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CONTENTSCONTENTS
• IntroductionIntroduction
• Operating Principle of Circuit BreakerOperating Principle of Circuit Breaker
• Over view of SF6(Electrical properties)Over view of SF6(Electrical properties)
• Physical and chemical propertiesPhysical and chemical properties
• AdvantageAdvantage
• Principle of operation of SF6 CBPrinciple of operation of SF6 CB
• ConclusionConclusion
• ReferencesReferences
WHAT IS A CIRCUIT WHAT IS A CIRCUIT BREAKER?BREAKER?
A circuit breaker is an equipment A circuit breaker is an equipment which canwhich can
make or break a circuit either make or break a circuit either manually or automatically under manually or automatically under normal conditionsnormal conditions
break a circuit automatically under break a circuit automatically under abnormal conditionsabnormal conditions
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 OVERVIEW OF ARCS IN BREAKERS-:BREAKERS-:
During the separation During the separation of contacts, due to of contacts, due to large fault current large fault current and high current and high current density at the density at the contact region the contact region the surrounding medium surrounding medium ionises and thus a ionises and thus a conducting medium conducting medium is formed. This is is formed. This is called the called the ARC.ARC.
PRODUCTION OF ARC PRODUCTION OF ARC
Factors responsible for arc:-Factors responsible for arc:-
Potential difference between the Potential difference between the contactscontacts
Ionized particles between the contactsIonized particles between the contacts
By removing any one of these the arc By removing any one of these the arc can be quenched.can be quenched.
OVERVIEW OF SFOVERVIEW OF SF66 GAS:-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
5. High density 5. High density
Dielectric properties of SFDielectric properties of SF66 gas:-gas:-
DS of SFDS of SF66 is 2.5 times of is 2.5 times of airair
DS of SFDS of SF66 is 30% less is 30% less than oilthan oil
DS of SFDS of SF66 is equal to oil is equal to oil at 650 gm/cm2at 650 gm/cm2
And 15% higher at 1.25 And 15% higher at 1.25 Kg/cm2Kg/cm2
Advantages of SFAdvantages of SF66 gas:- 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
SFSF66 DECOMPOSITION DECOMPOSITION PRODUCTSPRODUCTS
SF6
SF4 + 2F
SOF2 +
2HF
MFn
SO2 + HF
SiF4 + 2 H2O
SPARK
H2O
H2O
SiO2
M
magnitude & duration of discharge
materials of construction of equipment
contamination levels of moisture and air inside the equipment
Amount of each decomposition product depends on :-
REMOVAL OF SFREMOVAL OF SF66 BYPRODUCTS:-BYPRODUCTS:-Byproducts are corrosive & likely to affect the Byproducts are corrosive & likely to affect the
organic materials.organic materials.Absorbent materials used in circuit breakersAbsorbent materials used in circuit breakers activated alumina( effective for activated alumina( effective for SOF2,H2S,SF2)SOF2,H2S,SF2) molecular sievesmolecular sieves( sodalime-( sodalime-CaO.NaOH)-CaO.NaOH)-
removes stable gases such asremoves stable gases such as SF4,SiF4 & S2F2 SF4,SiF4 & S2F2
So suggested mix is 50/50 of sodalime& So suggested mix is 50/50 of sodalime&
alumina. The suggested weight of alumina. The suggested weight of absorbent is 10% of the weight of the gasabsorbent is 10% of the weight of the gas
ADVANTAGES OF SFADVANTAGES OF SF66 CIRCUIT BREAKERSCIRCUIT BREAKERS
Very short arcing periodVery short arcing period Can interrupt much Can interrupt much
larger currents as larger currents as compared to other compared to other breakersbreakers
No risk of fireNo risk of fire Low maintenance, light Low maintenance, light
foundation, minimum foundation, minimum auxiliary equipmentsauxiliary equipments
No over voltage problemNo over voltage problem
CONCLUSIONCONCLUSION
Harnessing the utilities of Harnessing the utilities of SFSF66 gas gas in power system and power in power system and power system equipments, makes it system equipments, makes it more reliable and safer to use.more reliable and safer to use.
The countless advantages this The countless advantages this SFSF66 gas has to offer will take us to gas has to offer will take us to new heights in the prevalent new heights in the prevalent orthodox power system.orthodox power system.
REFERENCES:REFERENCES:
• www.wikipedia.orgwww.wikipedia.org
• Power circuit breaker theory and Power circuit breaker theory and design bdesign by C.H. Flurscheimy C.H. Flurscheim
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