Silicone rubber has excellent mechanical and electrical properties and excellent resistance to high and low temperatures, which is widely used in the field of electrical insulation. In this paper, the effects of extreme ambient temperature on the mechanical and electrical properties of silicone rubber (SR) were reviewed. The crystallization behavior of silicone rubber at low temperature and the methods to improve the thermal stability of silicone rubber were introduced. Finally, the future development trend of silicone rubber was prospected.

The new environmentally friendly insulating medium C₄F₇N gas mixture will decompose under long-term overheating and partial discharge conditions, and some of the decomposition products will not only affect the stable operation of gas-insulated switchgear, but also cause personal safety hazards. Therefore, the internal of equipment need equip with adsorption materials to adsorb the decomposition products. Molecular sieves, with wide variety and ionic modification space, are regarded as the most promising adsorbent materials for the treatment of C₄F₇N decomposition products. In this paper, the adsorption isotherms and adsorption sites of 11 kinds of pure silica-type molecular sieves (three kinds with cage structure characteristics and eight kinds with pore structure characteristics) on C₄F₇N and its decomposition products were investigated by molecular dynamics calculations. Then the adsorption energy, electron transfer, and density of states parameters of ZSM molecular sieves modified by the cation (H⁺, Na⁺, Mn²⁺, and Fe²⁺) on C₄F₇N and its decomposition products were obtained based on density functional theory (DFT). The molecular dynamics results reveal that the molecular sieve topology and the window size between gas molecules and molecular sieve are important factors affecting the adsorption process. The density functional calculations show that the modification of Mn²⁺ and Fe²⁺ ions could effectively enhance the adsorption effect of ZSM molecular sieves on the decomposition products of C₄F₇N, and the adsorption process is chemisorption. During the adsorption, the main action site of C₄F₇N is C≡N bond, the main action site of C₂F₆ is C=C double bond and F atom, and the main action site of C₃F₈, C₂F₆, and CF₄ is F atom.

Polyethylene-based non-crosslinked cable insulation materials have better electrical and mechanical properties, simpler processing, lower energy consumption than XLPE, and can recycle, which are one of the most promising new environmentally friendly cable insulation materials. In this paper, LLDPE/HDPE blending insulating materials with different ratios were prepared using domestically produced base materials, and their electrical, mechanical, rheological, and thermal and oxygen aging resistance properties were tested and compared with the blending materials prepared by imported base materials. The results show that both the domestic and imported blending materials have the best electrical properties and mechanical properties when the mass ratio of LLDPE and HDPE is 7:3. The electrical properties of the domestic blending materials are similar to those of the imported blending materials at the optimal ratio, but the tensile strength is lower. There is a significant difference between domestic and imported blending materials in thermal and oxygen ageing resistance. Through the molecular weight and its distribution test, infrared spectroscopy analysis, it is found that the branching degree of domestic LLDPE is similar to that of imported LLDPE, but its molecular weight distribution range is wider and there is an obvious long-tailed distribution in the direction of low molecules, which may be one of the reasons for the lower tensile strength and antioxidant properties of domestic blending materials.

This paper focuses on the effect of melt radical graft modification of hindered phenolic antioxidant (AO3052) on the space charge and breakdown properties of polypropylene (PP) insulation. The DC conductivity, space charge distribution, and DC breakdown characteristics of grafted polypropylene with different antioxidant contents were tested and compared with the unmodified polypropylene. The results show that the antioxidants grafting can increase the sensitivity of conductivity to temperature and improve the conductivity activation energy of the samples. The 0.5% antioxidant grafting is effective in improving the space charge accumulation problem and reducing the degree of electric field distortion of PP. The DC electric strength of PP at 90℃ increases by 31.3%, and the ageing electric strength of PP at 90℃ increases by 36.1%, which is attributed to the ability of 0.5% antioxidant grafting in inhibiting the space charge accumulation. The energy band structure analysis suggests that the antioxidant grafting modification can introduce more local energy levels and potential traps in the forbidden bands of PP, which inhibits the charge transport. Meanwhile, the phenolic hydroxyl groups in the hindered phenolic antioxidants can scavenge the free radicals in PP, and the combined effect of the two enhances the breakdown performance of PP.

In cable accessories, the interface between cable body insulation and accessory insulation often coat with insulating oil for cable to enhance the sealing and insulating properties between the interfaces of cable accessories. In order to investigate the compatibility and applicability of cable body insulation and insulating oil, and to provide a reference for the selection of insulating oil for cables, the adsorption compatibility of PP and XLPE on three typical insulating oils (silicone oil, silicone grease, and polyisobutylene) at 25℃ and 75℃ was studied. The results show that affected by the molecular structure, PP and XLPE have limited adsorption capacity on silicone oil and silicone grease, and they can easily adsorb polyisobutylene, resulting in a significant increase of quality. PP coordinating with silicone grease have the best properties, which can improve the mechanical properties and electric strength of PP. XLPE exhibits close properties in silicone oil and silicone grease, among which silicone grease impregnation maintains good mechanical properties, while silicone oil impregnation maintains good insulating properties. Through analysis it is found that appropriate amount of adsorption improves the surface roughness, fills the internal defects of the insulation, and improves the insulating properties of material. By studying the influence of different types of coating materials on the main insulating material at different temperatures, the adaptability results of insulating medium and cable main insulation are obtained, which can provide a reference for standardizing the selection of insulating oils for cable terminals and improving the operating reliability of cable terminals.

