Download GTU B.Tech 2020 Winter 7th Sem 2170908 Switch Gear And Protection Question Paper

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GUJARAT TECHNOLOGICAL UNIVERSITY

BE- SEMESTER-VII (NEW) EXAMINATION - WINTER 2020

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Subject Code:2170908

Subject Name:Switch Gear and Protection

Time:10:30 AM TO 12:30 PM

Instructions:

1. Attempt any FOUR questions out of EIGHT questions.

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2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.

Q1

1. Define Following:
   • Under reach and over reach of relay
   • Plug setting multiplier

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   • Burden
   03 MARKS
2. Explain Following with reference to Circuit Breaker: (a) Breaking Current (b) Making Current 04 MARKS
3. Discuss various zones of protection for a modern power system. Explain primary and back-up protection. 07 MARKS

Q2

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1. Explain in brief, how the percentage differential relay overcomes the drawbacks of simple differential relay. 03 MARKS
2. What is power swing in power system? Evaluate performance of distance relay in case of a power swing. 04 MARKS
3. A 10 MVA, 13.2 kv generator is protected by restricted earth fault protection. The relay is set to operate on 20% out of balance current. If 85% of the generator winding is supposed to be protected by the relay, find out value of resistance to be added in the neutral circuit. 07 MARKS

Q3

1. Why does a generator needed to be tripped in the case of loss of excitation? 03 MARKS

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2. Explain following with respect to induction motor protection: (a) Single phasing (b) ground fault 04 MARKS
3. Explain with neat diagram: construction and working of the numerical relay. 07 MARKS

Q4

1. Explain why the first ground fault on the rotor does not cause any damage while a second fault can be catastrophic. 03 MARKS
2. Explain following with respect to a circuit breaker:
   • Resistance switching

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   • Arc chopping
   04 MARKS
3. Draw and explain protection of generator against unbalanced loading. 07 MARKS

Q5

1. Why can the secondary of a protection CT not to be open circuited? 03 MARKS

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2. Discuss the effects of arc resistance on impedance based protection scheme. 04 MARKS
3. Drew and explain carrier current based transmission line protection scheme. 07 MARKS

Q.6

1. What is the need of sample and hold circuit in a digital numeric relay? 03 MARKS
2. What is single phasing in Induction motor? How protection against single phasing is provided? 04 MARKS

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3. Compare Impedance relay, reactance relay and mho/ offset mho relay for transmission line protection. 07 MARKS

Q.7

1. Compose a suitable choice of circuit breakers for the following voltage ranges with appropriate reason. (a) 3.3kV to 33kV, (b) 400kV to 760kV. 03 MARKS
2. List important protections provided in a 100MW generator and explain harmonic restrain relay. 04 MARKS
3. In what manner the CTs are connected for biased differential protection of transformer having (i) delta-star connection. (ii) star-star connection. Give reason for the CT Connections employed. 07 MARKS

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Q.8

1. Give difference between measurement CT and protection CT. 03 MARKS
2. Explain Restricted Earth Fault Protection for generator in detail. 04 MARKS
3. Compare SF6 circuit breaker with Air blast circuit breaker. 07 MARKS

Date:21/01/2021

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Total Marks: 56

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