## electrical

### Transmission and Distribution MCQ Objective Questions and Answers Page - 6

1.
 Cables used for  220 kV  lines are invariably A Compressed oil or compressed gas insulated. B Paper insulated. C Mica insulated. D None of the above. Answer : A Explanation :
2.
 The insulation use in a cable designed for use on  1,000 kV  is usually A Impregnated paper B Compressed  SF6  gas C PVC D Any of the above Answer : B Explanation :
3.
 Sulphur hexafluoride cable is insulated by A Impregnated paper B Polyvinyl chloride C High pressure oil D Compressed gas Answer : D Explanation :
4.
 In compressed gas insulated cable  SF6  has the gas pressure in the range of A 10 – 20 mm Hg B 80 – 100 mm Hg C 3 – 5 kg/cm2 D 40 – 50 kg/cm2 Answer : C Explanation :
5.
 At bridge crossings and near the railway track ternary lead cables are used because they A Are of high tensile strength B Are of low coefficient of thermal expansion C Are of low specific gravity D Can withstand shocks and vibrations Answer : C Explanation :
6.
 Internal pressure cables have the advantage(s) of A Elimination of external accessories. B Suitability for vertical run without any fear of drainage with suitable designs C Marked improvement in the pf of the cable dielectric with the increased pressure. D All of the above Answer : D Explanation :
7.
 With the rise in temperature, the insulation resistivity A Remains unchanged B Decreases linearly C Increases linearly D Reduces exponentially Answer : D Explanation :
8.
 The insulation resistance of a single-core cable is 200 MΩ/km. the insulation resistance for  5 km  length is A 40 MΩ B 1000 MΩ C 200 MΩ D 8 MΩ Answer : A Explanation :
9.
 The power factor of an open-ended cable can be improved by A Increasing the capacitance B Decreasing the capacitance C Increasing the conductor resistance D Increasing the insulation resistance Answer : D Explanation :
10.
 The capacitance of a cable increases A Linearly with the increase in cable length B Linearly with the decrease in cable length C Exponentially with the increase in cable length D None of the above Answer : A Explanation :
11.
 The capacitance of a cable depends upon the A Length of the cable B Relative permittivity of dielectric used in cable C Ratio of sheath diameter and core diameter D All of the above Answer : D Explanation :
12.
 The charring current drawn by the cable A Lags behind the voltage by  900 B Leads the voltage by 900 C Leads the voltage by 1800 D None of the above Answer : B Explanation :
13.
 In underground cables, the electrostatic stress is A Maximum at conductor surface and minimum at the sheath B Minimum at conductor surface and maximum at the sheath C Same at the conductor and sheath D Zero at the conductor as well on the sheath Answer : A Explanation :
14.
 In a cable of conductor diameter  ‘d’  and overall diameter with dielectric material  ‘D’  the maximum dielectric stress. A Occurs at the conductor surface and is proportional to  d B Occurs at the conductor surface and is proportional to  1/d C Occurs at the middle of the dielectric and is proportional to 1/D D Occurs at the outer surface of the dielectric and is proportional to  D Answer : B Explanation :
15.
 To obtain the minimum value of stress in cable, the ratio  (R/r)  should be A 2.13 B 2.718 C 1.96 D 1.5 Answer : B Explanation :
16.
 The surface impedance of a  50  miles long underground cable is  50 Ω. For a 25 miles length it will be A 25 Ω B 50 Ω C 100 Ω D None of these Answer : B Explanation :
17.
 The breakdown of insulation of a cable can be avoided economically by using A Insulation layers of different dielectrics B Intersheath C Either (a) or(b) D None of the above Answer : C Explanation :
18.
 Capacitance grading of cable means A Use of dielectric in different concentrations. B Introduction of Capacitance at various lengths of cable to counter the effect of inductance. C Use of dielectric of different permittivities. D Grading according to Capacitance per  km  length of the cable. Answer : C Explanation :
19.
 Grading of cables A Reduces insulation cost and increases current rating. B Reduces insulation cost but decreases current rating. C Increases both. D None of the above. Answer : A Explanation :
20.
 The intersheaths in cables are used to A Provide proper stress distribution B Minimize the stress C Use inferior insulation D Provide protection against moisture and voltage surges Answer : A Explanation :
21.
