Transmission and Distribution line MCQ Part-4

1. The equivalent capacitor arrangement of a two-string insulator is shown in the figure. The maximum voltage that each unit can withstand should not exceed 17.5 kV. The line voltage of the complete string is________.

a. 17.5 kV

b. 33 kV

c. 35 kV

d. 37.3 kV

2. In a cable the sheath radius is R and conductor radius is r. As r changes from 0.5R to 0.25R 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%

3. Consider the following statements :

In the case of suspension type insulators, the string efficiency can be improved by________.

1. Using a longer cross arm                    2. Using a guard ring 

3. Grading the insulator discs                 4. Reducing the cross-arm length   

a. 1,2 and 3 are correct

b. 2,3 and 4 are correct

c. 2 and 4 are correct

d. 1 and 3 are correct

4. The ratio of puncture voltage to the flash-over voltage of a line insulator is________.

a. Equal to 1

b. Lower than 1

c. Much greater than 1

 

5. The insulator may fail due to________.

a. Flash over

b. Short-circuits

c. Deposition of dust

d. Any of the above

 

6. 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

7. The use of a guard ring________.

a. Equalises the voltage division between insulator discs

b. Is unnecessary complication

c. Decreases string efficiency 

8. Corona is____________.

a. Partial breakdown of  air

b. Complete breakdown of air

c. Sparking between lines

9. 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

10. Which of the following statements regarding corona are true ?

1. It causes radio interference 

2. It attenuates lightning surges

3. It amplifies power less

4. It causes power loss

5. It is more prevalent in the middle conductor of a transmission line employing a flat conductor configuration

Select thee correct answer using the codes given below.

Codes:

a. 1,3,5

b. 2,3,4

c. 1,2,4,5

d. 2,3,4,5 

11. Corona is accompanies by________.

a. Violet visible discharge in darkness

b. Hissing sound

c. vibration

d. power loss

e. Radio-interference

f. Ozone

g. All of the above

 

12. Ozone effect can be detected by__________.

a. Presence of ozone detected by odour

b. Hissing sound

c. Faint luminous glow of bluish color

d. All of the above

 

13. 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

14.  The good effect of corona on overhead line is to____________.

a. Increases the line carrying capacity due to conducting ionised air envelope around 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

15. Compared with 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 

16. 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 

17. Bundled conductors reduce_______.

a. Surface electric stress of conductor

b. Increases the line reactance

c. Decreases the line capacitance

18. Corona loss in a transmission line is dependent on_________.

a. Diameter of the conductor

b. Material of the conductor

c. Height of the conductor

19. 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)  

 

20. The effect of corona is_________.

a . Increased energy loss

b. Increased reactance

c. Increased inductance

d. All of the above

21. 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

22. 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

 

23.  The chances of occurrence of corona are maximum during_______.

a. Humid weather

b. Dry weather

c. Winter

d. Hot summer

24. Corona is likely to occur maximum in case of________.

a. Distribution lines

b. Transmission lines

c. Domestic wiring

d. Service mains

25. Corona is affected by___________.

a. Size of the conductor

b. Shape of surface condition of the conductor

c. Operating voltage

d. All of the above

26. The only advantage of corona is that it__________.

a. Produces a pleasing luminous glow

b. Make  line current sinusoidal

c. Works as a safety valve for surges

d. Ozone gas is produced

27. Presence of ozone owing to corona__________.

a. Improves the pf

b. Reduces the pf

c. Corrodes the material

d. Improves regulation

 

Transmission and distribution line MCQ Part-1

Transmission and Distribution line MCQ Part-2

Transmission and Distribution line MCQ Part-3

Transmission and Distribution line MCQ Part-5

Transmission and Distribution line MCQ Part-6

Transmission and Distribution line MCQ Part-7