AIR CIRCUIT BREAKER

TYPES OF CIRCUIT BREAKER (ON THE BASIS OF ARC EXTINCTION) OIL CIRCUIT BREAKER AIR CIRCUIT BREAKER AIR BREAK TYPE VACUUM CIRCUIT BREAKER (AIR IS USED AS DIELECTRIC MEDIUM) SF6 CIRCUIT BREAKER AIR BLAST TYPE

ARC FORMATION ,EXTINCTION &ROLL OF DIELECTRIC MEDIUM Separation of contact leads produces i. Thermal Ionization ii. Ionization by Collision iii.Thermal Emission from Surface of Contacts iv. Secondary Emission from Contact Surface v. Field Emission at Contact Surface vi. Photoemission EXTINCTION i. High Resistance Interruption a) Lengthening the arc b) Splitting of arc c) cooling of arc ii. Low resistance Or Zero point- -interruption ROLL OF DIELECTRIC MEDIUM i. Coolant Medium ii. At current zero, de-ionizing the space between contacts by introducing unionized medium iii. Increasing the dielectric strength of the contact space to such an extent that the arc does not continue after current zero (If dielectric strength of gap is less than the restriking voltage then voltage may reestablished the arc )

REASONS FOR USING AIR AS DIELECTRIC MEDIUM Air is used as dielectric medium for arc extinction(Dielectric strength-0.3-0.4 MVm-1) Dielectric strength of air increases with in increase in pressure It provides adequate insulation between the contacts and from each contacts to earth. Thermal and Chemical stability of dielectric Non-inflammability High thermal conductivity Cheapest and easily available

AIR BREAK CIRCUIT BREAKER

1. Main Contacts: low resistance (Silver Plated) 2 1.Main Contacts: low resistance (Silver Plated) 2. Arcing Contacts: High resistance (copper alloy)

TYPES OF AIR BREAK CIRCUIT BREAKERS PLANE BREAK TYPE MAGNETIC BLOW-OUT TYPE AIR BREAK CIRCUIT BREAKER ARC- CHUTE TYPE

PLAIN BREAK TYPE Contacts are horn shaped Initially arc strikes across shortest distance between 2 horns Driven upwards by convection of heated air & interaction of electric field Air flows down to upwards Result- lengthening & cooling of arc

MAGNETIC BLOW OUT TYPE Arc horns act as previous Magnetic field blows out arc into arc-chutes Arc-chutes lengthen the arc Air flows down to upwards Result- lengthening & cooling of arc Arc extinguishes within an confined area

ARC-CHUTE TYPE Main contacts & auxiliary contacts are provided Auxiliary contacts close before & open after main contacts The arc-chutes made by steel divides arc When arc comes contact with steel it cools down

AIR BLAST CIRCUIT BREAKER

Requires an auxiliary compressed air system (about 15kg/cm2 ). At opening time compressed air admitted to the arc extinction chamber. It pushes away the moving contact. Air is released through nozzle to produce high velocity jet. Dielectric strength increases in high pressure. Then air blast takes away the ionization gases along with it and assists arc extinction.

TYPES OF AIR BLAST CIRCUIT BREAKERS AXIAL-BLAST AIR CIRCUIT BREAKER AIR BLASTCIRCUIT BREAKER RADIAL-BLAST AIR CIRCUITBREAKER CROSS-BLAST AIR CIRCUIT BREAKER

AXIAL BLAST TYPE

RADIAL BLAST TYPE

CROSS BLAST TYPE

APPLICATION AREA & DISCUSSION Air break type Area: Both in D.C.&A.C. , up to 12kV & 2okA Placed in indoor, control of power station auxiliaries and industrial plants. Advantages: They do not require compressor, oil Free from fire & explosion hazards Disadvantages: Less efficient for lengthening & deionizing action at high currents Bulky Not suitable in modern power system Air blast type Area: 11kV to1100kV placed in out door Advantages: High speed of operation Negligible maintenance Elimination of fire hazarded Reduced size Disadvantages: Require air compressor of correct pressure, clean & dry Largest installation & costly Air leakages at the pipe fittings Drastic effect on small current & problem of current chopping arises leading to serious overvoltage

ThanQ