How much of SF6 gas leakage is harmful to people?- SF6在线监测系统_SF6检漏仪_SF6传感器_SF6密度继电器

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How much of SF6 gas leakage is harmful to people?

发布时间：2018-08-22 来源：ydlcb 浏览次数：32次

SF6 gas has a century-old history, it is two French chemists Moissan and Lebeau synthetic artificial inert gas in 1900, around 1940, the United States military used it for the Manhattan Project (nuclear military).

SF6 is a strongly electronegative gas, and its molecules are easy to adsorb free electrons and form heavy negative ions, weakening the collision ionization process in the gas, so its electrical insulation strength is very high, about 2.5 times the strength of air insulation in a uniform electric field. SF6 gas has a thermal decomposition peak at t≈2000K, so when the AC arc current crosses zero, SF6 has a much stronger cooling effect on the arc than air, and its arc extinguishing ability is about 100 times that of air. Because SF6 gas has excellent arc extinguishing and insulation properties and good chemical stability, it has been used as an arc extinguishing medium for high voltage circuit breakers since the late 1950s. In ultra-high voltage and UHV circuit breakers, SF6, as an arc extinguishing medium, has replaced oil and has largely replaced compressed air.

Since the mid-1960s, SF6 has been widely used as an insulating medium for high-voltage electrical equipment. SF6 gas-insulated switchgear covers a much smaller area than conventional open-type high-voltage distribution devices, and its operation is not affected by external meteorological and environmental conditions, so it is not only widely used in ultra-high voltage and UHV power systems, but also has begun to be used in distribution networks (SF6 gas-insulated switchgear and ring network power supply units). SF6 gas insulated pipeline transmission line has the advantages of low medium loss, large transmission capacity, and can be used in high drop occasions, so it is often used in hydropower station outlet, replacing conventional oil-filled cables. SF6 gas insulated transformer has the advantages of fire and explosion protection, this distribution transformer is especially suitable for densely populated areas and high-rise building power supply. SF6 gas insulated ultra-high voltage transformer has been successfully developed, and all gas insulated substation will be a direction of the development of power transformation technology.

The sealing test is to determine whether the annual leakage rate of the gas chamber is qualified by detecting the leakage amount of SF6 gas. The control standard is that the annual leakage rate of each independent gas chamber is not more than 0.5%; Two test methods and control standards are proposed in the provisions of the "Electrical Equipment Handover Test Standards" :

1. When the leak detector with sensitivity not less than l×10-6 (volume ratio) is used to detect the sealed part of the gas chamber and the pipe joint, the SF6 leak detector is considered qualified without alarm.

2, the local dressing method is used, and the SF6 content in each dressing chamber is not more than 30ppm (volume ratio) after 24h.

At present, the second test method is more accurate, and its implementation procedure is: vacuum test →SF6 gas → leak test. The specific process is as follows: After the GIS is detected by vacuum and the SF6 gas is stationary for 5 hours, the flange interface is wrapped with a plastic film, and the test is carried out after 24 hours. If the concentration of SF6 gas in a film is greater than 30 ppm, the gas leakage rate of the air chamber is unqualified. If the concentration of SF6 gas in all wrapped films is less than 30ppm, the gas leakage rate of the chamber is considered acceptable.

1. Acute toxicity: rabbit intravenous injection LD50:5790mg /kg.

2, sulfur hexafluoride is a choking agent, in high concentrations will be breathing difficulties, wheezing, skin and mucosa blue, systemic convulsion. After inhaling a mixture of 80% sulfur hexafluoride and 20% oxygen for a few minutes, the human body will experience numbness in the limbs and even suffocation. China stipulates that the allowable concentration of sulfur hexafluoride gas in the air in the operation room should not be greater than 6g/m3 or the oxygen content in the air should be greater than 18%; For short-term exposure, the allowable concentration of sulfur hexafluoride gas in the air is not greater than 7.5g/m3. Sulfur hexafluoride is an inert gas with low toxicity but asphyxiating effect on human body. In the course of life or use, some trace amounts of toxic sulfur of low fluorine compounds and fluorine oxides will be broken down.

3. Acute toxicity LD50:5790mg /kg (rabbit vein).

The specific process is as follows: after the GIS is vacuum detected and the SF6 gas is stationary for 5h, the flange interface is wrapped with a plastic film, and the test is carried out after 24h. If the concentration of SF6 gas in a film is greater than 30ppm, the gas leakage rate of the air chamber is unqualified. If the concentration of SF6 gas in all wrapped films is less than 30ppm, the gas leakage rate of the chamber is considered acceptable.