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The SF6/N2 gas mixture is an alternative gas to SF6. SF6/N2 will decompose and generate nitrogenous characteristic gases, such as NO, NO2, N2O, and NF3, when exposed to long-term partial discharge. The adsorption models of Ti3C2Tx (T=O, F, OH) and NO, NO2, N2O, NF3 were constructed, and the most stable adsorption structure was selected in this paper. The electron density and density of states of the adsorption system were further analyzed to study the adsorption behavior, and the sensing performance was evaluated in the end. The results are as follows: four gases could be spontaneously adsorbed on Ti3C2Tx, and strong adsorption occurred when surface terminal groups were OH, forming hydrogen or chemical bonds with significant charge transfer. Results show that Ti3C2(OH)2 had a stronger sensing ability than Ti3C2F2 and Ti3C2O2. The conductivity of the Ti3C2Tx with different terminal groups was improved after the adsorption of NO and NO2, showing Ti3C2Tx had a good sensing ability for NO and NO2. It was difficult for the four gases to desorb from the Ti3C2(OH)2 surface, but the adsorption on the Ti3C2F2, Ti3C2O2 surface had a short recovery time at room temperature. [ABSTRACT FROM AUTHOR]

How to use SF 6 decomposition feature component information to judge the form and degree of gas-insulated equipment (GIE) field discharge and overthermal faults quickly is a problem that remains unresolved. Based on the existing experimental data on SF 6 typical fault decomposition, this study considers the SF 6 decomposition mechanism under typical faults and uses the maximum correlation minimum redundancy criterion to filter out three decomposition feature components characterizing GIE typical fault attributes: SOF 2 +SO 2 , CF 4 , and SO 2 F 2. The weight of extracted feature components is optimized by the "area equivalence principle," and the triangle fault diagnosis method of the SF 6 decomposition component that is suitable for the rapid diagnosis of a GIE field is constructed. The diagnosis method is comprehensively tested using faulty data in different conditions, and the comprehensive recognition rate of lab tests reaches 96.2%. Results show that the constructed triangle fault diagnosis method of the SF 6 decomposition component can diagnose the internal fault nature of a GIE and identify the types of insulation defects that induce partial discharge faults. Moreover, the constructed method in this research is simple, effective, and suitable for field maintenance and online intelligent monitoring of GIE. [ABSTRACT FROM AUTHOR]

The use of SF6 gas decomposition components for the fault diagnosis of gas-insulated equipment (GIE) has received widespread attention and been extensively adopted by the power industry. However, the present focus is mainly on the use of a component type or absolute content for generating qualitative judgments on the existence of a fault, and the practical diagnosis method for field diagnosis is extremely lacking. In this paper, ten-year fault data were collected and analyzed. Decomposition components were extracted and combined, based on the decomposition characteristics of SF6, and enhancement factors were given to three component characteristic quantities using fuzzy C-means clustering algorithm. The component characteristic quantities that characterized the high-energy discharge fault, partial discharge, and partial over-thermal fault of the device were extracted: % (SOF2+SO2), % (9SO2F2), and % (5CO2). With adoption of these characteristic quantities as the coordinate axes of the triangle coordinate system, a triangle fault diagnosis method for field diagnosis of SF6 GIE was constructed. The diagnosis method was validated by a large number of experimental data and field failure data, and 128 of the 150 experimental samples were correctly recognized. Moreover, the test conditions did not considerably affect the diagnostic results of the method. This technique can provide a simple and effective field diagnostics technology for the power industry. [ABSTRACT FROM AUTHOR]

This study mainly aims to obtain the decomposition characteristics of SF6 under various degrees of negative partial discharge (PD) and establish a method for evaluating the internal PD fault for gas-insulated equipment (GIE). Thus, metal protrusion, a frequent insulation defect in DC GIE, was used in the study of PD characteristics from the initial discharge to the near breakdown process. Then, seven parameters for characterizing the development stage of PD were extracted, and the fuzzy C-means clustering algorithm was used for the categorization of PD into three degrees, namely, slight, medium, and severe. We performed SF6 decomposition experiments on the PD degrees to obtain the decomposition characteristics. Results show that the SF6 decomposition characteristics (formation and content variation of five characteristic components, namely, CF4, CO2, SO2F2, SOF2, and SO2) are closely related to PD status. Fuzzy comprehensive evaluation theory was used for the establishment of a PD fault status assessment model, which was based on SF6 decomposition characteristics. Then, we evaluated the collected samples, and the accuracy of the evaluation method was up to 87.5%. This paper lays the foundation for future comprehensive assessment and fault diagnosis of insulation status of DC GIE on the basis of SF6 decomposition characteristics. [ABSTRACT FROM AUTHOR]

