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Introduction
An electrical power system is very complex. It needs some form of switchgear in order that it may be safely and efficiently controlled or regulated under both normal and abnormal operating conditions.
Circuit breaker is an automatically operated electrical switch.
It protects an electrical circuit from damage caused by overload and short circuit.
Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow.
Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.
It can be of various size , from small device that protects the appliances of an household to large to protect the entire city.
FUNCTIONS:-
It carries the full load current continuously without over heating or damage.
It opens and closes the circuit on no load.
It makes and breaks the normal operating current.
It makes and breaks the short circuit current of magnitude up to which it is designed for.
Classification
The circuit breaker can be classified on the basis of the quenching (cooling) medium:
Air circuit breaker
Air blast circuit breaker
Tank type bulk oil circuit breaker
Minimum oil circuit breaker
SF6 circuit breaker
Vacuum circuit breaker
AIRBLAST CIRCUIT BREAKER
Introduction
These type of breakers employ ‘air blast’ as the quenching medium.
The contacts are opened by air blast produced by the opening of blast valve.
The air blast cools the arc and sweeps away the arcing products to the atmosphere.
This rapidly increases the dielectric strength of the medium between contacts and prevents from re-establishing the arc.
So the arc is extinguished and the flow of current is interrupted.
Classification
Types of Air blast circuit breaker
(1). Axial-blast type
(2).Cross-blast type
(3).Radial-blast type
Axial-blast type:-
In which the air-blast is directed along the arc path as shown in Fig. 
Types of Air blast circuit breaker
In which the air-blast is directed at right angles to the arc path as shown in Fig.
Types of Air blast circuit breaker
In which the air-blast is directed radially as shown in Fig
1) Axial blast Air blast circuit breaker
2) Cross-blast air breaker
Advantages
The risk of fire is eliminated.
The arcing products are completely removed by the blast
The growth of dielectric strength is so rapid that final contact gap needed for arc extinction is very small. This reduces the size of device.
The arcing time is very small due to the rapid build up of dielectric strength between contacts
Due to lesser arc energy, ABCB are very suitable for conditions where frequent operation is required
The energy supplied for arc extinction is obtained from high pressure air & independent of the current to be interrupted
Disadvantages
Air has relatively inferior arc extinguishing properties.
Air blast circuit breakers are very sensitive to the variations in the rate of restriking voltage.
Considerable maintenance is required for the compressor plant which supplies the air blast .
Application
The air blast circuit breakers are finding wide applications in high voltage installations. Majority of the circuit breakers for voltages beyond 110 kV are of this type.
Future perspectives
In the near future, present interrupting technologies can be applied to circuit-breakers with the higher rated breaking currents (63 kA to 80 kA) required in some networks with increasing power generation.

Submitted By
Durgesh Rawal

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ABSTRACT
An electrical power system is very complex. It needs some form of switchgear in order that it may be safely and efficiently controlled or regulated under both normal and abnormal operating conditions. A tumbler switch with a fuse serves to control the light and other electrical equipments and is, in a way, a form of switch gear. On the other hand, a Circuit Breaker in a station serves exactly the same purpose but it has many added and much more complex features.
An early form of circuit breaker was described by Thomas Alva Edison in an 1879 patent application, although his commercial power distribution system used fuses. Its purpose was to protect lighting circuit wiring from accidental short-circuits and overloads.
A circuit breaker is an electrical device used in an electrical panel that monitors and controls the amount of amperes (amps) being sent through the electrical wiring. Circuit breakers come in a variety of sizes. For instance, 10, 15 and 20 amp breakers are used for most power and lighting needs in the typical home. Some appliances and specialty items (washers, dryers, freezers, whirlpools, etc.) will require a larger circuit breaker to handle the electrical load required to run that appliance.If a power surge occurs in the electrical wiring, the breaker will trip. This means that a breaker that was in the "on" position will flip to the "off" position and shut down the electrical power leading from that breaker. Essentially, a circuit breaker is a safety device. When a circuit breaker is tripped, it may prevent a fire from starting on an overloaded circuit; it can also prevent the destruction of the device that is drawing the electricity. While a number of older homes and buildings still use fuses to monitor the electrical load, almost every newer home has circuit breakers in the electrical panel. Fuses perform much the same duty as circuit breakers. However, circuit breakers are safer to use than fuses and easier to fix. If a fuse blows, oftentimes a homeowner will not know which fuse controls which specific power areas of the house.
