GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER-VII (OLD) EXAMINATION — WINTER 2018
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Subject Code: 170903 Date: 26/11/2018
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) With neat diagram explain basic protection circuit with function of all elements. (07)
(b) Describe principle of differential protection with need of restraining coil. (07)
Q.2 (a) Derive torque equation of induction disc type electromagnetic relay with diagram. (07)
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(b) Discuss advantages and disadvantages of Numerical relays. Why more and more numerical relays are used nowadays. (07)
OR
(b) Define: PSM, TSM, Plug setting, Reset, Backup protection (07)
Q.3 (a) What protective scheme is used for the protection of Parallel Feeders and Ring main system. (07)
(b) How IDMT relay is provided with directional feature. Explain with diagram. (07)
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OR
Q.3 (a) Why are 30°, 60° and 90° connections required in directional relays. Draw vector diagram of the 90° connection finding what is the maximum torque angle. (07)
(b) What is importance of Busbar in substation. Explain Busbar protection scheme. (07)
Q.4 (a) What are the limitations found in the simple differential protection of transformer? How are they overcome? (07)
(b) Explain restricted earth fault protection of transformer. (07)
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OR
Q.4 (a) Explain characteristics of different types of distance relays: Impedance, reactance and mho relay. (07)
(b) Explain with neat sketch power line carrier current protection. (07)
Q.5 (a) Discuss protection employed against loss of excitation of alternator. (07)
(b) Explain the protection of large induction motor. (07)
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OR
Q.5 (a) Write short note on micro processor based over current relay. (07)
(b) Write brief note on type tests carried out on relays. (07)
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