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Download Protection and Switchgear – Exam Paper 2008- Electrical Engineering – 7th Semester and more Exams Electrical Engineering in PDF only on Docsity!
a rn iat a rg cg RU LO get Pag! Vib 88 ProteLroon oe Sealtehgacns ENGG: Con. 2887-08. (REVISED COURSE ) CO-3346 (3 Hours ) [Tetal Marks : 100 N.B.:(1) Question No. 1 is compulsory. pee (2) Attempt any four questions out of remaining six questions. (3) Assume suit data wherever required. . Me te My ea Nees f Seartel geen Er y4- 1. (a) Explain the role of protection in Power System. 5 ¢ 1° (b) Explain the following terms :— 2S] 10 (i) Are extinction in A.C. circuit and D.C. circuit. -(ii)-- Making and breaking capacity of circuit breaker. 2. (a) Describe the construction and principle of operation of an induction type 10 over current relay. Derive torque equation. (b) Discuss various parameters of protective relaying. 10 3, (a) Draw a schematic for motor protection against single phasing and explain 10 in brief. ; (b) The neutral point of a three phase 20 MVA, 11 KV alternator is earthed 10 through a resistance of 50 ohms, the relay is set to operate when there is an out of balance current of 1-5 A. The CTs have a ratio of 1000/5. What percentage of winding is protected against an earth fault and what should be the minimum value of earthing resistance to protect 90% of the winding ? 4, (a) Explain constructional details and aro extinguishing principle in HRC fuse. 10 State advantages of using HRC fuse. (b) A50 Hz,.11 KV, three phase alternator with earthed neutral has areactance 10 of 5 ohms per phase, and is connected to busbar through a circuit breaker. The capacitance to earth between the alternator and the circuit breaker is 0:02 ,.F per phase. Assuming the resistance of the generator to be negligible, calculate. (i) Maximum voltage across the contacts of the circuit breaker. (ii) Frequency of oscillation (iii) The average rate of rise of restriking voltage up to the first peak. 5. (a) Explain clearly the difference between impedance relay, reactance relay 10 and MHO relay with the help of their characteristics. (b) Explain the construction and working of vacuum circuit breaker. 10 6. (a) Explain the following — (i) Properties of SF, gas. 5 (ii) Different ratings of circuit breaker. 5 (b) Discuss the operation of Buchholz’s relay with neat diagram. 10 7. Write short notes on :— 20 (a) Minimum oil circuit breaker (b) Static and electromagnetic relays (c) Construction and working of SF, circuit breaker. 
