Circuit Breaker: Definition, Working Principle & Types

Circuit Breaker is an electrical switch designed to protect an electric circuit from overcurrent or short circuits. It helps in regulating the current by stopping it automatically. It stops the electric current in a circuit if it reaches its maximum limit. A circuit breaker can be thus recognized as a safety device. Circuit breakers are made in different sizes depending on their application. Small breakers are used to protect low-current circuits like households and large switchgear are used to protect high-voltage circuits working for an entire city. The general use of a circuit breaker is abbreviated as Over the Current Protection Device (OCPD).

Read More: NCERT Solutions for Class 7 Science Electric Current and its Effects

Key Terms: Circuit Breaker, Electrical Switch, Electrodes, Fuse, Arc Extinguisher, Electric Circuit, Air Circuit Breaker

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What is Circuit Breaker?

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Circuit Breakers are electrical safety devices designed to protect electric circuits from overloading and short circuit conditions. 

• Circuit Breakers perform the same function as fuses but are not destroyed when activated. 
• Unlike fuses, they don’t require replacing and can simply be reset once the fault has been recognized.
• A circuit breaker will open the circuit to prevent overload, and potential damage, like fires.
• They contain a switch to return to the closed position once they have been flipped.

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Advantages of Circuit Breaker

The advantages of a circuit breaker are

• It protects from the excessive flow of current which can cause damage.
• Circuit Breakers can be reset anytime as it is in a form of a switch.
• Circuit breakers are very reliable.

Disadvantages of Circuit Breaker

The disadvantages of a circuit breaker are: 

• Circuit Breakers’ installation and maintenance are expensive.
• A circuit Breaker reacts slower compared to a fuse.

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Working Principle of Circuit Breaker

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Circuit Breaker is made in such a manner that it can sense current. It is equipped to provide overload and short-circuit protection. If the current is flowing more than the capacity, it will automatically get tripped.

• Circuit Breaker consists of two contacts namely Fixed Contacts and Moving Contacts.
• When the circuit is closed and the contacts touch each other and carry the current. 
• These contacts carrying the current are knowns as electrodes.
• The switching and maintenance of the system are done by closing or opening the arms of the circuit breaker. 
• One can open the circuit breaker by applying a little pressure on the trigger. 
• When there is a problem with the current in any part of the system, it energizes the trip coil, leading to the parts moving away from each other. 
• This leads to the opening of the circuit.

Circuit Breaker

Read More: Working Principle of an Electrical Fuse

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Types of Circuit Breakers

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There are mainly four types of Circuit breakers:

1. Air Circuit Breaker
2. Vacuum Circuit Breaker
3. Oil Circuit Breaker
4. SF6 Circuit Breaker

All these types of circuit breakers function on a slightly different working principle and are employed in different sectors depending upon their advantages and disadvantages.

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Air Circuit Breaker

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Air Circuit Breaker is air-based and is also known as Air Blast Breaker. The arc extinguisher that is used is a high-pressure air blast. It works in the air at atmospheric pressure. In this way, it can protect the connected electric circuits. The blast valve opens the contact up if the current flow has a problem.

There are three types of Air Circuit Breaker:

• Axial blast type
• Cross blast type
• Radial blast type

Advantages of Air Circuit Breaker

• There is no risk of fire.
• As the dielectric strength increases faster, it leads to contacts having less gap in between.
• There is no need for arcing products.
• Since the arcing time and energy are small, frequent operations can be done.
• The interrupting current has no effect.

Disadvantages of Air Circuit Breaker

• In the air circuit breaker, the maintenance of the compressor is important.
• The variation of voltages can be harmful.
• The arc extinguishers used have inferior properties.

Air Circuit Breaker

Read More: Difference between Fuse and Circuit Breaker

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SF6 Circuit Breakers

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Sulfur hexafluoride circuit breaker has sulfur hexafluoride as the arc extinguishing medium. This gas can attract free electrons. The gas flows through the chamber affecting the arc when the circuit contacts are opened. SF6 generates immobile negative ions when the free electrons are absorbed. The insulating strength of the medium should be increased for the arc extinguisher to extinguish completely. In the arc chamber, fixed and moving contacts are along with the gas.

Advantages of SF6 Circuit Breaker

• The property of the arc extinguisher is very good.
• The interruption of the current is large as the gas in SF6 is three times greater than air.
• SF6 is good for the environment as well as there is no concept of exhausting.
• SF6 is suitable for difficult conditions as well such as in coal mines.

Disadvantages of SF6 Circuit Breaker

• The gas used in SF6 is expensive.
• SF6 needs maintenance after every use.

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Vacuum Circuit Breaker

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In vacuum circuit breakers, the arc extinguishing medium is the vacuum. The insulation of this circuit breaker is very good. There is ionization of the metal vapors when the vacuum is opened, forming an arc. The arc shield is mounted in the vacuum chamber along with the moving and fixed contacts.

Advantages of Vacuum Circuit Breaker

• The energy that the arc releases are low.
• It is strong enough to face lightning strikes.
• Little or no maintenance is required.

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Oil Circuit Breakers

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In this circuit, oil is used as the arc extinguishing medium. The contacts are opened in the oil when the arc strikes. It leads to the evaporation of oil into hydrogen gas. A hydrogen gas bubble surrounds the arc region. The arc is cooled down because of the Hydrogen gas which has a high thermal conductivity.

Oil circuit breakers are of two types:

• Bulk Oil Circuit Breakers
• Low Oil Circuit Breakers

Advantages of Oil Circuit Breaker

• The oil Circuit Breaker acts like an insulator between the earth and the live wires.
• It has a cooling property which is very good.

Disadvantages of Oil Circuit Breaker

• It can cause a fire hazard.
• It's difficult for arcing products to escape.

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Things to Remember

• Circuit Breaker is the most integral part of an electric circuit.
• It protects the devices from short-circuiting, overcurrent, and any sort of damage.
• Circuit Breaker consists of two contacts namely Fixed and Moving contacts.
• There are four types of Circuit Breakers which are Air Circuit Breakers, Vacuum Circuit Breakers, SF6 Circuit breakers, and Oil Circuit Breakers.
• Air Circuit breaker is of three types namely Axial blast type, Cross blast type, and Radial blast type.
• SF6 and Vacuum Circuit breakers are the most reliable and extensively used Circuit Breakers in today’s times.