SEMINAR REPORT

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SEMINAR REPORT ON
SF6
CIRCUIT BREAKER

BRANCH-EEE.
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CONTENTS

• Introduction
• Operating Principle of Circuit Breaker
• Over view of SF6(Electrical properties)
• Physical and chemical properties
• Advantage
• Principle of operation of SF6 CB
• Conclusion
• References

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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 automatically under abnormal
  conditions

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Fixed contact
Fixed contact
ARC
ARC
ARC IS QUENCHED BY MEDIUM
Moving contact
Moving contact
OPERATING PRINCIPLE OF BREAKER
IN A CIRCUIT BREAKER
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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.

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PRODUCTION OF ARC

• Factors responsible for arc-
• Potential difference between the contacts
• Ionized particles between the contacts
• By removing any one of these the arc can be
  quenched.

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OVERVIEW OF SF6 GAS-
Electrical properties
1. High dielectric strength
2. Excellent arc quenching ability
3. Excellent thermal stability
4. Good thermal conductivity
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Physical Chemical properties
1. Chemically inert
2. Non-toxic
3. Non-corrosive
4. Non-flammable
5. High density
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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 650 gm/cm2
• And 15 higher at 1.25 Kg/cm2

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Advantages of SF6 gas-
1. Increased safety
2. Reduced size
3. Easy installation
4. Low maintenance
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SF6 CIRCUIT BREAKER OPERATION
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(No Transcript)
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SF6 DECOMPOSITION PRODUCTS
SF6
SPARK
SF4 2F
H2O
M
SOF2 2HF
MFn
SiO2
H2O
SiF4 2 H2O
SO2 HF
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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

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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

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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
• No over voltage problem

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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.

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REFERENCES

• www.wikipedia.org
• Power circuit breaker theory and design by C.H.
  Flurscheim

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THANK YOU
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• ANY
• QUESTIONS?