In order to more finely evaluate the influence of factors such as the microstructure and material composition of the shed on the macroscopic performance of insulators, the mechanical properties, thermal weight loss, and Fourier infrared spectrum of AC composite insulators with different operating years were tested combined with the molecular dynamic simulation method in this paper. The results show that with the increase of operating years, the tear strength, tensile strength, and elongation at break of the insulator shed from low-voltage end to high-voltage end show a decreasing trend. The content of organic silicone and SiO₂ in the outer layer of shed significantly decrease, which can cause a decrease in macroscopic mechanical properties. In the electro-thermal environment, the bulk modulus, Young′s modulus, and Poisson′s ratio of the shed decrease with the increase of temperature and fluctuate with the increase of electric field strength. The high-voltage end of insulator has the most severe electric field distortion and the worst mechanical properties. The multi-scale model of the composite insulator shed ageing established in this paper can provide a reference for evaluating the ageing state of insulator.

In order to investigate the surface discharge process and its microscopic characteristics of glass fiber reinforced epoxy resin composite insulating material, an experimental platform of slant plate electrode was constructed in this paper. Surface tracing and corrosion tests were conducted on samples by a constant tracing voltage method, and the formation mechanism of electric trace was analyzed by combining the Bernoulli equation of ideal liquid. The change of functional groups, surface roughness, and three-dimensional morphology of epoxy resin materials under different stages of tracing corrosion were tested. The results show that the damp and polluted area of insulation composite material is very easy to generate leakage current and discharge, and the most serious corrosion situation always occurs at the bottom electrode firstly. With the increase of tracing corrosion degree on the surface of sample, the epoxy group, hydroxyl group, amino group, aldehyde group in epoxy resin molecular chain gradually decompose, and the carbonyl group decompose not completely after its generation. The surface morphology of the material gradually becomes rough and irregular, the surface roughness shows an upward trend, and the roughness during the explosive period is about 2.8 times bigger than that during the starting period.

To reduce the errors of the ageing state evaluation method based on the extended Debye model in describing the degradation process and explaining the ageing mechanism of oil-paper insulation, the polarization-depolarization (PDC) curves of oil-paper insulation samples with different ageing degrees were tested and analyzed in this paper. A distributed Debye model considering the relaxation branches with probability distribution was established, and an accurate evaluation method for the ageing state of oil-paper insulation bushing was finally proposed by solving through regularization method. The results show that with the increase of ageing degree, the polarization current overall shifts towards the direction of increasing the depolarization current and decreasing the relaxation time, and the time for the curve to reach a stable value is shortened. The distributed Debye model can effectively describe the multiple relaxation processes of the aged oil-paper insulation samples, and the regularization method can effectively solve the system ill-posed problems encountered when solving ill-conditioned linear equation. As the ageing degree increases, the probability density of the relaxation time distribution function corresponding to the main relaxation peak of sample increases, and the most probable relaxation time constant gradually decreases. The ageing state evaluation model constructed in this paper has high evaluation accuracy, whose error is less than 1.37%.

The ultra-high frequency (UHF) method for detecting partial discharge (PD) is currently one of the important means to evaluate the state and insulation performance of gas insulated switchgear (GIS). In this paper, in order to solve the problem of a large number of missing and false alarms in UHF detection of GIS partial discharge, GIS insulator with metal foreign object attached on the surface was conducted long-term constant voltage experiments. The successful capture probability of discharge signal was analyzed by combining with the existing UHF detection strategies, and optimization schemes of the existing UHF signal detection strategies were proposed from detection time and detection threshold. The results show that the partial discharge of metal foreign object defect attached on the insulator surface has intermittent characteristics, and the existing UHF live detection and online monitoring strategies have low detection probability of discharge. The capture probability of effective discharge can reach 85% by extengding the detection time to 2 247 seconds in optimization of live detection strategy. The detection probability of PD Event can increase by extengding the measurement time of forming a partial discharge event (PD Event) and reducing detection threshold in optimization of online monitoring strategy. In engineering application, the combination of appropriate measurement time and detection threshold can be selected to detect the intermittent discharge.

Cross-linked polyethylene (XLPE) and silicone rubber (SIR) are commonly used insulation materials for high-voltage direct current cables and reinforced insulation materials for accessories at present. The composite insulation composed of the two will age under long-term thermal stress. To investigate the charge transport characteristics of XLPE/SIR composite insulation with different ageing degrees, XLPE/SIR samples with different ageing degrees were prepared and subjected to simultaneous measurement of space charge and isothermal relaxation current. At the same time, by combining Fourier transform infrared spectroscopy (FTIR) testing and quantum chemical computation (QCC), an energy band model of XLPE/SIR system before and after ageing was constructed, and the charge transport behavior of XLPE/SIR was explored. The results show that negative charges always accumulate at the XLPE/SIR interface, and the amount of charge increases with ageing time. There are always homopolar charges accumulating near the cathode and anode, and the distribution range decreases with ageing time. After ageing, the depth of charge traps in SIR does not change much, while deeper charge traps appear in XLPE. The negative charge accumulation at the interface between the unaged XLPE/SIR is mainly caused by Maxwell-Wagner polarization, while the increase of negative charge accumulation at the interface of the aged samples is mainly related to the introduction of shallow electron traps in SIR and deep electron traps in XLPE.

