A circuit breaker is a automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit or in no load condition. Circuit breaker are made in varying sizes, from small devices that protect low current circuits or individual household appliances, up to large switchgear designed to protect high voltage circuit feeding an entire city. The generic function of a circuit breaker, RCD or a fuse, as an automatic means of removing power from a faulty system is often abbreviated as OCPD. Many classifications of circuit breakers can be made, based on their features such as voltage class, construction type, interrupting type, and structural features.
We classify the circuit breaker according to the voltage levels they can operate on. So there are three most used types of circuit breaker in this category.
- Low voltage circuit breaker
- Medium voltage circuit breaker
- High voltage circuit breaker
- Low voltage circuit breaker
1. Low voltage circuit breaker
- types are common in domestic, commercial and industrial application and include MCB miniature circuit breaker, rated current not more than 100 Amp. Trip characteristics normally not adjustable. Thermal or thermal magnetic operation. Breaker illustrated above is in this category. MCCB molded case circuit breaker rated current up to 2500 Amp. Thermal or thermal magnetic operation. Trip current may be adjustable in larger ratings. Low voltage circuit breaker can be mounted in multi-tiers in low voltage switchboards.
2. Medium voltage circuit breaker
- Medium voltage circuit breaker rated between 1 and 72 KV may be assembled into metal enclosed switchgear line ups for indoor use, or may be individual components installed outdoors in a substation. Air break circuit breakers replaced oil filled units for indoor applications, but are now themselves being replaced by vacuum circuit breakers up to about 40.5 KV.
3. High voltage circuit breaker
- Electrical power transmission networks are protected and controlled by high voltage breakers. The definition of high voltage varies but in power transmission work is usually through to be 72.5 KV or higher. High voltage breakers are nearly always solenoid operated with current sensing protective relays operated through current transformer. In substation the protective relay scheme can be complex, protecting equipment and buses from various types of overload or ground or earth fault. High voltage breaker is broadly classified by the medium used to extinguish the arc: there are four types in this category.
- Air circuit breaker
- Oil circuit breaker
- SF6 circuit breaker
- Vacuum circuit breakera
a) Air circuit breaker
- Air circuit breaker is an electrical device used to provide over current and short circuit protection for electric circuit over 800 Amps to 10K Amp. These are usually used in low voltage application below 450V. Air break circuit breaker the arc is initiated and extinguish in substantially static air in which the arc moves.
b) Oil circuit breaker
- Oil circuit breaker is such type of circuit breaker which used oil as a dielectric or insulting medium for arc extinction. In oil circuit breaker the contact of the breaker are made to separate within an insulating oil.
c) SF6 circuit breaker
- A circuit breaker in which SF6 (sulphur hexafluoride) under pressure gas is used to extinguish the arc is called SF6 circuit breaker. SF6 gas has excellent dielectric, arc quenching, chemical and other physical properties which have proved its superiority over other arc quenching mediums such as oil or air.
d)Vacuum circuit breaker
- A vacuum circuit breaker is a kind of circuit breaker where the arc quenching takes place in vacuum medium. The operation of switching on and closing of current carrying contacts and interrelated arc interruption takes place in a breaker which is called vacuum interrupter.