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Tuesday, 20 September 2016

Electricity Overhead Lines - Multiple Choice Questions

Electricity Overhead Lines - Multiple Choice Questions Points : Electricity Overhead Lines, Electrical Overhead Lines multiple choice questions and answers, electrical objective type question answers, mcqs 1. The potential across the various discs of suspension string is different due to
(i) self-capacitance
(ii) shunt capacitance
(iii) both (i) and (ii)
(iv) none of above

2. In a string of suspension insulators, if shunt capacitance decreases, then string efficiency
(i) decreases
(ii) increases
(iii) remains the same
(iv) none of above

3. The wind pressure is directly proportional to
(i) speed of wind
(ii) square of speed of wind
(iii) square root of speed of wind
(iv) none of above

4. The most commonly used material for insulators of overhead lines is
(i) porcelain
(ii) glass
(iii) steatite
(iv) none of above

5. On an overhead line, the wind load acts
(i) horizontally
(ii) vertically downward
(iii) vertically upward
(iv) none of above

6. For d.c. system, the string efficiency is
(i) 50%
(ii) 75%
(iii) 85%
(iv) 100%

7. if shunt capacitance in a string of suspension insulators is decreased, then string efficiency
(i) remains the same
(ii) decreases
(iii) increases
(iv) none of above

8. The conductor vibration of an overhead line may cause
(i) breaking of insulator discs
(ii) excessive sag
(iii) collapse of supporting structures
(iv) all of above

9. In overhead transmission line, the sag depends on
(i) tension in the conductor
(ii) conductor material
(iii) height of tower
(iv) all of above

10. Sag is provided in overhead lines so that
(i) safe tension is not exceeded
(ii) repair can be made
(iii) conductor material is saved
(iv) none of above

11. A string of suspension insulators has three discs. If the disc nearest to the conductor flashes over (i.e. breaks down), then,
(i) the remaining discs will flash over
(ii) the remaining discs will remain intact
(iii) only the top disc will flash over
(iv) none of above

12. In a string of suspension insulators, voltage across
(i) disc nearest to cross-arm is minimum
(ii) middle disc is maximum
(iii) disc nearest to conductor is minimum
(iv) disc nearest to cross-arm is maximum

13. In a string of suspension insulators, the charging current is maximum through the disc
(i) nearest to cross arm
(ii) nearest to the conductor
(iii) in the middle of the string
(iv) none of above

14. In order to improve string efficiency by the method of capacitance grading, the maximum capacitance is of the disc
(i) in the middle of the string
(ii) nearest to the cross-arm
(iii) nearest to the conductor
(iv) none of above

15. If the span is increased, the sag
(i) decreases
(ii) increases
(iii) remains same
(iv) none of above

16. Suspension type insulators are used for voltages beyond
(i) 400
(ii) 11 V
(iii) 33 kV
(iv) 800 V

17. The bundled-conductor arrangement reduces
(i) power loss die to corona
(ii) radio interference due to corona
(iii) inductance of the line
(iv) all above

18. In the length of transmission line increases, the resistance (R) of the line
(i) remains same
(ii) decreases
(iii) increases
(iv) none of above

19. Corona is affected by
(i) condition of atmosphere
(ii) size and spacing of conductors
(iii) line voltage
(iv) all above
20. If safety factor is doubled, the sag of the line will
(i) decrease
(ii) increase
(iii) remain the same
(iv) none of above

21. If span length is doubled with no change in other factors, the sag of the line will become
(i) 0.5 times
(ii) 2 times
(iii) 8 times
(iv) 4 times

22. In a string of suspension insulators, the discs are connected in
(i) parallel
(ii) series
(iii) series-parallel
(iv) none of above

23. The sag of an overhead line is affected by
(i) conductor weight per unit length
(ii) span and tension
(iii) wind and temperature
(iv) all above

24. Corona effect
(i) causes power loss in the line
(ii) causes interference in radio communication
(iii) produces radio frequency waves
(iv) all above

25. Corona effect
(i) produces ozone gas
(ii) reduces transmission efficiency
(iii) causes line to draw non-sinusoidal current
(iv) all above

26. If the string efficiency is increased, the voltage across the disc nearest to the conductor
(i) increases
(ii) decreases
(iii) remains the same
(iv) none of above

27. In a string of suspension insulators, the shunt capacitance can be decreased by using
(i) longer cross-arms
(ii) shorter cross-arms
(iii) longer spans
(iv) none of above

28. If the spacing between conductors increases, the corona effect
(i) increases
(ii) decreases
(iii) remains the same
(iv) none of above

29. In a 33 kV overhead line, there are 3 units in the string of insulators. The voltage across the string is
(i) 33kV
(ii) 11kV
(iii) 22 KV
(iv) 1905 kV

