SF6 circuit breaker SF6 gas moisture exceeded the cause analysis and improvement measures- 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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SF6 circuit breaker SF6 gas moisture exceeded the cause analysis and improvement measures

发布时间：2018-11-12 来源：ydlcb 浏览次数：41次

SF6 circuit breaker SF6 gas moisture exceeded the cause analysis and improvement measures

Abstract: This paper discusses the causes of SF6 circuit breaker exceeding the water level and the control and treatment measures, introduces the SF6 gas exceeding the water level of 500kV Conghua converter station SF6 circuit breaker, analyzes the causes of SF6 gas exceeding the water level, and puts forward the treatment plan and countermeasures for SF6 circuit breaker exceeding the water level. According to the treatment plan and countermeasures, SF6 circuit breaker SF6 gas water exceeding the standard is treated.

Key words: SF6 circuit breaker; SF6 gas; Water exceeding the standard; Converter; High voltage grid document identification code: A

1 Overview

With the rapid development of the power grid and the continuous improvement of the quality of electrical equipment, SF6 circuit breakers have the advantages of good insulation, fast breaking capacity, high fracture voltage, allowing more continuous breaking times, simple and convenient operation and maintenance in the high voltage and ultra-high voltage power grid, so SF6 circuit breakers are widely used in the high voltage and ultra-high voltage power grid. However, during the installation and operation process, there will be a phenomenon of excessive SF6 circuit breaker gas moisture. If the SF6 circuit breaker SF6 gas moisture monitoring is ignored, it will affect the stable and reliable operation of the power grid, and also lead to environmental pollution.

1.1 Advantages of SF6 gas

The molecules and free electrons of SF6 have very good miscibility. When the electrons and SF6 molecules are in contact, almost 100% of them are mixed to form heavy negative ions, which has great value for deionization and arc extinguishing of residual arc columns. That is, SF6 has a good negative point property. Its molecules quickly capture free electrons and form negative ions. The conduction effect of these negative ions is very slow, which accelerates the recovery rate of the arc gap medium strength, so it has a good arc extinguishing performance. Under the pressure of 1.01×10Pa, the arc extinguishing performance of SF6 is 100 times that of air, and does not deteriorate after arc extinguishing, and can be reused.

1.2SF6 moisture exceeds the standard

Under normal conditions, SF6 gas is colorless and odorless, has good insulation performance and arc extinguishing performance, once the water in the atmosphere is immersed or the surface of the solid medium is damp, the electrical strength will be significantly reduced. SF6 circuit breaker is an outdoor equipment, when the temperature drops sharply, the excess water in the SF6 gas will condense into a solid on the surface of the medium and flashover will occur, and in serious cases, it will cause the SF6 circuit breaker to explode. Pure SF6 gas will decompose into monomer fluoro sulfur and fluoro sulfur compounds after arc power generation or high temperature during operation, and then combine into stable SF6 gas after the arc disappears. When the gas contains water, the fluorine sulfur compounds will react with water to produce hydrofluoric acid and other highly toxic chemicals, which will endanger the safety of maintenance personnel, and cause corrosion to the insulation material or metal material of SF6 circuit breaker, so that the insulation deteriorates, and even the SF6 circuit breaker will explode in serious cases. The following takes 500kV SF6 circuit breaker of 500kV Conghua converter station as an example, analyzes the causes of SF6 gas exceeding the water level, puts forward the treatment countermeasures for SF6 gas exceeding the water level, and treats SF6 gas exceeding the water level according to the countermeasures.

2. Discovery of defects

500kV SF6 circuit breaker in AC field of Conghua converter station adopts 3AP2F1 type SF6 circuit breaker produced by Siemens, which is installed on the body and accessories of the equipment by the construction unit after transportation to the site. After installation, the SF6 circuit breaker is vacuumed and filled with SF6 gas. After SF6 circuit breaker was charged to the rated pressure and stood for 48 hours, the debugger tested SF6 gas moisture in the SF6 circuit breaker gas chamber and found that SF6 gas moisture was 220PPMS, which exceeded the national standard (note: SF6 circuit breaker SF6 gas moisture national standard is below 150PPMS).

3 Cause analysis of SF6 circuit breaker gas moisture exceeding the standard

First, the 500kV SF6 circuit breaker in the AC field of the 500kV Conghua converter station was installed in spring, and the rain weather in the southern spring and summer was particularly heavy, and the air was relatively humid. SF6 circuit breaker is not transported to the construction site as a whole, but adopts the body column porcelain sleeve and arc extinguishing chamber porcelain sleeve and accessories for separate transportation. Before leaving the factory, the body column porcelain sleeve and arc extinguishing chamber porcelain sleeve have not taken measures to prevent rain and moisture. There was a period of time from the factory transportation process to the construction site, during which the SF6 circuit breaker body pillar porcelain sleeve and arc extinguishing chamber porcelain sleeve and accessories were not installed in time. Due to the long placement time, no measures to prevent rain and moisture are taken, or a temporary sealing part is not sealed well, so that the external moisture slowly penetrates into the porcelain sleeve of the column or the inner air chamber of the porcelain sleeve of the arc extinguisher.

Second, the SF6 circuit breaker installation process did not pay attention to the weather conditions of the external environment at that time, when the SF6 circuit breaker installation humidity must be kept below 80% requirements, the SF6 circuit breaker body pillar porcelain sleeve and arc extinguishing chamber porcelain sleeve and accessories installation. In addition, during the installation process, the exposure time of SF6 circuit breaker body post porcelain sleeve and the arc extinguish chamber porcelain sleeve flange docking process is too long, so that the atmospheric moisture permeates into the SF6 circuit breaker porcelain sleeve internal space gas chamber.

