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Poor contact is one of the main causes of the internal fault of SF6 gas insulated equipment. Taking the most common over-thermal decomposition process of SF6 caused by poor silver-plated copper contacts as an example, this article combines with density functional theory (DFT) and establishes the gas–solid contact interface adsorption model of SF6 and its main decomposition characteristic products (SO2F2, SO2, SOF2, HF, and H2S) with solid silver. Adsorption energy, charge transfer, and density of electronic state were used to analyze the reaction activity of SF6 and its main decomposition products with the Ag surface. It is found that SF6 and SO2 are chemically adsorbed on the Ag surface, and the reaction activity is relatively strong. When chemical adsorption occurs, SF6 bonds with the metal surface by the 2p orbitals of F atoms, and SO2 is bonded to the metal surface by the 2p orbitals of O atoms. There is also a strong reaction trend between HF and Ag (1 1 1), while SO2F2, SOF2, and H2S only physically absorbed with the Ag (1 1 1) surface. This indicates that under the local overheating failure caused by metal contacts, SF6 will first undergo chemical adsorption in the SF6/Ag (1 1 1) system and then undergo a decomposition reaction near the metal surface rather than in free space. The participation of Ag reduces the difficulty of the decomposition reaction to some extent. The results lay a foundation for finally revealing the interfacial reaction process of SF6-Ag. [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]

The decomposition characteristics of SF6 gas-insulated equipment remarkably vary under different working pressures (0.3?0.7 MPa). Thus, the influence of pressure should be considered when adopting decomposed components for spark discharge fault diagnosis. A series of experiments on SF6 spark discharge decomposition under various pressures were performed on the spark discharge simulation experimental platform. The influence of pressure on SF6 spark discharge decomposed components were analyzed quantitatively combined with molecule chemical decomposition mechanisms. Results show that the species of spark decomposed components do not vary under different pressures. However, pressure directly affects the accumulated energy of the electrons in the spark channel, leading to diverse dissociation intensities of electrons on SF6. This phenomenon further affects the rate of neutral-neutral molecule and ion-molecule reactions responsible for the decomposed components. Finally, the yields and effective generation rates of decomposed components CF4, SOF4, SO2F2, SOF2, and SO2 decline with varying degrees under increasing pressure. Moreover, mathematic regression equations were derived for the effective generation rates of the components influenced by pressure. [ABSTRACT FROM AUTHOR]

To figure out the influence rules of trace H2O on SF6 decomposition characteristic components under spark discharge, a series of spark discharge decomposition experiments with various H2O contents were performed using needle-plate electrode to simulate metal protrusion insulation defect. The changing rules and mechanisms of five decomposition characteristic components were achieved quantitatively, indicating that no matter how much H2O was, there exist five main decomposition components: CF4, SOF2, SO2, SOF4 and SO2F2. The contents of the five decomposition components increased with the time extended, and resulting in the contents of SF6 spark decomposition components by the order: SOF2 > SO2F2 > SOF4 > SO2 > CF4. Additionally, the higher H2O content is, the stronger promoting effect on the generation of SO2F2, SOF2, SOF4 and SO2 is. [ABSTRACT FROM AUTHOR]

We explored the thermal decomposition characteristics of SF6 with partial overthermal fault in organic solid insulating materials. Results show that when organic solid insulating materials were around the fault point, the main overthermal decomposition characteristic products of SF6 were CS2, CO2, CF4, H2S, SO2F2, SOF2, and SO2. The difference in the generating reaction and degree of reaction of the seven decomposition components resulted in the complexity of concentration and growth regularity. Surface component analysis after the experiment showed that the thermode surface contained numerous S, O, C and F. Fe existed in the form of Fe2O3 and FeF2. The organic insulating materials added new elements, such as F and S, because HF and H2S easily reacted with O in the epoxy group. [ABSTRACT FROM AUTHOR]

