GTU BE 2019 Summer Question Papers || Gujarat Technological University
Subject Code: 2170908
GUJARAT TECHNOLOGICAL UNIVERSITY
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BE - SEMESTER-VII(NEW) EXAMINATION — SUMMER 2019
Subject Name: Switch Gear and Protection
Date: 14/05/2019
Time: 02:30 PM TO 05:00 PM
Total Marks: 70
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Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
| Q.1 | (a) Define following terms in context to protective relay (i) Reliability (ii) Selectivity (iii) Discrimination | 03 |
| (b) Discuss necessity of Back up protection and types of backup protection in brief. | 04 | |
| (c) Explain the principle of Directional relay with the help of appropriate phasor diagram. Also explain the significance of maximum torque angle of the directional relay. | 07 | |
| OR | ||
| (c) Explain the 3 zone protection of transmission line using MHO relays. How under-reach and over-reach are set to avoid in this type of protection? | 07 | |
| Q.2 | (a) Prove that the slope of the internal fault characteristics for a single-end fed system is 200%. | 03 |
| (b) What are the drawbacks of a simple differential scheme? Explain how the percentage differential relay overcomes the drawbacks of simple differential relay. | 04 | |
| (c) What are incipient faults? Discuss in detail the type of protection provided in transformer to cater to such type of faults. | 07 | |
| OR | ||
| (a) List and Explain various options for implementing the carrier communication channel. | 03 | |
| (b) How do different distance relays perform with respect to their behavior on load, effect of arc resistance on the reach and response to power swing? | 04 | |
| (c) Explain the operation of the unit type of carrier based directional protection. | 07 | |
| Q.3 | (a) Differentiate between longitudinal and transverse differential protection in context to generator protection. | 03 |
| (b) What causes loss of prime mover? Can a generator be allowed to run with its prime mover lost? If not, why? | 04 | |
| (c) Explain various abnormal conditions to which a modern turbo alternator is likely to be subjected. | 03 | |
| OR | ||
| (a) Why is protection of an induction motor against reversal of phase sequence required? | 04 | |
| (b) Explain ratio error and phase angle error in CTs. | 07 | |
| Q.4 | (a) List and explain various abnormal conditions an induction motor is likely to be subjected. | 07 |
| OR | ||
| (a) List and explain advantages of numerical relays over other conventional relays. | 03 | |
| (b) Derive an expression for the restriking voltage in terms of system inductance and capacitance. | 04 | |
| (c) Draw and explain block diagram of Numerical relay. | 07 | |
| Q.5 | (a) What causes the initiation of electric arc at the instant of contact separation ? Which of these is chiefly responsible for the creation of arc in circuit breaker and why? | 03 |
| (b) Explain current chopping in brief. | 04 | |
| (c) Explain auto reclosing. | 07 | |
| OR | ||
| (a) List the properties of SF6 gas and its advantages over other arc quenching medium. | 03 | |
| (b) Explain following terms: symmetrical breaking current, asymmetrical breaking current & making current as applied to circuit breaker and show how these currents can be determined from oscillograms taken during short circuit tests on a three phase circuit breaker. | 04 | |
| (c) Write short note on vacuum circuit breaker. | 07 |
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