Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2018 Winter 7th Sem New 2170908 Switch Gear And Protection Previous Question Paper
1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VII (NEW) EXAMINATION ? WINTER 2018
Subject Code: 2170908 Date: 19/11/2018
Subject Name: Switch Gear and Protection
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
MARKS
Q.1 (a) Explain the following requirements of protection system.
(i) Selectivity (ii) Reliability (iii) Security
03
(b) Discuss time and current grading schemes of over current protection. 04
(c) Discuss the working principle of an induction relay and also derive
an expression for the torque produced by it.
07
Q.2 (a) Clearly distinguish the terms ?Overload? and ?Overcurrent?. 03
(b) Explain, what are the basic requirements of a protective
System.
04
(c) Compare following
(i) Measuring CT and Protection CT
(ii) Electromagnetic type PT and Capacitor type PT
07
OR
(c) Define the terms ?Plug Setting Multiplier? and ?Time Multiplier
Setting? used in context of an IDMT relay. An IDMT type
overcurrent relay is used to protect a feeder through a 500/1A CT.
The relay has a plug setting of 125% and TMS=0.3. Find the time of
operation of the said relay if a fault current of 5000A flows through
the feeder. Make use of the following characteristics:
PSM 2 3 5 8 10 15
Time for
TMS=1
10 6 4.5 3.2 3 2.5
07
Q.3 (a) What problems, if any, do you anticipate in applying conventional
differential protection to a transmission line?
03
(b) What are the limitations found in the simple differential protection of
a transformer? How are they overcome?
04
(c) With the help of schematic diagram, discuss various components of
digital/numerical relays.
07
OR
Q.3 (a) What are the conditions which lead to incipient faults in transformer?
What type of protection is required?
03
(b) What are advantages of numerical relays? 04
(c) Draw a detailed protection scheme for biased differential Protection
of a 11/66KV, 45 MVA, DY power transformer. Suggest suitable CT
ratios. What is minimum recommended percentage bias?
07
Q.4 (a) Compare minimum oil CB and bulk oil CB. 03
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1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VII (NEW) EXAMINATION ? WINTER 2018
Subject Code: 2170908 Date: 19/11/2018
Subject Name: Switch Gear and Protection
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
MARKS
Q.1 (a) Explain the following requirements of protection system.
(i) Selectivity (ii) Reliability (iii) Security
03
(b) Discuss time and current grading schemes of over current protection. 04
(c) Discuss the working principle of an induction relay and also derive
an expression for the torque produced by it.
07
Q.2 (a) Clearly distinguish the terms ?Overload? and ?Overcurrent?. 03
(b) Explain, what are the basic requirements of a protective
System.
04
(c) Compare following
(i) Measuring CT and Protection CT
(ii) Electromagnetic type PT and Capacitor type PT
07
OR
(c) Define the terms ?Plug Setting Multiplier? and ?Time Multiplier
Setting? used in context of an IDMT relay. An IDMT type
overcurrent relay is used to protect a feeder through a 500/1A CT.
The relay has a plug setting of 125% and TMS=0.3. Find the time of
operation of the said relay if a fault current of 5000A flows through
the feeder. Make use of the following characteristics:
PSM 2 3 5 8 10 15
Time for
TMS=1
10 6 4.5 3.2 3 2.5
07
Q.3 (a) What problems, if any, do you anticipate in applying conventional
differential protection to a transmission line?
03
(b) What are the limitations found in the simple differential protection of
a transformer? How are they overcome?
04
(c) With the help of schematic diagram, discuss various components of
digital/numerical relays.
07
OR
Q.3 (a) What are the conditions which lead to incipient faults in transformer?
What type of protection is required?
03
(b) What are advantages of numerical relays? 04
(c) Draw a detailed protection scheme for biased differential Protection
of a 11/66KV, 45 MVA, DY power transformer. Suggest suitable CT
ratios. What is minimum recommended percentage bias?
07
Q.4 (a) Compare minimum oil CB and bulk oil CB. 03
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2
(b) Explain the need for a three stepped distance protection of a
transmission line.
04
(c) Explain power line carrier current protection by direction comparison
showing schematic connection dia. of equipments used in it.
07
OR
Q.4 (a) What are the advantages of power line carrier? 03
(b) Explain Following with reference to Circuit Breaker:
(a) Breaking Current (b) Making Current
04
(c) Write short note on SF6 circuit breaker. 07
Q.5 (a) Explain the effect of natural frequency on TRV. 03
(b) Explain the physics of arc phenomena. On what factors does the arc
phenomenon depends?
04
(c) What is meant by loss of excitation in a generator? What protection is
used against it?
07
OR
Q.5 (a) Explain reactance relay with characteristics. 03
(b) An air- blast CB designed to interrupt a transformer magnetizing
current of 15A (rms) chops the current at an instantaneous value of
12A. The value of L and C in the circuit are 8H and 0.009?F. Find
the voltage that appears across the circuit breaker. Assume that the
inductive energy is transformed to capacitance.
04
(c) List and explain various protections used for an induction motor. 07
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This post was last modified on 20 February 2020