Third, after the SF6 circuit breaker was installed, the SF6 circuit breaker gas chamber was not replaced with adsorbent and vacuumed in time. The vacuum time is too short, after meeting the requirements (SF6 circuit breaker vacuum degree of the national standard of 133Pa), did not continue to vacuum for 4 to 6 hours, resulting in SF6 circuit breaker porcelain sleeve in the air chamber of the moisture is not fully extracted in time to inflate the SF6 circuit breaker air chamber.

Fourth, after vacuuming the SF6 circuit breaker gas chamber, the SF6 circuit breaker gas chamber is inflated too fast, SF6 gas is not fully vaporized in the cylinder, but SF6 gas is charged into the SF6 circuit breaker gas chamber in the liquid state, which is also an important reason for SF6 gas exceeding the standard of water.

Fifth, the moisture brought into the insulation. The manufacturer does not dry the insulation before assembly or the drying treatment is unqualified. Circuit breakers are assembled when the external environment humidity is not below 80% during factory assembly, and the insulation parts are exposed to the air for a long time during assembly.

Sixth, the SF6 gas pressure in the SF6 circuit breaker is 5 times higher than the outside, but the outside water pressure is higher than the inside. For example, the circuit breaker inflation pressure is 0.5mpa, SF6 gas water volume fraction is 30×10-6, then the water pressure is 0.5×30×10-6=0.015×10-3MPa, when the external temperature is 20℃, the relative humidity is 70%. The saturated pressure of water vapor is 2.38×10-3×0.7=1.666×10-3MPa, so the external water pressure is 1.666×10-3/0.015×10-3=111 times higher than the internal water. The water molecule has a V-shaped structure, its equivalent molecular diameter is only 0.7 times that of the SF6 molecule, and the permeability is extremely strong. Under the action of huge pressure difference inside and outside, the water in the atmosphere will gradually penetrate into the SF6 gas of the circuit breaker through the seal.

4 SF6 Circuit breaker gas chamber SF6 gas moisture exceeded measures According to the above analysis of SF6 gas moisture exceeded causes of SF6 circuit breaker gas chamber, the relevant departments have developed a treatment plan for SF6 gas moisture exceeded by SF6 circuit breaker gas chamber. According to the steps of this scheme, the SF6 circuit breaker gas chamber is treated with water exceeding the standard of SF6 gas.

First, the SF6 circuit breaker gas chamber SF6 gas water exceeded the external environment should be sunny, its humidity should be kept below 80%, and take measures to prevent rain and moisture.

Second, use SF6 gas recovery device to recover SF6 gas with excessive water in the SF6 circuit breaker gas chamber, recover to micro positive pressure, and then replace the moisture absorption agent in the SF6 circuit breaker gas chamber.

Third, vacuum the SF6 circuit breaker gas chamber immediately after the replacement of moisture absorbant, and test the vacuum degree of SF6 circuit breaker gas chamber with a vacuum gauge. When the vacuum degree reaches 133Pa, continue to pump the SF6 circuit breaker gas chamber for 4-6 hours, and then test the vacuum degree of SF6 circuit breaker gas chamber with a vacuum gauge. After the SF6 circuit breaker gas chamber is vacuum-pumped to meet the requirements, fill the SF6 circuit breaker gas chamber with qualified high purity nitrogen and charge it to the rated pressure of SF6 circuit breaker.

Fourth, SF6 circuit breaker air chamber filled with high purity nitrogen after static for 48 hours, and SF6 circuit breaker air chamber part of the moisture, debugging personnel then use a micro water tester to test whether the SF6 circuit breaker air chamber filled with high purity nitrogen micro water qualified. After the high purity nitrogen water in the SF6 circuit breaker air chamber is qualified, the high purity nitrogen in the SF6 circuit breaker air chamber is excluded and discharged to the equilibrium with atmospheric pressure.

Fifth, vacuum the SF6 circuit breaker gas chamber again, and test the vacuum degree of SF6 circuit breaker gas chamber with a vacuum gauge when the vacuum degree reaches 133Pa, continue pumping for 4-6 hours, and then test the vacuum degree of SF6 circuit breaker gas chamber with a vacuum gauge. After vacuuming, fill the SF6 circuit breaker gas chamber with qualified SF6 gas. The rate of filling SF6 gas should not be too fast, so that SF6 gas is fully vaporized in the cylinder and filled into the SF6 circuit breaker gas chamber to the rated pressure of SF6 circuit breaker. After 48 hours of static, the debugger uses a micro-water tester to test whether SF6 gas micro-water in the SF6 circuit breaker air chamber is qualified. After processing according to the above program steps, the measured water content of SF6 gas in the SF6 circuit breaker gas chamber is 85PPMS, which is in line with national standards and industry standards.

5 Conclusion

Based on the analysis and treatment results of the defects of SF6 circuit breaker in 500kV Conghua converter station, it is found that the humidity of SF6 circuit breaker should be controlled in the workshop to meet the requirements. Before leaving the factory, the temporary sealing of the porcelain sleeve of the column and the porcelain sleeve of the arc extinguishing chamber should be carefully checked whether the sealing is reliable; When leaving the factory, the SF6 circuit breaker packaging should be well protected against rain and moisture. When installing, it should strictly control whether the weather conditions meet the installation conditions; When installing the ceramic sleeve of the body and the flange of the porcelain sleeve of the arc extinguishing chamber, the open time is strictly controlled; When the SF6 circuit breaker gas chamber is vacuumed and filled with SF6 gas, it should be carried out in strict accordance with the relevant regulations and specifications, so as to ensure that the installed SF6 circuit breaker gas chamber SF6 gas micro-water meets the national standards and industry standards, and ensure the safe and reliable operation of the power grid.