DC Generator MCQ

21. How many segments will be there for the commutator of a 6 pole d.c. machine having a simple wave wound armature with 72 slots?

  1. 73
  2. 72
  3. 71
  4. 70
Answer. b

22. An eight pole d.c. generator has a simple wave wound armature containing 32 coils of 6 turns each. Its flux per pole is 0.06 Wb. The machine is running at 250 rpm. The induced armature voltage is

  1. 192 V
  2. 96 V
  3. 768 V
  4. 384 V
Answer. d

23. The maximum efficiency occurs in a separately excited d.c.generator when the terminal voltage is 220 V and the induced emí is 240 V, the stray losses, if the armature resistance is 0.2 2, will be

  1. 2000 W
  2. 1000 W
  3. 4000 W
  4. 3000 W
Answer. a

24. Consider the following parts of a dc machine:

  1. Yoke
  2. Armature core
  3. Brushes
  4. Pole core

Which of the above parts are subjected to iron loss?

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

25. A shunt generator has a critical field resistance of 200 Ω at a speed of 800 r.p.m. If the speed of the generator is increased to 1000 r.p.m., what is the change in the critical field resistance of the generator?

  1. Decreases to 160 Ω
  2. Remains the same at 200 Ω
  3. Increases to 250 Ω
  4. Increases to 312.5 Ω
Answer. c

26. What are slot wedges in a dc machine, made of?

  1. Silicon steel
  2. Mild steel
  3. Cast iron
  4. Fibre
Answer. a

27. Which of the followings are true is respect of interpoles in dc machines?

  1. Reduce armature reaction effects in interpolar region.
  2. Windings are connected in series with armature.
  3. Have the same dimensions as main poles.

Select the correct answer using the code given below:

  1. i and ii
  2. ii and iii
  3. i and iii
  4. i, ii and iii
Answer. a

28. A DC shunt generator is supplying a load of 1.8 kW at 200 V. Its armature and field resistances are 0.4 Ω and 200 Ω respectively. What is the generated emf?

  1. 196 V
  2. 190 V
  3. 210 V
  4. 204 V
Answer. d

29. If the armature current is increased to double its previous value, and the time of commutation is halved, how will the reactance voltage vary?

  1. It will be halved
  2. It will remain the same
  3. It will be doubled
  4. It will become four times
Answer. d

30. Wave winding is employed in a d.c. machine of

  1. high current and low voltage rating
  2. low current and high voltage rating
  3. high current and high voltage rating
  4. low current and low voltage rating
Answer. d