Circuit Breaker

CIRCUIT BREAKER

Definition-

Circuit Breaker

        Circuit breaker is a device which use to make or break the circuit automatically or manually.

        Circuit breaker is an protecting device and plays an important roll in power system.

Basics-

        Circuit breaker is an one of the most important unit in electric power system. The protection, stability and continuity of system depends on circuit breaker. circuit breaker has ability to switch on the load and exciting current and interrupt the fault current.

There are many types of circuit breakers are used in power system some of them are as follows.

·       Air circuit breaker

·       Vacuumed circuit breaker

·       Oil circuit breaker

·       SF6 circuit breaker

Description-

        Circuit breaker has main application of tripping or disconnecting the non healthy part form healthy part when abnormal Current flowing through circuit. Tripping operation is done by using tripping coil, and closing operation is done by using closing coil.

        Each interrupter is filled with some arc quenching media like “sf6 gas” and the pressure of all the phases are same by using the copper pipe commonly connected between all phases and pressure gauge.

Construction-

A circuit breaker has basically divided in three parts

A)Interrupter and Support insulator

B)         Operating Mechanism

C)         Base Frame

A)Interrupter And Support Insulator-

Interrupter unit is again has following parts

1)  Puffer cylinder and piston

2)  Moving main contact

3)  Moving arcing contact

4)  Nozzle

5)  Fixed main contact

6)  Fixed Arcing contact

7)  Support Porcelain

Hole assembly is mounted on interrupter Porcelain and below that support insulator

·       Operation of Interrupter-

a)   Opening Operation-

Process of opening operation

For opening operation when moving contact is separated from fixed contact on that time moving main contact and arcing contact moves downwards (separated from fixed contact) on that time for some Specified distance arc is strikes between fix and moving arcing contact.

        And because these arc is not fusible for breaker we need to quench/extinguish that arc.

        For that extenuation two types are used

i)                 lengthening of arc

ii)             Splitting of Arc

b)  Closing Operation-

procrss of closing operation

In closing operation moving arc contact moves towards the fixed contacts.

Moving arc contact moves up till the moving contact overlaps fully as per wipe mention.

·       Support Porcelain-

Support porcelain is use to isolate interrupter from Ground. Inside the porcelain arc quenching media is placed and it is common with interrupter.

B)  Operating Mechanism-

a)   Motor-

Universal motors are used in circuit breaker For charging of Closing Springs. And its Operation Is just to Charge the closing spring During Every Operation of Circuit Breaker.

b)  Closing And Tripping Springs-

Energy for closing operation and opening operation is Provided from Operating mechanism

The energy required for closing operation is Stored in Closing Spring, and Energy required for opening operation is stored in tripping spring.

c)   Latch-

When breaker is in close condition it is hold by tripping holding latch, and when breaker is in open condition it is hold by closing holding latch.

d)   Coils-

·       Tripping Coil-

When Tripping signal is given to tripping coil it gets energies and hits the tripping holding latch and breaker trips (i.s. opening of  Circuit Breaker).

·       Closing Coil-

When closing signal given to closing coil ti gets energies and it hits the closing holding latch and breaker gets closed.

C)  Frame-

Frame is the Base part of circuit breaker operating mechanism and interrupters and supporting insulators are mounted on Base Frame.

D)Properties of SF6 gas-

i)                 Order less and Non toxic

ii)             Dielectric strength is high

iii)          Non flammable

iv)           High density

v)              Salability in water

vi)           Thermal conductivity – 0.0136w/mk