INTRODUCTION
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.
It is a device to open or close an electric power circuit either during normal power system operation or during abnormal conditions. A circuit breaker serves in the course of normal system operation to energize or de-energize loads. During abnormal conditions, when excessive current develops, a circuit breaker opens to protect equipment and surroundings from possible damage due to excess current. These abnormal currents are usually the result of short circuits created by lightning, accidents, deterioration of equipment, or sustained overloads.
Formerly, all circuit breakers were electromechanical devices. In these breakers a mechanism operates one or more pairs of contacts to make or break the circuit. The mechanism is powered either electromagnetically,pneumatically, or hydraulically. The contacts are located in a part termed the interrupter. When the contacts are parted, opening the metallic conductive circuit, an electric arc is created between the contacts. This arc is a high-temperature ionized gas with an electrical conductivity comparable to graphite. Thus the current continues to flow through the arc. The function of the interrupter is to extinguish.
The automatic circuit breakers perform the following duties:
• It carries the full load current continuously without over heating or damage.
• It opens and closes the circuit on no load.
• It makes and breaks the normal operating current.
• It makes and breaks the sort circuit current of magnitude up to which it is designed for.
Classification of Circuit Breakers
The circuit breaker can be classified on the basis of the quenching (cooling) medium:
• Air circuit breaker
• Air blast circuit breaker
• Tank type bulk oil circuit breaker
• Minimum oil circuit breaker
• SF6 circuit breaker
Some important point related to air blast circuit breaker
• These type of breakers employ ‘air blast’ as the quenching medium.
• The contacts are opened by air blast produced by the opening of blast valve.
• The air blast cools the arc and sweeps away the arcing products to the atmosphere.
• This rapidly increases the dielectric strength of the medium between contacts and prevents from re-establishing the arc.
• So the arc is extinguished and the flow of current is interrupted.
PRINCIPLE OF OPERATION
A circuit breaker is a switching and current interrupting device. It consists, essentially, of fixed and moving contacts, which are touching each other and carry the current under normal condition i.e. when circuit breaker is closed. During the normal operating condition the circuit breaker can be opened or closed by a station operator for the purpose of switching and maintenance. To open the circuit breaker only a small pressure is required to be applied on a trigger. Whenever a fault occurs on any part of the power system, the trip coil of the breaker gets energized and the moving contacts are pulled a part by some mechanism, thus opening the circuit.
In air-blast circuit breakers, air is compressed to high pressures. When the contacts part, a blast valve is opened to discharge the high-pressure air to ambient, thus creating a very-high-velocity flow near the arc to dissipate the energy.
The operating mechanism operates the rod when it gets a pneumatic or electrical signal. The valves open so as to send the high pressure air in the hollow of the insulator. The high pressure air rapidly enters the double arc extinction chamber. As the air enters into the arc extinction the pressure on the moving contacts becomes more than spring pressure and contacts open.
The contacts travel through a short distance against the spring pressure. At the end of the contact travel the port for outgoing air is closed by the moving and the entire arc extinction chamber is filled with high pressure air as the air is not allowed to go out. However, during the arcing period the air goes out through the openings and take away the ionized air of the arc.
While closing, the valve is turned so as to close connection between the hollow of the insulator the reservoir. The valve lets the air from the hollow insulator to the atmosphere. As a result of the pressure of air in the arc extinction chamber is dropped down to the atmospheric pressure and the moving contacts close over the fixed contacts by virtue of the spring pressure.
The opening is fast because the air takes a negligible time to travel from the reservoir to the moving contact. The arc is extinguished within a cycle.Therefore, air blast circuit breaker is very fast in breaking the current.
Closing is also fast because the pressure in the arc extinction chamber drops immediately as the valve operates and the contacts close by virtue of the spring pressure.
It needs an auxiliary compressed air system which supplies air to the air receiver of the breaker. For opening operation, the air is admitted in the arc extinction chamber. It pushes away the moving contacts. In doing so, the contacts are separated and the air blast takes away the ionized gases along with it and assists in extinction. After a few cycles the arc is extinguished by the air blast and the arc extinction chamber is filled with high pressure air (30 kg/cm2). The high pressure air has higher dielectric strength than that of atmospheric pressure. Hence a small contact gap of few centimetres is enough.