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Circuit Breakers Defined

defines a circuit breaker as: A

mechanical switching device, capable of making, carrying and breaking currents

under normal circuit conditions. Also capable of making and carrying for a

specified time and breaking currents under specified abnormal circuit conditions,

such as those of a short circuit.

Pneumatic Circuit Breaker

A pneumatic circuit breaker either stops, diverts or releases pneumatic pressure if itreaches a level too high for its designed application. You might see a need for such a

device in a system that uses both high and low pressure. For example, the source ofpneumatic pressure may be a pump capable of generating 1,000 lb. per square inch of

pressure to lift something; the pressure may also be used to operate simple switches,which may not need any more than one-hundredth of that pressure to operate. Thepneumatic circuit breaker would then respond to a predetermined amount of pressure,

protecting the lighter-duty circuitry from very high pressure, should a valve or regulator

malfunction.

Pneumatic Actuated Circuit Breaker

Not all pneumatic circuit breakers refer to mechanical systems, which actuate othermechanical systems. Pneumatics can be used to actuate an electric system, just as electric

systems can be used to actuate pneumatic systems. For example, another kind of

pneumatic circuit breaker would be one that senses pressure in a pneumatic system,which creates its pressure by an electric pump. If the pressure gets too high, then a

pneumatic control would mechanically flip an electrical circuit breaker, shutting off the

motor. It may work in reverse, too: an electrical circuit breaker could be used to shutdown the function of a pneumatic system

What is arc ?

During opening of current carrying contacts in a circuit breaker the medium in between opening

contacts become highly ionized through which the interrupting current gets low resistive path

and continues to flow through this path even the contacts are physically separated. During theflowing of current from one contact to other the path becomes so heated that it glows. This iscalled arc.

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Arc in Circuit Breaker

Whenever, on load current contacts of circuit breaker open there is an arc in circuit breaker,established between the separating contacts. As long as this arc is sustained in between the

contacts the current through the circuit breaker will not be interrupted finally as because arc is

itself a conductive path of electricity. For total interruption of current the circuit breaker it isessential to quench the arc as quick as possible. The main designing criteria of a circuit breaker is

to provide appropriate technology ofarc quenching in circuit breaker to fulfill quick and safe

current interruption. So before going through different arc quenching techniques employed in

circuit breaker, we should try to understand "e;what is arc"e; and basic theory ofarc in circuit

breaker, lets discuss.

Lets have a discussion on electrical principle of circuit breaker

The circuit breaker has to carry large rated or fault power. Due to this large power there is

always dangerously high arcing between moving contacts and fixed contact during operation of

circuit breaker. Again as we discussed earlier the arc in circuit breakercan be quenching safely ifthe dielectric strength between the current carrying contacts of circuit breaker increases rapidly

during every current zero crossing of the alternating current. The dielectric strength of the mediain between contacts can be increased in numbers of ways, like by compressing the ionized arcing

media since compressing accelerates the deionization process of the media, by cooling the arcing

media since cooling increase the resistance of arcing path or by replacing the ionized arcingmedia by fresh gasses. Hence a numbers of arc quenching processes should be involved in

operation of circuit breaker

Types of Circuit Breaker

According different criteria there are different types of circuit breaker

According to their arc quenching media the circuit breaker can be divided as

1) Oil Circuit Breaker

2) Air Circuit Breaker

3) SF6 Circuit Breaker

4) Vacuum Circuit Breaker

According to their services the circuit breaker can be divided as

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1) Outdoor Circuit Breaker

2) Indoor Breaker

According to the operating mechanism of circuit breaker they can be divided as

1) Spring operated Circuit Breaker

2) Pneumatic Circuit Breaker

3) Hydrolic Circuit Breaker

According to the voltage level of installation types of circuit breaker are referred as

1) High Voltage Circuit Breaker

2) Medium Voltage Circuit Breaker

3) Low Voltage Circuit Breaker

circuit breaker workingprinciple is that it is an automatically operated electric switch.It detects the fault

condition and interrupt the continuity to stop the flow of electricity immediately

E. Circuit Breakers - High-Voltage. High-voltage circuit breakers consist of oil,air, vacuum, or gas insulated circuit breakers, which operate in the range of above

15,000 voltsF . Circuit Breakers - Low-Voltage. Low voltage circuit breakers typically operateat 600 volts a.c. and below. There are three types:

1 . Molded Case Circuit Breakers. Molded case circuit breakers are available

in a wide range of ratings and are generally used for low-current, low energypower circuits. The breakers have self contained overcurrent trip elements.

2 . Insulated Case Circuit Breakers. Insulated case circuit breakers are

molded-case breakers using glass-reinforced insulating material for increased

dielectric strength. In addition, they have push-to-open button, rotary-operatedlow-torque handles with an independent spring charged mechanism providing

quick-make, quick break, protection.

3 . Heavy Duty Power Circuit Breakers. Heavy duty power circuit breakers

employ spring operated, stored energy mechanisms for quick-make, quickbreak

manual or electric operation. Generally, these breakers have draw-out

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