 The desired overall diameter of the conductor without increasing its x-sectional area can be had by A Using aluminium core instead of copper B Standing the copper conductors around a hemp centre C Standing the copper conductors over a lead tube D Any of the above Answer : D Explanation :
22.
 In a  3-core cable, the capacitance between two conductors  (with sheath earthed)  is  3 μF. The capacitance per phase will be A 1.5 μF B 3 μF C 6 μF D 12 μF Answer : C Explanation :
23.
 Underground cables are laid at sufficient depth so as to A Minimise temperature stresses B Minimise effects of shocks and vibrations owing to passing vehicles etc. C Avoid being unearthed easily owing to removal of soil D Both (a) and (b) Answer : B Explanation :
24.
 In case the communication cables are to be laid parallel to power cables the distance between the two should  be at least so that there is no interference. A 0.5 m B 2.0 m C 4.0 m D 0.05 m Answer : A Explanation :
25.
 While crossing the road the cable should be A Buried in trenches B Surrounded by sawdust to absorb vibrations C Laid in conduits or pipes D None of the above Answer : C Explanation :
26.
 The source(s) of heat generation in cables  is/are A Copper loss in conductor B Dielectric losses in cable insulation C Losses in metallic sheathings and armourings D All of the above Answer : D Explanation :
27.
 A cable carrying ac has A Leakage losses only B Hysteresis losses only C Hysteresis and leakage losses only D Hysteresis, leakage and friction losses Answer : C Explanation :
28.
 Dielectric hysteresis loss in a cable varies as A Impressed voltage B $\left&space;(Impressed&space;voltage&space;\right&space;)^{2}$ C $\left&space;(&space;Impressed&space;voltage\right&space;)^{\frac{1}{2}}$ D $\left&space;(&space;Impressed&space;voltage\right&space;)^{\frac{3}{2}}$ Answer : B Explanation :
29.
 The current carrying capacity of cables in dc is more than that in ac. It is mainly due to A Smaller hysteresis losses B Absence of harmonics C Absence of ripples D None of the above Answer : A Explanation :
30.
 The fault(s) which are likely to occur in cables  is/are A Breakdown of cable insulation B Cross-or short-circuit fault C Open-circuit fault D All of the above Answer : D Explanation :
31.
 The lead sheath of the cable may get damaged due to A Mechanically injury B Crystallisation of lead through vibrations C Chemical action with impurities present in the soil when buried in earth D Any of the above Answer : D Explanation :
32.
 The cables should not be operated too hot otherwise A Expansion of oil may cause sheath to burst. B The oil may loose its viscosity and it may start drawing off from higher levels. C Unequal Expansion may create voids in the insulation leading to ionization. D All of the above. Answer : D Explanation :
33.
 The breakdown voltage of a cable depends upon A Presence of moisture B Operating temperature C Time of application of the voltage D All of the above Answer : D Explanation :
34.
 Breakdown of cable insulation may occur due to A Thermal instability B Puncture C Tracking D Any of the above Answer : D Explanation :
35.
 Fibre-optic cables are used in power system applications mainly for A SCADA B Communication between power station and substation. C Communication between power station and load control centre. D All of these Answer : D Explanation :
36.
 The main criterion for selection of the size of a distributor for a radial distribution system is A Voltage drop B Corona loss C Temperature rise D Capital cost Answer : A Explanation :
37.
 The distribution system in India are mostly A Radial B Parallel C Network D Either (a)  or  (c) Answer : A Explanation :
38.
 As per electricity regulations in India the maximum permissible voltage change at consumer premises should be A $\pm&space;5$% of declared voltage B $\pm&space;6$% of declared voltage C $\pm&space;10$% of declared voltage D $\pm&space;12$%  of declared voltage Answer : B Explanation :
39.
 The cost of material used in a distribution circuit per kVA  of distributed power varies as A Square of linear dimensions of supply area B Directly according to  (supply area)2 C Cube of linear dimensions of supply area D None of the above Answer : B Explanation :
40.
 An approximate formula for loss factor in a distribution system is A Loss factor  =  0.3 × load factor + 0.7 (load factor)2 B Loss factor  =  0.5 (load factor) C Loss factor  =  load factor D Loss factor  =  0.7 × load factor + 0.3 (load factor)2 Answer : A Explanation :