Alternator MCQ | Synchronous Generator MCQ

151. Consider the following statements

  1. Salient pole alternators have small diameters and large axial lengths.
  2. Cylindrical rotor alternators have a distributed winding.
  3. Cylindrical rotor alternators are wound for large number of poles.
  4. Salient pole alternators run at speeds slower than cylindrical rotor machines.

Which of the above statements are correct?

  1. i and iii only
  2. ii and iv only
  3. i and iv only
  4. ii and iii only
Answer
Answer. b

152. Consider the following statements regarding capability curves of a synchronous generator:

  1. The MVA loading should not exceed the generator rating.
  2. The field current should not be allowed to exceed a specified value determined by field heating
  3. The MW loading should not exceed the rating of the prime mover.
  4. The load angle must be more than 90°.

Which of the above statements are correct?

  1. i, ii, iii and iv
  2. i and iv only
  3. i, ii and iii only
  4. ii, iii and iv only
Answer
Answer. c

153. In an alternator the armature winding is kept stationary while the field winding is kept rotating for the following reasons:

  1. Armature handles very large current and high voltage.
  2. Armature fabrication, involving deep slots to accommodate large colls, is easy if armature is kept stationary.
  3. It is easier to cool the stator than the rotor
  1. i and iii only
  2. i and ii only
  3. i, ii and iii
  4. ii and iii only
Answer
Answer. a

154. What are the signs of load angle in an alternator during generator and motor operations, respectively?

  1. Negative, negative
  2. Positive, negative
  3. Negative, positive
  4. Positive, positive
Answer
Answer. b

155. The breadth factor for 3rd harmonic emf of a 3-phase, 4-pole, synchronous machine having 36 stator slots is

  1. 0.53
  2. 0.47
  3. 0.73
  4. 0.67
Answer
Answer. d

156. Consider the following advantages of a distributed winding in a rotating machine

  1. Better utilization of core as number of evenly placed small slots are used.
  2. Improved waveform as harmonic emf’s are reduced.
  3. Dimensional armature reaction and efficient cooling.

Which of the above advantages are correct?

  1. i and iii only
  2. i and ii only
  3. i, ii and iii
  4. ii and iii only
Answer
Answer. c

157. Compared to the salient-pole Hydroelectric generators, the steam and the gas turbine generators have cylindrical rotors for

  1. Better air-circulation in the machine
  2. Reducing the eddy-current losses in the rotor
  3. Accommodating larger number terms in the field winding
  4. Providing higher mechanical strength against the centrifugal stress
Answer
Answer. d

158. A cylindrical-rotor generator with internal voltage 2.0 pu and Xs = 1.0 pu is connected by a line of reactance 0.5 pu to a round-rotor synchronous motor of synchronous reactance 1.2 pu and excitation voltage 1.35 pu. When 0.5 pu power is supplied by the generator, the electrical angular difference between the rotors would be

  1. 25°
  2. 30°
  3. 60°
  4. 120°
Answer
Answer. b

159. The nature of armature mmf for a zero power factor lagging load in a 3-phase alternator is

  1. magnetizing
  2. de-magnetizing
  3. neutral
  4. cross-magnetizing
Answer
Answer. b

160. A uniformly distributed winding on the stator has three full-pitched coils, each coil having N turns and each turn carrying a current I. The mmf produced by this winding is

  1. sinusoidal in waveform with an amplitude 3 NI
  2. sinusoidal in waveform with an amplitude (3/2) NI
  3. trapezoidal in waveform with an amplitude 3 NI
  4. trapezoidal in waveform with an amplitude (3/2) NI
Answer
Answer. c
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