Jiaming Yan

Two bio-based insulating oils (BHOs) with average carbon chain lengths of approximately 18 and 22 were investigated as short- and long-chain BHOs. By constructing an oil-paper composite insulation system, the generation law of characteristic gases in the two systems was studied by partial discharge experiments. Based on the ReaxFF reaction molecular dynamics simulation under electrothermal coupling stress, the cracking path, cracking rate, evolution of oxygen-containing small molecules, and generation path of characteristic gases of cellulose polymer were revealed. Both systems produced H₂, CH₄, C₂H₂, C₂H₄, C₂H₆, CO, and CO₂, with CO₂ dominant and C₂H₆ least abundant. The short-chain BHO generated markedly higher amounts of H₂, CO, C₂H₂, and C₂H₄ than the long-chain BHO; after 15 min, its H₂ and CO concentrations were about 3.4- and 2.1-times those in the long-chain system, respectively. ReaxFF simulations showed that cellulose degradation in the short-chain BHO followed stepwise chain scission and continuous decarbonylation, favoring CO and unsaturated gas precursors. In contrast, cellulose chains disappeared faster in the long-chain BHO, producing more oxygen-containing organic fragments and C₁-C₅ oxygenated molecules and a higher small-molecule conversion ratio. Characteristic gas pathway analysis revealed that all seven gases could be generated from cellulose pyrolysis intermediates, and different oil environments primarily influenced gas generation behavior by altering the evolution pathways of these intermediates. These findings, at the molecular scale, elucidate the impact of BHO environments on the degradation mechanism of cellulose polymers, providing a theoretical basis for the condition assessment and design of environmentally friendly oil-paper insulation systems.

To investigate the thermal decomposition characteristics of high-temperature vulcanized silicone rubber (HTV) and liquid silicone rubber (LSR) under different aging conditions, scanning electron microscopy (SEM) and thermogravimetric analysis (TG) were employed to characterize the surface microstructure and chemical properties of silicone rubber samples that had been in service for 15 years. The influence of aging degree on the thermal stability of silicone rubber was initially investigated. ReaxFF-based reactive molecular dynamics simulations were conducted to analyze the decomposition pathways of silicone rubber under high-temperature conditions, as well as the dynamic evolution of decomposition products. In addition, key parameters—including glass transition temperature, mean square displacement, cohesive energy density, and free volume fraction—were calculated before and after decomposition using the Materials Studio platform. The results indicate that LSR exhibits higher thermal stability than HTV, while the thermal stability of both materials decreases after thermal decomposition. Furthermore, the variation in thermal stability was discussed based on these parameters from the perspectives of molecular mobility and intermolecular interactions. This research can provide a reference for the safety operation assessment, aging status determination, and high-temperature service reliability design of silicone rubber insulating materials.

Cellulose paper, a natural polymeric dielectric, determines the lifetime of oil–paper insulation systems in transformers, yet its molecular degradation behavior in ester-based insulating media remains insufficiently clarified. This study investigates the electro–thermal aging of cellulose polymer immersed in soybean-based natural ester (SBNE) and palm fatty acid ester (PFAE), with emphasis on depolymerization and its relationship with partial discharge (PD) activity. Accelerated aging experiments were conducted under combined electrical and thermal stress, and the evolution of the degree of polymerization (DP) was measured to quantify polymer chain scission. Phase-resolved PD (PRPD) patterns were recorded during aging, and multi-dimensional statistical features were extracted and reduced using principal component analysis to characterize degradation-sensitive electrical responses. The results show a progressive decrease in DP with aging time in both ester media, accompanied by distinct PD evolution characteristics, indicating different influences of the two esters on cellulose polymer stability. An ensemble learning model integrating multiple classifiers was further employed to identify aging stages based on PD features, achieving reliable discrimination performance. These findings establish a correlation between cellulose depolymerization and dielectric discharge behavior, providing a polymer-centered interpretation of aging mechanisms in ester-based oil–paper insulation systems.

With growing environmental concerns, the search for alternative gases to replace SF₆ has become a key focus in the power industry. Perfluoromethyl vinyl ether (PMVE), with its low global warming potential (GWP) and excellent insulation properties, is a promising candidate. When mixed with N₂, PMVE not only decreases the liquefaction temperature but also enhances insulation performance, making the gas mixture more suitable for engineering applications. In this study, reactive molecular dynamics (ReaxFF-MD) and density functional theory (DFT) calculations were combined to investigate the influence of temperature on the decomposition characteristics of a PMVE/N₂ mixture. The reaction pathways and reaction enthalpy of PMVE and its major decomposition products were analyzed in detail. The results showed that, as temperature increases, the decomposition intensity of PMVE is enhanced, leading to a higher reaction rate and accelerated formation of decomposition products. Moreover, the main decomposition products of the PMVE/N₂ mixture include C, C₂F₂, CF₂, CN, CO, CF₂O, F, O, and other small molecules and free radicals. The dynamic balance between the generated free radicals helps maintain the system’s insulation capacity. However, toxic decomposition byproducts such as CF₂O, C₂N₂, and CO were also detected. This study provides valuable insights into the engineering applications of PMVE/N₂ mixtures.

This paper studied the relationships between evolution of phase‐resolved partial discharge (PRPD) patterns and damaging characteristics, such as surface topography, surface roughness, and surface conductivity, and the constitution of gas within cavity for oil‐impregnated insulation paper during the damaging process caused by partial discharge (PD). According to PRPD patterns, the damaging process can be divided into five stages. At each of the stages, surface conditions of insulation were analyzed by optical microscopy, scanning electron microscopy, atomic force microscopy, and high‐resistance meter. Gas constitution was analyzed by gas chromatography‐mass spectrometry, as well. Meanwhile, PRPD patterns of different gas constitution were compared, and analyzed, as well as those of different surface‐damaging conditions. Results reveal that during the damaging process, the percentage content of electronegative gases descends and ascends alternately, and discharging types alternate between pseudo‐glow (or glow) and spark. PRPD pattern of pseudo‐glow‐type discharge chiefly depends on the properties of weak electronegative gases generated during PD. PRPD patterns of spark‐type discharge are chiefly determined by surface damage conditions. PRPD patterns of spark‐type discharge manifest different levels of “rabbit‐ear” and periodical features. The level of “rabbit‐ear” feature is mostly determined by surface conductivity, while the level of periodical feature generally depends on surface trap density. In addition, surface roughness does not change shapes of PRPD patterns; however, the amount of discharge increases as the value of surface roughness declines. Copyright © 2010 John Wiley & Sons, Ltd.