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.

A new graphene-based electrochemical biosensor was constructed and applied for the simple, rapid and highly selective determination of glucose. The modified glassy carbon electrode (GCE) was prepared using dopamine (DA) as a reducing agent for graphene oxide (GO) and as a capping agent to stabilize and coat the resulting reduced graphene oxide (RGO) surface as it can polymerize to form polydopamine (PDA). PDA-RGO composites were dropped onto a glassy carbon electrode surface, and glucose oxidase (GOx) was immobilized on the surface of the composites by Michael addition. Finally, Pt nanoparticles (PtNPs) were electrodeposited on the modified electrode. Such modified electrodes (denoted as GCE/PDA-RGO/GOx/PtNPs) were characterized by UV-visible spectroscopy, atomic force microscopy, X-ray power diffractometry, Fourier-transform infrared spectroscopy, and scanning electron microscopy. Electrochemical behaviors were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The fabricated biosensor exhibited a high sensitivity of 33 μA mM⁻¹ cm⁻² over a wide linear range of 0.2 mM to 1 mM, good stability, excellent repeatability, and a detection limit of 0.10 mM.

The interface is the weakness of composite insulators. As the interface bonding fails, the uniform distribution of electric field will be affected, which accelerates the aging of composite insulators and affects the safe operation of transmission lines. Because of the stress between the sheath and the rod, the air gap at the interface is generally less than 10 um and there is extrusion contact in some areas. Therefore, conventional nondestructive testing technology based on refraction and reflection principle cannot effectively identify the faulty insulators in the initial stage of bonding failure. Based on the constitutive model of the interface of composite insulators, the friction force of the interface after bonding failure introduces more nonlinearity in mechanical properties than hydrogen bond under well bonding condition. The numerical results show that under the influence of the nonlinear constitutive relation, the higher harmonic components in the spectrum will increase significantly. The experimental results of plate and insulator samples confirm the validity of numerical calculation. Based on the normalized nonlinearity coefficient, the interface state of composite insulators at the initial stage of bonding failure can be effectively identified.

The holes in composite insulator rods are a type of quality defects. However, not all holes can be identified by the dye penetration test according to existing standards and some holes can cause abnormal heating of the composite insulator during operation. Micro‐computed tomography is used to study the structure of these holes. Based on the pore structure, the holes are classified as dependent or independent. The dependent hole is formed by several interconnected adjacent pores and the overlong equivalent penetration path makes it cannot be effectively identified by the standard dye penetration test. Considering the structure of the dependent hole, ethanol gas was used to increase the effectiveness of the dye penetration test. The experimental results show that the detection rate of dependent holes is approximately 80% as the ethanol concentration is close to saturation, and the porosity can be inferred based on the number of penetration points.

In recent years, the quantity and proportion of heating defects have increased significantly with more composite insulators used in transmission lines and deterioration of early composite insulators. End heating is the main characteristic of this kind of defect in high‐temperature and high‐humidity areas. In this paper, microstructures of the housing material were observed through scanning electron microscopy and the key factors leading to temperature rise were studied through water absorption and power loss experiments. The results show that polarisation loss is the main cause of temperature rise and power loss increases exponentially with higher electric field intensity. The microporous structures of the housing material not only enhance the moisture absorption effect, but also affect the uniform distribution of the electric field. Due to the concentration of the local electric fields at high‐voltage end, the effect of porosity on temperature rise is more significant. By adjusting the shielding depth (i.e. installation height) of grading ring or adding a racetrack ring to restrain electric field intensity at high‐voltage end of composite insulator, the temperature rise in high‐humidity areas can be effectively reduced.