1- SF6-Gas circuit Breaker :

The SF6 circuit breaker is used in the HT panel for switching and controlling the power supply from overload and short circuit. Sulphur hexafluoride gas is used for arc quenching as a medium of insulation. it is called an SF6 circuit breaker.

The SF6 circuit breaker has a very short arcing time so it works as insulating gas. So dielectric strength of (SF6) gas is 2 to 3 times more against air. If we compare it to another circuit breaker then the SF6 breaker is very effective for and high voltage and high-power system.

2- Connection Diagram of SF6- GCB:

3- Working Principle of SF6- GCB:

It is used as other normal circuit breakers. When we switch on the breaker then moving and fixed contact is connected into SF6 gas pressurized chamber during this connectivity arc generates but it is quenched by high-pressure isolation SF6 gas.
The pressure of SF6 gas is 1.4 bar & temp 20° C in the operating chamber. The closing time of the breaker should be approx. 30 mS.

When the SF6 gas passes into the arc, then it will reduce the increasing area of the arc. It is said that resistance is inversely proportional to the arc. The resultant arc will be quenched.

4- Properties of SF6 Gas:

1- Harmless:

it is no smell, colorless, no taste, and nontoxic type gas.it can be decreased oxygen label very fastly as 21 percent to 13 percent.it means suffocation.

2- Arc Extinguish:

it has more capacity of arc quenching against air.it can observe more temp off arc without increasing temp.

3- Dielectric Strength:

Dielectric strength of SF6 is three times more in comparison to Air pressure in one atmosphere. If we compare it roughly, it is similar to transformer oil.

4-Thermal conductivity:

It has more thermal observing capacity.

5-Electrical Properties:

SF6 molecules behave as a non-electronegative character.it collects free electrons and converts them into negative ions.it is said to be the electronegative of SF6.

5- Parts of GCB(SF6):

• Operating Mechanism
• SF6 Interrupter chamber
• Fixed and moving contacts
• breaker rackin and rackout mechanism

6- Types of GCB(SF6):

• Indoor type: 33-36 KV
• Outdoor type: Above 66 KV to 400 KV.
• Single pressure puffer type.
• Double pressure type.

7- Advantage and Disadvantage of GCB(SF6):

Advantage of SF6 gas Circuit Breaker

1. Very short arcing time due to fast extinguish property.
2. High interrupts the larger current of the arc due to more dielectric strength.
3. Compact design.
4. Environmentally friendly.
5. Contact disconnect time is very low due to high-pressure SF6.

Disadvantage of the SF6 gas Circuit Breaker

1. High cost in comparison to another breaker.
2. It does not support life due to decreased oxygen labels.
3. For the SF6 circuit breaker special facility is required for maintenance and transportation
4. Required gas leakage monitoring.

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