Dissolved Gas Analysis (DGA) of insulating oil is widely used for diagnosing transformer incipient faults. Moisture is a major contaminant and degradation byproduct of transformer insulating oil. In this paper, molecular dynamics simulation was used to study the influence of moisture on the diffusion movement of dissolved gases in the insulating oil. Cycloalkanes (C₂₀H₄₂), alkanes (C₂₀H₃₈), and aromatic hydrocarbons (C₂₀H₂₆) are selected as the basic structural units in the constructed transformer oil simulation system. 0%, 1%, 3%, and 5% moisture molecules are added to insulating oil, respectively, and the insulating oil generates seven kinds of gas molecules through cracking. With an anhydrous model used as a benchmark, we researched the diffusion trajectory, the diffusion coefficient (D), free volume (V _F), and the moisture-gas interaction energy of each gas molecule as a function of moisture content. Through this study, we found that the increase of moisture content enlarges the V _F value of dissolved gas in insulating oil, which makes the gas in oil easier to diffuse. Besides, the moisture can also alter the mean square displacement (MSD) of dissolved gases; the mutual energy of molecules is mainly affected by the electrostatic interaction energy. This study can contribute to a better understanding of the influence of different moisture contents on the diffusion movement of dissolved gas in transformer oil from the micro level.

In this article, a silicone rubber-based composite material is selected as the test sample, and a 100-h corona aging test is conducted under different environments using multiple pin-plate electrodes to study the corona discharge characteristics of pin-plate under different humidity, salt fog, and haze environments. The corona aging characteristics of silicone rubber material are analyzed by the static contact angle, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR). The results show that, with the increase in the relative humidity (RH), the frequency and energy of corona discharge increase. The discharge frequency under a haze environment is small, but the number and amplitude of the positive half-cycle pulse are larger. With the increase in RH and the deterioration of the environment, the oxidation degree and hydrophobicity loss rate of the material surface are accelerated, and the material surface damage is also aggravated. The aging characteristics of silicone rubber have a positive correlation with the content of water molecules in the air, some hydrophilic -OH, and acidic -COOH appear on the material surface, leading to the insulation performance decrease. As the aging of silicone rubber deepens, its equivalent transverse relaxation time drop increases, the number of H atoms that become low bond energy state inside increases, and the resistance to corona aging decreases. The results of this article can provide some reference for the evaluation, diagnosis, and production of composite insulators in different regions.

Nuclear Magnetic Resonance (NMR) detection is a non-destructive testing method that can be used to detect the aging state of organic materials. A unilateral NMR sensor is used in this study to detect the aging state of the corona aging samples of silicone rubber materials after 100-hour’s corona aging under different humidity. At the same time, a comparative analysis is made between the NMR results and the conventional methods results such as Fourier Transform Infrared Spectroscopy (FTIR) and static contact angle test. The results show that with the effect of corona discharge, the polymer structure of the silicone rubber materials change to a certain extent. These changes are shown as the effective transverse relaxation time $T_{\mathrm {2eff}}$ of aged sample decreases in the NMR detection. The results of NMR and FTIR both show that the molecular crosslinking density of silicon rubber materials increases, and the activity of the H-containing group decreases. With the increase of relative ambient humidity, $\Delta T_{\mathrm {2eff}}$ gradually increase, and it means the corona aging state is becoming much severer. The results of NMR are consistent with the results of FTIR and contact angle tests. The $T_{\mathrm {2eff}}$ of the same sample tested at different time does not have significantly changes. This indicates that the NMR characteristic of silicon rubber materials after corona are irreversible. The NMR method can test the permanent damage of silicon rubber materials caused by corona. Compared with the static contact angle test, the NMR method can analyze silicon rubber materials from the molecular structure level, and it has good portability and orientation. Meantime, NMR method can achieve a non-destructive aging state detection. Hence the NMR method will provide reference for the operation and maintenance of the silicone rubber composite insulator.

In this paper, bisphenol A epoxy resin (E-51) as A group, Methyl tetrahydrodiphosphonic anhydride (MTHPA) as A curing agent, and acid anhydride crosslinking system epoxy resin samples were prepared. By establishing a condensation discharge platform, the surface condensation of epoxy resin was studied by temperature, relative humidity, and filth degree. The influence of hygrothermal corona aging on the surface flashover voltage of epoxy resin in the condensation state was analyzed by static contact Angle, scanning electron microscope, and infrared spectrum. The results showed that with the increase of temperature difference, relative humidity, and fouling degree, the surface condensation quality of epoxy resin also increased, and the temperature difference had the greatest effect on the surface condensation quality. With the increase of aging time, the static contact Angle decreased from 83.8° to 36.7°. At the same time, a large number of cracks appeared on the surface of the material, accompanied by skin shedding, and the surface decomposition and carbonization phenomenon occurred. The decomposition of -COOR group and -C=O group inside epoxy resin is accompanied by the generation of -OH and -COOH groups. The surface flashover characteristics of epoxy resin are positively correlated with the content of water molecules in the air, and the hydrophilic -OH and -COOH groups lead to the degradation of its electrical properties. The research results of this paper can provide reference for the operation and maintenance of switchgear with epoxy resin as the main insulation structure.

In this paper, bisphenol A epoxy resin was used as a sample for hygrothermal corona aging test. It summarizes the characteristics of corona aging in hygrothermal environments based on the analysis of the infrared spectral characteristics, surface topography, dielectric loss and electrical resistivity test of epoxy resin. The test results show that epoxy resin has two different stages of moisture absorption. the first stage is physical moisture absorption, which is reversible, and the second stage is chemical moisture absorption, which is irreversible. When aging, the epoxy resin will have an increasing number of cracks, accompanied by gradual oxidation. As the temperature and humidity climb up, the cross-linked structure inside the epoxy resin is decomposed and thus produces more free radicals. The expansion of the -OH group also promotes the chemical hygroscopicity. At the same time, the bombardment of high-energy electron beam destructs the surface structure of the epoxy resin. The sample surface becomes fluffy and even falls off due to hygroscopicity. In this sense, higher ambient temperature or relative humidity will intensify the internal deterioration of the aged epoxy resin sample, make the polar groups easier to turn and bring up polarization relaxation losses and dielectric losses as a result. The research results aim to provide reference for the operation and maintenance of epoxy resin materials in different electrical equipment in harsh environments.