The intrusion of moisture may induce an abnormal increase in temperature or may even cause fractures in insulation equipment. Therefore, the hygroscopicity of rubber materials must be characterized. However, the existing methods for weighing organic polymer materials, such as silicone rubber, for moisture-absorption tests are time-consuming. In this article, a practical method for testing the moisture-absorption performance of silicone rubber materials for external insulation is proposed. The basic characteristics of the Langmuir diffusion equation for the water-absorption characteristics of silicone rubber are analyzed. A Langmuir curve fitting method based on the contraction–expansion (C–E) algorithm is developed, and its fitting effect is preliminarily verified by combining the experimental errors obtained from the experiment. Results show that the fitting effect has a strong relationship with the initial range of diffusion coefficient, bonding coefficient, and debonding coefficient. The time-consuming process of directly applying the fitting method is reduced from 70 to 50 days. The initial ranges of diffusion, bonding coefficient, and debonding coefficient are determined via the results of molecular simulations and experiments combined with an analysis of the literature. A prediction model is optimized and then validated against the experimental data from the recent literature on the water-absorption characteristics of silicone rubber at different temperatures. The experimental time required to reach saturated water absorption is remarkably reduced from 70 days to 1 day. Therefore, the method developed herein is feasible for engineering applications. Moreover, the entire water-absorption curve can be possibly plotted with an error of not greater than 5% via this prediction method.

The rod in the composite insulator is a load-bearing component, and glass-fiber-reinforced plastic (GRP) has always been regarded as the most suitable material. However, the investigation reveals that the performance shortcomings of GRP rods are the main cause of emergency heating defects of 131 new 500-kV ac composite insulators in South China. The finite-element simulation is conducted to understand the potential mechanism of heating. It is demonstrated that the holes with moisture distort the electric field, increasing heating power. A hole with moisture in the GRP rod longer than 500 mm could lead to emergency heating defects with temperature rise exceeding 5 K. For the holes in the GRP rod are formed by adjacent voids, the emergency heating defect is inevitable unless the porosity decreases. The fiber infiltration process of the GRP rods is analyzed on the basis of Darcy’s Law, and an improved process is proposed to reduce porosity. Maintaining the mass fraction of fiber by at least 70% and replacing the damp infiltration fluid in time in the production of GRP rods are necessary to restrain porosity. 300-h water diffusion test with a 50- $\mu \text{A}$ threshold is an effective evaluation method of the GRP rod performance. This method should be used before putting composite insulators into operation.

Moisture is detrimental to the performance of epoxy resin material for electrical equipment in long-term operation and insulation. Therefore, moisture absorption is one of the critical indicators for insulation of the material. However, some relevant test methods, e.g., the direct weighing method, are time-consuming, and it usually takes months to complete a test. For this, it is necessary to have some modification to save the test time. Firstly, the study analyzes the present prediction method (according to ISO 62:2008). Under the same accuracy, the time required is reduced from 104 days to 71 days. Subsequently, the Langmuir curve-fitting method for water absorption of epoxy resin is analyzed, and the initial values of diffusion coefficient, bonding coefficient, and de-bonding coefficient are determined based on the results of molecular simulation, relevant experiment, and literature review. With the optimized prediction model, it takes only 1.5 days (reduced by 98% as compared with the standard prediction method) to determine the moisture absorbability. Then, the factors influencing the prediction accuracy are discussed. The results have shown that the fluctuation of balance at the initial stage will affect the test precision significantly. Accordingly, this study proposes a quantitative characterization method for initial trace moisture based on the terahertz method, by which the trace moisture in epoxy resin is represented precisely through the established terahertz time-domain spectroscopy system. When this method is used to predict the moisture absorbability, the experimental time may be further shortened by 33% to 1 day. For the whole water absorption cycle curve, the error is less than 5%.

Oil-immersed transformers, with safe reliability and high utilization, plays an irreplaceable role in power transmission and transformation. Unavoidable insulation defects can occur that affect the safety of the power system and socio-economic, thus timely online monitoring becomes a focus of attention in the power sector. In this study, n ZrO ₂ (n = 1-2) modified GaN nanotubes are firstly proposed as a novel gas-sensing material for estimating the discharge faults in oil-immersed transformers through dissolved gas analysis. Density functional theory calculations are carried out to deeply explore the characteristic dissolved gases adsorption and sensing mechanisms. The density of states, charge density difference, band structures, and theoretical recovery time are analyzed to evaluate the feasibility and applicability of the gas sensor. The data shows that ZrO ₂ dopant provides active sites for gas adsorption. n ZrO ₂ -GaNNTs (n = 1-2) has limited gas sensitivity to H ₂ and CH ₄ but demonstrates considerable ability to capture C ₂ H ₂ . Moreover, all adsorption has excellent gas-sensitive recovery properties, aiding in the rapid recycling of sensors. Meanwhile, the verification is carried out by experiments. Results in this work can be employed for practical production of n ZrO ₂ (n = 1-2) modified GaN nanotubes gas sensors, ultimately realizing online monitoring of oil-immersed transformer.

Moisture intrusion into the silicone rubber (SR) sheath may trigger composite insulator failure, so it is especially crucial to study the water absorption and permeability characteristics of SR under different conditions to prevent and control the failure, however, there are few studies on the influence of electric field. In this work, the effect of electric field on the water absorption and permeability characteristics of SR is reported. The results show that the electric field has an inhibitory effect on the water absorption of SR, the diffusion coefficient and the percentage of saturated water absorption decrease by 34.4% and 82.6%, respectively, with the increase of the electric field intensity. Meanwhile, the permeability characteristics of moisture through SR are studied, and it is found that the permeation rate increases with the increase of forward voltage, while the reverse voltage is the opposite. Finally, molecular simulation is utilized to calculate the diffusion coefficient, free volume and intermolecular interaction energy of the SR system containing water under the effect of different electric fields, which further verifies the accuracy of the experimental results. By this study, the variation rules of water absorption and permeability of SR under the effect of electric field are supplemented.