SEMINAR REPORT
ON
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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:-PRINCIPLEARCSCLASSIFICATIONSF6 CIRCUIT BREAKER—DETAILSCONCLUSION
Fixed contact
Moving contact
ARC
Fixed contact
Moving contact
ARCARC IS QUENCHED BY MEDIUM
IN A CIRCUIT BREAKER
OPERATING PRINCIPLE OF 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
OIL CIRCUITBREAKER
AIR BLASTCIRCUITBREAKER
VACCUMCIRCUITBREAKER
SF6CIRCUITBREAKER
OVERVIEW OF SF6 GAS:-
1. High dielectric strength 1. High dielectric strength
2. Excellent arc quenching ability 2. Excellent arc quenching ability
3. Excellent thermal stability 3. Excellent thermal stability
4. Good thermal conductivity 4. Good thermal conductivity
Electrical properties
1. Chemically inert 1. Chemically inert
2. Non-toxic2. Non-toxic
3. Non-corrosive 3. Non-corrosive
4. Non-flammable 4. Non-flammable
Physical & Chemical properties
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 1. Increased safety
2. Reduced size 2. Reduced size
3. Easy installation 3. Easy installation
4. Low maintenance 4. Low maintenance
SF6 CIRCUIT BREAKER OPERATION
SF6 DECOMPOSITION PRODUCTS
SF6
SF4 + 2F
SOF2 + 2HF
MFn
SO2 + HF
SiF4 + 2 H2O
SPARK
H2O
H2O
SiO2
M
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.