Using styrene-butadiene-styrene (SBS) as the resin matrix and SiO₂ as the filler, SiO₂/hydrocarbon high frequency hydrocarbon copper clad laminate with low dielectric loss were prepared by hot-pressing method using a double-roll open mill and a flat vulcanizing machine. The resin film forming method and the influence of different contents and morphologies of SiO₂ under the open mill film on the dielectric performance, peel strength, thermal conductivity, tensile performance, and water absorption rate of high frequency hydrocarbon copper clad laminate were explored. The results show that compared with the traditional solvent-based resin film method, the solvent-free film production using an open mill has obvious advantages in the molding of composite resins and material properties. With the increase of SiO₂ content, the dielectric constant and dielectric loss of the high frequency hydrocarbon copper clad laminate increase, while the peel strength and water absorption rate decrease. Under the same particle size and filling content of SiO₂, the dielectric constant, dielectric loss factor, and water absorption rate of spherical SiO₂/hydrocarbon high frequency hydrocarbon copper clad laminate are lower than those of angular SiO₂/hydrocarbon high frequency hydrocarbon copper clad laminate. When the mass fraction of spherical SiO₂ is 75%, the comprehensive performance of the carbon-hydrogen high-frequency board is relatively superior, with a dielectric constant lower than 3.3, a dielectric loss factor of 0.002 2, and a water absorption rate lower than 0.040%.

In order to suppress surface charge accumulation on the insulation in HVDC wall bushings and improve their flashover performance, the epoxy resins used for the supporting insulator and the tube body were surface fluorinated under the same conditions using a fluorine/nitrogen mixture. The results show that fluorine atoms are introduced into the surface layers of two types of epoxy resins by the substitution for hydrogen atoms and the addition to carbon-carbon double bonds, forming C-F bonds. The fluorination is accompanied by chain breaking, which mainly occurs at the crosslinking sites. Due to the difference in epoxy value, two types of epoxy resins show different crosslinking densities. SEM imaging shows that they have different thicknesses of the fluorinated layer and surface morphologies. Surface potential decay and surface conductivity measurements reveal that the fluorination increases surface conductivity of two types of epoxy resins and inhibits their surface charge accumulation to different degrees. Flashover tests show that their DC flashover voltages are significantly increased by the fluorination to almost the same degree.

To investigate the thermal ageing mechanism of dry air core reactor encapsulated insulating materials at the molecular level, this study conducted 336-hour accelerated thermal ageing tests on epoxy/glass fiber composites at 180℃. The evolutionary characteristics of functional groups, molecular chain segment motions, activation energies, and AC electric strength of the epoxy/glass fiber composites after ageing were characterized by infrared spectroscopy, dielectric spectroscopy, and AC electric strength test. The effect of the decrease in activation energy caused by the changes in chemical structure and the evolution of molecular chain segment movement properties during ageing on the AC electric strength was investigated. The results show that a lot of carbonyl groups and small molecular chains dominated by ester and ketone groups generate during the ageing process. These small molecule chains and polar groups greatly increase the free volume and the number of free electrons inside the epoxy matrix, so that the chain segment movement is gradually enhanced and the activation energy is reduced, which ultimately leads to a significant reduction in insulation capacity.

In this paper, different types of polyurethane potting materials were developed successfully by taking propylene epoxide-tetrahydrofuran polyether or polytetrahydrofurane glycol as polymer polyols, toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and 3,3′-dimethyl-4,4′-biphenyl diisocyanate (TODI) as curing agents, and adding an appropriate amount of silica aerogel. The mechanical property, proccessability, low temperature resisitance, high temperature resistance, resistance to high and low temperature shock, and insulting property of the polyurethane potting materials were analyzed systematically. The results show that the polyurethane potting material formulated with propylene oxide-tetrahydrofuran copolymer and TODI as primary components, supplemented with silica aerogel with the mass fraction of 0.5%, exhibits outstanding processability, mechanical strength, and electrical insulation. It also demonstrates exceptional tolerance to extreme temperature fluctuations. This material achieves a glass transition temperature as low as -69.3°C and maintains a compression cold resistance coefficient of 0.54 at -60°C. Its 5% weight loss temperature reaches 302.3°C. After enduring 20 cycles of thermal shock between -65°C and 125°C, the material retains 93.5% of its tensile strength with a dimensional change rate of merely -0.6%, while preserving excellent insulation properties: volume resistivity of 4.2×10¹² Ω·cm and dielectric strength of 25 kV/mm.

