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What is SF6 Gas Circuit Breaker?
A circuit breaker in which the contacts open and close in sulfur hexafluoride (SF6) gas is known as an SF6 circuit breaker.
Where Do We Use Sulfur Hexafluoride Breaker?
These circuit breakers are available for complete range of medium voltage and high voltage application up to 800 kV and above. This medium is most suitable for metal clad and hybrid HV substations. In fact, in the past this medium was primarily developed for metal clad switchgear at HV range.
However, with the development of single pressure puffer design for medium fault currents, the conventional open terminal designs for EHV/UHV transmission application have become economically very attractive. At present, it is possible to design a single-interrupter 245 kV, two-interrupter 420 kV and four interrupter 800 kV circuit breaker.
SF6 is a Greenhouse Gas
Since SF6 gas has been identified as a greenhouse gas, safety regulations are being introduced in many countries in order to prevent its release into the atmosphere. Hence the HV circuit breaker would be designed to ensure that there is minimum leakage during the service period and that the utilities let out the least amount of SF6 gas into the atmosphere during maintenance.
Conventionally, SF6 circuit breakers with a puffer type design need a high mechanical energy, which is almost five times that of a minimum oil circuit breaker of equivalent rating. For this reason, most of the designs use a high energy hydraulic or pneumatic system.
Working Principle of Sulfur Hexafluoride Breaker
An innovation in the puffer type design of an SF6 circuit breaker is the ‘thermal assist’ principle. In this type of design, the arc energy is utilized to develop pressure in the arcing chamber for arc quenching. Since this innovation has reduced the energy requirement of the operating mechanism it has become possible to use a spring mechanism for application in SF6 circuit breakers up to 245 kV.
Although the share of SF6 circuit breakers in medium voltage application is gradually shrinking, this technology is still emerging as the only choice in the HV range.
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