SF6 Gas Circuit Breaker MCQ Quiz in தமிழ் - Objective Question with Answer for SF6 Gas Circuit Breaker - இலவச PDF ஐப் பதிவிறக்கவும்

Concept:

Sulphur hexafluoride possesses very good insulating and arc-quenching properties. These properties are

• It is a colourless, odourless, non-toxic, and non-inflammable gas.
• SF6 gas is extremely stable and inert, and its density is five times that of air.
• It has high thermal conductivity better than that of air and assists in better cooling current carrying parts.
• SF6 gas is strongly electronegative, which means the free electrons are easily removed from discharge by the formation of negative ions.
• It has a unique property of fast recombination after the source energising spark is removed. It is 100 times more effective as compared the arc quenching medium.
• Its dielectric strength is 5 times that of air and 30% less than that of the dielectric oil. At high pressure the dielectric strength of the gas increases.
• Moisture is very harmful to the SF6 circuit breaker. Due to a combination of humidity and SF6 gas, hydrogen fluoride is formed (when the arc is interrupted) which can attack the parts of the circuit breakers.

SF₆ Circuit Breaker Maintenance:

• For maintenance of circuit breaker or circuit breaker maintenance, it must be first switched off and then isolated from both sides by opening the concerned electrical isolator.
• At this no isolated condition the circuit breaker must be operated for local and remote conditions yearly and when required.
• The circuit breaker should be operated electrically from local and remote then mechanically from local.
• This type of operation makes the breaker more reliable by removing any coating developed between sliding surfaces.

SF₆ circuit breaker:

• The SF₆ circuit breaker is a type of circuit breaker that uses pressurized SF6 gas to extinguish the arc.
• It is a dielectric gas having superior insulating and arc quenching properties far better than air or oil.
• It is used for arc quenching in high voltage circuit breakers up to 800 kV in power stations, electrical grids, etc.

Advantages of SF₆ circuit breaker:

• The gas is inflammable and chemically stable.
• These breakers give noiseless operations. 
• It requires less maintenance and costly compressed air, systems are required.
• Due to the superior quenching property of SF6, such breakers have a very short arcing time.
• There are no carbon deposits.

Disadvantages of SF6 circuit breaker:

• The entrance of moisture level in the SF₆ breaker tank is very harmful to the breaker, and it causes several parts failures. 
• SF₆ breakers are costly due to the reason for the high cost of SF₆.

Concept:

SF6 circuit breaker:

• The SF6 circuit breaker is a type of circuit breaker that uses pressurized SF6 gas to extinguish the arc.
• It is a dielectric gas having superior insulating and arc quenching properties far better than air or oil.
• It is used for arc quenching in high-voltage circuit breakers up to 800 kV in power stations, electrical grids, etc.

Advantages of SF6 circuit breaker:

• The gas is inflammable and chemically stable.
• These breakers give noiseless operations.
• It requires less maintenance and costly compressed air, systems are required.
• Due to the superior quenching property of SF6, such breakers have a very short arcing time.
• There are no carbon deposits.

Disadvantages of SF6 circuit breaker:

• The entrance of moisture level in the SF6 breaker tank is very harmful to the breaker, and it causes several parts failures.
• SF6 breakers are costly due to the reason for the high cost of SF6.

• In SF6 circuit breaker, Sulphur hexafluoride gas is used as the arc quenching medium.
• Due to its low gaseous viscosity and high molecular weight, the SF6 gas can efficiently transfer heat by convection.
• It has high insulating properties and highly electronegative properties.
• Pure Sulphur hexafluoride gas is inert and thermally stable.
• SF6 has a very high dielectric strength (breakdown strength). It has 100 times more effective than air and oil as interrupting mediums.
• Its dielectric strength is 2.5 times that of air and 30% less than that of the dielectric oil.

Additional Information

Circuit breaker: 

A circuit breaker is a switching device which can be operated manually and automatically for controlling and protecting an electrical power system.

