JNTU III B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008
Switchgear and protection
(Electrical & Electronic Engineering)
1. Explain the terms Recovery voltage, Restriking voltage and RRRV.
Derive an expression for the restriking voltage in terms of system capacitance and inductance.
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. Define the following terms and explain their significance in distance protection
(a) Reach of a distance relay.
(b) Under reach.
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. (a) Discuss earth fault protection for transformers.
(b) A 3-phase transformer rated for 33kV/6.6kV is connected star-delta and the protecting current transformer on the low voltage side have a ratio of 400/5. Determine the ratio of the current transformer on the HV side.
6. (a) What are the requirements of protection of lines?
(b) Write short notes on the following:
i. Fault bus protection
ii. Translay scheme.
7. (a) Discuss ungrounded system and resonant grounded system.
(b) Write short notes on Protection against arcing grounds.
8. (a) Explain clearly why lightning arresters are used.
(b) Explain about lightning absorbers and diverters.