 ## electrical

### Transmission and Distribution MCQ Objective Questions and Answers Page - 2

1.
 The maximum tension in a section of overhead line conductor between two supports of unequal height occurs at A The higher support B The lower point C The midpoint of the conductor D None of the above Answer : A Explanation :
2.
 Stringing chart is useful A For finding the sag in the conductor B In the design of tower C In the design of insulator string D Finding the distance between towers Answer : A Explanation :
3.
 Hot template curves are plots of A Temperature and humidity B Conductor sag and span lengths C Conductor weight and sag D None of the above Answer : B Explanation : Hot template curves are used to show the relationships between Conductor sag and span lengths.
4.
 The effect of wind pressure is more predominant on A Insulators B Transmission  lines C Supporting towers D None of the above Answer : C Explanation :
5.
 Galloping in transmission line conductors arises due to A Asymmetrical layers of ice formation B Vortex phenomenon in light winds C Heavy weight of the line conductors D Adoption of horizontal conductor configuration Answer : A Explanation :
6.
 Which of the following is reduced by using stock bridge dampers on power overhead transmission lines  ? A Sag B Conductor vibration C Line losses D Mechanical tension Answer : B Explanation :
7.
 The sag of the conductors of a transmission line is 2.5 m when the span is  250 m. now if the height of supporting tower is increased by  25%, the sag will A Reduce by 25% B Increase by 25% C Reduce by 12.5% D Remain unchanged Answer : D Explanation :
8.
 For a 400 kV line, the spacing between phase conductors is around A 8 m B 11 m C 14 m D 17 m Answer : A Explanation :
9.
 Stranded conductors usually have a central wire around which there are successive layers of  6,12,18,24  wires.  For  n-layers, the total number of individual wires is A 3 n (n+1) B 2 n (n+1) C 3 n (n+1) + 1 D 2 n (n+1) + 1 Answer : C Explanation :
10.
 The diameter of each strand is  d  then the diameter of  n-layer  stranded conductor will be A (2 n + 1) d B 3 (n + 1) d C (2 n – 1) d D 3 (n – 1) d Answer : A Explanation :
11.
 Strain type insulators are used A At dead ends B At intermediate anchor towers C On straight runs D Any of (a) or (b) Answer : D Explanation :
12.
 Wavy structure of pin insulator increases its A Mechanical strength B Puncture strength C Flash-over voltage D Thermal strength Answer : C Explanation :
13.
 Which type of insulators are used on  132 kV transmission lines? A Pin type B Disc type C Shackle type D Pin and Shackle type Answer : B Explanation : The insulators are used on  132 kV transmission lines is Disc type.
14.
 Whenever the conductors are dead-ended or there is a change in the direction of transmission line, the insulators used are of the A Pin type B Suspension type C Strain type D Shackle type Answer : C Explanation :
15.
 The number of discs in a string of insulators for  400 kV  ac overhead transmission line lies in the range of A 32 to 33 B 22 to 23 C 15 to 16 D 9 to 10 Answer : B Explanation :
16.
 100 per cent string efficiency means A One of the insulators discs shorted B Zero potential across each disc C Equal potential across each insulator disc D None of the above Answer : C Explanation :
17.
 If the frequency of a transmission system is changed from  50 Hz to 100 Hz, the string efficiency A Will increase B Will decrease C Remain unchanged D May increase or decrease depending on the line parameters. Answer : C Explanation :
18.
 The string efficiency of a high-voltage line is around A 100% B 80% C 40% D 10% Answer : B Explanation :
19.
 In three-unit insulator string, voltage across the lowest unit is  17.5 kV and string efficiency is 84.28%. the total voltage across the string will be equal to A 8.285 kV B 44.25 kV C 88.25 kV D 442.5 kV Answer : B Explanation :
20.
 Two-insulator discs of identical capacitance value  C  makes up a string for a  22 kV , 50 Hz, single-phase overhead line insulation system. If the pin to earth capacitance is also  C, then the string efficiency is A 50% B 75% C 90% D 86% Answer : B Explanation :
21.
 In a cable the sheath radius is  R and conductor radius is  r. as  r changes from  0.5 R  to  0.25 R  the maximum voltage gradient in the dielectric A Decreases by about 6% B Increases by about 6% C Increases by about 15% D Decreases by about 15% Answer : B Explanation :
22.
 The insulators may fail due to A Flash over B Short-circuits C Deposition of dust D Any of the above Answer : D Explanation :
23.
 The purpose of guard ring in transmission lines is to A Reduce the earth capacitance of the lowest unit B Increase the earth capacitance of the lowest unit C Reduce the transmission line losses D None of the above Answer : A Explanation : The purpose of guard ring in transmission lines is to reduce the earth capacitance of the lowest unit.
