GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER-VII (Old) EXAMINATION — WINTER 2019
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Subject Code: 170903 Date: 28/11/2019
Subject Name: Power System Protection
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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Q.1 (a) What do you understand by a zone of protection? Discuss various zones of protection for a modern power system. [07]
(b) What do you understand by time multiplier setting and plug setting multiplier in over current relay? Explain with the help of relay characteristic. [07]
Q.2 (a) What is amplitude and phase comparator? What is duality between them? [07]
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(b) Explain difference between protective C.T. and measuring C.T. [07]
OR
(b) Derive an expression for torque produced by an induction relay. Using the expression find the necessary conditions for two alternative fluxes acting on a rotor to produce torque and maximum torque. [07]
Q.3 (a) Explain with a neat diagram the over current protection of a 3 phase feeder against phase faults and earth faults. How many phase fault and earth fault relays are used? [07]
(b) Explain the impedance relay characteristic on the R-X diagram. Discuss the range setting of three impedance relays placed at a particular location. [07]
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OR
Q.3 (a) Explain under reach and over reach of a distance relay. [07]
(b) Discuss the advantages of numerical protection. [07]
Q.4 (a) Explain the restricted earth fault protection scheme applicable to transformer. [07]
(b) A 3 phase transformer having line voltage ratio of 400 V/ 33000 V is connected in star-delta. The CTs on the' 400 V side have a current ratio of 1000/5. What must be the ratio of CT's on the 33000 V side? [07]
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OR
Q.4 (a) Explain the differential protective scheme for protection of bus-zone. [07]
(b) Discuss the protection employed against loss of excitation of an alternator. [07]
Q.5 (a) With the help of block diagram explain the organization of numerical relay. [07]
(b) Explain installation and commissioning tests of relays in brief. [07]
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OR
Q.5 (a) Explain the phase comparison method of carrier current protection. [07]
(b) What are various abnormal operating condition from the load side and supply side to which an induction motor is subjected to? [07]
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