About D.C. Generators

Following are some of the multiple choice questions on the D.C. Generators with answers that will help the students in developing their knowledge.

D.C. Generators MCQ

1. What is Superman's birth name?

  • nal-el
  • kal-el
  • mal-el
  • dal-el

2. Cables, generally used beyond 66 kV are

  • oil filled
  • S.L. type
  • belted
  • armoured

3. The metallic sheath may be made of lead or lead alloy or of aluminium.

  • Yes
  • No
  • none
  • none

4. The electrostatic stress in underground cables is

  • same at the conductor and the sheath
  • minimum at the conductor and maximum at the sheath
  • maximum at the conductor and minimum at the sheath
  • zero at the conductor as well as on the sheath

5. The breakdown of insulation of the cable can be avoided economically by the use of

  • inter-sheaths
  • insulating materials with different dielectric constants
  • both (a) and (b)
  • none of the above

6. The insulation of the cable decreases with

  • the increase in length of the insulation
  • the decrease in the length of the insulation
  • either (a) or (b)
  • none of the above

7. A cable carrying alternating current has

  • hysteresis losses only
  • hysteresis and leakage losses only
  • hysteresis, leakage and copper losses only
  • hysteresis, leakage, copper and friction losses

8. In a cable the voltage stress is maximum at

  • sheath
  • insulator
  • surface of the conductor
  • core of the conductor

9. Capacitance grading of cable implies

  • use of dielectrics of different permeabilities
  • grading according to capacitance of cables per km length
  • cables using single dielectric in different concentrations
  • capacitance required to be introduced at different lengths to counter the effect of inductance

10. Underground cables are laid at sufficient depth

  • to minimise temperature stresses
  • to avoid being unearthed easily due to removal of soil
  • to minimise the effect of shocks and vibrations due to gassing vehicles, et
  • for all of the above reasons

11. The thickness of metallic shielding on cables is usually

  • 0.04 mm
  • 0.2 to 0.4 mm
  • 3 to 5 mm
  • 40 to 60 mm

12. Is a cable is to be designed for use on 1000 kV, which insulation would you prefer ?

  • Polyvinyle chloride
  • Vulcanised rubber
  • Impregnated paper
  • Compressed SFe gas

13. If a power cable and a communication cable are to run parallel the minimum distancebetween the two, to avoid interference, should be

  • 2 cm
  • 10 cm
  • 50 cm
  • 400 cm

14. Copper as conductor for cables is used as

  • annealed
  • hardened and tempered
  • hard drawn
  • alloy with chromium

15. The insulating material should have

  • low permittivity
  • high resistivity
  • high dielectric strength
  • all of the above

16. The advantage of oil filled cables is

  • more perfect impregnation
  • smaller overall size
  • no ionisation, oxidation and formation of voids
  • all of the above

17. In capacitance grading a homogeneous dielectric is used.

  • Yes
  • No

18. In congested areas where excavation is expensive and inconvenient 'draw in system'of laying of underground cables is often adopted.

  • Yes
  • No

19. Natural rubber is obtained from milky sap of tropical trees.

  • Yes
  • No

20. Rubber is most commonly used insulation in cables.

  • Yes
  • No

21. Cables for 220 kV lines are invariably

  • mica insulated
  • paper insulated
  • compressed oil or compressed gas insulated
  • rubber insulated

22. High tension cables are generally used upto

  • 11kV
  • 33kV
  • 66 kV
  • 132 kV

23. The current carrying capacity of cables in D.C. is more thanthat in A.C. mainly due to

  • absence of harmonics
  • non-existence of any stability limit
  • smaller dielectric loss
  • absence of ripples

24. In case of three core flexible cable the colour of the neutral is

  • blue
  • black
  • brown
  • none of the above

25. Cables are used for 132 kV lines.

  • High tension
  • Super tension
  • Extra high tension
  • Extra super voltage

26. Conduit pipes are normally used to protect _____ cables.

  • unsheathed cables
  • armoured
  • PVC sheathed cables
  • all of the above

27. The minimum dielectric stress in a cable is at

  • armour
  • bedding
  • conductor surface
  • lead sheath

28. In single core cables armouring is not done to

  • avoid excessive sheath losses
  • make it flexible
  • either of the above
  • none of the above

29. Dielectric strength of rubber is around

  • 5 kV/mm
  • 15 kV/mm
  • 30 kV/mm
  • 200 kV/mm

30. Low tension cables are generally used upto

  • 200 V
  • 500 V
  • 700 V
  • 1000 V

31. In a cable, the maximum stress under operating conditions is at

  • insulation layer
  • sheath
  • armour
  • conductor surface

32. The surge resistance of cable is

  • 5 ohms
  • 20 ohms
  • 50 ohms
  • 100 ohms

33. In the cables, the location of fault is usually found out by comparing

  • the resistance of the conductor
  • the inductance of conductors
  • the capacitances of insulated conductors
  • all above parameters

34. Pressure cables are generally not used beyond

  • 11 kV
  • 33 kV
  • 66 kV
  • 132 kV

35. The intersheaths in the cables are used to

  • minimize the stress
  • avoid the requirement of good insulation
  • provide proper stress distribution
  • none of the above

36. In the cables, sheaths are used to

  • prevent the moisture from entering the cable
  • provide enough strength
  • provide proper insulation
  • none of the above

37. If a cable of homogeneous insulation has a maximum stress of 10 kV/mm, then thedielectric strength of insulation should be

  • 5 kV/mm
  • 10 kV/mm
  • 15 kV/mm
  • 30 kV/mm

38. A certain cable has an insulation of relative permittivity 4. If the insulation is replaced by one of relative permittivity 2, the capacitance of the cable will become

  • one half
  • double
  • four times
  • none of the above

39. In cables the charging current

  • lags the voltage by 90°
  • leads the voltage by 90°
  • lags the voltage by 180°
  • leads the voltage by 180°

40. Solid type cables are considered unreliable beyond 66 kV because

  • insulation may melt due to higher temperature
  • skin effect dominates on the conduc¬tor
  • of corona loss between conductor and sheath material
  • there is a danger of breakdown of insulation due to the presence of voids

41. The relative permittivity of rubber is

  • between 2 and 3
  • between 5 and 6
  • between 8 and 10
  • between 12 and 14

42. The material for armouring on cable is usually

  • steel tape
  • galvanised steel wire
  • any of the above
  • none of the above

43. In capacitance grading of cables we use a ______ dielectric.

  • composite
  • porous
  • homogeneous
  • hygroscopic

44. If the length of a cable is doubled, its capacitance

  • becomes one-fourth
  • becomes one-half
  • becomes double
  • remains unchanged

45. In a cable immediately above metallic sheath _____ is provided.

  • earthing connection
  • bedding
  • armouring
  • none of the above

46. Which generator would you prefer for feeding long D.C. transmission lines ?

  • Series generator
  • Shunt generator
  • Over compound generator
  • Flat compound generator

47. The essential condition for parallel operation of two D.C. generators is that they have

  • same kW rating
  • the same operation r.p.m.
  • the same drooping voltage charac-teristics
  • same percentage regulation

48. When two D.C. generators are running in parallel an equilizer bar is used

  • to increase the series flux
  • to increase the generated m.f.
  • to reduce the combined effect of ar-mature reaction of both the machines
  • so that the two identical machines will pass approximately equal currents to the load

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

  • 100% regulation
  • infinite regulation
  • 50% regulation
  • 1% regulation

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

  • 2
  • 4
  • 6
  • 8

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