SWITCHGEAR AND PROTECTION JNTU previous years question papers

SWITCHGEAR AND PROTECTION JNTU previous years question papers

Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks



1. Write a short notes on the rate of restriking voltage and explain its importance in arc extinction. [8+8]

2. (a) What are the key features of SF6 Circuit Breaker over other circuit breakers.
(b) Write a short notes on the maintenance of Oil circuit breaker. [8+8]

3. (a) Expain the following terms with respect to switch gear protection
i. Pick up level
ii. operating time
iii. Reach
iv. Under Reach
v. Over Reach.
(b) An earth fault setting relay has a setting of 20%, current rating 5A, it is connected to a C.T of ratio 500:5. Calculate pick up current in primary for which the earth fault relay operates. [8+8]

4. Discuss the unbalanced loading and overload protection in alternators. Overload protection is not necessary for alternators’ ? Justify yourself? [8+8]

5. Draw the connection diagram of a differential relay for the protection a star-delta transformer. How does bias the winding of a differential relay restricts malfunctioning of the relay against
(a) CT mismatch
(b) Onload changing and
(c) Magnetising current? What is magnetising Inrush current? What is the principle used to make a differential relay insensitive to magnetizing inrush current.[4+6+2+4]

6. (a) Explain bus bar protection need special attention. Why?
(b) What is back up protection of bus bars? [10+6]

7. (a) Discuss about effectively grounded system and ungrounded system.
(b) A 132 kV, 3-Phase, 50Hz, 100km long transmission line has a capacitance of 0.012µF per km per phase. Determine the inductive reactance and kVA rating of the arc suppression coil suitable for this line.

8. Explain the working lightning arrests. [16]
(a) Rod gap
(b) Horn gap
(c) Multi gap
(d) Expulsion type.

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