A Glance at protective devices

-
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!

Comments

Post a Comment

Popular posts from this blog

Electrical Substations

-
Image
     Electrical Substations An electrical substation forms an integral part of the power system. It is placed at the both ends of the long distant transmission line... but why??!! Of-course to transform voltage!  A substation at the beginning End or say generation side normally used to boost up the voltage to higher magnitude suitable for transmitting the generated power to long distant load with minimum losses.( Uses a step up transformer )!! Yes the other type is at the other end of the long distant transmission line nearer to load centre... here the high voltage is stepped down to a relevant magnitude which may be used for distribution purpose or another voltage level transmission for near by substations.                    The heart of a substation is nothing but our transformer, depending upon the purpose transformer can be step up or step down!! Now we are considering a load end substation as a...
Read more

Differential Protection Scheme (Transformer)

-
Image
Hey friends! you are familiar with the power system equipment which we discussed earlier.! Now it's time to protect it to total safety. As soldiers protect our country from enemies likewise our system should be protected from fault. The line of control is decided by fixing the current transformers on the right place. So our boundaries is decided by their location. Here in a substation, we have many equipments such as transmission lines, bus-bar, transformers, etc in the system which need atmost care. Starting from the bulkiest, transformers are having different level of protections such as phase to phase and phase to ground. In other words differential protection and earth-fault protection. Over-current protection is also implemented in it. Let's talk about the differential type of protection for transformers. It's quite simple to explain the theory but some complicated while coming into the calculation. The term itself gives a brief idea about the ...
Read more

Capacitor banks and reactors

-
Image
Capacitor banks and Reactors We have already discussed the significance of reactive power in a power system, As we know the availability of reactive power depends on the excitation of the alternators.This reactive power can be provided by the generators themselves, through the adjustment of generator excitation, but it is often cheaper to provide it through capacitors, hence capacitors are often placed near inductive loads to inject reactive power.the so called capacitors are mainly of two, static condensers and synchronous condensers. The synchronous condensers have a variable value of VAR which can be varied by the excitation of the synchronous motor and the static capacitors have a fixed value of VAR.                                       The capacitor bank simply means that a group of  individual capacitors connected in  parallel and series accordingly to the design of the c...
Read more