(a) between 2 and 3✔
(b) between 5 and 6
(c) between 8 and 10
(d) between 12 and 14
27. Solid type cables are considered unreliable beyond 66 kV because
(a) insulation may melt due to higher temperature
(b) skin effect dominates on the conductor
(c) of corona loss between conductor and sheath material
(d) there is a danger of breakdown of insulation due to the presence of voids✔
28. If the length of a cable is doubled, its capacitance
(a) becomes one-fourth
(b) becomes one-half
(c) becomes double✔
(d) remains unchanged
29. In cables the charging current
(a) lags the voltage by 90°
(b) leads the voltage by 90°✔
(c) lags the voltage by 180°
(d) leads the voltage by 180°
30. 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
(a) one half✔
(6) double
(c) four times
(d) none of the above
31. If a cable of homogeneous insulation has a maximum stress of 10 kV/mm, then the dielectric strength of insulation should be
(a) 5 kV/mm
(b) 10 kV/mm✔
(a) 15 kV/mm
(d) 30 kV/mm
32. In the cables, sheaths are used to
(a) prevent the moisture from entering the cable✔
(b) provide enough strength
(e) provide proper insulation
(d) none of the above
33. The intersheaths in the cables are used to
(a) minimize the stress
(b) avoid the requirement of good insulation
(c) provide proper stress distribution✔
(d) none of the above
34. The electrostatic stress in underground cables is
(a) same at the conductor and the sheath
(b) minimum at the conductor and maximum at the sheath
(c) maximum at the conductor and minimum at the sheath✔
(d) zero at the conductor as well as on the sheath
35. The breakdown of insulation of the cable can be avoided economically by the use of
(a) inter-sheaths
(b) insulating materials with different dielectric constants
(c) both (a) and (b)✔
(d) none of the above
36. The insulation of the cable decreases with
(a) the increase in length of the insulation✔
(b) the decrease in the length of the insulation
(c) either (a) or (b)
(d) none of the above
37. A cable carrying alternating current has
(a) hysteresis losses only
(b) hysteresis and leakage losses only✔
(c) hysteresis, leakage and copper losses only
(d) hysteresis, leakage, copper and friction losses
38. In a cable the voltage stress is maximum at
(a) sheath
(6) insulator
(e) surface of the conductor
(d) core of the conductor✔
39. Capacitance grading of cable implies
(a) use of dielectrics of different permeabilities✔
(b) grading according to capacitance of cables per km length
(c) cables using single dielectric in different concentrations
(d) capacitance required to be introduced at different lengths to counter the effect of inductance
(e) none of the above
40. Underground cables are laid at sufficient depth
(a) to minimise temperature stresses
(b) to avoid being unearthed easily due to removal of soil
(c) to minimise the effect of shocks and vibrations due to gassing vehicles, etc.✔
(d) for all of the above reasons
41. The advantage of cables over overhead transmission lines is
(a) easy maintenance
(b) low cost
(c) can be used in congested areas✔
(d) can be used in high voltage circuits
42. The thickness of metallic shielding on cables is usually
(a) 0.04 mm✔
(b) 0.2 to 0.4 mm
(e) 3 to 5 mm
(d) 40 to 60 mm
43. Cables for 220 kV lines are invariably
(a) mica insulated
(b) paper insulated
(c) compressed oil or compressed gas insulated✔
(d) rubber insulated
(e) none of the above
44. Is a cable is to be designed for use on 1000 kV, which insulation would you prefer ?
(a) Polyvinyle chloride
(b) Vulcanised rubber
(c) Impregnated paper
(d) Compressed SFe gas✔
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