SF6 Circuit Breaker Advantages Disadvantages Applications
SF6 Circuit breakers are made from 72-550kV with interruption current of 20 to 63 kA and rated current of 1,200 to 12000 amps.
Because of the properties of SF6 gas such as excellent arc quenching, high electronegative nature, and excellent dielectric strength SF6 circuit breakers are popular for high voltage applications and above. Some of the advantages of SF6 circuit breakers, their disadvantages are covered below
SF6 Circuit Breakers Advantages:
- Excellent insulating, arc extinguishing, physical and chemical properties of SF6 gas is greater advantage of SF6 circuit breakers
- The gas is non-inflammable and chemically stable. The decomposition products are non-explosive i.e, rhere is no risk of fire or explosion
- Electrical clearances are very much reduced because of high dielectric strength of SF6
- Outdoor EHV SF6 circuit breaker has less number of interrupters per pole in comparison to the air-blast circuit breaker and minimum oil breaker. Outdoor SF6 circuit breaker is simple, comparatively cheaper in cost, maintenance free and compact
- Its performance is not affected due to variation in atmospheric conditions
- It gives noiseless operation it does not make sound like air-blast circuit breaker during operation
- 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
- Therefore is no reduction in dielectric strength of SF6 since no carbon particle is formed during the arcing
- Minimum maintenance. The breaker may require maintenance once in four to ten years
- The sealed construction avoids the contamination by moisture, dust, sand etc. No costly compressed air system is required as in the case of air blast circuit breaker
- Same gas is re-circulated into the circuit thereby reducing the requirement of SF6 gas.
- No over voltage problem. The arc is extinguished at natural current zero without the current chopping and associated over-voltages originating across the circuit breaker terminals
- 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
- 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 superior heat transfer capability of the SF6 gas
SF6 Circuit Breaker Diadvantages:
- Imperfect joints leading to leakage of the SF6 gas. Continuous monitoring devices are required
- 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
- Arced SF6 gas is poisonous and should not be inhaled
- The internal parts need thorough cleaning during periodic maintenance under clean and dry environment. Dust of Teflon and sulphides should be removed
- Special facilities are required for transportation of gas, transfer of gas an maintenance of quality of the gas. The deterioration of quality of gas affects the performance and hence reliability of the SF6 circuit breaker
SF6 Circuit Breakers Applications:
SF6 Circuit breakers are mostly employed for High voltage applications. Because of the above said features and properties of SF6 gas they are mostly employed in switching duties related to high voltage and extra high voltage applications
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