Alternator MCQ | Synchronous Generator MCQ

21. The power factor of an alternator depends on

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

22. In an alternator, at lagging power factor, the generated voltage per phase, as compared to that at unity power factor

  1. must be same as the terminal voltage
  2. must be less than the terminal voltage
  3. must be more than the terminal voltage
  4. must be 1.41 time the terminal voltage
Answer. c

23. The magnitude of various voltage drops that occur in an alternator, depends on

  1. power factor of the load
  2. load current
  3. power factor x load current
  4. power factor x (load current)2.
Answer. b

24. In an alternator, voltage drops occur in

  1. armature resistance only
  2. armature resistance and leakage reactance
  3. armature resistance, leakage reactance, and armature reaction
  4. armature resistance, leakage reactance, armature reaction and earth connections.
Answer. c

25. As the speed of an alternator increases

  1. the frequency increases
  2. the frequency decreases
  3. the frequency remains constant but the power factor decreases
  4. none of the above
Answer. a

26. Average value of flux density wave over one pole pitch ________ times the maximum flux.

  1. 2
  2. 2/π
  3. π/2
  4. 3
Answer. b

27. If both the generator active and reactive power are doubled, KVA loading on the generator

  1. Quadruples
  2. Doubles
  3. Increases by a factor of $\sqrt{2}$
  4. Remains the same
Answer. b

28. An alternator A is connected to bus bar and another alternator B supplies its own constant impedance load. If field excitation is changed, then _________

(where pf represents power factor)

  1. pf of both A and B changes
  2. pf of A changes but pf of B remains unchanged
  3. armature current of both A and B changes
  4. terminal voltage of both A and B remains constant
Answer. b

29. A 400 kVA, 11 kV star-connected alternator has a resistance of 5 Ω per phase. At half load, short circuit load loss will be

  1. 4958.7 W
  2. 1652.9 W
  3. 550.9 W
  4. 2582.6 W
Answer. b

30. Because of which one of the following reasons the phasor addition of stator and rotor mmf is possible in a cylindrical rotor synchronous machine?

  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 is rotating
Answer. c