What is a Circuit Breaker? How does a Circuit Breaker work?

What is a Circuit Breaker?

Circuit breakers are automated electrical switches that are specifically designed to safeguard an electrical circuit from any damage caused due to excess current from an overload or short circuit. The mechanical device disturbs the flow of high magnitude faulty current and further performs the function of a switch. It is mainly designed for the closing or opening of an electrical system, thus protecting the electrical system from getting damaged.

Circuit breakers are usually made in different sizes, from small devices that shield low-current circuits or individual household appliances, up to bigger switchgear designed to shield high voltage circuits feeding an entire city. The generic function of a circuit breaker is often abbreviated as OCPD (Over Current Protection Device).Circuit Breaker There are various kinds of circuit breakers that cater to specific scenarios. The classification of the circuit breaker is on the basis of the medium of arc extinction; such types of circuit breakers are listed below:

1. Oil Circuit Breaker
⇒ Bulk Oil Circuit Breaker
⇒ Minimum Oil Circuit Breaker
2. Sulphur Hexafluoride Circuit Breaker
3. Air Blast Circuit Breaker
4. Air Break Circuit Breaker
5. Vacuum Circuit Breaker

How does a Circuit Breaker work?

All circuit breakers have similar features in their operation, but details vary depending on the voltage class, current rating and the type of circuit breaker.

Firstly, there must be a fault detected by the circuit breaker. In small mains and low voltage circuit breakers, this is normally done within the device itself. Typically, the heating or magnetic effects of electric current are employed. Circuit breakers for large currents or high voltages are usually organized with protective relay pilot devices that sense fault conditions and operate the opening mechanism. These usually need a separate power source, such as a battery, although some high-voltage circuit breakers are self-contained with current transformers, protective relays, and an internal control power source.

Once a fault has been detected, the circuit breaker opens to interrupt the circuit – this is commonly done using mechanically stored energy contained within the breaker, such as a spring or compressed air to separate the contracts. Circuit breakers may also use the higher current caused by the fault to separate the contracts, such as thermal expansion or a magnetic field. Usually, small circuit breakers have a manual control lever to switch off the load or reset a tripped breaker, while larger ones use solenoids to trip the mechanism, and electric motors to restore energy to the springs.

When a high current or voltage is interrupted, an arc is generated. The length of this arc is usually proportional to the voltage while the intensity or heat is proportional to the current. The arc needs to be contained, cooled and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit. Some circuit breakers use vacuum while other use air, insulating gas or oil as the medium the arc forms in. Finally, once the fault condition has been cleared, the contacts require closing to restore power to the interrupted circuit.

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