Model Question Paper-I with effect from 2018-19
15EE72
Seventh Semester B.E.(CBCS) Examination
Power System Protection
(Core subject, E&EE)
Time: 3 Hrs Max.Marks: 80
Note: Answer any FIVE full questions, choosing at least ONE question from each module.
Module-1
1. List and explain the essential qualities of a protective relay. (06 Marks)
Derive an expression for torque produced by an induction relay. (05 Marks)
What are the advantages of static relays over electromechanical relays? (05 Marks)
OR
2. With a neat sketch, explain the operating principle of a rectifier bridge amplitude type comparator. (05 Marks)
Draw the schematic diagram of a numerical relay and explain the functions of various components. (06 Marks)
The current rating of an Overcurrent relay is 5A. The relay has a plug setting of 150% and the time setting of 0.4. The CT ratio is 400/5. Determine the operating time of the relay for a fault current of 6000A. At TMS=1, operating time at various PSM are given in the below table. (05 Marks)
PSM
2
4
5
8
10
20
Operating Time in Seconds
10
5
4
3
2.8
2.4
Module-2
3. With a neat sketch, explain the construction and working principle of a reverse power
or directional relay. (08 Marks)
What is an impedance relay? Explain its operating principle, torque equation and
operating characteristics for impedance relay. (08 Marks)
OR
4. (a)What are the advantages of numerical overcurrent relays over conventional
overcurrent relays. (04 Marks)
(b)Explain stepped time-distance characteristic of three distance relaying units used for
II, III zone of protection. (06 Marks)
Figure.a shows distance protection for a section of a power system.
The I zone setting at A and B is 150Ω.
What will be impedance seen by the relay at A for a fault at F1?
ii) Will the relay at B trip for a fault at F1 before the circuit breaker at A has tripped?
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iii) If the circuit breaker C2 fails for a fault at F2, will the fault be cleared by relays at A
and
iv) How will the fault at F2 be cleared? (06 Marks)
Module-3
5. (a)Define the term with reference to power line protection. List the different types of wire pilot protection schemes and explain for any one of the scheme.(08 Marks)
(b)With a neat sketch explain the working of differential protection of 3-Phase circuits and balanced (opposed) voltage differential protection. (08 Marks)
OR
6. What are the protective devices employed for the protection of an alternator against
Overvoltage. ii) Overspeed? Discuss them in brief. (06 Marks)
Write a short note on "Buchholz relay" used for the protection of transformers to
detect incipient fault. (05 Marks)
With a neat sketch explain the working of frame leakage protection used for buszone
protection. (05 Marks)
Module-4
7. With a neat sketch, explain the recovery rate theory and energy balance theory of arc interruption in a circuit breaker. (09 Marks)
With a neat sketch and waveform explain the interruption of capacitive current.
(07 Marks)
OR
8. (a)With a neat sketch explain the working of axial blast circuit breaker. (05 Marks)
(b)What are the advantages and disadvantages of SF6 circuit breaker. (06 Marks)
With a neat sketch, explain the direct testing of circuit breaker. (05 Marks)
Module-5
9. Explain the construction and operation of the HRC Cartridge fuse. What are its advantages and disadvantages? (08 Marks)
With a neat figure explain the working of
i)Rod gap arrestor. ii) Expulsion type arrestor. (08 Marks)
OR
10. (a)State any four essential requirements of a surge diverter. (04 Marks)
With a neat sketch, explain the construction and working of Klydonograph instrument used for the measurement of surge voltage. (06 Marks)
Explain the modules/ components of GIS. (06 Marks)
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