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


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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