ELECTRICIAN 2nd YEAR MODULE – DC Generator

Question 1 of 56

1. 5. What is the formula to calculate back emf of a DC motor?

D

A

B

C

Question 1 of 56

Question 2 of 56

2. 37. What is the property of wave winding in DC generators?

High current, low voltage

High current, high voltage

Low current, high voltage

Low current, low voltage

Question 2 of 56

Question 3 of 56

3. 34. Which method improves insulation resistance in DC generators?

Regular commutator cleaning

Frequent brush replacement

Blowing hot air during maintenance

Periodic machine heating

Question 3 of 56

Question 4 of 56

4. 51. Calculate the EMF generated in a 4-pole, simplex wave-wound DC generator with 1020 conductors at 1500 rpm and 0.007 Wb flux/pole.

357 V

428 V

178 V

243 V

Question 4 of 56

Question 5 of 56

5. 52. How is armature reaction neutralized in large DC generators?

Increased brush contact resistance

Additional interpoles

Resistance wires in windings

Compensating winding

Question 5 of 56

Question 6 of 56

6. 35. Which DC generator works without residual magnetism?

Series generator

Separately excited generator

Shunt generator

Compound generator

Question 6 of 56

Question 7 of 56

7. 14. How many parallel paths are there in a duplex lap winding of a 4-pole DC generator?

8

6

12

4

Question 7 of 56

Question 8 of 56

8. 48. What is the purpose of compensating winding in DC generators?

Minimize rough commutation

Maintain constant output voltage

Decrease field coil excitation current

Neutralize demagnetizing effect

Question 8 of 56

Question 9 of 56

9. 10. What is the principle of a DC generator?

Cork screw rule

Fleming’s right hand rule

Faraday’s laws of electromagnetic induction

Fleming’s left hand rule

Question 9 of 56

Question 10 of 56

10. 22. Why is the armature resistance of a DC generator kept very low?

Reduce armature voltage drop

Reduce temperature of armature

Reduce armature current

Run armature with less weight

Question 10 of 56

Question 11 of 56

11. 27. What is the purpose of pole shoes in a DC generator?

Increase field strength

Minimize magnetic losses

Reduce air gap

Spread flux uniformly in the air gap

Question 11 of 56

Question 12 of 56

12. 23. Why should a DC generator run only in the clockwise direction?

Protect brushes from damage

Avoid generator overloading

Protect residual magnetism

Avoid short circuit in armature

Question 12 of 56

Question 13 of 56

13. 54. Calculate the induced EMF of a 4-pole, lap-wound dynamo at 1000 rpm with 600 conductors and 0.064 Wb flux/pole.

480 V

640 V

320 V

160 V

Question 13 of 56

Question 14 of 56

14. 46. Why are pole core stampings laminated in DC generators?

Reduce eddy current loss

Reduce friction loss

Reduce windage loss

Reduce hysteresis loss

Question 14 of 56

Question 15 of 56

15. 21. Why is the armature core of a DC generator laminated?

Reduce friction loss

Reduce hysteresis loss

Reduce eddy current loss

Reduce copper loss

Question 15 of 56

Question 16 of 56

16. 41. What is the function of split rings in a DC generator?

Continuous output supply

Collect output from alternate conductors

Unidirectional output

Opposite direction output

Question 16 of 56

Question 17 of 56

17. 50. What is the effect of armature reaction in DC generators?

Decreased output voltage

Pulsating output voltage

Increased output voltage

Zero output voltage

Question 17 of 56

Question 18 of 56

18. 12. Which rule is used to find the direction of a magnetic field?

Right hand palm rule

Fleming’s left hand rule

Cork screw rule

Fleming’s right hand rule

Question 18 of 56

Question 19 of 56

19. 44. What is the purpose of field coils in a DC generator?

Increase air gap flux

Reduce magnetizing current

Increase magnetic path reluctance

Magnetize poles to produce flux

Question 19 of 56

Question 20 of 56

20. 13. What is the name of the part of a DC generator that provides mechanical support and a path for magnetic flux?

Stator

Pole core

Pole shoes

Yoke (or frame)

Question 20 of 56

Question 21 of 56

21. 16. How are interpoles connected in a DC generator?

In parallel with the armature

In series with the armature

In series with the shunt field

In parallel with the shunt field

Question 21 of 56

Question 22 of 56

22. 24. Why is compensating winding provided in large DC generators?

Neutralize armature reaction effect

Reduce commutation effect

Connect more loads

Increase generator efficiency

Question 22 of 56

Question 23 of 56

23. 53. What happens if a DC generator is idle for a long time?

Field coil resistance increases

Armature resistance increases

Loss of residual magnetism

Increased armature reaction

Question 23 of 56

Question 24 of 56

24. 18. Which two points measure the brush contact resistance in DC machines?

Resistance between brush and armature conductors

Resistance between brush and commutator

Resistance between brush and commutator riser

Resistance between the opposite brushes

Question 24 of 56

Question 25 of 56

25. 8. Which type of energy is converted into electrical energy by a generator?

Chemical energy

Mechanical energy

Kinetic energy

Heat energy

Question 25 of 56

Question 26 of 56

26. 17. What is the necessity of residual magnetism in a self-excited DC generator?

To maintain constant output voltage

To reduce armature current

To reduce the field current

To build up the voltage

Question 26 of 56

Question 27 of 56

27. 49. What happens if shunt field resistance exceeds critical value in a DC generator?

Voltage buildup failure

Pulsating output voltage

Normal voltage buildup

Above-normal output voltage

Question 27 of 56

Question 28 of 56

28. 15. Name the part of a DC generator that consists of thin laminated sheets to reduce eddy currents.