Sulfur hexafluoride (SF₆) gas-insulated equipment (GIE) has been widely used in extra/ultra high voltage power transmission systems. During its operation, GIE inevitably experiences partial overthermal faults caused by poor contact. In this study, the SF₆ decomposition characteristic of partial overthermal faults was used to solve problems that cannot be detected effectively in GIE. First, a large number of experiments were conducted on an SF₆ overthermal decomposition system to obtain the overthermal decomposition characteristic of SF₆ below 400 °C. Then, from the perspective of the physical significance of engineering, three feature parameters, namely, total decomposition amount, effective formation rate, and ratio of characteristic components, were proposed to reveal the deterioration degree of the gas insulation medium as well as to represent the development trend and severity of a partial overthermal fault. Results show that total decomposition amount CT, CT1, and CT2 can depict the degradation degree of the GIE insulation medium and the carbonic metal structure caused by a partial overthermal fault, which can be a good index to differentiate partial overthermal fault temperatures. The effective formation rate of each characteristic component RRMS is closely related to temperature and can reflect the development trend of a partial overthermal fault. The feature ratio CO2/(SO₂F₂+SOF₄+SOF₂+SO₂+H2S) can reveal whether a partial overthermal fault involves organic insulation materials. H2S/(SO₂F₂+SOF₄) can depict the severity of a partial overthermal fault. Log10(SOF₂+SO₂)/(SO₂F₂+SOF₄) and its effective value TCRRMS3 can represent the deterioration degree of GIE and provide excellent correlation with the severity of a partial overthermal fault, and thus, it can be used to evaluate the severity of a partial overthermal fault quantitatively. [ABSTRACT FROM PUBLISHER]

To explore the influence mechanism of trace H2O on SF6 decomposition characteristics under partial thermal fault and establish the foundation of using SF6 thermal decomposition principle to diagnose the thermal fault of SF6 electrical equipment, a series of artificial thermal fault decomposition experiments with different H2O concentrations were conducted on the designed SF6 thermal decomposition experimental system. A trace water injector was used to control the content of trace H2O accurately and gas chromatograph, chromatography-mass spectrometry as well as Fourier transform infrared spectroscopy were used to measure decomposed components. Finally, the thermal decomposition characteristic under 340 ° was achieved. The analysis results indicate no matter how much H2O content is, SF6 can decomposes into many kinds of decomposition characteristics, such as CO2, SOF2, SO2, SOF4, SO2F2, H2S, HF. The concentrations of all these decomposition characteristics increase with the time extended, but change differently with the increase of H2O content, because H2O plays different role in the formation process of each decomposition characteristic components. The variation of H2O content not only affects the production of the decomposition characteristic components, but also makes SO2 and HF gradually evolved into the main characteristic components of SF6 thermal decomposition. In addition, the higher the H2O content is, the stronger the promoting effect on SO2 and HF is. [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]

This paper aims to explore the decomposition characteristics of SF6 under thermal fault, which can further improve the method of using SF6 decomposed components to diagnose inner insulation status of SF6 insulated equipment. Hence, the thermal fault simulation system of SF6 electrical equipment is designed and serials of experiments are conducted. It initially gets SF6 thermal decomposition characteristic for temperature below 400°C. Then it analyzes decomposed component species and their generation regularity, determines the main characteristic component of SF6 thermal decomposition and chooses the key component to represent fault severity. The result shows that: SF6 begins to decompose obviously at 300°C and the main decomposition components contain CO2, SO2F2, SOF2, SOF4, SO2 and H2S; the improvement of fault temperature will promote the decomposition of SF6, but the formation regularity of each decomposed component is different; H2S is the special component only appears when thermal fault proceeds to some degree (above 360°C). Hence, decomposed components and their formation regularity can be used to diagnose the SF6 equipment thermal fault. H2S can be used as the key component to represent fault severity. [ABSTRACT FROM AUTHOR]

To obtain relationship between concentration of SF6 decomposed characteristic components (or their concentration ratio) during the formation process and partial discharge qualities and pulse repetition rate, this paper used needle-plate electrode to simulate outthrust insulation fault and conducted a serial of experiments. First, the SF6 decomposition characteristic under different PD strengths is obtained. Then this paper defines average discharge qualities per second as QSEC. It considers both apparent discharge qualities and discharge pulse repetition rate, and analyzes the relation feature between SF6 decomposition characteristic (both concentration of component and their effective formation rates RRMS) and QSEC. Besides, it proposes C(SO2F2)/C(SOF2) as the energy characteristic ratio (ER) to represent PD energy, and defines the effective energy characteristic ratio as (ERRMS). Moreover, it achieves the inner correlation feature between QSEC and all the characteristic component concentration, the RRMS of each characteristic component and ERRMS. The results show that: since number of C atoms from stainless steel surface and content of trace H2O and O2 in gas chamber were limited, both decomposed component concentration and component concentration ratio accords with the famous "Logistic Population Model" growth trend in ecology, which means they present ???S???-curve increase with QSEC. The proposed ER can effectively indicate the amount of PD energy and the defined ERRMS can objectively reveal the variance regularity of PD energy with QSEC. Hence, the correlation mathematic formula between ERRMS and QSEC is obtained and ERRMS can be used as the new characteristic parameter to represent PD energy. It establishes the foundation for the further fault diagnosis research. [ABSTRACT FROM PUBLISHER]