Important Questions of Mechanical Design of Overhead Lines :

1. Name the Important components of an overhead transmission lines.

2. Discuss the various conductor materials used for overhead lines. What are their relative advantages and disadvantages ?

3. Discuss the various types of line supports.

4. Why are insulators used with overhead lines ? Discuss the desirable properties of insulators.

5. Discuss the advantages and disadvantages of (i) pin-type insulators (ii) suspension type insulators.

6. Explain how the electrical breakdown can occur in an insulator.

7. What is a strain insulator and where is it used ? Give a sketch to show its location.

8. Give reasons for unequal potential distribution over a string of suspension insulators,

9. Define and explain string efficiency. Can its value be equal to 100% ?

10. Show that in a string of suspension insulators, the disc nearest to the conductor has the highest voltage across it.

11. Explain various methods of improving suing efficiency.

12. What is corona ? What are the factors which affect corona ?

13. Discuss the advantages and disadvantages of:corona.

14. Explain the following terms with reference to corona :

(i) Critical disruptive voltage

(ii) Visual critical voltage

(iii) Power loss due to corona

15. Describe the various methods for reducing corona effect in an overhead transmission line.

16. What is a sag in overhead lines ? Discuss the disadvantages of providing too small or too large sag on a line.

17. Deduce an approximate expression for sag in overhead lines when

(i) supports are at equal levels

(ii) supports are at unequal levels.

18. What is the need for stranding the conductors ?

19. Is sag a necessity or an evil ? Discuss.

20. String efficiency for a d.c. system is 100% ? Discuss.

21. Can string efficiency in an a.c. system be 100%?

22. Why are suspension insulators preferred for high voltage power.

23. Give reasons for the following :

(i) C.S.R. conductors are preferred for transmission and distribution lines.

(ii) Conductors are not fully stretched between supports.

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