24.
 Which of the following statements is true regarding corona  ? A Corona takes place at a voltage lower than breakdown voltage. B Corona takes place at a voltage higher than breakdown voltage. C Corona is a current phenomenon. D Corona increases the transmission line efficiency. Answer : A Explanation :
25.
 Corona is accompanied by A Violet visible discharge in darkness B Hissing sound C Power loss D All of the above Answer : D Explanation :
26.
 Ozone effect can be detected by A Presence of ozone detected by odour B Hissing sound C Faint luminous glow of bluish colour D All of the above Answer : D Explanation :
27.
 Corona loss increases with A Decrease in conductor size and increase in supply frequency. B Increase in both conductor size and supply frequency. C Decrease in both conductor size and supply frequency. D Increase in conductor size and decrease in supply frequency. Answer : A Explanation :
28.
 The good effect of corona on overhead lines is to A Increase the line carrying capacity due to conducting ionised air envelope around the conductor. B Increase the power factor due to corona loss. C Reduce the radio interference from the conductor. D Reduce the steepness of surge fronts. Answer : D Explanation :
29.
 Compared with a solid conductor of the same radius, corona appears on a stranded conductor at a lower voltage, because stranding A Assists ionisation B Makes the current flow spirally about the axis of the conductor C Produces oblique sections to a plane perpendicular to a axis of the conductor D Produces surfaces of smaller radius Answer : D Explanation :
30.
 Corona loss can be reduced by using A Solid conductor of diameter  ‘d’ B Hollow conductor of diameter  ‘d+d’ C Bundle conductor D Both (b) and (c) Answer : D Explanation :
31.
 Corona loss can be reduced by the use of hollow conductors because A The current density is reduced B The eddy current in the conductor is eliminated C For a given cross section, the radius of the conductor is increased. D Of better ventilation in the conductor Answer : C Explanation :
32.
 Corona occurs between two transmission conductors when they A Have high potential difference B Are closely spaced C Carry dc power D Both (a) and (b) Answer : D Explanation :
33.
 In humid weather, the corona occurs at a voltage A Much less than that needed in fair weather B Much higher than that needed in fair weather C Equal to that needed in fair weather D None of the above Answer : A Explanation :
34.
 The effect of corona is A Increased energy loss B Increased reactance C Increased inductance D All of the above Answer : A Explanation :
35.
 The charging current in a transmission line increases due to corona effect because corona increases A Line current B Effective line voltage C Power loss in lines D The effective conductor diameter Answer : D Explanation :
36.
 The chances of occurrence of corona are maximum during A Humid weather B Dry weather C Winter D Hot summer Answer : A Explanation : The chances of occurrence of corona are maximum during Humid weather.
37.
 Corona is likely to occur maximum in case of A Distribution lines B Transmission lines C Domestic wiring D Service mains Answer : B Explanation :
38.
 The only advantage of corona is that it A Produces a pleasing luminous glow B Makes line current sinusoidal C Works as a safety valve for surges D Ozone gas is produced Answer : C Explanation :
39.
 Presence of ozone owing to corona A Improves the pf B Reduces the pf C Corrodes the material D Improves regulation Answer : C Explanation :
40.
 What is the approximate breakdown strength of atmospheric air at N.T.P.  ? A 0.3 kV/cm B 1.0 kV/cm C 3 kV/cm D 30 kV/cm Answer : D Explanation :
41.
 Which of the following are the constants of the transmission lines? A Resistance B Inductance C Capacitance D All of the above Answer : D Explanation :
42.
 The phenomenon of rise in voltage at the receiving end of the open-circuited or lightly loaded line is called the A Seeback effect B Ferranti effect C Raman effect D None of the above Answer : B Explanation :
43.
 The square root of the ratio of line impedance and shunt admittance is called the A Surge impedance of the line B Conductance of the line C Regulation of the line D None of the above Answer : A Explanation : The square root of the ratio of line impedance and shunt admittance is called the Surge impedance of the line.
44.
 Low voltage cables are meant for use up to A 1.1 kV B 3.3 kV C 6.6 KV D 11 kV Answer : C Explanation :
45.
 The operating voltage of high voltage cables is up to A 1.1 kV B 3.3 kV C 6.6 KV D 11 kV Answer : D Explanation :
46.
 The operating voltage of super-tension cables is up to A 3.3 kV B 6.6 KV C 11 kV D 33 kV Answer : D Explanation :
47.
 The operating voltage of extra high-tension cables is up to A 6.6 kV B 11 kV C 33 kV D 66kV Answer : D Explanation :
48.
 Which of the following methods is used for laying of underground cables? A Direct laying B Draw-in-system C Solid system D All of the above Answer : D Explanation :