The danger of SF6 gas

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What are the dangers of SF6 gas?

发布时间：2015-10-22 来源：ydlcb 浏览次数：37次

SF6 was synthesized by two French chemists in 1900. Since the 1960s, SF6 has been widely used in high-voltage circuit breakers and transformer equipment in the world's power industry as an extremely superior insulating and arc-extinguishing medium. Today, SF6 gas is almost the only insulating and extinguishing medium in high voltage and ultra-high voltage circuit breakers and GIS.

1. Physical and chemical properties of SF6 gas

Pure SF6 gas is colorless, tasteless, non-flammable, and has particularly stable chemical properties at room temperature. It is an inert gas, which is more than 5 times the proportion of air. However, in the power system, SF6 gas mainly acts as insulation and arc extinguishing medium, under the influence of arc, partial discharge, high temperature and other factors, SF6 gas will decompose. Its decomposition becomes corrosive electrolyte after water, especially some highly toxic decomposition substances, such as SF4, S2F2, SOF2, HF, SO2, etc., such as large inhalation of human body will cause dizziness and pulmonary edema, and even coma and death.

In a relatively sealed room, due to poor air circulation, SF6 and its decomposition are deposited in the room, and SF6 gas is colorless and tasteless, which causes great harm to inspection and maintenance personnel. When GIS leakage occurs, SF6 gas accumulates in the lower space above the floor, causing local hypoxia, causing suffocation and causing a major accident.

2, SF6 switch room leakage hazards

Installation of SF6 high-pressure equipment indoor space is generally more closed, once the SF6 gas leakage, due to the extremely slow air flow, toxic decomposition in the room deposition, not easy to discharge, thus into the SF6 switch room staff have a great danger, and because the proportion of SF6 gas is larger than oxygen. When SF6 gas leakage occurs, SF6 gas will accumulate in the lower level space, causing local hypoxia. Suffocate. On the other hand, because SF6 gas itself is colorless and odorless, it is not easy to be detected after leakage, which increases the potential danger to the workers who enter the leak site, and seriously threatens the safety and health of personnel. Even cause a vicious accident.

3. Safe concentration of SF6 gas

According to the research of chemical protection scientists in the United States and the former Soviet Union, the results show that in the presence of pure SF6 gas environment, the skin is exposed to SF6 gas for 8 consecutive hours, the highest SF6 gas content that can be withstand is 1000*10ˉ6(1000ppm) at this concentration, it will not cause dangerous and long-term effects on human life and health. According to the research results quoted in the State Grid Corporation's Power Safety Work Regulations, 1000*10ˉ6 is the safety alarm line that allows the presence of SF6 gas in the SF6 switch room. If the concentration exceeds this level, the monitoring alarm device should automatically start the fan and give an alarm.

SF6 as an insulating gas, has many advantages, is a colorless, tasteless, non-toxic, non-flammable inert gas, and has excellent cooling arc characteristics, especially in the switching equipment has a high arc temperature under the action of high cooling effect, to avoid local high temperature flammability. The insulation performance of SF6 gas far exceeds that of traditional oil and air insulating media. It is used in electrical equipment, which can reduce the size of the equipment and improve the oil and air insulating medium of the equipment insulation. It is used in electrical equipment, which can reduce the size of the equipment and improve the reliability of the equipment insulation. Its disadvantage is that the low fluorine compounds that decompose to form sulfur during arc discharge are not only toxic, but also have a corrosive effect on some insulating materials and metals.

SF6 is a relatively heavy gas, with a density of five times that of air under the same conditions, and the relationship between pressure and temperature follows the ideal gas law. The critical temperature is the highest temperature at which SF6 gas liquefaction occurs. The critical pressure indicates the gas pressure required for liquefaction to occur at this temperature. SF6 can only remain gaseous when the temperature is above 45 degrees, under normal conditions of use, it has the possibility of liquefaction, so SF6 can not be used at low temperatures and too low pressure.

The excellent thermal conductivity of SF6 is one of the reasons for the arc extinguishing performance of SF6. The good thermal conductivity of SF6 can be attributed to two reasons: first, the molecular weight of SF6 is large, the specific heat is large, and the heat transfer capacity of convection is better than that of air.

SF6 gas toxicity (gas is not pure, containing low sulfur fluoride, hydrogen fluoride and other toxic gases);

Harm to animals (mainly manifested as fatigue, poor memory, sore throat, chest tightness, etc.);

Harm to the environment (SF6 gas a molecule is equivalent to 25,000 times the CO2 molecule, and long life, about 3400 years, not easy to decompose).