The temperature difference in the southeastern region of Tibet is relatively large, which has negative influence on the insulation performance of composite insulators, and affects the continuous and reliable transmission of West East power. Silicone rubber samples were conducted 720 hours of high and low temperature cyclic ageing tests at -20-150℃ in this paper, and the silicone rubber sampes with different cycles were conducted various tests to study the changes of ageing performance in large temperature difference environments. The 12 kinds of tested characteristic parameters were conducted selection of characteristic parameters using Fisher Score, and 4 kinds of significantly correlated characteristic parameters were selected. Taking composite insulators running for 0-11 years as the research object, we conducted performance testing and result analysis on in-service composite insulators based on correlated characteristic parameters, and proposed an improved genetic algorithm to optimize the BP (Back Propagation) neural network prediction algorithm. On the one hand, this algorithm improves the optimal preservation strategy selection operator, and on the other hand, this algorithm dynamically adjusts the mutation probability and crossover probability during the iterative process. The results show that the four ageing characteristic parameters, which are tensile strength, dielectric loss factor tanδ, TGA residual ratio, and Si-OH transmittance reduction rate, are significantly correlated. Compared with the traditional BP and GA-BP (genetic algorithm back propagation) neural networks, the improved GA-BP neural network has stronger nonlinear learning and global optimization capability, and faster network convergence speed. The test error result of the improved GA-BP neural network on a group of samples aged for 11 years is 2.33%. The error between the predicted operating life and the actual service life of five groups of composite insulators is within 5%.

The surface charge accumulation of basin insulators is one of the important factors restricting the development of HVDC GIL, and the heat transfer inside the GIL would aggravate the surface charge accumulation. In this paper, an electrical-thermal coupling simulation model of charge accumulation was established. The time-varying temperature distribution inside the GIL under different external ambient temperature and gas pressure was simulated. The surface charge accumulation characteristics under constant and time-varying external ambient temperature were studied, and its effect on the surface charge accumulation was also analyzed. The results show that when the external ambient temperature is a constant value, the external temperature increases every 10℃, the steady-state temperature on the insulator surface increases by more than 9.2%, and the steady-state surface charge density of insulator increases by more than 17.3%. When the external ambient temperature changes with time, the temperature on the insulator surface eventually fluctuates with time around a stable value after continuously rising for a period of time, and the surface charge density is approximately equal to that under the average external ambient temperature. In addition, the surface temperature and charge density of the insulator decrease with the increase of gas pressure. The research results are expected to provide reference for the design and operation of DC GIL, which can improve the safety and stability of DC GIL operation.

High-power air-insulated RF coaxial cable has a broad application prospect in the field of Internet of Things. It is of great significance to study the electric field distribution of its important insulating component—insulating gasket in the presence of common defects for the safe and stable operation of RF coaxial cables. Firstly, a numerical model of RF coaxial cable containing inner and outer conductors and insulating gaskets was established and a simulation model of electrostatic field was constructed in finite element software, and the accuracy of the model was verified through experiments. Secondly, on the basis of constructed model, the effects of internal air bubbles, surface foreign objects, and interface defects on the electric field distribution of insulating gaskets were studied by adjusting the morphology and positional parameters of defects, and compared with the simulation results of electric field intensity in the absence of defects. The results show that the electric field distribution of the insulating gasket is related to the morphology of internal bubbles, and the closer the distance from the inner conductor, the more serious the electric field distortion; the size, location, and arrangement of the surface foreign objects will affect the electric field distribution, and the influence of conductive particles on the electric field is larger than that of sand particles; the interface defects have a negative correlation with the thickness of defects, and have a positive correlation with the depth of defects. In summary, it is surface foreign object leading to the most serious electric field distortion in three kinds of defects, followed by interface defect.

In view of the problem of uneven electric field distribution and severe local electric field distortion in insulation partitions of high-voltage switchgear, dielectric functional gradient materials were introduced into the preparation of insulation partitions, and two optimization schemes, which are internal insulation structure optimization and surface insulation structure optimization, were proposed. By changing the upper limit of dielectric constant of material, the thickness of insulation partition, and the thickness of surface coating, electric field and temperature field simulation calculations were carried out to compare and analyze their effects on the optimization of electric field distribution. Finally, simulations and dielectric loss characteristics tests were conducted to compare the two optimization schemes. The results show that compared to the traditional homogeneous insulation partitions, changing the internal insulation structure and adding surface coatings can reduce the maximum field strength along the surface without considering the influence of internal operating environmental factors in the switchgear. When the thickness of insulation partition increases to 12 mm, the electric field optimization effect is optimal, and the maximum field strength along the surface can be reduced by 69.8%. When the surface coating thickness is 1 mm, the electric field optimization effect is optimal, and the maximum field strength along the surface can be reduced by 62.9%. Through simulation and experimental comparison, it is proved that the partition with optimized internal insulation structure has better electric field control effect and insulation performance.

Air discharge results from the interaction between electric field and atmospheric environment, therefore the air gap switching impulse discharge voltage is affected by the interelectrode electric field distribution and the atmospheric parameters. In order to calculate the discharge voltage of rod-plane long air gaps at high altitude areas, we construct an insulation prediction model based on k-nearest neighbor (KNN) algorithm with air pressure, temperature, humidity, altitude, and electric field characteristic parameters as feature set. The KNN algorithm was trained by the test data in the altitude range of 55-4 300 m to establish the mapping relationship between air gap features and the insulation strength, and then discharge voltage prediction of rod-plane air gaps at the high altitude of 5 000 m with different gap distances was realized. The maximum relative error and the mean absolute percentage error are 8.58% and 3.78%, respectively, which verifies the effectiveness of the proposed method. When the model was extrapolated to the rod-plane air gaps in plain area under different atmospheric parameters, the predicted discharge voltages also had good agreement with the experimental values. This study results can provide references for the calculation of air gap insulation strength in different atmospheric environment.