  • back pitch

  • 54. 
    The winding where dummy coils are used is sometimes called

  • duplex winding
  • triplex winding
  • forced winding
  • none of the above

  • 55. 
    Dummy coil should not be used in

  • small machines
  • large machines
  • either (a) or (b)
  • none of the above

  • 56. 
    Power transformers should be designed to have maximum efficiency

  • at one-fourth load
  • at one-half load
  • at or near full load
  • any of the above

  • 57. 
    In transformers using hot rolled steel, the cross-section of the yoke is made about _____ greater than that of the core

  • 5 percent
  • 10 percent
  • 15 percent
  • 30 percent
  • none of the above

  • 58. 
    Yokes with rectangular cross-section are used for

  • small capacity transformers
  • medium capacity transformers
  • large capacity transformers
  • any of the above

  • 59. 
    The cold rolled grain oriented steel has ______ permeability in the direction of the grain orientation.

  • minimum
  • maximum
  • nil
  • none of the above

  • 60. 
    Cylindrical windings using circular conductors, employed in transformers, are

  • single layered
  • double layered
  • multi-layered
  • none of the above

  • 61. 
    Helical windings are used in

  • distribution transformers
  • power transformers
  • shell type transformers
  • none of the above

  • 62. 
    Multi-layer helical windings are commonly used in the transformers as high voltage windings

  • upto 20 kV
  • upto 50 kV
  • upto 80 kV
  • for 110 kV and above

  • 63. 
    Disc windings are primarily used in

  • short capacity transformers
  • medium capacity transformers
  • high capacity transformers
  • any of the above

  • 64. 
    The heat dissipating capability of transformers of ratings higher than 30 kVA in increased by providing which of the following ?

  • Corrugations
  • Fins
  • Tubes
  • Radiator tanks
  • All of the above

  • 65. 
    Transformers with a capacity of up to _____ have a cooling radiator system with natural cooling

  • 2 MVA
  • 5 MVA
  • 7.5 MVA
  • 10 MVA

  • 66. 
    The forced oil and air circulation method is usual one for transformers of capacities

  • upto 5 MVA
  • upto 10 MVA
  • upto 20 MVA
  • 30 MVA upwards

  • 67. 
    The flash point of transformer oil should be higher than

  • 40°C
  • 60°C
  • 80°C
  • 104°C

  • 68. 
    The voltage control in electric supply networks in required on account of which of the following reasons ?

  • Adjustment of voltage at consumers premises within statutory limits
  • Control of active and reactive power
  • Adjustment of short period daily and seasonal voltage variations in accordance with variations of load
  • All of the above

  • 69. 
    D.C. windings are

  • sometimes 2-layer type
  • never 2-layer type
  • always 2-layer type
  • none of the above

  • 70. 
    The usual values of maximum flux densities for distribution transformers using hot rolled silicon steel are

  • 0.5 to 0.8 Wb/m2
  • 0.8 to 1.0 Wb/m2
  • 1.1 to 1.35 Wb/m2
  • 1.4 to 1.8 Wb/m2

  • 71. 
    For 275 kV transformers, using cold rolled grain oriented steel, which of the following values of flux density may be used?

  • 1.0 Wb/m2
  • 1.1 Wb/m2
  • 1.3 Wb/m2
  • 1.6 Wb/m2
  • None of the above

  • 72. 
    For large power transformers, self oil cooled type or air blast type which of the following values of current density may be used ?

  • 1.0 to 1.2 A/mm2
  • 1.5 to 2.0 A/mm2
  • 2.2 to 3.2 A/mm2
  • 3.2 to 4.2 A/mm2

  • 73. 
    A current density of _____ is ilsed for large power transformers with forced circulation of oil or with water cooling coils

  • 1.5 to 2.5 A/mm2
  • 3.5 to 4.5 A/mm2
  • 4.0 to 5.0 A/mm2
  • 5.4 to 6.2 A/mm2

  • 74. 
    The high voltage winding is usually which of the following type ?

