Epoxy resin has been widely used in the field of insulating materials due to its excellent mechanical properties, thermal stability, chemical stability, and electrical insulation. The stable three-dimensional cross-linked network structure not only gives epoxy resin excellent properties, but also brings great difficulties to its reprocessing, degradation, and recycling. At this stage, more and more researches have begun to focus on the environmentally friendly epoxy resin materials to solve problems such as reprocessing and degradation. In this paper, several typical design ideas and methods of epoxy resin based on dynamic covalent bonds were reviewed, and the environmentally friendly epoxy resin materials through introducting ester bonds, disulfide bonds, silicon-oxygen bonds, imine bonds, D-A structure, acetal bonds, host-guest interaction, and multiple dynamic bonds into the epoxy resin were introduced emphatically. Meanwhile, it is introduced that the topology structure of epoxy resin cross-linked network can be reversibly changed by dynamic covalent bonds under certain stimuli to realize the function of remodeling, reprocessing, self-repairing, and degradation. Finally, the application prospects of insulating materials based on dynamic covalent bonds were summarized and prospected.

The frequent disconnection of inverter power devices and load characteristics of motor can lead to high-frequency pulse overvoltage, which would lead to premature failure of generator insulation and bring challenges to the stability and reliability of system. From the failure mechanism of inverter motor insulation, the different stress failure forms of inverter motor insulation were investigated firstly, and the main factors affecting the failure of the insulation system were sorted out. Then the state detection methods of inverter motor insulation and the delay measures were comprehensively reviewed. Finally, the major challenges and future research direction currently faced by inverter motor insulation were emphasized.

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.

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.

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 application of conventional polyimide in the insulation structure of rail transit traction motors is prone to corona breakdown failure, which seriously affects the reliability and safety of the motor's long-term operation. In this paper, three corona-resistant polyimide materials were prepared by using 4,4′-diaminodiphenyl ether (ODA) as the diamine, pyromellitic dianhydride (PMDA) as the dianhydride, and nano-alumina surface treated with different silane coupling agents as the inorganic filler. The impact of various coupling agents on their surface morphology, mechanical properties, corona-resistant lifetime, and electrical breakdown performance were investigated. The results show that the surface treatment with silane coupling agents can improve the dispersibility of alumina in the polyimide matrix, reduce the agglomeration of nano-alumina, and enhance the corona-resistant properties of the polyimide material, while its excellent mechanical properties are maintained. Among them, the dispersion stability of nano-alumina surface treated with bis-amino silane coupling agent is the best, and the prepared corona-resistant polyimide material also has the best surface morphology and comprehensive performance. The corona-resistant time is 25 min and 120 min, respectively under 3 kV and 2 kV, the tensile strength reaches 167 MPa, and the elongation at break is 29.5%.

In order to solve the problem of printing contamination on the surface of silicone rubber cables, the application of low temperature plasma jet in surface treatment of silicone rubber was proposed in this paper. Ar plasma jet was generated with needle-ring structure electrode driven by AC power source, and the surface of silicone rubber cables was dynamically treated at different moving speeds. The influence of processing speed on the hydrophobicity, surface voltage, and breakdown strength of silicone rubber cable was systematically studied. The changes in surface physical morphology and chemical composition of silicone rubber were detected by SEM and EDS. The results show that static jet treatment can cause an increase of the material surface temperature, while dynamic treatment can significantly reduce the temperature rise. The water contact angle and flashover voltage of silicone rubber slightly decrease after treatment. With the increase of processing speeds, the hydrophobic and electrical insulation performance gradually recover. Under the speed of 5 mm/s, the anti-ink adhesion of silicone rubber surface is significantly improved. It can be concluded that the degree of cross-linking polymerization on the surface of silicone rubber increases after the plasma jet treatment, and the diffusion movement of interface molecules at the interface is hindered, which decrease the anti-ink adhesion of the silicone rubber surface.

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%.

Post insulator is an important supporting component in gas insulated metal enclosed switchgear (GIS), its insulating properties affects the reliability and stability of GIS. Taking the post insulator for engineering GIS as research object, we selected the surface tangential electric field strength of the insulator as the insulating properties index, and analyzed the influence of the umbrella skirts number, starting position, root radius, top radius parameters of the insulator as well as the shrinkage umbrella skirt structure on the insulating properties. The results show that the tangential electric field of insulator shows wave peaks and troughs oscillation distribution by increasing the umbrella skirt number, which is conducive to hinder the development of insulator surface discharge. The maximum tangential electric field strength increases with the increase of umbrella skirts number, and decreases with the increase of the distance between the starting position of umbrella skirt and the high-voltage electrode. The location of the maximum tangential electric field value shifts with the radius at the base of umbrella skirt. Compared with the original structure, the maximum tangential electric field strength along the surface of optimized structure decreases from 12.66 kV/mm to 9.69 kV/mm, and the decrease rate is 23.5%. It is found that the insulation margin is more than 1.3 times through the negative lightning impulse voltage test and margin test.

Taking the DC submarine cable in ±525 kV DC transmission project as the research object, we conducted DC voltage withstand test, impact voltage withstand test, and gradient voltage withstand test. The breakdown strength, ageing life index, Bahder's coefficient and other key parameters of the insulation material were analyzed. The insulation thickness of the ±525 kV DC cable under different voltage withstand condition was designed and calculated. The insulation design thickness was calibrated on the basis of the electric field distribution and temperature distribution of DC cable. The results show that the distortion degree of electric field distribution in DC cables is mainly determined by the temperature difference of insulation layer, and the insulation temperature difference is mainly determined by the magnitude of current passing through the cable conductor. Taking into account the research results and the long-term safety and reliability of cable, it is recommended that the insulation thickness of ±525 kV DC cables is designed to be 28 mm.

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.

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.

To solve the problem that frequency domain reflectometry (FDR) can only distinguish defect polarity and cannot identify the defect length and type, a defect type discrimination method was proposed on the basis of signal attenuation intensity evaluation in this paper. The difference between the total refracted reflection intensity at each defect and the initial reflection intensity was calculated, and then the defect length and type can be discriminated by comparing the magnitude of difference. Combined with the polarity judgment method, the defect can be subdivided into four types. The results show that the method proposed in this paper can successfully identify the length and type of four common defects in cables, including grounding faults, excessive bending, cable body moisture, and long intermediate joints of cables, and the recognition results are consistent with the simulation modeling results. The defect type discrimination method in this paper can identify the common point defects and segment defects in cables.

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.