Power Generator

61. If a power transformer is operated at very high frequencies then

  1. primary reactance is too much increased
  2. primary will draw large power
  3. core losses will be excessive
  4. core loss is negligible

Correct answer: (C)
core losses will be excessive

62. If a transformer core has air gaps then

  1. reluctance of magnetic path is decreased
  2. hysteresis loss is decreased
  3. magnetizing current is greatly increased
  4. eddy current is increased

Correct answer: (C)
magnetizing current is greatly increased

63. If the excitation of an alternator operating in parallel with other alternators is increased above the normal value excitation of excitation its

  1. power factor becomes more lagging
  2. output current decreases
  3. power factor becomes more leading
  4. output kw decreases

Correct answer: (A)
power factor becomes more lagging

64. If the excitation of an alternator operating in parallel with pther alternators is decreased, its

  1. power factor becomes more leading
  2. output kW will change
  3. power factor becomes more lagging
  4. power factor becomes unity

Correct answer: (A)
power factor becomes more leading

65. If the lagging load power factor of an alternator is decreased, the demagnetizing effect of the armature reaction

  1. remains the same
  2. is increased
  3. is decreased
  4. becomes infinite

Correct answer: (B)
is increased

66. In a chemical cell current is the movement of

  1. positive and negative ions
  2. positive charges
  3. positive ions only
  4. negative ions only

Correct answer: (A)
positive and negative ions

67. In a dc generator armature reaction ___________ pole tip

  1. weakens the flux at the trailing
  2. weakens the flux at the leading
  3. strengthens the flux at the leading
  4. strengthens the flux at the trailing

Correct answer: (B)
weakens the flux at the leading

68. In a dc machine the number of commutator segments is equal to

  1. number of conductors
  2. number of coils
  3. twice the number of poles
  4. twice the number of coils

Correct answer: (B)
number of coils

69. In a dc motor, the brushes are shifted from the mechanical neutral palne in a direction opposite to the rotation to

  1. decreased speed
  2. reduced sparking
  3. increase speed
  4. produce flat characteristics

Correct answer: (B)
reduced sparking

70. In a lap winding, the number of the brushes required is equal to

  1. number of poles
  2. commutator pitch
  3. number of pairs of poles
  4. number of coils

Correct answer: (A)
number of poles

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