JNTU B.Tech II Semester Examinations, SWITCHGEAR AND PROTECTION, Apr/May 2008

JNTU B.Tech II Semester Examinations, SWITCHGEAR AND PROTECTION, Apr/May 2008

(Electrical & Electronic Engineering)

Time: 3 hours Max Marks: 80

Answer any FIVE Questions

All Questions carry equal marks

SET-II

1. Explain Slepian’s theory of arc interruption and discuss its limitations. How does energy balance theory, explain the process of arc interruption? [8+8]

 

2. (a) Classify the types of circuit breakers when the arc quenching medium is the criterion?

(b) Mention the voltage range for which a particular type of circuit breaker is recommended. [8+8]

 

3. Explain the ‘Differential protection’. State the various applications of differential

protection. [8+8]

 

4. (a) Explain how the inclusion of a resistance in the neutral earthing circuit of an

alternator affects the performance of the differential protection of the three-phase stator.

(b) Describe how protection is provided in large turbo-alternators against earth fault in the rotor [8+8]

 

5. (a) Discuss biased differential protection for transformers.

(b) A 3-phase, 33/6.6 kV transformer is connected in star/delta and the protecting current transformer on the LV side have a ratio of 300/5. What will be the ratio of the current transformer on the HV side? [6+10]

 

6. (a) Explain over-current protection of feeders.

(b) How is the protection system graded with respect to the time of operation of relays. [8+8]

 

7. (a) Describe the various methods of grounding.

(b) A 132kV, 3 phase, 50Hz overhead line of 100 km length has a capacitance to earth of each line of 0.01 ?F per km. Determine inductance and kVA rating of the arc suppression suitable for this line. [10+6]

 

8. (a) What are volt time curves.

(b) What is their significance in power system studies. [8+8]

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