An electrical circuit breaker is a switching device which can be operated manually and automatically for controlling and protection of electrical power system respectively. As the modern power system deals with huge currents, the special attention should be given during designing of circuit breaker for safe interruption of arc produced during the operation of circuit breaker. The modern power system deals with huge power network and huge numbers of associated electrical equipments. During short circuit fault or any other types of electrical fault these equipment as well as the power network suffer a high stress of fault current in them which may damage the equipment and networks permanently. For saving these equipment and the power networks the fault current should be cleared from the system as quickly as possible. Again after the fault is cleared, the system must come to its normal working condition as soon as possible for supplying reliable quality power to the receiving ends. In addition to that for proper controlling of power system, different switching operations are required to be performed. So for timely disconnecting and reconnecting different parts of power system network for protection and control, there must be some special type of switching devices which can be operated safely under huge current carrying condition. During interruption of huge current, there would be large arcing in between switching contacts, so care should be taken to quench these arcs in circuit breaker in safe manner. The circuit breaker is the special device which does all the required switching operations during current carrying condition.

1. High Voltage Circuit Breakers
BESCOM

2. CONTENTS:
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 Introduction
 Operating Mechanism
 Types of Circuit Breakers:
 Air Blast Circuit Breaker
 Oil Circuit Breaker
 SF6 Circuit Breaker
 Vacuum Circuit Breaker
 Conclusion

3. Introduction:
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 A circuit breaker is a mechanical switching
device, capable of making, carrying & breaking current
under normal circuit conditions. It is also capable of
making and carrying currents for a specified time and
breaking current under specified abnormal conditions,
Such as those of a short circuit.

4. OPERTING MECHANISM:
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FIXED CONTACT
MOVING CONTACT
FIXED CONTACT
ARC IS QUENTCHED
BY MEDIUM
MOVING CONTACT

5. OPERTING MECHANISM:
 Circuit Breaker consists of two contacts:
Fixed Contact
Moving Contact
 Moving contact is used to make and break the circuit using stored energies in the
form of spring and compressed air.
 Spring, pneumatic or oil damping is used to arrest the spped of moving contact while
closing.
 Fixed contact contains a spring which holds the moving contact after closing.
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6. 6
 Circuit Breaker consists of two coils:
Closing Coil : Used to close the circuit
Tripping Coil : Used to trip the circuit.
 These coils activate the stored energy and directs the moving contact to open or
close.
 DC batteries are used to energies these coils.
 Solenoid are used to close or trip it.
 Circuit Breakers are usually arranged with pilot devices to sense a fault current and
to operate the trip opening mechanism.

7. ELECTRIC ARC:
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During the separation of contacts, due to large fault current and high current density at
the contact region the surrounding medium ionizes and thus a conducting medium is
formed is called “ARC”.
Factor Responsible for ARC:
 Potential difference between the contacts
 Ionized particle between the contacts.

8. PRINCIPLES OF ARC EXTINSION
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Arc Quenching is achieved by:
 Greater Dielectric strength than restriking voltage.
 Faster rate of heat removal than rate of heat of generation.
Arc Extinction methods are:
 By lengthening the gap.
 Cooling the arc.
 Inserting medium of high dielectric strength.

9. TYPES OF CIRCUIT BREAKER
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CIRCUIT BREAKER
OIL CIRCUIT
BREAKER
BREAKER
AIR BLAST
CIRCUIT
BREAKER
VACUUM
CIRCUIT
BREAKER
SF6 CIRCUIT
BREAKER

10. OIL CIRCUIT BREAKER:
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 It is designed for 11kV-765kV.
 There are of two types:
BOCB - Break oil circuit breaker.
MOCB- Minimum oil circuit breaker.
 The contacts are immersed in oil bath.
 Oil provides cooling by hydrogen created by
arc.
 It acts as a good dielectric medium and
quenches the arc.

11. OIL CIRCUIT BREAKER
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 Advantage:
I. Oil has good dielectric strength.
II. Low cost
III. Oil is easily available
IV. It has wide range of breaking capability.
 Disadvantage:
I. Slower operation. Takes 20 cycles for arc
quenching.
II. It is highly infalamable, so high risk of fire.
III. High maintenance cost.

12. VACCUM CIRCUIT BREAKER:
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 It is designed for medium voltage
range(3.3kV-33kV).
 It consists of vacuum of pressure
1*10−6 inside arc extension chamber.
 The arc burns in metal vapour when
the contacts are disconnected.
 At high voltage, Its rate of dielectric
recovery strength is very high.
 Due to vacuum, arc extinction is very
fast.
 The contacts loose metal gradually
due to formation of metal vapours.

13. VACCUM CIRCUIT BREAKER:
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 Advantage:
I. Free from arc and fire hazards.
II. Low cost for maintenance and simpler
mechanism.
III. Low arcing time and high contact life.
IV. Silent and less vibrational operation.
V. Due to vacuum contacts remain free from
corrosion.
VI. No byproducts formed.
 Disadvantage:
I. High initial cost due to creation of vaccum.
II. Surface of contacts are depleted due to
metal vapours.
III. High cost and size required for high voltage
breakers.

14. AIR BLAST CIRCUIT BREAKER:
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 This operates high velocity blast of air which
quenches the arc.
 It consists of blast valve, blast tube &
contacts.
 Blast valve contains air at high pressure.
 Blast tube carries air at high pressure and
opens the moving contact attached to spring.
 There is no carbonization of surface as in
VCB
 Air should be kept clean and dry to operate it
properly.

15. AIR BLAST CIRCUIT BREAKER:
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 Advantage:
I. High speed operation as compared to OCB.
II. Ability to withstand frequent switching.
III. Facility for high speed closure.
IV. Less maintenance as compared to OCB.
 Disadvantage:
I. Little moisture content prolongs arcing time
II. Pressure should be checked frequently for
frequent operation.
III. Risk of fire hazards due to over voltage.
IV. It can not be used for high voltage
operation due to prolonged arc quenching.

16. SF6 CIRCUIT BREAKER:
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 It contains an arc extension chamber containing SF6 gas.
 In closed position the contact remain surrounded by SF6 gas at a pressure of 2.8
Kg/cm2
.
 During opening high pressure SF6 gas at 14Kg/cm2 from its reservoir flows towards
the chamber by valve mechanism.
 SF6 rapidally absorbs the free electrons in the arc path to form immobile negative ions
to build up high dielectric strength.
 It also cools the arc and extinguishes it.
 After operation the valve is closed by the action of a set of springs.
 Absorbent material are used to absorb the byproducts and moisture.

17. SF6 CIRCUIT BREAKER:
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18. SF6 CIRCUIT BREAKER:
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 Advantage:
I. Very short arcing period due to to superior arc quenching property of
SF6.
II. Can interrupt much larger current as compared to the other breakers.
III. No risk of fire.
IV. Low maintenance, light foundation.
V. No overvoltage problem.
VI. There are no carbon deposits.
 Disadvantage:
I. It is costly due to high cost of SF6 gas.
II. SF6 gas can be reconditioned after every operation of the breaker,
additional equipment is required for this purpose.

19. CONCLUSION:
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Therefor we conclude that circuit breaker is the most essential
part of the electrical network as it protects every device from
damage. It help us to detect the fault and area affected by it.
Nowadays vacuum and SF6 circuit breakers are widely used
due to their reliable and fast operations.

20. Thank You