Methanol is considered to be a new chemical marker to estimate the aging state of transformer cellulose insulation paper. The key to improve the assessment accuracy is to establish the precise relationship between the concentration of methanol in oil and degree of polymerization (DP) of insulation paper. The previous research in this area has shortcomings and needs to be further improved. In this article, first, an aging assessment basic model (temperature 20 °C, moisture content of insulation paper 0.637%) is established based on the theoretical derivation of cellulose degradation kinetics, and is calculated by 130 °C thermal aging experiment. Furthermore, the effects of different temperatures (20 °C–90 °C) and moisture contents of insulation paper (0.6%–3.4%) on methanol in oil are studied by diffusion experiment. Based on the above effects, the temperature and moisture correction factors are established by mathematical reduction. What is more, a modified model is proposed by integrating the basic model and the correction factors. Eventually, the verification experiment is randomly prepared to test the accuracy of modified model and the result shows that the relative error of DP is within 7%. The physical meaning and accuracy of aging assessment are improved by model derivation and modification of influencing factors.

High-voltage direct-current (HVDC) dry bushing capacitor-core insulation is composed of epoxy resin-impregnated insulating paper (RIP). To improve the thermal conductivity, breakdown strength, and space charge characteristics of RIP, 0.1 wt % nano-cellulose fiber (CNF)-modified RIP (CNF/RIP), 2.5–30 wt % hexagonal boron nitride (h-BN)-modified RIP (h-BN/RIP), and 2.5–30 wt % h-BN + 0.1 wt % CNF-modified RIP (h-BN + 0.1 wt % CNF/RIP) were prepared. Scanning electron microscopy (SEM) was implemented; the thermal conductivity, DC conductivity, DC breakdown strength, and space charge characteristics were tested. The maximum thermal conductivity of h-BN + 0.1 wt % CNF/RIP was 0.376 W/m.K with a h-BN content of 30 wt %. The thermal conductivity was 85.2% higher than that of unmodified RIP. The breakdown strength and charge suppression were the best in the case of 10 wt % h-BN + 0.1 wt % CNF/RIP. The maximum breakdown strength was 11.2% higher than that of unmodified RIP. These results can play a significant role in the research and development of insulation materials for HVDC dry bushing.

The increasing attention towards Natural Ester (NE) as a feasible substitute for mineral insulating oils is attributed to its exceptional biodegradability and high heat resistance. However, the limited temperature tolerance of NE-paper insulation, stemming from the low temperature resistance of cellulose paper, poses a hindrance to its application. In contrast, Polyimide (PI) insulation paper exhibits superior heat resistance and holds potential for effectively replacing cellulose paper when utilized in conjunction with NE, thereby expanding the permissible temperature range. This study entailed the preparation and testing of samples of PI insulation paper impregnated with NE (PI-NE). The dielectric properties of PI-NE were investigated under various temperatures, especially the breakdown strength, dielectric constant, dielectric loss, and volume resistivity. The results indicate that the breakdown strength enhances by 25% at elevated temperatures, in contrast to room temperature circumstances. Meanwhile, the dielectric constant and volume resistivity decline while the dielectric loss increases. Additionally, molecular dynamics simulations are used to clarify how intermolecular forces impact insulation performance under various temperatures. The simulations reveal that PI insulating paper introduces traps which inhibit space charge accumulation, thereby the composite’s insulation effectiveness enhanced. As temperature rises, the distance between PI molecules and natural ester molecules decreases, so that interface defects between the insulation paper and insulating oil reduced. These ensure the new oil-paper insulation structure maintains stable insulation performance under high-temperature conditions.

The space charge accumulation is an important factor to design the oil-pressboard composite insulation of convertor transformer, which is greatly affected by the temperature. In this paper, the space charge accumulation and attenuation in the two layers and single layer under DC voltage were studied by the Pulsed Electro-Acoustic Method from 20°C to 60°C and the electric field distribution was calculated by the space charge distribution. The studied results have indicated that the distributions of space charge and electric field in the test results do not follow the Maxwell-Wagner polarization. The space charge distribution is affected by the surface trap, bulk trap, charge migration and electric field. The temperature affected the polarity and amount of the charge at oil-pressboard interface. The space charge accumulation of the two layers is more complex than that of the single layer, and the space charge accumulation and attenuation of two layers need longer time to reach the stable stage. The space charge accumulation in the single layer is largest at 40°C, whereas the space charge accumulation in the two layers is largest at 20°C. Moreover, the increase in the temperature increases the attenuation amplitude and speed of space charge.

Nanoflower-like Ag-doped MoSe₂ nanocomposites were prepared by a simple hydrothermal method for room-temperature ethanol detection with enhanced sensing performance.