Pole shoe lamination

Commutator segment

Armature core lamination

Side end plates

Question 28 of 56

Question 29 of 56

29. 33. Which DC generator is used for long-distance distribution lines?

Cumulative compound generator

Shunt generator

Series generator

Differential compound generator

Question 29 of 56

Question 30 of 56

30. 36. Which DC generator is used for arc welding?

Series generator

Differential compound generator

Cumulative compound generator

Shunt generator

Question 30 of 56

Question 31 of 56

31. 31. How does the magnetic circuit complete through the yoke and poles in a generator?

Laminated pole core

Field coils

Armature core

Armature winding conductors

Question 31 of 56

Question 32 of 56

32. 55. What happens to induced EMF if main field flux distorts in a DC generator?

EMF increases

No change in EMF

EMF becomes zero

EMF decreases

Question 32 of 56

Question 33 of 56

33. 40. Which metal is used for large-capacity DC generator yokes?

Aluminium

Cast iron

Rolled steel

Soft iron

Question 33 of 56

Question 34 of 56

34. 56. What causes heavy sparking in DC generator brushes?

Shift in MNA and GNA positions

Excessive brush spring tension

Short circuit in armature winding

Short circuit in field winding

Question 34 of 56

Question 35 of 56

35. 39. Why are solid pole shoes used in DC generators?

Reduce magnetic path reluctance

Increase residual magnetism

Reduce copper loss

Decrease residual magnetism

Question 35 of 56

Question 36 of 56

36. 4. Which formula is used to calculate the generated emf in a DC generator?

A

D

B

C

Question 36 of 56

Question 37 of 56

37. 32. Why does terminal voltage decrease with increased load in a DC shunt generator?

Increased armature resistance

Increased shunt field inductance

Armature reaction effect

Reduced brush voltage drop

Question 37 of 56

Question 38 of 56

38. 43. What is the purpose of the slot marked 'X' in a DC generator?

Easy shaft removal

Lubrication

Fix the keyway

Enable air circulation

Question 38 of 56

Question 39 of 56

39. 26. What is the name of the generator if its field is connected in parallel with the armature?

Series generator

Compound generator

Shunt generator

Self-excited generator

Question 39 of 56

Question 40 of 56

40. 9. What is the name of the DC generator's field where the series field opposes the shunt field?

Short shunt compound generator

Long shunt compound generator

Differential compound generator

Cumulative compound generator

Question 40 of 56

Question 41 of 56

41. 42. Which voltage is induced dynamically in a DC generator?

Direct current voltage

Alternating voltage

Pulsating voltage

Oscillating voltage

Question 41 of 56

Question 42 of 56

42. 20. What is the name of the compound generator if the shunt field is connected in parallel with the armature?

Differential compound

Short shunt compound

Cumulative compound

Long shunt compound

Question 42 of 56

Question 43 of 56

43. 6. What is the name of the part marked 'X' in a DC generator (pole assembly)?

Pole shoe

Pole core

Pole coil

Pole tip

Question 43 of 56

Question 44 of 56

44. 11. What is the formula for dynamically induced emf?

BL sinθ volts

BLV volts

BLV sinθ volts

BLV cosθ volts

Question 44 of 56

Question 45 of 56

45. 47. Which DC generator is used for electroplating?

Shunt generator

Series generator

Cumulative compound generator

Differential compound generator

Question 45 of 56

Question 46 of 56

46. 25. What is the reason a DC generator fails to build up voltage?

High armature resistance

Loose brush contact

Field resistance above critical value

Prime mover running above rated speed

Question 46 of 56

Question 47 of 56

47. 19. Which voltage drop is indicated in the portion marked as 'X' in a DC generator?

Armature voltage drop

Armature reaction drop

Full load voltage drop

Shunt field voltage drop

Question 47 of 56

Question 48 of 56

48. 1. What is the name of the part marked as 'X' in a DC generator?

Commutator segment

Brush

Commutator riser

Armature core

Question 48 of 56

Question 49 of 56

49. 3. Which rule is used to find the direction of induced emf in a DC generator?

Fleming's right hand rule

Fleming's left hand rule

Cork screw rule

Right hand palm rule

Question 49 of 56

Question 50 of 56

50. 30. Why do DC generators lose residual magnetism?

Continuous no-load running

Frequent direction changes of rotation

Heavy short circuit in load

Uninterrupted operation

Question 50 of 56

Question 51 of 56

51. What is the name of the DC generator described as having cumulative short shunt compounding?

Cumulative short shunt compound

Differential long shunt compound

Differential short shunt compound

Cumulative long shunt compound

Question 51 of 56

Question 52 of 56

52. 45. Which metal is used for pole cores in large DC generators?

Cast iron

Stainless steel

Cast steel

Soft iron

Question 52 of 56

Question 53 of 56

53. 28. What is the function of split rings in a DC generator?

Reduce voltage drop at brushes

Increase terminal voltage beyond rated

Maintain constant voltage

Collect current unidirectionally

Question 53 of 56

Question 54 of 56

54. 38. What is the purpose of resistance wire in commutator connections?

Smooth current direction reversal

Increase statically induced EMF

Maintain constant voltage

Nullify statically induced EMF

Question 54 of 56

Question 55 of 56

55. 29. Which material is used to make brushes in generators?

Carbon and graphite

Aluminium and graphite

Steel and graphite

Cast iron and graphite

Question 55 of 56

Question 56 of 56

56. 7. What is the name of the DC generator that requires separate excitation?

Compound generator

Series generator

Separately excited generator

Shunt generator

Question 56 of 56