Alternator MCQ | Synchronous Generator MCQ

191. Which one of the following method gives more accurate result for determination of voltage regulation of an alternator?

  1. m.m.f. method
  2. Synchronous impedance method
  3. Potier triangle method
  4. American Institution Standard method
Answer
Answer. d

192. When a 3-phase alternator is suddenly short-circuited at its terminals, the initial value of the short-circuit current is limited by which one of the following?

  1. Subtransient reactance xd“
  2. Transient reactance xd‘
  3. Synchronous reactance xs
  4. Sum of xd“, xd‘ and xs
Answer
Answer. a

193. Which one of the following is the primary reason for placing field on rotor in an alternator?

  1. Small power in field circuit
  2. Insulation of high voltage is made easy on stator than on rotor
  3. Large power in stator
  4. Large current in the stator
Answer
Answer. d

194. The leakage reactance of a three-phase alternator is determined by performing

  1. Open circuit and zero power factor tests
  2. Zero power factor and slip tests
  3. Open-circuit and short-circuit tests
  4. Short-circuit and slip tests
Answer
Answer. a

195. The synchronous reactance is the

  1. Reactance due to armature reaction of the machine
  2. Reactance due to leakage flux
  3. Combined reactance due to leakage flux and armature reaction
  4. Reactance either due to armature reaction or leakage flux
Answer
Answer. c

196. A 3-phase, 50 MVA, 10 kV generator has a reactance of 0.2 ohm per phase. Hence the per-unit value of the reactance on a base of 100 MVA, 25 kV will be

  1. 1.25
  2. 0.625
  3. 0.032
  4. 0.32
Answer
Answer. c

197. For maximum current during ‘Slip test’ on a synchronous machine, the armature mmf aligns along

  1. q-axis
  2. d-axis
  3. 45° to q-axis
  4. 45° to d-axis
Answer
Answer. a

198. A 6-pole, 3-phase alternator running at 1000 rpm supplies to an 8-pole, 3-phase induction motor which has a rotor current of frequency 2 Hz. The speed at which the motor operates is

  1. 960 rpm
  2. 1000 rpm
  3. 720 rpm
  4. 750 rpm
Answer
Answer. c

199. The ‘synchronous-impedance method’ of finding the voltage regulation by a cylindrical rotor alternator is generally considered as

  1. a pessimistic method because saturation is not considered.
  2. an optimistic method because saturation is not considered.
  3. a fairly accurate method even if power factor is not taken into account while determining synchronous impedance.
  4. a fairly accurate method when power factor is taken into account while determining synchronous impedance.
Answer
Answer. a

200. In a cylindrical rotor synchronous machine, the phasor addition of stator and rotor mmfs is possible because

  1. two mmfs are rotating in opposite direction
  2. two mmfs are rotating in same direction at different speed
  3. two mmfs are stationary with respect to each other
  4. one mmf is stationary and the other mmf rotating
Answer
Answer. c
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