Alternator MCQ | Synchronous Generator MCQ

61. Alternator used in hydel power station has more number of poles in it than that used in thermal power station, because

  1. speed of the prime mover may be changed whenever required
  2. power generated by the alternator may be changed according to demand
  3. speed of its prime mover is less
  4. power generated by this alternator is less
Answer
Answer. c

62. The emf induced per phase in a three-phase star-connected synchronous generator having the following data:

Distribution factor = 0.955; Coil-span factor = 0.966; Frequeney = 50 Hz, Flux per pole = 25 mWb; Turns per phase = 240

The emf per phase is

  1. 2128.36 Volts
  2. 1228.81 Volts
  3. 869.46 Volts
  4. 1737.80 Volts
Answer
Answer. b

63. A 300 kW alternator is driven by a prime mover of speed regulation 4% While the prime mover of another 200 kW alternator has a speed regulation of 3%. When operating in parallel, the total load they can take without any 0f them being overloaded is

  1. 500 kW
  2. 567 kW
  3. 425 kW
  4. 257 kW
Answer
Answer. c

64. Alternators are usually designed to generate which type of A.C. voltage?

  1. With fixed frequency
  2. With variable frequency
  3. Fixed current
  4. Fixed power factor
Answer
Answer. a

65. Two alternators rated 40 MVA and 60 MVA respectively are working in parallel and supplying a total load of 80 MW. Speed regulation of both the alternators is 5%. The load sharing between them will be

  1. 32 MW, 48 MW
  2. 36 MW, 44 MW
  3. 40 MW each
  4. 30 MW, 50 MW
Answer
Answer. c

66. The positive, negative and zero sequence impedances of 3-phase synchronous generator are j0.5 pu, j0.3 pu and j0.2 pu respectively. When symmetrical fault occurs on the machine terminals. Find the fault current. The generator neutral is grounded through reactance of j0.1 pu.

  1. −j 2.5 pu
  2. −j 2.0 pu
  3. −j 1.67 pu
  4. −j 3.33 pu
Answer
Answer. c

67. Which of the following condition is not mandatory for alternators working in parallel?

  1. The machines must have equal kVA ratings.
  2. The alternators must operate at the same frequency.
  3. The alternators must have the same phase sequence.
  4. The terminal voltage of each machine must be the same.
Answer
Answer. a

68. Turbo alternators have rotors of

  1. small diameter and long axial length
  2. large diameter and long axial length
  3. large diameter and small axial length
  4. small diameter and small axial length
Answer
Answer. a

69. In an alternator, the effect of armature reaction is minimum at a power factor of

  1. 0.5 lagging
  2. 0.866 lagging
  3. 0.866 leading
  4. unity
Answer
Answer. d

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

  1. Power factor becomes more lagging
  2. Power factor becomes more leading
  3. Output current decreases
  4. Output kW decreases
Answer
Answer. a

71. An exciter for a turbo generator is a

  1. separately excited generator
  2. shunt generator
  3. series generator
  4. compound generator
Answer
Answer. b

72. If the speed of rotation of a dynamo is doubled, then the induced emf will

  1. become half
  2. become double
  3. become four times
  4. remain unchanged
Answer
Answer. b

73. A dynamo is sometimes said to generate electricity. It actually acts as a source of

  1. charge
  2. magnetism
  3. emf
  4. energy
Answer
Answer. c

74. Synchronous Generator is a source of

  1. Real Power
  2. Reactive power
  3. Apparent power
  4. Both real and reactive power
Answer
Answer. b

75. The rotor of an alternator has

  1. Four slip rings
  2. Three slip rings
  3. Two slip rings
  4. No slip rings
Answer
Answer. c

76. On which of the following parameters does the power factor of an alternator depend?

  1. Load
  2. Speed of rotor
  3. Core losses
  4. Armature losses
Answer
Answer. a

77. What is the value of load angle at a point where the power output of a salient pole synchronous generator is maximum?

  1. 0°
  2. 45°
  3. 120°
  4. 90°
Answer
Answer. d

78. Large turbo-generators are usually driven by

  1. Coal turbine
  2. Steam turbine
  3. Diesel turbine
  4. Water turbine
Answer
Answer. b

79. An alternator’s operating principle is quite similar to that of

  1. A.C. Generator
  2. D.C. Generator
  3. A.C. Inverter
  4. A.C. Stabilizer
Answer
Answer. b

80. For fixed Voltage synchronous impedance and variable excitation the maximum power Pm is given by

  1. $P_m=\frac{V^2}{4R_a}$
  2. $P_m=\frac{V^3}{4R_a}$
  3. $P_m=\frac{V^2}{R_a}$
  4. $P_m=\frac{V}{4R_a}$
Answer
Answer. a
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