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What is the standard for SF6 gas leakage?

Author:Winfoss Seeker Technology (Shanghai) Co., Ltd.Release time: 2018-05-17 Browsing

Pure SF6 gas is colorless, odorless, odorless, non-flammable, chemically stable at room temperature, and is inert gas. However, in the power industry, sulfur hexafluoride gas (SF6) is widely used as a dielectric and arc extinguishing medium for high-voltage switchgear and its equipment, during the operation of circuit breakers and GIS, due to arc, corona, spark discharge and Under the influence of partial discharge, high temperature and other factors, SF6 gas will be decomposed, and its decomposition product will become corrosive electrolyte when it encounters moisture. In particular, there are some highly toxic decomposition products such as SF4, S2F2, S2F10 SOF2, HF and S02, which can irritate the skin, eyes and mucous membranes. If the inhalation amount is large, it can cause dizziness, pulmonary edema, and even cause death.

The sealing test is to determine whether the annual leakage rate of the air chamber is qualified by detecting the leakage of SF6 gas. The control standard is that the annual air leakage rate of each independent air chamber is not more than 0.5%; the "Electrical Equipment Handover Test Standard" provisions Two test methods and control standards are proposed in the study. The annual leakage rate of SF6 combined electrical equipment is not more than 1.0% and is controlled at 0.5%.

1, The SF6 leak detector has no alarm and is considered to be qualified when a leak detector with a sensitivity of not less than lx10-6 (volume ratio) is used to detect the sealed portion of the air chamber, pipe joints, and the like.

2, using a partial dressing method, wait 24 hours after testing each dressing cavity SF6 content of not more than 30PPM (volume ratio) is qualified.

At present, the second test method is more accurate, and its implementation procedure is: vacuum test → SF6 gas → leak test. The specific process is: After the GIS is vacuum leak-detected and the SF6 gas is still for 5 hours, it is wrapped with a plastic film at the flange interface, etc. After another 24 hours, the gas is detected. If the concentration of SF6 gas in one film is greater than 30 PPM, the gas Room leak rate is not qualified. If the concentration of SF6 gas in all the wrapping films is less than 30 PPM, the gas chamber leakage rate is considered to be acceptable.

SF6 switch room leak hazard

The indoor space where SF6 high-voltage equipment is installed is generally tightly closed. Once SF6 gas leaks, the toxic decomposition products are deposited in the room and are not easily discharged due to extremely slow air circulation, which poses a great danger to the workers entering the SF6 switch room. Because of the greater proportion of SF6 gas than oxygen. When SF6 gas leak occurs, SF6 gas will accumulate in the low-level space and cause local oxygen deficiency. People suffocate. On the other hand, since the SF6 gas itself is colorless and odorless, it is not easy to be noticed after a leak occurs, which increases the potential danger to the personnel entering the leak site, and seriously threatens the safety and health of the personnel, and even causes vicious accidents.

Improper use of sulfur hexafluoride gas will bring consequences

Sulfur hexafluoride is itself a non-toxic and harmless gas, but under the effect of high temperature and high pressure arc, it tends to decompose and release a variety of products. Some of these decomposition products are toxic substances that cause harm to the human body. At the same time, if a large amount of sulfur hexafluoride gas is inhaled, adverse reactions such as asphyxiation can also occur. However, high-purity sulfur hexafluoride is an “oxygen” that is not available to the power industry. What happens if there is gas poisoning? How can we prevent it? How do we know if it is gas poisoning?

Why sulfur hexafluoride gas poisoning? Due to technical issues and other reasons, some SF6 gas products do not meet the standard purity, and some harmful impurities may be present at the factory. Another situation is that when handling gas equipment, improper operation of personnel leads to leakage of SF6 power equipment, leakage of toxic and hazardous substances, and gas poisoning. Of course, some companies cut corners during regular inspections and leak detections, leading to equipment failures and gas poisoning.

Once sulfur hexafluoride gas encounters high heat and high temperatures (eg, arcs), by-products—sulfur oxide and hydrogen fluoride gas—are produced that coexist with undecomposed gases. At this point there are three types of poisonous gas. Sulfur oxide is a kind of sulfuric anhydride, which is easily absorbed by human wet mucous membrane surface to generate sulfuric acid and sulfurous acid, which has a strong stimulatory effect on eye and respiratory mucosa. Specific manifestations include tearing, coughing, burning in the throat, conjunctiva and tingling in the respiratory tract.

If high-purity sulfur hexafluoride meets the body's sweat, it will make people's skin red and swollen. Hydrogen fluoride, soluble in water. Hydrofluoric acid is also produced on the surface of the mucous membrane, which is easily absorbed by the human body. It has the same harm to the human body as sulfur oxide—eyes and respiratory tract, but it is more harmful. Hydrofluoric acid is often used to etch glass, which shows that it is highly corrosive. If human sweat is encountered, hydrofluoric acid forms on the surface of human skin. It penetrates deep into the skin and forms ulcers and necrosis, and should not be cured. If bone damage causes fluorosis, it will not be restored. Hydrogen fluoride is more toxic than sulphur oxide and sulphur hexafluoride.

The presence of toxic gases in sulfur hexafluoride and the dust generated in the equipment pose a certain hazard to the human respiratory system and mucous membranes. Generally, sulfur hexafluoride gas poisoning will cause varying degrees of tearing, sneezing, and runny nose. Throat has a hot feeling, hoarseness, cough, dizziness, nausea, chest tightness, neck discomfort and other symptoms. When the above poisoning occurs, the person poisoning the gas should be quickly moved to a fresh air and treated promptly.

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