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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:-

 PRINCIPLE  ARCS  CLASSIFICATION  SF6 CIRCUIT BREAKER—DETAILS  CONCLUSION

Fixed contact

ARC

Moving contact OPERATING PRINCIPLE OF BREAKER Fixed contact ARC IS ARC MEDIUM Moving contact IN A CIRCUIT 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 CIRCUIT BREAKER AIR BLAST CIRCUIT BREAKER VACCUM CIRCUIT BREAKER SF6 CIRCUIT BREAKER

OVERVIEW OF SF6 GAS:-

Electrical properties

1.

High dielectric strength

2.

Excellent arc quenching ability

3.

Excellent thermal stability

4.

Good thermal conductivity

Physical & Chemical properties

1.

Chemically inert

2.

Non-toxic

3.

Non-corrosive

4.

Non-flammable

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

2.

Reduced size

3.

Easy installation

4.

Low maintenance

SF6 CIRCUIT BREAKER

OPERATION

SF6 DECOMPOSITION PRODUCTS SF6 SPARK SF4 + 2F H2O M H2O SOF2 + 2HF SO2 + HF SiO2 MF SiF4 + 2 H2O n

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 SF 6 gas in power system and power system equipments, makes it more reliable and safer to use.

The countless advantages this SF 6 gas has to offer will take us to new heights in the prevalent orthodox power system.