A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and interrupt current flow.

1. Presented By

2. CIRCUIT BREAKER

3. WHAT IS A CIRCUIT BREAKER?
• A circuit breaker is an automatically operated electrical
switch designed to protect an electrical circuit from
damage caused by overload or short circuit. Its basic
function is to detect a fault condition and interrupt current
flow.
• Unlike a fuse, which operates once and then must be
replaced, a circuit breaker can be reset (either manually or
automatically) to resume normal operation. Circuit
breakers are made in varying sizes, from small devices that
protect an individual household appliance up to large
switchgear designed to protect high voltage circuits
feeding an entire city.

4. Working Principle of Circuit BeakerWorking Principle of Circuit Beaker
When a fault occurs in the
protective circuit, relay
connected to CT and PT
actuate and close its
contacts. Current flows
from battery in trip circuit.
As the trip coil is
energized the circuit
operating mechanism is
actuated and it operates
for opening operation.

5. Arc PhenomenonArc Phenomenon
• An arc is struck when contacts are separated. The current
is thus able to continue. Thus the main duty of a circuit
breaker is to distinguish the arc within the shortest
possible time.
• The arc provides the low resistance path to the current
and the current in the circuit remains uninterrupted.

7. Air Blast Circuit Breakers
• Air blast circuit breaker used compressed air or gas as
the arc interrupting medium. In the air blast, circuit
breaker compressed air is stored in a tank and released
through a nozzle to produce a high-velocity this is used
to extinguish the arc. Air blast circuit breakers are used
for indoor services in the medium high voltage field and
medium rupturing capacity. Generally up to voltages of
15 KV and rupturing capacities of 2500 MVA.

8. • Though gasses such as carbon dioxide, nitrogen,
freon or hydrogen are used as the arc interrupting
medium, compressed air is the accepted circuit
breaking medium for gas blast circuit breakers.
• It is very necessary on large interconnected networks
so that the system stability can be maintained. This is
achieved in circuit breaker because the time interval
between the discharge of triggering impulse and
contacts separation are very short.
Air Blast Circuit Breakers

9. Principle of Air Blast Circuit Breaker
• The air blast needs an additional compressed air system which
supplies air to the air receiver.
• When opening air is required, compressed air is admitted to
the arc extinction chamber. It pushes away the moving
contacts.
• In doing so, the contacts are pulled apart, and the air blast
moves away the ionized gas along with it and assists arc
extinction.

10. Principle of Air Blast Circuit Breaker
•Air blast extinguishes the arc within one or more cycles, and the
arc chamber is filled with high-pressure air, which prevents
restrikes.
•The air blast circuit breakers fall under the category of external
extinguishing energy type.
•The energy supplied for arc quenching is achieved from the high-
pressure air, and it is free from the current to be interrupted.

11. Types of
Air Blast Circuit Barker

12. Axial Blast Air Circuit Breaker
Under Normal Condition
The fixed and moving contacts are held in closed position with the
help of spring pressure.
There is an air reservoir connected to the arcing chamber through
an air valve. The air valve control the flow of air into the arcing
chamber. The valve is closed under normal conditions.

13. Axial Blast Air Circuit Breaker
Fig: Axial Blast Air Circuit Breaker

14. Axial Blast Air Circuit Breaker
Under Faulty Condition
When a fault occurs a tripping impulse is produced which causes
opening of the air valve. Since the air valve connects the
air reservoir and the arcing chamber, a high pressure air enters to
the arcing chamber. This air pushes away the moving
contact against the spring pressure. The moving contact is separated
and an arc is struck. At the same time high pressure air blast flows
along the arc and takes away the ionised gases along with it.
Consequently the arc is extinguished and current flow is
interrupted.

15. Cross Blast Circuit Breaker
Under Faulty Condition
When a fault occurs a tripping impulse is produced
which causes opening of the air valve. Since the air
valve connects the air reservoir and the arcing chamber,
a high pressure air enters to the arcing chamber. This
air pushes away the moving contact against the spring
pressure. The moving contact is separated and an arc is
struck. At the same time high pressure air blast flows
along the arc and takes away the ionised gases along
with it. Consequently the arc is extinguished and
current flow is interrupted.

