UNIT – II
CIRCUIT BREAKERS
PART – A (2
MARKS)
1. What is an arc?
2. Define restricting voltage.
3. Define recovery voltage.
4. Define current chopping.
5. Mention the different methods
of high resistance arc interruption.
6. What is switchgear?
7. What is breaking capacity?
8. What are the functional
requirements of a circuit breaker under fault condition?
9. What are the advantages of low
oil circuit breaker?
10. What are the types of air
blast circuit breaker?
11. What are the advantages of SF6
circuit breaker?
PART - B
1. Discuss the recovery rate
theory and energy balance theory of arc interruption in a circuit breaker. (16)
2. Explain terms:
i) Restriking voltage (3)
ii) Recovery voltage (3)
iii) RRRV (3)
iv) Derive expressions for
restriking voltage and RRRV. (3)
v) What measures are taken to
reduce them? (4)
3. (a) What is resistance
switching? (4)
(b) Derive the expression for
critical resistance. (12)
4. (a) Explain the phenomenon of
current chopping in a circuit breaker. (12)
(b) What measures are taken to
reduce it? (4)
5. Discuss the problem associated
with the interruption of
(i) Low inductive current (5)
(ii) Capacitive current and (5)
(iii) Fault current if the fault
is very near the substation. (6)
6. With neat sketch, describe the
working principle of an axial air blast type circuit breaker. (16)
7. (a) Discuss the operating
principle of SF6 circuit breaker. (10)
(b) What are its advantages over
other types of circuit breakers? (3)
(c) For what voltage range is it
recommended? (3)
8. Describe construction,
operating principle and application of vaccum circuit breaker. For what voltage
range is it recommended? (16)
9. (a) What are the various types
of operating mechanisms which are used for opening and closing of the contacts
of a circuit breaker? (10)
(b)Discuss their merits and
demerits. (6)
10. (a) Enumerate various types
of ratings of a circuit breaker. (4)
(b) Discuss symmetrical and
asymmetrical breaking capacity, (4)
(c) Making capacity (4)
(d) Short-time current capacity.
(4)
11. What are the different
methods of testing of circuit breakers? Discuss their merits and demerits. (16)
12. What is the difficulty in the
development of HVDC circuit breaker? Describe its construction and operating
principle. (16)
13. (a) What are the physical
chemical and dielectric properties of SF6 Gas (8)
(b) Define switchgear. What are
the essential features of switchgear (8)
14. A 3-phase alternator has the
line voltage of 11kV. The generator is connected to a circuit breaker. The
inductive reactance upto the circuit breaker is 5Ω/phase. The distributed
capacitance upto circuit breaker between phase and neutral is 0.001 μF. Determine
peak restriking voltage across the CB, frequency of restriking voltage, average
rate of restriking voltage upto peak restriking voltage, maximum RRRV. (16)