A Glance at protective devices

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A protective device is an equipment that can protect machinery,components and man in operation. Or in electrical aspects, a protective device can act against short circuit, over current and such abnormalities in a system.
          There are many types of protective devices employed in the modern era though a major part includes the former.
The main types among them are:
1) Fuses
2) Circuit breaker
3) Relays
4) Earthing devices

FUSE:



A fuse is a small crosection conducting path or wire and it is enclosed by a insulating non combustible cartridge. It allows only a rated value of current passing through it say the 'rated amps" And also it sacrifices it's life when an increased or abnormal current flows through it.!
Principle of operation of a fuse is obviously the melting of wire when it us heated Up while caring more than rated value in prior to eqn i2rt. And there by breaks the circuit.
A main drawback of a conventional fuse is it's replacement after one time use!
So a similar advanced equipment say circuit breaker is introduced.

CIRCUIT BREAKERS:

A circuit breaker is a switching device which can be operated manually or automatically to make or break a circuit, a circuit breaker generally consist of a moving and fixed contacts, in normal ON condition the two contacts are physically attached each other so they can make flow of current through them and in normal OFF position these two are separated each other by a distance and blocks the flow of current. [img side] while in the operation that is switching ON or OFF an arc is produced between the two contacts and this arc should be quenched immediately for a safe operation so in between these two contacts a high resistance quenching media is filled such as vacuum, oil , SF6 etc.. also they are classified according to the arc quenching medias used in them.

A circuit breaker can easily disconnect a faulty part from the healthy system unlike a fuse which operates once and must be replaced, a circuit breaker can be just reset to resume its normal operation after removing the fault.

A circuit breaker that is used in low voltage systems can be abbreviated as miniature circuit breaker and it can detect fault itself and trip, but in large circuit breakers the fault is detected by protective relays(can be discussed later) and the in-turn sends trip signal to act circuit breaker!

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