JNTU III B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008
Switchgear and protection
(Electrical & Electronic Engineering)
1. Explain Slepian’s theory of arc interruption and discuss its limitations. How does energy balance theory, explain the process of arc interruption?
2. (a) Compare the arc rupture in oil and air blast circuit breakers and summarize the relative advantages and disadvantages of these types of switch gear.
(b) Explain the operating duty of a circuit breaker.
3. With the help of neat sketch explain the principle of operation of Differential relays.
4. Explain with a diagram, the application of the Merz-Price circulating current system to the protection of alternators. What precautions must be taken in installing this system?
5. Describe with a neat sketch, the operation of Buchholtz relay.
6. (a) Explain over-current protection of feeders.
(b) How is the protection system graded with respect to the time of operation of relays.
7. (a) Explain the phenomenon of arcing ground.
(b) Suggest some methods to minimize the effect of this phenomenon with neat sketch.
8. (a) How over head transmission lines are protected from lightning strokes.
(b) Why ground wire is provided as the top lost conductor in high voltage transmission lines.