There are four types of circuit breaker

• Oil circuit breaker
• Air circuit breaker
• SF6 circuit breaker
• Vacuum circuit breaker

SF₆ circuit breaker:

• SF₆  circuit breaker is a type of circuit breaker in which sulfur hexafluoride gas or SF₆ gas is used as the arc quenching medium.
• SF6  circuit breaker may suffer from gas leakage problem. Because of that, the pressure of the gas inside the extinguisher chamber decreases.
• The arc quenching capability of the breaker may weaker if the pressure of the gas decreases. to avoid this, regular checking/maintenance of an SF₆ CB. 
• The current chopping phenomenon is less in SF6 circuit breaker and so the high reliability obtained.

Additional Information

​Circuit breaker:

A circuit breaker is a switching device which can be operated manually and automatically for controlling and protecting an electrical power system.

There are four types of circuit breaker

• Oil circuit breaker
• Air circuit breaker
• SF₆ circuit breaker
• Vacuum circuit breaker

Concept:

SF6 circuit breaker:

• The SF6 circuit breaker is a type of circuit breaker that uses pressurized SF6 gas to extinguish the arc.
• It is a dielectric gas having superior insulating and arc quenching properties far better than air or oil.
• It is used for arc quenching in high-voltage circuit breakers up to 800 kV in power stations, electrical grids, etc.

Advantages of SF6 circuit breaker:

• The gas is inflammable and chemically stable.
• These breakers give noiseless operations. 
• It requires less maintenance and costly compressed air, systems are required.
• Due to the superior quenching property of SF6, such breakers have a very short arcing time.
• There are no carbon deposits.

Disadvantages of SF6 circuit breaker:

• The entrance of moisture level in the SF6 breaker tank is very harmful to the breaker, and it causes several parts failures. 
• SF6 breakers are costly due to the reason for the high cost of SF6.

Concept:

• SF6 gas has excellent insulating property and it has a high electronegativity. 
• Due to high electronegativity, the recovery of dielectric strength after the arc interruption in the SF6 circuit breaker is very fast.
• It has a high affinity for absorbing free electrons.
• It absorbs electrons from a negative ion. The attachment of electron with SF6 molecules may occur in two different reactions as shown below,
• Ions are obviously much heavier than a free electron and the overall mobility of charged particles in SF6 gas is much less compared to the other common gases.

Advantages of SF6 Circuit Breaker:

• High dielectric strength
• Take minimum time in installation
• The gas is non-inflammable and chemically stable; The decomposition products are non-explosive
• It gives noiseless operation it does not make a sound like an air-blast circuit breaker during operation
• Minimum maintenance
• The same gas is re-circulated into the circuit thereby reducing the requirement of SF6 gas.

Disadvantages of SF6 Circuit Breaker:

• The SF6 gas is identified as a greenhouse gas, safety regulation is being introduced in many countries in order to prevent its release into the atmosphere.
• Puffer type design of SF6 CB needs high mechanical energy which is almost five times greater than that of the oil circuit breaker.

Explanation:

SF6 (Sulphur Hexafluoride) Circuit Breaker

Definition: An SF6 circuit breaker is a type of circuit breaker that uses sulphur hexafluoride (SF6) gas as the insulating and arc-quenching medium. SF6 gas possesses excellent dielectric properties, making it highly effective in interrupting high-voltage electric currents. These breakers are widely used in high-voltage applications due to their high reliability, compact design, and ability to handle large fault currents.

Working Principle: In an SF6 circuit breaker, the arc generated during the interruption of current is extinguished by the SF6 gas. When the contacts of the circuit breaker separate, an arc is formed between them. The arc heats up the SF6 gas, causing it to decompose into ions and other reactive components. These components absorb energy from the arc, cooling and extinguishing it rapidly. The gas then recombines into its original form, ready for subsequent operations.