The condition monitoring and fault diagnosis method based on decomposed component analysis (DCA) for SF6 gas‐insulated equipment, which mainly aiming at AC SF6 gas‐insulated equipment, has become a research hotspot. Therefore, SF6 positive DC partial discharge (PD) decomposition experiments under four typical insulation defects were conducted in this work. The result showed that there is a significant correlation between the generation rules of the five SF6 decomposition components (CF4, CO2, SO2F2, SOF2 and SO2) and the types of defects. The phenomenon was attributed to the variations in the properties of the four insulation defects. In addition, comparing with AC PD experiment, for the protrusion, contamination and gap defect models, the amounts and generation rates of the five characteristic decomposition components under positive DC are less than those under AC by the same defect; however, for the particles defect, it is by contrary. This could be attributed to the essential difference between AC PD and positive DC PD. Therefore, the theory of AC DCA could provide reference to construct DCA diagnostic model for DC SF6 gas‐insulated equipment, but cannot be applied mechanically. [ABSTRACT FROM AUTHOR]

To clarify the influence of pressure on SF6 decomposition under positive DC partial discharge (PD), SF6‐positive DC partial discharge decomposition experiments at different pressures were carried out. We found that the contents of SF6 primary decomposition products are proportional to E / P 3 / 2 exp − B d P / E. Keeping the chamber volume and external temperature constant, the difference of air chamber pressure means that the electronic mean free path is different. So, different pressures make a difference in the energy of free electrons obtained in a single flight, which results in the difference in the reaction rates of SF6 primary decomposition and further influences the formation of SF6 PD characteristic decomposition components. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

To investigate the difference between the sulfur hexafluoride (SF6) decomposition characteristics initiated by two sorts of insulation defects — free metal particles and metal protrusion defects — under negative DC partial discharge (PD), SF6 decomposition data was obtained under different DC voltages on the basis of constructing a SF6 decomposition experimental platform. The differences between the characteristic components and the characteristic ratios of the two defects at the same discharge quantity and voltage were systematically analyzed. Results show that the two defects have significant differences in the type of decomposition components, the yield sizes of the components, and the changes in the component ratios. This paper proposed c(CF4 + CS2)/c(CO2) and c(CF4)/c(SO2F2) as the characteristic ratios to characterize the fault severity of the two defects, and their physical nature were revealed. The combination of the above ratios with the existing c(SO2F2)/c(SOF2 + SO2) can construct a feature quantity for identifying the two defects. [ABSTRACT FROM AUTHOR]

To study the correlation characteristics between SF6 decomposition components and discharge strength under negative DC partial discharge (PD) initiated by free metal particle defect, SF6 decomposition data were obtained under different voltages on the basis of constructing SF6 decomposition experimental platform. The variation law of SF6 decomposition components and characteristic ratios were systematically analyzed. The study shows that SF6 decomposes into CO2, SO2F2, SOF2, SO2, CF4, and a very small amount of CS2 under PD. The SOF2 concentration and its formation rate have the highest correlation with the PD discharge quantity among all components. The yield relationship of decomposition components is different at different discharge quantities. In addition, the fluctuation of each characteristic ratio is small after 72 h and can achieve a certain degree of steady state. c(CF4+CS2)/c(CO2) and the proposed c(SO2)/c(SO2F2) can be used as the fault severity characteristic ratio in free metal particle defect. [ABSTRACT FROM PUBLISHER]

Aimed to clarify the correlation characteristics between the internal partial discharge (PD) in the negative direct current (DC) gas‐insulated system (GIS) and gas pressure, and to establish an insulation fault diagnosis method based on decomposition component analysis, this study on PD decomposition of sulphur hexafluoride (SF6) was conducted under different pressures on the basis of constructing a SF6 decomposition experimental platform under DC PD. A stainless steel needle‐plate electrode was used to simulate the insulation defects of metal protrusions in GIS. SOF2, SO2 F2, CO2, SO2, and CF4 data generated from SF6 decomposition were obtained under different pressures. The variation law of component concentration and effective characteristic ratio with pressure were analysed in detail. In addition, a mathematical formula for pressure and decomposition components was deduced according to gas micro‐ionisation theory. The effective content and formation rate were defined to validate the relationship. Results show that the concentration of SF6 decomposition components decreased gradually with increasing pressure with a strong regularity. Furthermore, the relationship between pressure and component concentration derived from the theory can explain the relationship between the effective content of SF6 decomposition components and the effective formation rate and pressure variations. [ABSTRACT FROM AUTHOR]

