The statistics of the Conference International des Grands Reseaux Electriques (CIGRE) indicate that the operational reliability of SF ₆ gas‐insulated equipment (GIE) is very high; however, the failure rate of the GIE in operation is much higher than that of the IEC standard, and the fault occurs frequently in the GIE at a high voltage level. The reason is due to the complex and strong on‐site electromagnetic interference environment and fully enclosed structure of GIE. The key method and technology for effective on‐line monitoring and fault diagnosis of GIE are still lacking. Given the partial strong electromagnetic energy and high temperature induced by early latent insulation faults in the equipment, SF ₆ gas insulation presents different degrees of decomposition. The decomposition products mainly include SO ₂ F ₂ , SOF ₂ , SO ₂ , HF, and H ₂ S. The decomposition characteristics of SF ₆ are closely related to the property of insulation faults. At present, this area is attracting attention from the power industry and research institutes. This study summarises the current research on SF ₆ decomposition component analysis (DCA). The content mainly includes the latest progress of SF ₆ decomposition characteristics and mechanism under fault conditions, and fault diagnosis methods based on decomposition components.

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 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 (FCM). The component characteristic quantities that characterized the high-energy discharge fault, partial discharge, and partial over-thermal fault of the device were extracted: % $\rm (SOF_{2}+SO_2)$ , % $\rm (9SO_{2}F_2)$ , and % $\rm (5CO_2)$ . 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.

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 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 evaluate the collected samples and the accuracy of the evaluation method is up to 87.5%. This paper lays the foundation for the future comprehensive assessment and fault diagnosis of insulation status of DC GIE on the basis of SF6 decomposition characteristics.

In this paper we investigated SF ₆ decomposition behaviour of typical insulation defects in gas‐solid insulated converter transformer valve‐side bushing under partial discharge (PD). Additionally, we compared the results with that of gas insulated switchgear (GIS). The results indicated that SF ₆ decomposition behaviour varies with the insulation defects type. For metal protrusion defects, the proportion ranking of CO ₂ and SO ₂ can be related to whether the needle tip is wrapped with epoxy resin‐impregnated paper (ERIP). The proportion of carbon‐containing products is much higher under contamination defect than under other defects. Moreover, the proportion of carbon‐containing components is higher under flashover condition than under PD condition and is accompanied by the appearance of H ₂ S and CS ₂ . However, the yield of SO ₂ F ₂ is always low. Compared to negative DC voltages, positive DC voltages have a higher proportion of carbon‐containing components, mainly in the form of more CO ₂ and less SOF ₂ . Compared to the PD decomposition behaviour of typical insulation defects in GIS, when PD involves ERIP, the proportion of carbon‐containing products, especially CO ₂ , is significant higher, while the proportion of sulphur containing products, especially SO ₂ F ₂ , is lower.

It has been recognized that the gas insulating medium SF ₆ decomposes when the partial over-thermal fault (POF) occurs inside the equipment. The insulation condition monitoring and fault diagnosis of the equipment can be carried out by utilizing the decomposition characteristics of SF ₆ under POF. Similar to the discharge decomposition of SF ₆ , trace H ₂ O is an important factor affecting the decomposition of SF ₆ under POF while its mechanism is not clear yet. In order to investigate the characteristics and micro mechanism of decomposition, the paper combines isotope tracer by adding H ₂ ¹⁸ O as a tracer into SF ₆ gas and carries out experiments. Detecting the concentration and isotope abundance of products by gas chromatography–mass spectrometry, the paper studied the influence of H ₂ O on the production of decomposition products and the specific formation process of CO ₂ , SO ₂ F ₂ , SOF ₂ and SO ₂ under the influence of H ₂ O. The research further verified the assumption on formation process of CO ₂ and SO ₂ and also brought up with new theory on the formation of SO ₂ F ₂ and SOF ₂ based on experimental results.