How circuit breakers work?

Category: Technology

A circuit breaker is used to protect electrical circuits from all sorts of damage caused by overloading of power or short-circuit. This procedure is done automatically. The main function of these sorts of switches is to discover a fault condition and interrupt the flow of current to protect the circuit from any major damage. The basic function matches it with a fuse, but the major difference is that the fuses can be used only once and should be replaced after use but the circuit-breakers can be reset manually or automatically to resume normal operation. Thomas Edison was first to describe the circuit-breakers in 1879 in his patent edition. Circuit breakers can be of any size; they are made to protect small home appliances to switchgears.

Operation procedure

The circuit-breakers first identify a fault condition. This detection is done by a different way in different circuits. If the circuit-breaker is used for a low-voltage circuit, then it will be done within the breakers’ enclosure. And if it is used for a high-voltage circuit then a pilot device would be there to detect the fault. The moment this fault has been detected the circuit breakers open to interrupt the current flow. Some times the mechanically-stored energy contained within the breakers used to separate the circuit, some times the required energy obtained from the fault current itself. Small or house-hold circuit breakers can be reset manually while the large units have a different mechanism to reset the procedure for future use.

Types of circuit breakers

The circuit breakers can be divided into three types depending on their mechanism.

The first type utilizes electro-magnetism. In this process, the magnetic circuit breaker has an electromagnet. The magnetism of this electromagnet increases the power load and as the load surpassed a certain level, the electromagnet’s pull become enough strong to enforce the circuit breaker’s lever down. The moment this happens the circuit breaker’s contact plate moves away from the stationary contact plate. Thus, the circuit opens and the current flow is stopped.

The next type of circuit-breakers utilizes heat to break the circuit. This sort of thermal circuit breakers have a bi-metallic strip. The two different metals expand, but their expansion rate is different at the same temperature. So the strip is bent at a certain angle if the heat crosses the level and this is adequate to pull the circuit-breakers lever to separate the connection between the circuit-breaker’s contact plate with the stationary plate and discontinue the current flow.

The third type of circuit-breakers utilizes both heat and electro-magnet to guard electrical system. In this system the electro-magnet pulls the lever down if there is a sudden jump in the current load while in the case of lengthened current overload the bimetallic strips works to guard the circuit.

The arc

Arc is generated in the circuit-breakers when the current is stopped. This arc needs to be cooled and extinguished in a restricted way to resume the contacts again so that the current flow can be normal. Different circuit breakers use different things as arc-form medium such as vacuum, air, insulating gas or oil. There are different ways to put-out the arc. Sometimes the arc may be expanded to put it out, sometimes intense cooling needed to put it off. Some times, division into the partial arcs or connecting capacitors in parallel with contacts in DC circuit is also used to extinguish the arc.

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