SF6 decomposition characteristics under partial discharge (PD) are not only associated with insulation fault type and its severity but also closely related to the H2O content of in the equipment. This paper studies the decomposition characteristics of mixture gas SF6/H2O with six different gradients of trace H2O under the same PD energy, selects SO2F2, SOF2, CO2, and CF4 as the characteristic components, and analyzes the influence regularity of trace H2O on each of the component concentration, effective formation rate and characteristic ratio. Results show that H2O creates favorable conditions for generating SO2F2 and SOF2 owing to the capacity to capture F atom and inhibit low fluorine sulfides from recombining into SF6. As a result, the concentration and effective formation rate of SO2F2 and SOF2is positively related with H2O. Whereas H2O has no evident influence on CO2, it can consume intermediate by-products CF2 and CF3 which restrain CF4 generation. Each characteristic ratio decreases sharply and then becomes stable with increment of H2O. The defined effective characteristic ratio effectively reflects its relationship with H2O, whereas obtained mathematical expression between each effective characteristic ratio and trace H2O lays solid foundation for fault diagnosis of SF6 insulated equipment based on SF62 decomposition characteristics. [ABSTRACT FROM AUTHOR]

To obtain the influence regularity of trace O2 on SF6 decomposition characteristics under partial discharge (PD) and establish the foundation of using SF6 decomposed components to diagnose the insulation status of SF6 electrical equipment, first, a series of PD decomposition experiments with different O2 concentrations (%)were conducted on a special experiment platform. The variation regularity between the concentrations of characteristic components and the different content of O2 were obtained quantitatively. Second, the correlation coefficient r testing method was applied to identify the associated influence of trace O2 on the decomposed characteristic components and characteristic ratios. Based on this, an exponential regression model of the related characteristics was developed. Finally, the influence mechanism of trace O2 on SF6 decomposition progress was explained reasonably. The results show that under the PD caused by metal protrusion insulation fault without organic solid insulated materials, CO2, SO2F2, and SOF2 were the mainly decomposed components in the specific range of trace O2. Although no obvious influences of the trace O2 on the concentrations of CO2 and SOF2 as well as the ratio c(CO2)/c(SO2F2+SOF2), it is notable that the trace O2 is negatively and positively related to the concentration of SO2F2 and the ratio c(SOF2)/c(SO2F2), respectively. The exponential regression model can minimize the effect of trace O2 on the fault diagnostic result when using SF6 decomposed components. [ABSTRACT FROM AUTHOR]

[Display omitted] • The adsorption of CS 2 and COF 2 on the surface of α-Al 2 O 3 (0 0 0 1) presents a state of energy release. • CS 2 is more easily adsorbed on the α-Al 2 O 3 (0 0 0 1) Surface by C atoms ;the surface of α-Al 2 O 3 (0 0 0 1) has a good adsorption effect on all three atom adsorption directions of COF 2 gas. • It is believed that new bonds may be generated during the adsorption process of the CS 2 and COF 2 gas molecules, and the structure after adsorption is more stable. As the typical carbon-containing decomposition components of SF 6 under partial discharge in high-voltage insulation devices, CS 2 and COF 2 , will not only corrode devices, but also pollute the environment. Remove these gases through SF 6 adsorbent is an effective approach to eliminate the above hazards. In this paper, the adsorption performance of CS 2 and COF 2 on α-Al 2 O 3 (0 0 0 1) surface was calculated by first-principle based density functional theory, including the adsorption enthalpy change, charge transfer and structural parameters, and five relatively stable adsorption structures were initially obtained through analysis. Results indicate that all adsorption processes are exothermic. To further understand the adsorption mechanism, the density of states, frontier molecular orbital and deformation charge density diagram were analyzed. Calculations show that both CS 2 and COF 2 has a fine adsorption effect on α-Al 2 O 3 (0 0 0 1) surface, besides, for CS 2 , it is easier to be adsorbed on α-Al 2 O 3 (0 0 0 1) surface through C atom while there is no significant difference in performance parameters of the adsorption configuration for COF 2. Furthermore, frontier molecular orbital analysis also confirmed that the adsorbed system is more stable. This work provide theoretical basis for the experiments of SF 6 adsorbents adsorbing typical carbon-containing decomposition components. [ABSTRACT FROM AUTHOR]