16. Cross Blast Circuit Breaker
In this type of breaker, an air-blast is directed at right
angles to the arc. The cross blast lengthens and forces
the arc into a suitable chute for arc extinction. Figure
shows the essential components of a typical cross-blast
air circuit breaker.
Fig: Cross Blast Circuit Breaker

17. Cross Blast Circuit Breaker
• When the moving contact is withdrawn, an arc is
struck between the fixed and moving contacts. The
high pressure cross-blast forces the arc into a chute
consisting of arc splitters and baffles.
• The splitters serve to increase the length of the arc
and baffles give improved cooling. The result is that
arc is extinguished and flow of current is interrupted.
• Since blast pressure is same for all currents, the
inefficiency at low currents is eliminated. The final
gap for interruption is great enough to give normal
insulation clearance so that a series isolating switch
is not necessary.

18. Advantages of
Air Circuit Breaker
• The risk of fire is eliminated.
• The arcing products are completely removed by
blast.
• The growth of dielectric strength is so rapid that
final contact gap needed for arc extinction is very
small. This reduce the size of device .
• The arcing time is very small due to the rapid
build up of dielectric strength between contacts.
• Due to lesser arc energy, ABCB are very suitable
for conditions where frequent operation is
required.

19. Disadvantage of
Air circuit Breaker
• Air has relatively inferior arc extinguishing
properties.
• Air blast circuit breakers are very sensitive to the
variation is the rate of restriking voltage.
• Considerable maintenance is required for the
compressor plant which supplies the air blast.

20. Sulphur Hexafluoride(SF6)
Circuit Breaker
Sulphur Hexafluoride (SF6) gas is used as an arc
quenching medium.
SF6 is an electro-negative gas.
It has strong tendency to absorb electrons.
When contact are opened in a high pressure flow of SF6
gas, arc produced.
Free electron in the arc are captured by the gas.
Which build up enough insulation strength to extinguish
arc.
it is much effective for high power and high voltages
services.

21. Construction of
SF6 Circuit Breaker
An sulphur hexaflouride (SF6) circuit breaker consists
of fixed and moving contacts enclosed in a chamber. The
chamber is called arc interruption chamber which contains
the sulphur hexaflouride(SF6) gas. This chamber is connected
to sulphur hexaflouride (SF6) gas reservoir. A valve
mechanism is there to permit the gas to the arc interruption
chamber. When the contacts of breaker are opened, thevalve
mechanism permits a high pressure sulphur
hexaflouride (SF6) gas from the reservoir to flow towards the
arc interruption chamber.

22. Construction of
SF6 Circuit Breaker
Fig: Construction of SF6 Circuit Breaker

23. Construction of
SF6 Circuit Breaker
• The fixed contact is a hollow cylindrical current carrying
contact fitted with an arc horn. The moving contact is also
a hollow cylinder with rectangular holes in the sides. The
holes permit the sulphur hexaflouride gas (SF6) gas to let
out through them after flowing along and across the arc.
The tips of fixed contact, moving contact and arcing horn
are coated with copper-tungsten arc resistant material.
Since sulphur hexaflouride gas (SF6) gas is costly, it is
reconditioned and reclaimed using suitable
auxiliary system after each operation of breaker.

24. Advantages of SF6 Circuit
Breaker
• Simple construction, less cost.
• SF6 gas is non flammable, non toxic & chemical inert gas.
• Same gas is recirculated in the circuit.
• Maintenance free C.B.
• Ability to interrupt low and high fault current.
• Excellent Arc extinction.

25. Sulphur Hexaflouride (SF6) Circuit Breaker
* Disadvantages :
* SF6 breakers are costly due to high cost of SF6.
* Additional equipments are to be incorporated for
reconditioning of SF6.

26. Sulphur Hexaflouride (SF6) Circuit Breaker
* Applications :
* A typical SF6 unit is capable of dealing 60 KA and
50-80 KV.
* Number of units are incorporated in series to serve
higher ratings.
* Conventional ratings of SF6 breakers are 230 KV,
10-20 MVA and interrupting time less than 3 sec.