## electrical

### Transmission and Distribution MCQ Objective Questions and Answers Page - 3

1.
 Disruptive corona begins in smooth cylindrical conductors in air at  NTP  if the electric field intensity at the conductor surface goes up to A 21.1 kV(rms)/cm B 21.1 kV(peak)/cm C 21.1 kV(average)/cm D 21.1 kV(rms)/m Answer : A Explanation :
2.
 The dielectric strength of air is A Proportional to barometric pressure B Proportional to absolute temperature C Inversely Proportional to barometric pressure D None of the above Answer : A Explanation :
3.
 Visual critical voltage is A Lower than disruptive critical voltage B Higher than disruptive critical voltage C Equal to critical voltage D None of the above Answer : B Explanation :
4.
 Critical voltage limit of a transmission line is increased by A Increasing the radius of the conductors B Increasing the spacing between conductors C Reducing the spacing between conductors D Reducing the radius of the conductors Answer : A Explanation :
5.
 Corona losses are minimised when A Conductor size is reduced B Smooth conductor is used C Sharp points are provided in the line hardware D Current density in conductor is reduced Answer : B Explanation :
6.
 The corona loss on a particular system at  50 Hz  is  1kW/km per phase. What is the corona loss at  60 Hz in kW/km per phase  ? A 0.83 B 1.0 C 1.13 D 1.2 Answer : C Explanation :
7.
 In a transmission line the distributed constants are A Resistance and shunt conductance only B Resistance and inductance only C Resistance, inductance and capacitance only D Resistance, inductance, capacitance and shunt conductance Answer : D Explanation :
8.
 Skin effect depends upon A X-section of conductor B Supply frequency C Permeability of conductor material D All of the above Answer : D Explanation :
9.
 Skin effect in transmission line is due to A Supply frequency B Self-inductance of conductor C High sensitivity of material in the centre D Both (a) and (b) Answer : D Explanation :
10.
 Increasing the frequency of transmission line will A Increase shunt reactance B Decrease line resistance C Increase line resistance D Decrease series reactance Answer : C Explanation :
11.
 Skin effect exists in A Cable carrying DC current B DC transmission line only C AC transmission line only D DC as well as AC transmission line Answer : C Explanation :
12.
 Skin effect A Increases the effective resistance and effective internal reactance B Reduces the effective resistance and effective internal reactance C Increases the effective resistance but reduces the effective internal reactance D Reduces the effective resistance but increases the effective internal reactance Answer : C Explanation :
13.
 The skin effect of a conductor reduces with the increase in A Supply frequency B Resistivity of the conductor material C X-section of conductor D Permeability of conductor material Answer : B Explanation :
14.
 Skin effect in conductor is proportional to A $\left&space;(&space;diameter&space;of&space;conductor&space;\right&space;)^{\frac{1}{2}}$ B diameter of conductor C $\left&space;(&space;diameter&space;of&space;conductor&space;\right&space;)^{2}$ D $\left&space;(&space;diameter&space;of&space;conductor&space;\right&space;)^{4}$ Answer : C Explanation :
15.
 In order to reduce the skin effect at  UHF A Copper tubes with silver plating are used B Copper rods with silver plating are used C Anodised conductors are used D Painted conductors are used Answer : A Explanation :
16.
 A  100 km  long transmission line is loaded at  110 kV . if the loss of line is  15 MW  and the load is  150 MVA, the resistance of the line is A 8.06 ohms per phase B 0.806 ohms per phase C 0.0806 ohms per phase D 80.6 ohms per phase Answer : A Explanation :
17.
 Consider a long, two-wire line composed of solid round conductors. The radius of both conductors is  0.25 cm  and the distance between their centres is  1 m. if this distance is doubled, then the inductance per unit length. A Doubles B Halves C Increases but does not double D Decreases but does not halve Answer : C Explanation :
18.
 The inductance of single-phase two-wire power transmission line per  km  gets doubled when the A Distance between the wires is doubled B Distance between the wires is increased four fold C Distance between the wires is increased as square of the original distance D Radius of the wire is doubled Answer : C Explanation :
19.
 For  11 kV line, the inductance per  km  per phase will be of the order of A 1 H B 0.1 H C 1 mH D 0.1 mH Answer : C Explanation :
20.
 A 3-phase transmission line has its conductors at the corners of an equilateral triangle with side  3 m. the diameter of each conductor is  1.63 cm. the inductance of the line per phase per  km  is A 1.232 mH B 0.182 mH C 1.093 mH D 1.043 mH Answer : A Explanation :
21.
