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2003 Course Switchgear & Protection

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Total No. of Questions : 12] [Total No. of Pages : 3 [3664]-188 P941 B.E. (Electrical) SWITCHGEAR & PROTECTION (2003 Course) Time : 3 Hours] [Max. Marks : 100 Instructions to the candidates : 1) Answer any three questions from each section. 2) Answers to the two sections should be written in separate books. 3) Neat diagrams must be drawn wherever necessary. 4) Figures to the right indicate full marks. 5) Use of logarithmic tables, slide rule, Mollier charts, electronic pocket calculator and steam tables is allowed. 6) Assume suitable data, if necessary. SECTION - I Q1) a) b) What do you mean by Protective Relaying? Explain the concept with basic block diagram? Why it is essential? [10] Explain the terms with reference to relay. i) Plug setting. ii) [6] Time setting. OR Q2) a) b) What do you mean by zones of protection? Explain Primary and Backup Protection. [12] List out the essential qualities of Protective Relaying. Q3) Describe in detail concept of: [4] [16] a) Resistance switching. b) Current chopping of capacitive current. OR Q4) a) Derive the expression for i) Restriking voltage. ii) [12] Maximum R.R.R.V. iii) Frequency of oscillations. State factors affecting Restriking voltage. P.T.O. b) In a system of 220 kV, the circuit phase to ground capacitance is of 0.04 F and circuit inductance is 7H. The circuit breaker interrupts a magnetic current of 8Amp. (Peak). Find [4] i) The voltage across the circuit breaker contacts after the current interruption. ii) The value of resistance to be used across the contacts to supress restriking voltage. Q5) Write short note on: [18] a) Ratings of circuit breaker. b) Classification of high voltage circuit breaker. c) Auto reclosing. OR Q6) Explain the following circuit breakers: a) SF6 circuit breaker b) Vacuum circuit breaker in reference to i) Constructional features. ii) Working principle. iii) Advantages and limitations. [18] SECTION - II Q7) a) Explain the effect of inrush magnetising current on the protective system of transformers. Also explain the principle of harmonic restraint with the help of necessary schematic diagram. [8] b) A 11 kV, 3 phase alternator has full load rated current of 250A. Reactance of armature winding is 15 percent. The differential protection system is set to operate on earth fault currents of more than 250A. Find the neutral earthing resistance so as to give earth fault protection to 90% of stator winding. [8] Q8) a) OR A 11 kV, 100 MVA alternator is provided with differential protection. The percentage of winding to be protected against phase to ground fault is 85%. The relay is set to operate when there is 20% out of balance current. Determine the value of the resistance to be placed in the neutral to ground connection. [8] [3664] - 188 2 b) Draw a neat and labelled sketch of Buchholz relay and explain it with reference to its operation, installation merits and limitations. [8] Q9) a) Explain the carrier current scheme of protection with the help of block diagram and neat sketch. Also discuss how the phase comparison scheme can be used for protecting a feeder from (i) one end (ii) both the ends.[9] b) Explain the three step distance protection scheme for transmission. Also draw the neat sketch for the same. [7] OR Q10)a) Explain the effect of power swings and arc resistance on the performance of distance relay. [7] b) What are the merits of carrier current relaying? Where is it used? Compare pilot wire relaying with carrier current protection. [9] Q11)a) Draw a neat block diagram of static relays and explain function of each [8] block. Compare the static relays with electromagnetic relays. b) Explain the realisation of over current relay by using a microprocessor.[5] c) Justify the preference of half cycle data over full cycle data window for numerical protective relaying. [5] OR Q12)Write short notes on (any three): [18] a) Walsh Hadamard transform technique. b) Principle of duality. c) Sampling theorem. d) Time delay ckts in static relays. Y [3664] - 188 3

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