SOLUTION

SF6 gas circuit breakers are widely used for EHV applications today, as Sulphur hexafluoride(SF6) gas is an electronegative gas having excellent dielectric and arc quenching properties resulting in many advantages such as compactness and less maintenance of EHV circuit breaker

The excellent insulating properties of SF6 gas make it possible to design circuit breakers with smaller overall dimensions, shorter contact gaps, which help in the construction of outdoor breakers with fewer interrupters, and the evolution of metal-enclosed SF₆ gas-insulated switchgear.

Advantages of SF6 Circuit Breaker

1. Non-inflammable: The gas is non-inflammable and chemically stable. The decomposition products are non-explosive i.e, there is no risk of fire or explosion
2. Insulating: SF₆ gas provides Excellent insulating, arc extinguishing, physical, and chemical properties.
3. Atmospheric Condition: Its performance is not affected due to variation in atmospheric conditions.
4. Clearance: Electrical clearances are very much reduced because of the high dielectric strength of SF₆.
5. Noiseless Operation: It gives noiseless operation it does not make the sound like an air-blast circuit breaker during operation
6. No overvoltage problem. The arc is extinguished at natural current zero without the current chopping and associated over-voltages originating across the circuit breaker terminals
7. Low Contamination: The sealed construction avoids contamination by moisture, dust, sand, etc. No costly compressed air system is required as in the case of air blast circuit breaker
8. Multipurpose: The SF₆ gas circuit breaker can perform various duties like clearing short-line faults, opening unloaded transmission lines, capacitor switching, transformer reactor switching, etc without any problem
9. Excellent Dielectric: Since no carbon particle is formed during the arcing therefore there is no reduction in the dielectric strength of SF₆ circuit breaker.
10. Minimum maintenance: The breaker may require maintenance once in four to ten years
11. Outdoor EHV SF₆ circuit breaker has less number of interrupters per pole in comparison to the air-blast circuit breaker and minimum oil breaker. The outdoor SF₆ circuit breaker is simple, comparatively cheaper in cost, maintenance-free, and compact
12. Ample overload margin. For the same size of the conductors, the current carrying capacity of the SF6 circuit breakers is about 1.5 times that of the air blast circuit breakers because of the superior heat transfer capability of the SF₆ gas
13. Low gas Required: Same gas is re-circulated into the circuit thereby reducing the requirement of SF₆ gas.
14. No oxidation: No frequent contact replacement-arcing time is small owing to outstanding arc quenching properties of SF6 and therefore contact erosion is less. Hence contacts do not suffer oxidation

 Disadvantages of SF6 Circuit Breaker:

1. Imperfect joints lead to leakage of the SF₆ gas. Continuous monitoring devices are required
2. SF₆ gas is suffocating to some extent. In case of leakage in the breaker tank SF6 gas being heavier than the air settles in the surroundings and may lead to suffocation of the operating personnel. However, it is not poisonous
3. Arced SF₆ gas is poisonous and should not be inhaled
4. The internal parts need thorough cleaning during periodic maintenance under a clean and dry environment. Dust of Teflon and sulfides should be removed
5. Special facilities are required for the transportation of gas, transfer of gas maintenance of the quality of the gas. The deterioration of the quality of gas affects the performance and hence reliability of the SF₆ circuit breaker.