1. SEMINAR REPORT ON
SF6
CIRCUIT BREAKER
BRANCH-EEE.

2. 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

3. 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

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

5. 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.

6. 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.

7. OVERVIEW OF SF6 GAS:- Electrical properties
1. High dielectric strength
2. Excellent arc quenching ability
3. Excellent thermal stability
4. Good thermal conductivity

8. Physical & Chemical properties
1. Chemically inert
2. Non-toxic
3. Non-corrosive
4. Non-flammable
5. High density

9. 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

10. Advantages of SF6 gas:- 1. Increased safety 2. Reduced size
3. Easy installation
4. Low maintenance

11. SF6 CIRCUIT BREAKER OPERATION

13. SF6 DECOMPOSITION PRODUCTS
SPARK
SF F
H2O M
SOF HF
MFn
SiO2
H2O
SiF H2O
SO HF

14. 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

15. 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

16. 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

17. 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.

18. REFERENCES: www.wikipedia.org
Power circuit breaker theory and design by C.H. Flurscheim

19. THANK YOU

20. ANY QUESTIONS?