SEMINAR
REPORT
ON
www.fakengineer.com
WHAT IS A CIRCUIT
BREAKER?
A circuit breaker is an equipment which
can
 make or break a circuit either manually
or automatically under normal conditions
 break a circuit under abnormal
conditions
POINTS TO BE DISCUSSED:PRINCIPLE
ARCS
CLASSIFICATION
SF6 CIRCUIT BREAKER—DETAILS
CONCLUSION
Fixed
contact
Fixed
contact
ARC
Moving
contact
OPERATING
PRINCIPLE OF
BREAKER
ARC IS
ARC
QUENCHED BY
MEDIUM
Moving
contact
IN A CIRCUIT BREAKER
OVERVIEW OF ARCS IN BREAKERS-:
During the separation of
contacts, due to large
fault current and high
current density at the
contact region the
surrounding medium
ionises and thus a
conducting medium is
formed. This is called the
ARC.
PRINCIPLES OF ARC
EXTINCTION
Factors responsible for arc:-
Potential difference between the contacts
Ionised particles between the contacts
By removing any one of these the arc can
be quenched.
CLASSIFICTION OF CIRCUIT
BREAKERS
OIL
AIR
VACCUM
SF6
SF6
OIL
AIR
VACCUM
CIRCUIT BLAST
CIRCUIT CIRCUIT
BREAKER CIRCUIT BREAKER BREAKER
BREAKER
OVERVIEW OF SF6 GAS:Electrical properties
1. High dielectric strength
2. Excellent arc quenching ability
3. Excellent thermal stability
4. Good thermal conductivity
Physical & Chemical properties
1. Chemically inert
2. Non-toxic
3. Non-corrosive
4. Non-flammable
Dielectric properties of SF6 gas:DS of sf6 is 2.5 times of air
DS of sf6 is 30% less than oil
DS of sf6 is equal to oil at
63700 N/m2
And 15% higher at 122500
N/m2
Advantages of SF6 gas:1. Increased safety
2. Reduced size
3. Easy installation
4. Low maintenance
SF6 CIRCUIT BREAKER
OPERATION
SF6 DECOMPOSITION PRODUCTS
SF6
SPARK
SF4 + 2F
H2O
M
SOF2 + 2HF
MFn
H2O
SO2 + HF
SiO2
SiF4 + 2 H2O
Amount of each decomposition product depends on :-
 magnitude & duration of discharge
 materials of construction of equipment
 contamination levels of moisture and air inside the
equipment
REMOVAL OF SF6 BYPRODUCTS:Byproducts are corrosive & likely to affect the
organic materials.
Absorbent materials used in circuit breakers
 activated alumina( effective for SOF2,H2S,SF2)
 molecular sieves( sodalime-CaO.NaOH)-removes
stable gases such as SF4,SiF4 & S2F2
So suggested mix is 50/50 of sodalime &
alumina. The suggested weight of absorbent is
10% of the weight of the gas
ADVANTAGES OF SF6 CIRCUIT
BREAKERS
 Very short arcing period
 Can interrupt much larger
currents as compared to
other breakers
 No risk of fire
 Low maintenance, light
foundation, minimum
auxiliary equipments
CONCLUSION
Harnessing the utilities of SF6 gas in
power system and power system
equipments, makes it more reliable and
safer to use.
The countless advantages this SF6 gas
has to offer will take us to new heights in
the prevalent orthodox power system.