airblast circuit breakers

8/3/2019 AirBlast Circuit Breakers

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Air Blast Circuit Breakers by

Engr. Khurram Hashmi

UCP, FOE



•Circuit breakers

•Principle of operation of a circuit Breaker

• Arc phenomenon

•

Principle of arc extinction



Circuit Breaker

• A circuit breaker is a piece of equipment whichcan:

i. make or break a circuit either manually or byremote control under normal conditions

ii. break a circuit automatically under fault

conditionsiii. make a circuit either manually or by remote

control under fault conditions



Principle Of Operation of a CircuitBreaker• A circuit breaker essentially consists of fixed and

moving contacts, called electrodes.

• Under normal operating conditions, thesecontacts remain closed

• When a fault occurs on any part of the system,

the trip coils of the circuit breaker get energisedand the moving contacts are pulled apart

• The Circuit may also be broken under normalconditions: manually or by remote control.



Arc Phenomenon

• When the Contacts of acircuit breaker begin toseparate the contact areadecreases rapidly.

• Large fault current causesincreased current density

• Temperature rises rapidly

• Heat produced ionizes themedium surrounding thecontacts and an arc is struck

• Current flow isuninterrupted in the circuitso long as the arc persists



Principles Of Arc Extinction

High resistance method Methods employed

• Arc resistance is made toincrease with time so thatcurrent is reduced to a value

insufficient to maintain thearc.

• Finally the current flow isinterrupted

• The principal disadvantage of

this method is that enormousenergy is dissipated in the arc.

• It is employed only in D.C.circuit breakers and low-capacity A.C. circuit breakers.

• Lengthening the arc

• Cooling the arc• Reducing cross sectional

area of the arc

• Splitting the arc



Principles of Arc extinction

Low resistance Method

Methods Employed • This method is employed for

arc extinction in A.C. circuitsonly.

• Arc resistance is kept low untilcurrent reduces to zero wherethe arc extinguishes naturally and is prevented fromrestriking when the voltage

across the contacts is restored

• Lengthening of the gap

• High pressure.

• Cooling.

• Blast effect.



•Principle of Arc extinguishing in ABCBs

•Types



Principle Of Arc Extinguishing in ABCBs• These breakers employ a high

pressure air-blast as an arcquenching medium.

•

The contacts are opened in aflow of air-blast: established by the opening of blast valve

• The air-blast cools the arc andsweeps away the ionic

products to the atmosphere• This rapidly increases the

dielectric strength of themedium between the contactsand prevents the arc fromre-establishing



Types Of Air Blast Circuit breakers

• Axial-blast type in which the air-blast is directed along the arc path(as shown in Fig. (i))• Cross-blast type in which the air-blast is directed at right angles to the arc path( as shown in Fig (ii)).• Radial-blast type in which the air-blast is directed radially

(as shown in Fig (iii).)



• Axial

•Cross



Axial Air Blast Circuit Breaker



Cross Air Blast Circuit Breaker



Contacts in Air Blast Circuit Breaker



Air Blast Circuit Breaker Module



Voltage Ratings Of Air Blast CircuitBreakers



Thank You

Your feedback valued at: [email protected]

airblast circuit breakers

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