Perlindungan Sistem kuasa-Basic Protection Equipment - Bahagian 2

Low voltage circuit breaker

a)Function of circuit breaker

Pemutus litar (circuit breaker-CB) peranti pensuisan yang boleh dikendalikan secara manual dan juga secara automatik untuk mengawal dan melindungi sistem kuasa elektrik masing-masing.  CB adalah suis automatik yang boleh mengganggu (interrupt) arus 'fault'.
Semasa keadaan operasi normal, pemutus litar berada dalam kedudukan tertutup. Semasakeadaan tidak normal atau rosak, relay mengesan 'fault' dan menutup litar 'trip' CB. 
Selepas itu CB dibuka. Jadi CB adalah peranti yang actually isolates bahagian yang rosak dan peranti keluaran akhir skim pelindung. Semasa membuka contact CB, arka dihasilkan di antara mereka.

A circuit breaker is a switching device which can be operated manually as well as automatically for controlling and protection of electrical power system respectively.     Circuit Breakers are automatic switches which can interrupt fault currents. During normal operating conditions the circuit breaker is in closed position. During abnormal or faulty conditions, relays sense the fault and close the trip circuit of circuit breaker. There after the circuit breaker opens. So circuit breaker is the device which actually isolates the faulty part and is final output device of protective scheme. On opening of circuit breaker contacts an arc is drawn out between them.

CB adalah peralatan yang direka untuk melindungi litar elektrik daripada kerosakan yang disebabkan oleh litar pintas atau beban. Prinsip kerja CB asas ialah ia merupakan suis elektrik yang dikendalikan secara automatik. Ia mengesan keadaan kerosakan dan interrupt kesinambungan untuk menghentikan aliran elektrik serta-merta. Ia tidak seperti fius yang beroperasi sekali dan perlu diganti, CB boleh direset semula (sama ada secara manual atau secara automatik) untuk meneruskan operasi normalnya. Terdapat pelbagai saiz dan jenis CByang boleh didapati mengikut penggunaannya. Ia digunakan untuk melindungi peralatan rumah  sehingga sistem pengedaran besar (Stesen Kuasa).

A circuit breaker is equipment which is designed to protect an electric circuit from damage caused by short circuit or overload. The basic circuit breaker working principle is that it is an automatically operated electric switch. It detects the fault condition and interrupts the continuity to stop the flow of electricity immediately. It is not like a fuse which operates once and need to be replaced, a circuit breaker can be reset (either manually or automatically) to resume its normal operation. There are variable sizes and varieties of circuit breakers are available according to the use. It is used for the protection of small household appliances up to the large distribution systems (Power Stations).

the arc phenomenon and methods of eliminating it
fenomena arka dan cara menghapuskannya

Apabila litar pintas berlaku, arus tinggi mengalir melalui contact CB sebelum dibuka oleh sistem pelindung. Seketika apabila contact mula berpisah, kawasan contact berkurangan dengan cepat dan menyebabkan arus 'fault' yang besar menyebabkan density arus meningkat, oleh itu suhu meningkat.


Semasa  contact CB terbuka, medium di antara pembukaan contact menjadi sangat terionisasi di mana interrupt mendapat laluan rintangan yang rendah dan arus terus mengalir melalui laluan ini walaupun contact ini secara fizikal dipisahkan. Semasa  arus mengalir dari satu contact ke yang lain, laluan menjadi sangat panas sehingga ia bersinar. Ini dipanggil arka.

When short-circuit occurs, a heavy current flows through the contact of the circuit breaker before they are opened by the protective system. At the instant when the contacts begin to separate, the contact area decrease rapidly and large fault current causes increased current density and hence rise in temperature.

During opening of current carrying contacts in a circuit breaker the medium in between opening contacts become highly ionized through which the interrupting current gets low resistive path and continues to flow through this path even the contacts are physically separated. During the flowing of current from one contact to other the path becomes so heated that it glows. This is called arc.

Methods of eliminating it

There are two methods of extinguishing the arc in circuit breaker which are:-

a.    High resistance method

b.    Low resistance or current zero method