SF6 CIRCUIT BREAKER

Hello friends, welcome to ELECTRICAL ENCYCLOPEDIA. In this article, we will study about the SF6 Circuit Breaker.

CONTENTS

* What is SF6? 
* Construction of SF6 Circuit Breaker 
* Working of SF6 Circuit Breaker 
* Advantages of SF6 Circuit Breaker 
* Disadvantages of SF6 Circuit Breaker

WHAT IS SF6?

SF6 means Sulphur Hexaflouride gas. It is an electro-negative gas which means that it has a strong tendency to absorb free electrons. due to this property of SF6 gas, it is used in circuit breakers as the arc quenching medium. The contacts of the breaker are opened in a high pressure flow of SF6 gas. The conducting free electrons present in the arc are rapidly captured by the gas and due to this loss of conducting electrons in the arc , arc gets extinguished.

The SF6 Circuit Breakers have been found to be very effective for high power and high voltage service.

CONSTRUCTION OF SF6 CIRCUIT BREAKER

SF6 CIRCUIT BREAKER 

Above figure shows the parts of SF6 circuit breaker. The circuit breaker consists of fixed and moving contacts enclosed in a chamber (called interruption chamber). This chamber is connected to SF6 gas reservior. Arrangements are made in such a way that when the contacts of the breaker are open, then the valve mechanism makes the high pressure SF6 gas to flow from reservior to the chamber. 

Fixed Contacts is a hollow cylindrical current carrying contact fitted with an arc horn. Moving contact contains holes so that the SF6 will let out after extinguishing the arc. Tips and corners of contacts are coated with copper-tungsten arc resistant material.

WORKING OF SF6 CIRCUIT BREAKER

During the normal condition contacts of circuit breaker remains closed and contacts are surrounded by SF6 gas at a pressure of 2.8 kg/cm². During the fault condition, moving contact of circuit breaker is pulled and an arc struck between them. This movement of moving contact opens the valve which permits the SF6 at 14 kg/cm² pressure  to flow from reservior to the arc interruption chamber. This high pressure flow of SF6 gas rapidly absorbs the free electrons present in the arc. The result is that the medium between the contacts quickly builds up the high dielectric strength and arc gets extinguished.

After the operation of breaker, the valve is closed by the spring action.

ADVANTAGES OF SF6 CIRCUIT BREAKER

1. Because of excellent arc quenching property SF6 gas, such circuit breakers have very short arcing time.

2. Dielectric Strength of SF6 gas is very high, so such breaker can interrupt larger current.

3. Since the SF6 is non-inflammable, so there is no risk of fire.

4. SF6 gas does not contain any carbon content so there is no carbon deposits

5. SF6 circuit breaker provides the noiseless operation unlike Air blast circuit breaker.

6. SF6 breakers are completely enclosed and sealed from atmosphere, so there are no explosion hazards.

DISADVANTAGES OF SF6 CIRCUIT BREAKER

1. SF6 breakers are costly due to the high cost of SF6 gas.

2. SF6 gas has to be reconditioned after every operation of circuit breaker, so additional equipment is required for this purpose.

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