DC Generator MCQs Quiz Multiple Choice Questions & Answers

1. In a four-pole D.C. machine

1. all the four poles are north poles
2. alternate poles are north and south
3. all the four poles are south poles
4. two north poles follow two south poles

2. In over compounded generator, full load terminal voltage is

1. almost zero
2. less than noload terminal voltage
3. more than noload terminal voltage
4. equal to no-load terminal voltage

3. Armature coil is short circuited by brushes when it lies

1. along neutral axis
2. along field axis
3. in any of the above positions
4. in none of the above positions

4. Lap winding is composed of

1. any even number of conductors
2. any odd number of conductors
3. that even number which is exact multiple of poles + 2
4. that even number which is exact multiple of poles

5. Wave winding is composed of

1. any even number of conductors
2. any odd number of conductors
3. that even number which is exact multiple of poles + 2
4. that even number which is exact multiple of poles

6. The terminal voltage of a D.C. shunt generator drops on load because of all of thefollowing reasons except

1. armature reaction
2. armature resistance drop
3. field weakening due to armature reaction and armature
4. commutation

7. The bearings used to support the rotor shafts are generally

1. ball bearings
2. bush bearings
3. magnetic bearmgs
4. needle bearings

8. In a D.C. generator the critical resistance refers to the resistance of

1. brushes
2. field
3. armature
4. load

9. Brushes of D.C. machines are made of

1. carbon
2. soft copper
3. hard copper
4. all of above

10. Laminations of core are generally made of

1. case iron
2. carbon
3. silicon steel
4. stainless steel

11. In D.C. generators, current to the external circuit from armature is given through

1. commutator
2. solid connection
3. slip rings
4. none of above

12. Which of the following could be lamina-proximately the thickness of laminations of a D.C. machine ?

1. 0.005 mm
2. 0.05 mm
3. 0.5 m
4. 5 m

13. Which of the following statement about D.C. generators is false ?

1. Compensating winding in a D.C. machine helps in commutation
2. In a D. C. generator interpoles winding is connected in series with the armaturewinding
3. Back pitch and front pitch are both odd and approximately equal to the pole pitch
4. Equilizing bus bars are used with parallel running of D.C. shunt generators

14. In a commutator

1. copper is harder than mica
2. mica and copper are equally hard
3. mica is harder than copper
4. none of the above

15. The commutator segments are connected to the armature conductors by means of

1. copper lugs
2. resistance wires
3. insulation pads
4. brazing

16. Armature reaction of an unsaturated D.C. machine is

1. crossmagnetising
2. demagnetising
3. magnetising
4. none of above

17. A cumulatively compounded long shunt generator when operating as a motor would be

1. cumulatively compounded long shunt
2. differentially compounded long shunt
3. cumulatively compounded short shunt
4. differentially compounded short shunt

18. In case of D.C. machines, mechanical losses are primary function of

1. current
2. voltage
3. speed
4. none of above

19. With a D.C. generator which of the following regulation is preferred ?

1. 100% regulation
2. infinite regulation
3. 50% regulation
4. 1% regulation

20. Armature reaction in a generator results in

1. demagnetisation of leading pole tip and magnetisation of trailing pole tip
2. demagnetisation of trailing pole tip and magnetisation of leading pole tip
3. damagnetising the centre of all poles
4. magnetising the centre of all poles

21. If brushes of a D.C. generator are moved in order to bring these brushes in magneticneutral axis, there will be

1. demagnetisation only
2. cross magnetisation as well as magnetisation
3. crossmagnetisation as well as demagnetising
4. cross magnetisation only

22. While applying Flemings right-hand rule to And the direction of induced e.m.f., the thumb points towards

1. direction of induced e.m.f.
2. direction of flux
3. direction of motion of the conductor if forefinger points in the direction of generatede.m.f.
4. direction of motion of conductor, if forefinger points along the lines of flux

23. In lap winding, the number of brushes is always

1. double the number of poles
2. same as the number of poles
3. half the number of poles
4. two

24. Which of the following components of a D.C, generator plays vital role for providingdirect current of a D.C. generator ?

