Sulfur hexafluoride gas circuit breaker
The properties of SF6 gas
The sulfur hexafluoride gas circuit breaker is a new type of high-voltage circuit breaker that uses SF6 gas as both the insulating medium and the arc-extinguishing medium.
SF6 gas has a relatively high dielectric strength. Using SF6 gas as the electrical insulation medium can significantly reduce the size of the electrical equipment and decrease the occupied space.
SF6 gas has excellent arc-extinguishing performance. The main reasons are as follows: SF6 gas has high insulation strength; the electrical conductivity of the arc column is high, the arc-overvoltage is very low, and the energy of the arc column is small; after the current crosses zero, the insulation strength of the medium recovers very quickly, with a recovery time constant only 1% of that of air, that is, its medium recovery speed is 100 times faster than that of air, and it can also be said that its arc-extinguishing ability is 100 times higher than that of air.
Classification of SF6 Circuit Breakers
According to their structural types, SF6 circuit breakers are divided into porcelain pillar type and tank type; according to their operating types, they are classified as double-pressure type and single-pressure type SF6 circuit breakers. The double-pressure type SF6 circuit breaker has two pressure systems. One is a low-pressure gas system ranging from 200 to 300 kPa, which is used to ensure insulation inside the circuit breaker; the other is a high-pressure gas system of approximately 1400 kPa, which is used for arc extinguishing. Its advantages are strong breaking capacity and rapid operation, but the structure is complex.
The single-pressure SF6 circuit breaker only uses one type of SF6 gas with a pressure of 300-500 kPa as the internal insulation of the circuit breaker. During the opening and closing process, the electric arc is extinguished by the pressure piston that simultaneously moves with the contacts, which pushes out the SF6 gas. After the opening and closing are completed, the pressurization stops, and the gas pressure between the contacts returns to a low level. The single-pressure circuit breaker has a simple structure, high reliability, and is easy to maintain. In recent years, there has been a trend of gradually replacing the double-pressure SF6 circuit breaker.
The characteristics of sulfur hexafluoride circuit breakers
The advantages of sulfur hexafluoride circuit breakers are: high withstand voltage at the breaking gap; excellent breaking performance; numerous allowable breaking cycles, long maintenance intervals; low operating noise, insensitivity to recovery voltage, and long service life. Therefore, they have been increasingly widely used in various voltage levels, especially in the high-voltage field.
However, the disadvantages of SF6 circuit breakers are as follows: They require much higher processing technology and materials than ordinary electrical appliances; a dedicated SF6 gas system is needed; under the influence of high-temperature electric arcs, SF6 gas will decompose into highly toxic gases, so an adsorption device with active aluminum (Al2O3) or molecules should be installed inside the circuit breaker to absorb these toxic gases.
Installation and commissioning of sulfur hexafluoride circuit breakers
The installation of sulfur hexafluoride circuit breakers should be carried out in an environment free from sandstorms and rain or snow. During the inspection and assembly of the arc suppression chamber, the relative humidity of the air should not exceed 80%, and dust-proof and moisture-proof measures should be taken.
The bolts, gaskets, sealants, cleaning agents and lubricants used for installation should comply with the technical specifications of the product. The surface of the porcelain sleeve should be smooth, without cracks or damages. If there are any doubts during the visual inspection, non-destructive testing should be conducted for verification.
The fixed position of the circuit breaker should be firm and reliable.
The flange surfaces of the corresponding columns of porcelain sleeves are all on the same horizontal plane. The error in the spacing of the center lines of each column and the error in the center distance between phases shall not exceed 5mm.
The position indicator should be able to accurately and reliably display the actual open and closed states.
Before operating the mechanism, the circuit breaker must be filled with SF6 gas at the rated pressure.
Those equipped with slow opening and closing mechanisms should perform slow opening and closing operations before conducting rapid opening and closing.
After installation, the circuit breaker and all its components should be kept in the specified horizontal or vertical position as per the manufacturer’s instructions. All operational parameters should comply with the product technical specifications.
Post time: Jul-10-2026