30. The inductance of the line will be small when
(i) GMD is high
(ii) GMR is high
(iii) both GMD and GMR high
(iv) GMD is low but GMR is high

31. The capacitance of a transmission line is neglected in case of
(i) medium line
(ii) long line
(iii) short line
(iv) none of above

32. 100 % string efficiency means
(i) self-capacitance is zero
(ii) shunt capacitance is maximum
(iii) self-capacitance is maximum
(iv) shunt capacitance is zero

33. The minimum phase-neutral voltage at which corona occurs is called
(i) critical disruptive voltage
(ii) visual critical voltage
(iii) flash-over voltage
(iv) none of above

34. If the conductor diameter decreases, inductance of the line
(i) remains same
(ii) decreases
(iii) increases
(iv) none of above

35. The effect of increase in temperature of overhead line is to
(i) increase the stress and length
(ii) decrease the stress but to increase length
(iii) decrease the stress and length
(iv) none of above

36. When the length of transmission line increases, its inductive reactance (XL)
(i) increases
(ii) decreases
(iii) remains same
(iv) none of above

37. The cost of an overhead line will increase if
(i) conductor spacing is decreased
(ii) conductor spacing is increased
(iii) ground clearance is decreased
(iv) none of above

38. The presence of earth wire in case of overhead lines
(i) increases line capacitance
(ii) decreases line capacitance
(iii) increases line inductance
(iv) decreases line inductance

39. Corona effect can be reduced by
(i) increasing conductor size
(ii) decreasing conductor size
(iii) decreasing conductor spacing
(iv) none of above

40. If supply frequency increases, the skin effect
(i) is increased
(ii) is decreased
(iii) remains same
(iv) none of above

41. A stranded conductor has
(i) less corona effect than a solid conductor
(ii) more corona effect than a solid conductor
(iii) same corona effect as in a solid conductor
(iv) none of above

42. The power loss in an overhead transmission line is mainly due to
(i) inductance of the line
(ii) capacitance of the line
(iii) resistance of the line
(iv) none of above

43. As the length of transmission line increases, is capacitive reactance (XC)
(i) increases
(ii) decreases
(iii) remains same
(iv) none of above

44. In d.c..transmission, the skin effect is
(i) large
(ii) small
(iii) zero
(iv) depends on voltage

45. The diameter of a round conductor is 1 cm. Its geometrical mean radius (G.M.R.) is
(i) 0.5 cm
(ii) 0.485 cm
(iii) 0.7788 cm
(iv) 1.256 cm

46. Capacitance of a transmission line
(i) affects transmission efficiency
(ii) affects power factor
(iii) causes charging current
(iv) all above

47. The skin effect depends upon
(i) nature of material
(ii) diameter of wire
(iii) frequency
(iv) all above

48. As the transmission voltage increases, the percentage resistance drop
(i) increases
(ii) decreases
(iii) remains same
(iv) none of above

49. The skin effect increases the
(i) resistance of the line
(ii) inductance of the line
(iii) capacitance of the line
(iv) all above

50. The voltage regulation of a transmission line is greatest for
(i) lagging p.f.
(ii) leading p.f
(iii) both (i) and (ii)
(iv) none of above

52. If spacing between the conductors is decreased, the inductance of the line
(i) increases
(ii) decreases
(iii) remains same
(iv) none of above

53. The charging current in a transmission line
(i) lags the voltage by 90°
(ii) leads the voltage by 90°
(iii) leads the voltage by 45°
(iv) lags the voltage by 45°

54. Transposition of transmission line is done to
(i) reduce line loss
(ii) balance line voltage drop
(iii) reduce skin effect
(iv) reduce corona

55. The charging current due to line capacitance depends upon
(i) line capacitance
(ii) line voltage
(iii) supply frequency
(iv) all above

56. Bundled conductors are used to
(i) reduce line inductance and capacitances
(ii) increase line inductance and capacitance
(iii) reduce corona loss and tine inductance
(iv) none of above

57. The capacitance of a transmission line is a
(i) shunt element
(ii) series element
(iii) shunt-series element
(iv) none of above

58. If lagging power factor of the load decreases, the line losses will
(i) decrease
(ii) increase
(iii) remain same
(iv) none of above

59. The length of a short transmission line is upto about
(i) 120km
(ii) 200km
(iii) 80 km
(iv) 400 km

60. The efficiency of a transmission line
(i) increases with the decreases in load p.f.
(ii) is independent of load p.f.
(iii) increases with the increase in load p.f.
(iv) decreases with the increase in load p.f.

61. The line constants of a transmission line are
(i) lumped
(ii) non-uniformly distributed
(iii) uniformly distributed
(iv) none of above

62. The receiving end power factor of a short transmission line is changing from lagging to leading. The voltage regulation of the line will
(i) remain same
(ii) increase
(iii) decrease
(iv) none of above

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