The "thermal expansion and contraction" behavior of the internal atoms in epoxy resin and the intrinsic issue of low thermal conductivity seriously restrict the application of epoxy resin in dry-type DC sleeve insulation. To address this, we introduced boron nitride whiskers with low thermal expansion coefficient into epoxy resin to prepare a new boron nitride whisker/epoxy (BNw/EP) composite dielectric, and its microstructure, thermal expansion coefficient, thermal conductivity, electrical properties, thermal stability, and mechanical properties were tested and analyzed. The results show that within the temperature range of 20-100℃, the thermal expansion coefficient of the composite dielectric with 10% mass fraction of boron nitride whisker is reduced by 15% compared to pure epoxy resin, while the thermal conductivity increases to 0.28 W/(m·K), which is 33.33% higher than that of pure epoxy resin. In addition, its dielectric constant is below 5.28 and the dielectric loss is below 0.02 in the frequency range of 10²-10⁶ Hz, the volume resistivity is 10¹⁴ Ω·cm, and the tensile strength is maintained at about 49.5 MPa. This study proves that on the basis of ensuring the insulation, dielectric and mechanical properties of the composite dielectric be not damaged, filling the epoxy resin matrix with boron nitride whiskers can effectively reduce the thermal expansion coefficient of the material and improve the thermal conductivity.

With the rapid development in the field of microelectronics and microelectronics processing technology, manufacturing microelectronic devices using inkjet printing technology has become a popular direction in additive manufacturing. In this paper, an UV-curable vinyl-terminated polyarylether prepolymer was prepared by nucleophilic substitution reaction with twisted non-coplanar phthalazinone and hexafluoroisopropyl as structural units. A new low dielectric ink system for 3D printing was constructed by using diacrylate reactive diluents and free radical fast initiators into the prepolymer. The results show that the viscosity of the ink system before curing is lower than 300 mPa·s,indicating good processability. After UV and thermal curing, the infrared testing shows that the curing degree can reach over 87%, and the curing is basically complete. The minimum volume shrinkage is only 2.4%, which indicate the ink has excellent dimensional stability. The glass transition temperature of the material can reach up to 210℃, and the thermal decomposition temperature can reach up to 370℃, which indicate the ink has the potential of long-term use at 150℃. At 10 GHz, the dielectric constant of the material can reach 2.61, and the dielectric loss factor is only 0.014, which indicate the ink has excellent dielectric properties. The ink system prepared in this study is applicable to the additive manufacturing process of large curvature conformal circuit and has good application prospect in the field of microelectronics.

In order to investigate the effect of continuous changes in high and low temperatures on the epoxy composite insulation of cable terminals, micron Al₂O₃/epoxy composite insulation samples were prepared in this paper, and thermal-cooling cycling experiments were conducted on the samples. The changes in dielectric properties and degradation mechanism of epoxy composite insulation samples under different number of thermal-cooling cycling were analyzed through the AC breakdown, isothermal surface potential attenuation, and dielectric properties tests. The results show that during the process of thermal-cooling cycling, the cross-linked network of epoxy composite insulation deteriorates gradually under the combined action of high temperature thermal ageing and high and low temperature alternating stresses, the filler gradually separates from the matrix, microcracks and holes appear in the sample, the free volume increases, and the dielectric constant and electric strength continue to decrease. After 750 hours of thermal-cooling cycling, the AC electric strength of the sample decreases by 15.2%, the deep trap density decreases by 41%, the shallow trap density shows a fluctuating trend, and the dielectric loss factor (tanδ) firstly decreases and then slightly increases.

In order to explore the reasons for the differences in the properties of polyethylene cable materials at home and abroad, the molecular weight distribution, long branch chain content and short branch chain content of the materials were measured by gel permeation chromatography (GPC), rotational rheological test, and self-nucleation annealing thermal classification (SSA), and the relationship between the molecular chain structure of one domestic and two imported 500 kV cross-linked polyethylene cable materials and their dielectric properties were discussed. The results show that the order of long-chain chain content in polyethylene from small to large is: domestic sample, imported B sample, imported A sample. The order of short chain content from small to large is: imported sample B, imported sample A, domestic sample. Among them, the imported sample A has higher content of long-chain chains, which is conducive to the formation of ordered molecular arrangement and crystallization, and further improve its withstand voltage level. Excessive short chain content in domestic samples can hinder the molecular crystallization, resulting in lower breakdown strength. In addition, the differences in the molecular chain structure of the three types of polyethylene have little effect on their dielectric constant, dielectric loss factor, and resistivity.

In this paper, the general rules and characteristics of the failure damage of basin insulators in recent years were firstly summarized. Then, the typical failure area of sample was extracted to analyze the matrix microstructure morphology and the failure fracture surface morphology. Finally, the micro mechanical properties of the heterogeneous interface in composite materials were characterized and analyzed by nanoindentation mechanics technology, and the crack initiation and failure fracture mechanism of Al₂O₃/epoxy resin composite materials were expounded. The results show that the fracture toughness value of the epoxy resin matrix is about 0.55 MPa·m^1/2, and the cracks originate from the epoxy resin matrix under the action of load and continuously expand. When encountering high-strength Al₂O₃ particles, the cracks deflect due to the retardation and rapidly expand along the interface between the particles and matrix.