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SPPU Electrical Engineering (Semester 8)
Swichgear and Protection
December 2016
Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

Solve any one question fromQ.1(a,b) and Q.2(a,b)
1(a) Explain low resistance principle of are interruption in case of circuit breaker.
4 M
1(b) In a 220kv system, the reactance & capacitance upto the location of circuit breaker is 8Ω and 0.025μf respectively. A resistance of 600Ω is connected across the contacts of the circuit breaker.
Determine-
i) Natural frequency of oscillations
ii) Damped frequency of oscillations
iii) Critical value of resistance which will give no transient oscillations.
6 M

2(a) A Vacuum circuit breaker is rated as 3 phase 1500 Amp, 2000 MVA, 33 kv, 3 seconds. Determine-
i) the breaking current
ii) Making current
iii) Short time current
iv) Rated normal current
4 M
2(b) In case of circuit breaker, explain following ratings.
i) Making current
ii) Breaking current
iii) Short time current rating
6 M

Solve any one question fromQ.3(a,b) and Q.4(a,b)
3(a) Write a short note on 'zones of protection'
4 M
3(b) Explain important properties of SF6 gas used in case of SF6 CB
6 M

4(a) Classify relays on the basis of operating time.
4 M
4(b) Explain following essential qualities of protective relaying-
i) Stability
iii) Discrimination
6 M

Solve any one question fromQ.5(a,b) and Q.6(a,b)
5(a) Draw a block diagram of static relay & explain its working. State advantages & limitations of static relay.
10 M
5(b) Explain the construction & working of metal oxide arresters state its advantages & disadvantages.
8 M

6(a) Draw a block diagram of numerical relay. & explain its working state its advantages over conventional & static relays.
10 M
6(b) Write a short note on -
i) Smpling theorem
ii) PMU ( phasor measurement unit)
8 M

Solve any one question fromQ.7(a,b) and Q.8(a,b)
7(a) Explain with neat diagram protection scheme of transformer against incipient faults.
8 M
7(b) With neat diagram explain working of single phasing preventer in case of 3phase induction motor.
8 M

8(a) Explain the protection of alternater against
i) Loss of prime-mover
ii) Interturn faults
iii) Loss excitation
10 M
8(b) A 3phase 66kv/11kv, star-delta connected transformer is protected by merz price-system. The CTs on LT side have ration of 420/5. Calculate the CT ratio on HT side draw this protection scheme also.
6 M

Solve any one question fromQ.9(a,b) and Q.10(a,b)
9(a) Explain the effect of arc resistance and power swing on the performance of distance relay.
8 M
9(b) With a neat sketch, explain three step distance protection scheme for transmission lines.
8 M

10(a) Explain how impedance relay is used for transmission line protection. Derive its torque equation. Draw its characteristics on R-x plain.
8 M
10(b) Draw & explain block schematic of carrier aided protection.
8 M

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