Components of SF6 Circuit Breaker:

• Fixed Contact: The stationary part of the breaker where the moving contact makes and breaks the circuit.
• Moving Contact: The movable part of the breaker that moves away from the fixed contact to interrupt the circuit.
• Arc Quenching Chamber: The chamber where the arc is extinguished using SF6 gas.
• SF6 Gas Reservoir: The storage for SF6 gas under high pressure.
• Operating Mechanism: The mechanism that controls the movement of the contacts.

Correct Option Analysis:

The correct option is:

Option 4: A hollow cylinder contact with an arc horn.

The fixed contact in an SF6 circuit breaker is typically a hollow cylindrical contact equipped with an arc horn. This design is crucial for the effective operation of the circuit breaker. The hollow cylindrical shape allows the SF6 gas to flow uniformly around the contact area, ensuring efficient arc quenching. The arc horn serves to guide the arc and facilitate its extinction by ensuring that the arc is stretched and cooled effectively. This design ensures that the arc is extinguished quickly, minimizing damage to the contacts and ensuring reliable operation of the breaker.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: A spherical contact with an insulating shield.

This option is incorrect. While spherical contacts may be used in some types of electrical devices, they are not typically used as fixed contacts in SF6 circuit breakers. The spherical shape does not facilitate the effective flow of SF6 gas around the contact area, which is critical for efficient arc quenching. Moreover, an insulating shield is not a standard feature of the fixed contact in SF6 circuit breakers.

Option 2: A solid cylindrical contact with no additional fittings.

This option is also incorrect. While a solid cylindrical contact may provide a basic connection, it lacks the arc horn, which is essential for guiding and stretching the arc for efficient extinction. The absence of additional fittings like an arc horn would compromise the performance of the circuit breaker, making it less effective in handling high fault currents.

Option 3: A flat plate contact with thermal insulation.

This option is incorrect as well. A flat plate contact is not suitable for SF6 circuit breakers because it does not allow for the optimal flow of SF6 gas around the contact area. Additionally, thermal insulation is not a standard feature of fixed contacts in SF6 circuit breakers. The design of the fixed contact must prioritize efficient arc quenching, which is not achievable with a flat plate contact.

Conclusion:

In conclusion, the fixed contact in an SF6 circuit breaker is a hollow cylindrical contact equipped with an arc horn. This design ensures efficient arc quenching by allowing the SF6 gas to flow uniformly around the contact area and effectively cool the arc. The arc horn plays a crucial role in guiding and stretching the arc, facilitating its rapid extinction. The other options provided do not align with the design and operational requirements of SF6 circuit breakers, making option 4 the correct choice.

Transportation of SF6 Gas:

Sulfur hexafluoride (SF6) is a man-made gas used primarily in electrical equipment as an insulating and arc-quenching medium. It is known for its high dielectric strength and thermal stability, which makes it an excellent electrical insulator. However, due to its potent greenhouse gas properties, its handling and transportation are subject to stringent regulations.

Transport in Liquid Form:

• SF6 gas is typically transported in liquid form within cylinders. This method of transportation is efficient because SF6 can be liquefied under pressure at room temperature. This allows a large quantity of the gas to be stored and transported in a smaller volume, maximizing efficiency and safety.
• The gas liquefies at a pressure of about 2.2 MPa at room temperature. This relatively low pressure makes it feasible to store and transport in standard gas cylinders designed to handle high-pressure gases.
• Transporting SF6 in liquid form also reduces the risk of accidental release and minimizes the volume of gas that would be emitted in the event of a cylinder leak.

Why not Air Cylinders or Solid Form?

• Transporting SF6 in air cylinders is not feasible because SF6 is denser than air and requires special containment to maintain its properties. Air cylinders are not designed to handle the pressures needed to keep SF6 in a liquefied state.
• SF6 does not exist in a solid form under normal transportation conditions. It transitions from a gas to a liquid at room temperature and under high pressure, and it would require extremely low temperatures to solidify, which is impractical for transport purposes.

Conclusion:

• Therefore, the correct method of transporting SF6 gas is in liquid form within cylinders, as it ensures safe, efficient, and regulated transportation.