Analysis of SF6 gas decomposition products of GIS electrical equipment- 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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Analysis of SF6 gas decomposition products of GIS electrical equipment

发布时间：2018-11-24 来源：ydlcb 浏览次数：34次

Abstract: This paper describes the causes of SF6 gas decomposition products, and proposes the use of SF6 gas decomposition products to diagnose the internal faults of GIS and other equipment through the correlation analysis of decomposition products. Practice shows that the use of detecting the components and content of SF6 gas decomposition products can judge the internal faults of GIS. It has a good guiding significance for the operation monitoring and fault diagnosis of GIS in power switching station.

GIS is one of the commonly used enclosed combined electrical equipment in the power industry. GIS optimally combines all primary equipment including isolation equipment, circuit breaker, transformer, ground switch, bus bar, etc. in substation except transformer, and encloses it in a shell with metal grounding. During the sealing process, SF6 gas with good insulation and arc extinguishing performance, and with certain purity, is injected as the insulation and arc extinguishing medium of the equipment. However, overheating and discharge of GIS internal components can easily lead to slight changes in SF6 gas composition. If the purity of SF6 gas in GIS fails to meet the requirements, SF6 performance deteriorates sharply, and it is easy to cause faults.

The causes of SF6 gas decomposition products in GIS and other equipment: In the normal working process of GIS equipment, the insulation material of GIS in the circuit breaker is SF6 gas and insulation body, made of thermosetting epoxy resin and tie rod in the ethylene arc chamber; Other equipment and used as turning layer insulation and capacitor layer polyester vinyl, paper and paint. SF6 gas when the temperature is higher than 500℃, it begins to decompose and connect after; Interlayer with polyester vinyl, paper and paint at about 120 ° C. Pyrolysis temperature For the normal operation of SF6 equipment, as long as the internal temperature is below 80℃, decomposition products will not be produced. Circuit breaker opening and closing process produces a very high arc temperature, generally more than 2000 ° C, so that SF6 generates high temperature charged ions and molecules, but because of the opening and closing speed, but also has the function of arc extinction efficiency, so the charged ions and torque compounds transform SF6, The compound recombination rate of more than 99.9% and SF6 gas-solid insulation materials do not decompose significantly, and the adsorbent produces a small amount of decomposition products on top of the absorption. Therefore, for the normal operation of the circuit breaker, after opening and closing for a week, the content of decomposition products in the air chamber is not more than 1 mu litres. However, the presence of partial discharge and severe overheating faults inside the device will decompose the gases in the insulation and solid fault area S, producing sulfides, fluorides and carbides.

There are many reasons for arc discharge, spark discharge, corona or partial discharge caused by GIS equipment. The main links and processes lie in the loosening of components during storage, transportation and installation, and scratches on the electrode surface of the equipment. The discharge faults may be caused by technical deviations in the installation of GIS equipment, defects on the electrode surface, conductive particles, or tools left inside the equipment. Studies have shown that simple SF6 gas has excellent chemical stability under general conditions, and can react with other substances only under extreme conditions, such as high temperature discharge reaction, material consumption and product reaction depend on the contact and energy of SF6 gas, the main reason for gas discharge failure is the occurrence of SF6 decomposition, there are three main forms: Arc discharge, spark discharge, corona discharge or partial discharge.

First, in the arc discharge, the temperature often reaches 20000K, which will result in the thermal decomposition of the gas. High temperature SF6 and its decomposition products react with metals to form metal fluoride. In decomposition products, SOF2 is mainly a stable decomposition product. CF4 is formed in an arc contact with an organic material; SO2 is formed by hydrolysis of SOF2.

Second, the spark discharge energy is lower than the arc discharge, and SOF2 is the main decomposition product. The volume fraction of SO2F2 is higher than that of arc discharge. The first important product of SF4 is produced when the spark is discharged.

