M.E. DEGREE EXAMINATION, JUNE 2012.
Second semester
Power Systems Engineering
PS 9221/236205/PS 921—POWER SYSTEM PROTECTION
(Regulation 2009)
Time: Three hours Maximum: 100 marks
Answer ALL the Questions
PART A—(10 × 2 = 20 marks)
1. What do you meant by inrush phenomenon in Transformation?
2. What is rotor fault in generator?
3. What is a directional relay?
4. What are the advantages of static over current relay?
5. Draw the R-X diagram of mho relay?
6. What is the purpose of carrier coupling?
7. List some Busbar faults?
8. What is supervisory relay?
9. Define least error squared technique.
10. What is numerical relay?
PART B—(5 × 16 = 80 marks)
11. (a) (i) A three phase power transformer having a line voltage ratio of 400 V to 33 kV is connected in star-delta .The C.T.s on 400 V side have current ratio as 1000/5. What must be the C.T. ratio on 33 kV side. Assume current on 400V side of transformer to the 1000 A? (8)
(ii) Explain the method to overcome the magnetizing current inrush using Harmonic Restraint method. (8)
Or
(b) (i) A generator is protected by restricted earth fault protection. The generator ratings Are 13.2 kV. 10 MVA. The percentage of winding protected against phase to ground fault is 85%. The relay setting is such that it trips for 20% out of balance. Calculate the resistance to be added in the neutral to ground connection.
(ii) Explain the restricted earth fault protection of generator and the effect of earth Resistance on percentage of winding unprotected.
12. (a) Explain the directional unit incorporated in a over current relay with neat Diagram.
Or
(b) Explain with block diagram the static over current relay and list the advantages over Electromagnetic relay.
13. (a) Explain in detail the stepped characteristics and three stepped distance time characteristics protection with neat diagram.
Or
(b) Explain neatly with blocks each components of carrier aided protection and their advantages.
14. (a) Discuss the effects of short-circuits currents on CT performance. How does It affect the differential protection. What are the possible modifications to Overcome the problem?
Or
(b) Describe the principle of high impedance differential protection based on Voltage drop?
15. (a) (i) Draw the block diagram of numerical relay and explain it in detail.
(ii) Briefly explain Sampling theorem.
OR
(b) (i) Explain in detail about Numerical over current protection.
(ii) Explain in detail about Numerical transformer differential protection.