Circuit breaker
A circuit
breaker is an automatically operated electrical switch designed to protect an
electrical circuit from damage caused by excess current from an overload or
short circuit. Its basic function is to interrupt current flow after a fault is
detected. Unlike a fuse, which operates once and then must be replaced, a
circuit breaker can be reset (either manually or automatically) to resume
normal operation. Circuit breakers are made in varying sizes, from small
devices that protect low-current circuits or individual household appliance, up
to large switchgear designed to protect high voltage circuits 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 (Over
Current Protection Device).
Types Of Circuit breaker
- · Bulk
- · Minimum oil
- · Air blast
- · Vacuum
- · SF6
Bulk Oil Circuit Breake
Bulk Oil
Circuit Breaker: A breaker which uses a large quantity of oil for arc
extinction is called a bulk oil circuit breaker. Such type of circuit breaker
is also known as dead tank-type circuit breaker because their tank is held at
ground potential. The quantity of oil requires in bulk oil circuit breaker
depends on the system voltage. If the output rating of the voltage is 110 KV,
then it requires 8 to 10 thousand kg of oil, and if their output rating is 220
KV, then breakers need 50 thousand Kg of oil.
Minimum
Oil Circuit Breaker
In this type of circuit breaker minimum oil is used as an arc
quenching medium and it is mounted on a porcelain insulator to insulate it from
the earth. The arc chamber of such type of circuit breaker is enclosed in a
bakelised paper. The lower portion of this breaker is supported by the
porcelain and the upper porcelain enclosed the contacts.
Air Blast Circuit Breaker
Air blast circuit breaker used compressed air or gas as the
arc interrupting medium. In the air blast, circuit breaker compressed air is
stored in a tank and released through a nozzle to produce a high-velocity jet;
this is used to extinguish the arc. Air blast circuit breakers are used for
indoor services in the medium high voltage field and medium rupturing capacity.
Generally up to voltages of 15 KV and rupturing capacities of 2500 MVA. The air
blast circuit breaker is now employed in high voltage circuits in the outdoors
switch yard for 220 KV lines.
Vacuum
Circuit Breaker
A breaker which used vacuum as an arc extinction medium is
called a vacuum circuit breaker. In this circuit breaker, the fixed and moving
contact is enclosed in a permanently sealed vacuum interrupter. The arc is
extinct as the contacts are separated in high vacuum. It is mainly used for
medium voltage ranging from 11 KV to 33 KV.
Vacuum circuit breaker has a high insulating
medium for arc extinction as compared to the other circuit breaker. The
pressure inside the vacuum interrupter is approximately 10-4 torrent and at
this pressure, very few molecules are present in the interrupter.
Sulphur Hexafluoride (SF6) Circuit Breaker
A circuit breaker in which SF6 under pressure gas is used to
extinguish the arc is called SF6 circuit breaker. SF6 (sulphur hexafluoride)
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. The SF6 circuit breaker is mainly divided into three types.
- Non-puffer piston circuit breaker.
- Single- puffer piston circuit breaker.
- Double-puffer piston circuit breaker.
The circuit breaker which used air and oil as an insulating
medium, their arc extinguishing force builds up was relatively slow after the
movement of contact separation. In the case of high voltage circuit breakers
quick arc extinction properties are used which require less time for quick
recovery, voltage builds up. SF6 circuit breakers have good properties in this
regards compared to oil or air circuit breakers. So in high voltage up to 760
kV, SF6 circuit breakers is used.
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