Third, in corona or partial discharge, SO2F2 has a much higher volume fraction than arc discharge, spark discharge case, and can be used as a characteristic corona or low energy discharge of the main gas product. As the discharge energy decreases (from arc to spark), it increases as the volume fraction of SO2F2 increases. The corona discharge contains trace amounts of water and oxygen, and the stable gas is based on SOF2, SO2F2 and SOF4. The signal characteristics vary with the duration and energy of the arc discharge and spark discharge, but the structure of the discharge and the test results are similar, so the mechanism is consistent with the test results and the analysis described in the two discharge fault types.

According to the analysis of relevant data at home and abroad, some of the sulfides produced by the decomposition of GIS electrical equipment during internal failure are SF4, SOF2, SO2, SO2F2, H2S, S2OF10 and S2F10. The fluoride decomposition substances are CF4, ALF3, HF, WF6 and CuF2, etc. Carbides will have CO2, CO and some low molecular hydrocarbons.

3 Detection of SF6 gas decomposition products

The molecular structure of SF6 is that under normal working conditions, the electrical equipment is very stable (below 0.8 mpa, -40 ° C ~ 80 ° C), SF6 does not react with metal materials (such as stainless steel, aluminum, copper, silver, silicon steel, brass, low carbon steel, etc.) and organic solid materials (such as glass, resin, etc.). Generally above 200℃ and under the thermal effect of arc discharge, SF6 gas is chemically decomposed into solid, metal fluoride and gas. This is the theoretical basis of the analysis.

For the potential fault diagnosis of gas insulation equipment, after the equipment accident occurs, fault location, SF6 gas decomposition by external environment interference detection has the characteristics of small size, high sensitivity, good precision and so on. SF6 circuit breakers, GIS and other equipment due to SF6 gas insulation electrical equipment exhibition opening charging detection work SF6 gas decomposition products, gas insulation safety hazards equipment operation fault investigation.

At present, the detection of decomposition products of SF6 gas decomposition products and analysis methods include total detector method, gas chromatography, infrared absorption spectroscopy, electrochemical sensors, detection tubes and dynamic ion methods.

The decomposition and reduction of SF6 gas under GIS discharge is shown in Figure 1:

Internal fault diagnosis of GIS equipment using SF6 gas decomposition products

1 Analysis of the detection of SF6 gas decomposition products

According to the data of 12 42-spaced 168 gas chambers, there are 153 S0: +SOF gas chambers, accounting for 72.2%, and 56 chambers in 0-1L, accounting for 26.4%. There were 107 undetected gas chambers in HS, accounting for 63.7%, and five gas chambers in 0 ~ 1LL, accounting for 2.3%. A total of 109 chambers (64.9%) were undetected at high frequency, and 0 ~ 1LL were two chambers (0.9%). The SOF, HF, and CO contents in one air chamber are abnormally high. After inspection, it is found that the equipment has an overtemperature fault.

Statistics show that in the normal operation of GIS equipment, SO+SOF, HS, HF three groups generally do not exceed 1 content, SO2+SOF2 should not exceed 2L; CO content generally does not exceed 100LL, should not exceed 200LL.

4.2 Diagnosis case analysis

Discharge the SF6 combined electrical appliance of the faulty equipment, the discharge part is the switch B phase gas chamber, the equipment voltage level is 220 kV: the switch normal shutdown operation is about 1 minute, the switch fault trip protection action, according to records, the fault current of the knife door B phase is about 10kA, there is 20kg of gas in the equipment, during this period of 300 milliseconds of fault arc time. The equalizing cap of the knife switch moving contact found during the disassembly inspection has come off and there are clear signs of surface discharge. In the calculation of copper-W contact formula. Failure conditions through the production of decomposition products:

Formula:

I -- Current intensity, unit is kA

t -- arc time, in s

m -- inflation weight, in kg

146 -- SF6 molecular weight

22.4 -- The standard molar volume of a gas in L

The amount of decomposition products measured in practice is 783.4, which is close to the theoretical value.

5 Conclusion

Rapid and accurate analysis of SF6 decomposition products detection is an important means to judge the internal faults of GIS equipment. A normal mechanism for the detection of decomposition products should be established to regularly detect the decomposition products of GIS and other equipment, and combined with the equipment structure, operation and maintenance, comprehensive analysis of electrical testing, protection and fault recording. Improve the ability to identify and handle faults.