 The conductors of a  10 km  long, single-phase, 2-wire line are separated by a distance of  1.5 m. the diameter of each conductor is  1 cm. if the conductors are of coper, the inductance of the circuit is A 50.0 mH B 45.3 mH C 23.8 mH D 19.6 mH Answer : C Explanation :
22.
 The inductance of a power transmission line increases with A Decrease in line length B Increase in diameter of conductor C Increase in spacing between the phase conductors D Increase in load current carried by the conductors Answer : C Explanation :
23.
 The inductance of a transmission line minimum when A GMD is high B GMR is high C Both GMD and GMR are high D GMD is low and GMR is high Answer : D Explanation :
24.
 Hollow conductors are used in transmission lines to A Reduce weight of copper B Improve stability C Reduce corona D Increase power transmission capacity Answer : C Explanation :
25.
 In  hv  transmission, the spacing between sub-conductors of a bundle is approximately A 20 cm B 40 cm C 80 cm D 3.5 cm Answer : B Explanation :
26.
 For a stranded conductor, the ratio of GMR to actual radius is A Equal to 1 B More than 1 C Equal to 0.7788 D Less than 0.7788 Answer : D Explanation :
27.
 Bundled conductors in EHV transmission system provide A Reduced capacitance B Increased capacitance C Increased inductance D Increased voltage gradient Answer : B Explanation :
28.
 Which one of the following statements is not correct for use of bundled conductors in transmission lines  ? A Control of voltage gradient B Reduction in corona loss C Reduction in radio interference D Increase in interference with communication lines Answer : D Explanation :
29.
 Bundled conductors are mainly used in high voltage overhead transmission lines to A Reduce transmission line losses. B Increase mechanical strength of the line. C Reduce corona. D Reduce sag. Answer : C Explanation :
30.
 Proximity effect A Is more pronounced for large conductors, high frequencies and close proximity. B Increases the resistance of the conductors and reduces the self-reactance. C Is substantially eliminated with stranded conductors. D All of the above Answer : D Explanation :
31.
 Capacitance in equivalent circuit of transmission line is due to A Difference in potential of line. B Leakage of current. C Presence of magnetic flux. D Current in the line. Answer : A Explanation :
32.
 If the separation between the three phases of transmission line in increased then A The inductance will increase and capacitance will remain unchanged. B Both the inductance and capacitance will increase. C The inductance will increase and capacitance will decrease. D The inductance will decrease and capacitance will increase. Answer : C Explanation :
33.
 The recharging reactance of  50 km  length of the line is  1500 Ω. What is the charging reactance for  100 km  length of the line  ? A 1500 Ω B 3000 Ω C 750 Ω D 600 Ω Answer : C Explanation :
34.
 Bundled conductors are used to A Reduce inductance of the line. B Reduce both inductance and capacitance. C Reduce corona loss. D Reduce corona loss and the line inductance Answer : D Explanation :
35.
 If the effect of earth is taken into account, the capacitance of line to ground A Decreases B Increases C Remains unaltered D Becomes infinite Answer : B Explanation :
36.
 For equilateral spacing of conductors of an untransposed  3-phase line, we have A Balanced receiving-end voltage  and  no communication interference. B Unbalanced  receiving-end voltage  and  no communication interference. C Balanced receiving-end voltage  and  communication interference. D Unbalanced  receiving-end voltage  and  communication interference. Answer : A Explanation :
37.
 Transmission lines are transposed to A Reduce corona loss. B Reduce skin effect. C Prevent interference with neighbouring telephone lines. D Prevent short-circuit between any two lines. Answer : C Explanation :
38.
 Transposition of Transmission line is done to A Reduce line loss. B Reduce skin effect. C Balance line voltage drop. D Reduce corona Answer : C Explanation :
39.
 High voltage Transmission lines are transposed because then A Corona losses can be minimized. B Computation of inductance becomes easier. C Voltage drop in the lines can be minimized. D Phase voltage imbalances can be minimized. Answer : D Explanation :
40.
 The concept of an electrically short, medium and long line is primarily based on the A Nominal voltage of the line. B Physical length of the line. C Wavelength of the line. D Power transmitted over the line. Answer : B Explanation :
41.
 Equivalent  $\pi$  model is quite suitable for analysing the performance of transmission line of A 50 km length B 150 km length C 250 km length D All of the above lengths Answer : C Explanation :