2. CONTENTS
Introduction
Circuit Breaker
Components of circuit breaker
Working Principle
Arc Formation
Methods of Arc quenching
Types of Circuit Breakers
Conclusion
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3. INTRODUCTION
Nowadays, the modern power system deals with huge
power network and huge numbers of associated
electrical equipment.
During short circuit fault or any other types of electrical
fault these equipment suffer a high stress of fault current
which may damage the equipment and networks.
For saving these equipments and the power networks,
the fault current should be cleared from the system as
quickly as possible.
These complications have paved the way for the
evolution of circuit breakers.
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4. CIRCUIT BREAKER
A circuit breaker is an electromechanical switch that breaks
the circuit either manually or automatically under all
conditions at no load, full load or short circuit.
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.
Its basic function is to detect a fault condition, by interrupting
continuity and immediately discontinue the electrical flow.
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6. WORKING PRINCIPLE
The circuit breaker mainly consists of fixed contacts and moving
contacts.
In normal ON condition of circuit breaker, these two contacts are
physically connected to each other due to applied mechanical
pressure on the moving contacts.
The potential energy can be stored in the circuit breaker by
different ways like by deforming metal spring, by compressed
air, or by hydraulic pressure.
During fault condition, potential energy must be released.
Release of potential energy makes sliding of the moving contact
at extremely fast manner and breaks the circuit.
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7. ARC FORMATION
During the separation of contacts, due to large fault current and
high current density at the contact region, the surrounding
medium is ionized. Thus an electric arc is formed.
Factors responsible for arc are:
Potential difference between the contacts
Ionized particles between the contacts.
MOVING CONTACT
FIXED CONTACT ARC
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8. METHODS OF ARC
QUENCHING
High Resistance Method:
Arc resistance is made to increase with time so that
current is reduced to a value insufficient to maintain the arc.
Low Resistance Method:
Dielectric Medium between the contacts is built up more
rapidly so that the arc fails to restrike and the current will be
interrupted.
Arc Resistance depends on factors like:
Degree of Ionization
Length of the arc
Cross section of arc
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10. OIL CIRCUIT BREAKERS
These are the oldest type circuit breakers.
It can be operated 11kV - 765kV.
Oil is used as arc quenching media as well
as insulating media between current
carrying contacts and earthed parts of
the breaker.
These are of two types:
BOCB (Bulk oil Circuit Breaker)
MOCB (Minimum oil Circuit Breaker)
The oil used here is same as transformer
insulating oil.
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11. VACUUM CIRCUIT
BREAKERS
It is operated at medium voltage range
(3.3 - 33kV).
The arc quenching takes place in vacuum.
A vacuum interrupter is a switch which
uses electrical contacts in a vacuum for the
process of quenching the arc.
The vacuum pressure inside a vacuum
interrupter is normally maintained at 10-6 bar.
The technology is suitable for mainly
medium voltage application. For higher voltage
vacuum technology has been developed but not
commercially viable.
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12. AIR BLAST CIRCUIT
BREAKERS
It operates using high velocity blast
of air which quenches the arc.
The contacts are opened in a flow
of air blast and quenches the arc.
This rapidly increases the dielectric
strength of the medium between
contacts and prevents from arc.
Then the arc is extinguished and
flow of current is interrupted.
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13. SF6 CIRCUIT BREAKERS
It uses Sulphur Hexafluoride (SF6) gas
as an arc quenching medium.
In closed position, SF6 gas pressure -
2.8 kg/cm2
In opened position SF6 gas pressure-
14 kg/cm2
SF6 is released from a valve and
rapidly absorbs the free electrons in
the arc path to form immobile negative
ions to build up high dielectric strength
and extinguishes it.
After operation the valve is closed by
the action of a set of deformed springs.
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14. CONCLUSION
Circuit breaker is the most essential part of the electrical
networks as it protects every device from damage.
By using appropriate circuit breaker for appropriate
operating voltages we can provide protection for bus bar
and electrical equipments like Power transformers,
generators, C.T, P.T, etc. from different faults that occur in
power system.
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