  • Cylindrical winding with circular conductors
  • Cross-over winding with either circular or small rectangular conductors
  • Continuous disc type winding with rectangular conductors
  • All of the above types

  • 75. 
    Which of the following is the basic consideration in the design of insulation ?

  • Electrical considerations
  • Mechanical considerations
  • Thermal considerations
  • All of the above

  • 76. 
    The insulation between windings and grounded core and the insulation between the windings of the same phase is called

  • minor insulation
  • major insulation
  • either of the above
  • none of the above

  • 77. 
    The cylindrical windings using circular conductors are used for current rating of

  • upto 20 A
  • upto 40 A
  • upto 60 A
  • upto 80 A

  • 78. 
    The surge phenomenon is particularly important in case of

  • low voltage transformers
  • medium voltage transformers
  • high voltage transformers
  • any of the above

  • 79. 
    Which of the following in an application of D.C. motors?

  • Traction
  • Drives for process industry
  • Battery driven vehicles
  • Automatic control
  • All of the above

  • 80. 
    The laminations of the armature of a D.C. machine are usually _____ thick.

  • 0.1 to 0.2 mm
  • 0.2 to 0.3 mm
  • 0.3 to 0.4 mm
  • 0.4 to 0.5 mm

  • 81. 
    is usually used for brush rockers

  • Mild steel
  • Copper
  • Aluminium
  • Cast-iron

  • 82. 
    ______ brushes are fragile and cause excessive wear of commutator,

  • Natural graphite
  • Hard carbon
  • Electro graphitic
  • Metal graphite

  • 83. 
    Which of the following brushes can be used for high values of current density ?

  • Metal graphite brushes
  • Hard carbon brushes
  • Electro-graphitic brushes
  • Natural graphite brushes

  • 84. 
    ________ is the common method of applying brushes to the commntator.

  • Radial
  • Trailing
  • Reaction
  • All of the above

  • 85. 
    Which of the following problem arises in D.C. motors which are fed from thyristor bridge circuits ?

  • Increased I R losses
  • Increased core losses
  • Poor commutation
  • Change in motor parameters
  • All of the above

  • 86. 
    The weight of copper of both armature and field windings decreases with _____ in number of poles.

  • increase
  • decrease
  • either of the above
  • none of the above

  • 87. 
    In a D.C. machine the number of brush arms is _____ the number of poles.

  • less than
  • equal to
  • greater than
  • none of the above

  • 88. 
    In a D.C. machine, the value of peripheral speed should not, normally, exceed

  • 10 m/s
  • 20 m/s
  • 30 m/s
  • 40 m/s

  • 89. 
    In D.C. machines the width of the duct is usually

  • 4 mm
  • 6 mm
  • 8 mm
  • 10 mm

  • 90. 
    D.C. machines designed with a large value of air gap length have

  • worst, ventilation
  • poor ventilation
  • better ventilation
  • none of the above

  • 91. 
    In D.C. machines, ir order to prevent excessive distortion of field form by the armature reaction, the field mmf must be made

  • equal to that of armature mmf
  • less in comparison with the armature mmf
  • large in comparison with the armature mmf
  • none of the above

  • 92. 
    In D.C. machines, the ____ in field mmf results in increase in size and cost of machines.

  • increase
  • decrease
  • either of the above
  • none of the above

  • 93. 
    The operation of a D.C. machine with large air gap lengths is comparatively

  • quiet
  • noisy
  • either of the above
  • none of the above

  • 94. 
    . Which of the following methods may be adopted to reduce the effects of armature reaction ?

  • Increase in length of air gap at pole tips
  • Increasing reluctance of pole tips
  • Compensating windings
  • Interpoles
  • All of the above

  • 95. 
    . In D.C. machines the usual limit of slot pitch is

  • between 5 to 10 mm
  • between 10 to 15 mm
  • between 15 to 20 mm
  • between 25 to 35 mm

  • 96. 
    . In D.C. machines the number of slots per pole usually lies

  • between 2 to 4
  • between 6 to 8
  • between 9 to 16
  • between 20 to 30
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