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Types of Circuit Breakers

Electrical circuit breaker is a switching device which can be operated manually as well as automatically for controlling and protection of electrical power system respectively. As the modern power system deals with huge currents, the special attention should be given during designing of circuit breaker to safe interruption of arc produced during the operation of circuit breaker. This was the basic definition of circuit breaker.

Circuit breakers have been classified into a number of types, based on different categories they have been subdivided into.

It should be noted here that there is no specific criteria of classifying the circuit breakers, but instead there are a number of ways in which we can categorize them for our easier understanding and knowledge of the operating conditions of the device.

These different categorizes can be according to the medium in which the circuit breaker operates, the actuating signal on which its works, the different types of constructing and working principles etc.

Each type of circuit breaker has its own advantages and disadvantages. The construction and working of these circuit breakers with special emphasis on the way the arc extinction is facilitated are explained in the articles listed in this page. 

An overview of all the different types of circuit breakers, mentioning their names and how they have been classified is shown in the first part. Further ahead, we will discuss some of the widely used types now-a-days.

Types of Circuit Breakers

Firstly we classify the circuit breakers according to the voltage levels they can operate on. So there are three most used types of circuit breakers in this category. These are:
  1. Low Voltage Circuit Breakers (< 1 kV)
  2. Medium Voltage Circuit Breakers (1-72 kV)
  3. High Voltage Circuit Breakers (> 72 kV)
Another very important category is where to use the circuit breaker. This may seem a bit weird at first, but when installing a breaker, you must have to take care if it will be used inside your home or any other building or it has to be installed somewhere outdoors. This is because the outer mechanical body of the breaker has to be designed accordingly for it to be tough and protective to prevent the internal circuitry from damaging. So two more types can be:

   
  1. Outdoor circuit breaker
  2. Indoor circuit breaker

There is another category which is based on the mechanism used to actuate the circuit breaker, which specifies the mechanism of operation of the breaker, there are three further types:

  1. Spring operated circuit breaker
  2. Pneumatic circuit breaker
  3. Hydraulic circuit breaker

Now considering the medium in which a circuit breaker can operate. Most of us would have the concept that circuit breakers can only be installed in the circuits present in our homes so that the medium surrounding them is air. But now here is something for you to ponder over. Not Only air, but circuit breakers can also be installed in water or other mediums. Here are the basic types according to the medium of installation:

  1. Oil circuit breaker.
  2. Air Blast circuit breaker.
  3. SF6 circuit breaker.
  4. Vacuum circuit breaker.

Important Circuit Breaker Types

Here is a brief description of most important types of circuit breakers used in different places.

Air Blast circuit breaker.

Air blast circuit breakers employ a high pressure air blast as an arc quenching medium. 
Under normal condition the contacts are closed. When a fault occurs contacts are opened and an arc is struck between the them. The opening of contacts are done by a flow of air blast established by the opening of blast valve (located between air reservoir and arcing chamber ). The air blast cools the arc and sweeps away the arching products in to the atmosphere. Thus the dielectric strength of the medium is increased, prevents from re-establishing the arc. The arc get extinguished and flow of current is interrupted.

The circuit breakers are classified on the basis the direction of air blast to the arc. They are classified into :

1. Axial Blast Type - air blast is directed along the arc path.
2. Cross Blast Type - air blast is directed at right angles to the arc path.
3. Radial Blast Type - air blast is directed radially.

SF6 Circuit Breakers

In SF6 Circuit Breakers, sulphur hexaflouride gas (SF6) is used as the arc quenching medium. 
The sulphur hexaflouride gas (SF6) is an electronegative gas and has a strong tendency to absorb free electrons. The contacts of the breaker are opened in a high pressure flow of sulphur hexaflouride (SF6) gas and an arc is struck between them. The gas capture the conducting free electrons in the arc to form relatively immobile negative ions. 

This loss of conducting electrons in the arc quickly builds up enough insulation strength to extinguish the arc. The sulphur hexaflouride (SF6) circuit breakers have been found to be very effective for high power and high voltage service.

Vacuum Circuit Breaker.

In vacuum circuit breakers, vacuum is used as the arc quenching medium. Vacuum offers the highest insulating strength. So it has far superior arc quenching properties than any other medium. 

For example, when contacts of a breaker are opened in vacuum, the interruption occurs at first current zero with dielectric strength between the contacts building up at a rate thousands of times higher than that obtained with other circuit breakers. 

The technology is suitable for mainly medium voltage application. For higher voltage vacuum technology has been developed but not commercially viable.