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Air Blast Circuit Breakers by
Engr. Khurram Hashmi
UCP, FOE
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•Circuit breakers
•Principle of operation of a circuit Breaker
• Arc phenomenon
•
Principle of arc extinction
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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
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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.
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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
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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
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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.
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•Principle of Arc extinguishing in ABCBs
•Types
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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
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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).)
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• Axial
•Cross
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Axial Air Blast Circuit Breaker
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Cross Air Blast Circuit Breaker
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Contacts in Air Blast Circuit Breaker
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Air Blast Circuit Breaker Module
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Voltage Ratings Of Air Blast CircuitBreakers
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