1. Dummy coils
2. Commutator
3. Eye bolt
4. Equilizer rings

25. The e.m.f. generated by a shunt wound D.C. generator is E. Now while pole flux remainsconstant, if the speed of the generator is doubled, the e.m.f. generated will be

1. E/2
2. 2E
3. slightly less than E
4. E

26. The series field of a short-shunt D.C. generator is excited by

1. external current
2. armature current
3. shunt current
4. load current

27. In a D.C. generator

1. external resistance = internal char-acteristic - armature reaction
2. internal characteristic = magnetisation characteristic - ohmic drop
3. external characteristic = magnetisation characteristic - ohmic drop - armature reaction
4. magnetisation characteristic = external characteristic

28. The critical resistance of the D.C. generator is the resistance of

1. field
2. brushes
3. armature
4. load

29. Permeance is the reciprocal of

1. flux density
2. reluctance
3. ampere-turns
4. resistance

30. A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If the speedincreases to 1200 r.p.m., the generated e.m.f. will be nearly

1. 150 V
2. 175 V
3. 240 V
4. 290 V

31. The e.m.f. generated in a D.C. generator is directly proportional to

1. flux/pole
2. speed of armature
3. number of poles
4. all of the above

32. The insulating material used between the commutator segments is normally

1. graphite
2. paper
3. mica
4. insulating varnish

33. The voltage drop for which of the following types of brush can be expected to be least ?

1. Graphite brushes
2. Carbon brushes
3. Metal graphite brushes
4. None of the above

34. In D.C. generators, lap winding is used for

1. high voltage, high current
2. low voltage, high current
3. high voltage, low current
4. low voltage, low current

35. If a D.C. generator fails to build up the probable cause could not be

1. imperfect brush contact
2. field resistance less than the critical resistance
3. no residual magnetism in the generator
4. faulty shunt connections tending to reduce the residual magnetism

36. In a D.C. generator in case the resistance of the field winding is increased, then outputvoltage will

1. increase
2. decrease
3. remain unaffected
4. fluctuate heavily

37. In a D.C. generator the critical resistance can be increased by

1. increasing its field resistance
2. decreasing its field resistance
3. increasing its speed
4. decreasing its speed

38. In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in thecoil is neutralised by all of the following except

1. interpoles
2. dummy coils
3. compensating winding
4. shifting of axis of brushes

39. In a separately excited generator supplying rated load the armature reaction ,

1. is always present
2. is always absent
3. may be sometimes present
4. none of the above

40. A separately excited generator as compared to a self-excited generator

1. is amenable to better voltage con-trol
2. is more stable
3. has exciting current independent of load current
4. has all above features

41. In D.C. generators the polarity of the interpoles

1. is the same as that of the main pole ahead
2. is the same as that of the immediately preceding pole
3. is opposite to that of the main pole ahead
4. is neutral as these poles do not play part in generating e.m.f.

42. Welding generator will have

1. lap winding
2. wave winding
3. delta winding
4. duplex wave winding

43. The number of armature parallel paths in a two-pole D.C. generator having duplex lapwinding is

1. 2
2. 4
3. 6
4. 8

44. A D.C. welding generator has

1. lap winding
2. wave moving
3. duplex winding
4. any of the above

45. The resistance of armature winding depends on

1. length of conductor
2. cross-sectional area of the conductor
3. number of conductors
4. all of the above

46. A D.C. generator works on the principle of

1. Lenzs law
2. Ohms law
3. Faradays law of electromagnetic induction
4. none of the above

47. In D.C. generators, the brushes on commutator remain in contact with conductorswhich

1. lie under south pole
2. lie under north pole
3. lie under interpolar region
4. are farthest from the poles

48. Flemings right-hand rule regarding direction of induced e.m.f., correlates

1. magnetic flux, direction of current flow and resultant force
2. magnetic flux, direction of motion and the direction of e.m.f. induced
3. magnetic field strength, induced voltage and current
4. magnetic flux, direction of force and direction of motion of conductor

49. Compensating windings are used in D.C. generators

1. mainly to reduce the eddy currents by providing local short-circuits
2. to provide path for the circulation of cooling air
3. to neutralise the cross-magnetising effect of the armature reaction
4. none of the above

50. The field coils of D.C. generator are usually made of

1. mica
2. copper
3. cast iron
4. carbon