## 2 Decomposition Mechanism of SF\({}_{6}\) and Influencing Factors  
The purity of the SF\({}_{6}\) gas used in the electrical equipment is higher than 99.7%, and the impurities in the equipment are mainly traces of water, oxygen (O\({}_{2}\)), and sulfur tetrafluoride (SF\({}_{4}\)). The property of the SF\({}_{6}\) gas is very stable. When the temperature is below 150 \({}^{\circ}\)C, it is difficult for SF\({}_{6}\) to react with other substances, and it does not decompose in the normal working environment. However, in the process of arc, corona discharge, sparks, and overheating (Table 1), SF\({}_{6}\), in the case of electron collision or internal heat, will split into a variety of low fluoride sulfide and can be decomposed into low sulfur fluoride, such as sulfur difluoride (SF\({}_{2}\)) and SF\({}_{4}\), which will react with impurities or some materials (electrodes and surface materials of the equipment) in the equipment to produce toxic or corrosive compounds [8; 9; 10; 11; 12; 13; 14; 15], such as SO\({}_{2}\)F\({}_{2}\), SO\({}_{2}\), SOF\({}_{2}\), and hydrogen sulfide (H\({}_{2}\)S), as shown in Figure 2. When the fault involves solid insulation materials, carbon tetrafluoride (CF\({}_{4}\)), carbon monoxide (CO), carbon dioxide (CO\({}_{2}\)), carbon disulfide (CS\({}_{2}\)), etc., are also generated [13; 14; 15]. In the normal state, the chemical activity of SF\({}_{6}\) gas discharge decomposition products is higher than other gases, which are corrosive and toxic. The accumulation of these decomposition gases will corrode the electrode, reduce the insulation performance of the electrical equipment, and affect the normal safe operation of the electrical equipment. Figure 1: Monitoring and leak diagnostics of SF\({}_{6}\) and its decomposition gases from power equipment. The concentration and rate of SF\({}_{6}\) decomposition characteristic gases are correlated with the insulation fault difference during and at the end of the generation process [16]. Different insulation defects can lead to different compositions of the decomposition gas, and the composition, generation amount, and stage production rate of the corresponding decomposition gas components will also be very different [17]. For example, the characteristic decomposition product of SF\({}_{6}\) under superheating conditions is H\({}_{2}\)S. However, the production of SF\({}_{4}\) and CS\({}_{2}\) is related to solid insulation failure. The concentration and generation rates of SF\({}_{6}\) decomposition gases are also associated with the concentration of O\({}_{2}\) and water in the SF\({}_{6}\) buffer gas. [PERSON] et al. found that the higher the O\({}_{2}\) concentration was, the more SOF\({}_{2}\) and SO\({}_{2}\)F\({}_{2}\) were produced [11]. In addition, humidity also affects the service life of the insulation equipment. Water vapor has the ability to trap fluorine atoms and inhibit the recombination of low-fluorine sulfides into SF\({}_{6}\), which promotes the production of corrosive acid gases. In electrical equipment, water  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Discharge Type** & **Discharge Motor Theory** & **Signal Characteristics** & **Duration** & **Discharge Energy/I** & **Gas Products** & **Refs. ** \\ \hline \multirow{4}{*}{Arc discharge} & Current interruption of circuit breakers, short circuits in gas chambers, and disconnector operation Air gap capacitive discharge, such as breakdown during high-voltage tests when high-frequency current passes through the contact of the oxide layer; electrical fault or short circuit caused by damaged insulation or excessive current load. & Temperatures up to 20,000 K, more than a few KA milliseconds & Tens to hundreds of 10\({}^{5}\)–10\({}^{7}\) & S\({}_{5}\)P\({}_{2}\), SOF\({}_{2}\), SF\({}_{4}\), CO\({}_{2}\), Hf, CO\({}_{2}\), Hf, CO\({}_{2}\), Hf, CO\({}_{  
vapor can be released gradually from the inner surface and electrode material or come from outside in unsealed components.