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Seat No.: Enrolment
GUJARAT TECHNOLOGICAL UNIVERSITY
PDDC SEMESTER-V EXAMINATION WINTER 2018
Subject Code:X50904 Date: 27/11/2018
Subject Name: Switchgear
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.
Q.1

Explain a trip circuit diagram for the automatic operation of circuit breaker on fault.
07

What is transient re-striking voltage? Derive an expression for the TRV appearing across the circuit breaker contacts.
07
Q.2

Discuss the arc interruption theories.
07

Discuss the properties of arc with neat diagram. Also draw its V-I characteristics.
07
OR

Discuss the phenomenon of current chopping found in circuit breakers.
07
Q.3

With a neat diagram, show the construction and working of an air break circuit breaker.
07

Define the following time quantities related to circuit breaker:(i) Total fault clearing time(ii)Break time(iii)Arcing time(iv)Opening time
07
OR
Q.3

Explain the working of a minimum oil CB.
07

What is RRRV? How does it affect the arc interruption.
07
Q.4

Explain resistance switching in ABCB.
07

With a neat diagram, show the construction and working of an air blast circuit breaker.
07
OR
Q.4

With a neat diagram, show the construction and working of a vacuum circuit breaker.
07

What are the various methods of indirect testing? Describe unit testing.
07
Q.5

With a neat diagram, show the construction and working of an SF6 circuit breaker.
07

What are the advantages and dis-advantages of SF6 Circuit breaker.
07
OR
Q.5

Why are short circuit test necessary? What information can be obtained from short circuit tests?
07

Explain Out of phase switching
07