SEMINAR REPORT

ON

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

5. High density 5. High density

6.High electro-negativity6.High electro-negativity

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

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 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

No over voltage problem

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.

THANK U ALL FOR A PATIENT HEARING. HOPE I SATISFIED THE CURIOSITY OF THE AUDIENCE.

NOW I WELCOME ALL QUERIES FROM MY REPORT.