Thick-film heating has become a key thermal-management solution for new-energy vehicles. To meet the relevant application demands, it is necessary to develop dielectric slurries for aluminum-based thick-film heating elements. This study utilized the built-in machine learning model of the Inorganic Glass Engineer System for property prediction to assist in the development of dielectric insulating glass formulations for aluminum-based thick-film heating elements, and conducted experimental verification. The results show that the insulating glass prepared by the optimal formula can be sintered at 580℃, with a thermal expansion coefficient of 18.8×10^-⁶℃^-1. When the dielectric-layer thickness exceeds 110 μm, it has a breakdown voltage over 1.29 kV and a leakage current less than 0.21 mA, which can meet the usage requirements of the medium layer of aluminum-based thick-film heating elements.

Mastering the distribution pattern of surface charges during DC pre-flashover is essential for clarifying the intrinsic mechanism of charge-induced flashover. This paper investigated the surface charge distribution characteristics of epoxy resin at DC pre-flashover moment and their influences on flashover voltage magnitude based on a plate-type insulation structure. Under two testing conditions—with and without pre-deposited charges on specimen surfaces—the dynamic distribution of surface charges was captured during the process of applied voltage escalation leading to flashover. By introducing SiC-epoxy composite coatings to modify specimen surface states, the dominant charge accumulation patterns during flashover triggering and the charge accumulation modes preceding flashover occurrence were comparatively analyzed. The results show that homopolar charge accumulation predominates on specimen surfaces during voltage escalation toward flashover. The charge accumulation mode exhibites a transition phenomenon shifting from the micro-charge zone to the charge surge zone during flashover triggering. Immediately before flashover, homopolar charges nearly coveres the entire specimen surface, while the pre-deposited charges primarily influence the flashover voltage magnitude by altering the homopolar charge accumulation quantity at the pre-flashover moment.

The compatibility of cable termination structural materials with insulating fluids has an important impact on the safe and stable operation of cables. In this paper, the compatibility of cable termination materials with polyisobutylene is studied by analyzing the changes in morphology, swelling and mechanical properties of silicone rubber, ethylene-propylene insulating self-adhesive tape, and halogenated butyl + ethylene-propylene waterproof insulating tape before and after the compatibility test, as well as the changes in the physicochemical and dielectric properties of polyisobutylene before and after the compatibility test, and combined with the attenuated total reflectance Fourier transform infrared spectroscopy and thermogravimetric analysis with other means. The results show that the compatibility of the stress cone material silicone rubber with polyisobutylene is good, the compatibilities of ethylene-propylene insulating self-adhesive tape and halogenated butyl + ethylene-propylene waterproof insulating tape with polyisobutylene are not good, and the physicochemical and dielectric properties of the polyisobutylene impregnated insulating tape are also degraded after compatibility test.

To develop polyimide (PI)-based composite films with low dielectric constant (D_k), low dielectric loss (D_f), and high temperature resistance at high frequency, a water-soluble polyamic salt (PAAS) was prepared by adding organic base into the polyamic acid, which is the precursor of fluoropolyimide (FPI), and composite films were prepared by compounding low dielectric polytetrafluoroethylene (PTFE) concentrated dispersion with the dried PAAS to form a water dispersion system. The effects of PTFE content on the dielectric, thermal, and mechanical properties of the composite films were studied. The experimental results show that with the increase of PTFE content, the dielectric constant of the composite films decreases continuously, but there will be some effects on the thermal stability and mechanical properties. The dielectric constant of 50%PTFE/FPI reaches the minimum value (D_k=1.5@8.5 GHz), and the dielectric loss of 10%PTFE/FPI in the frequency band of 9.25-10.25 GHz is less than 0.005. The glass transition temperature of the composite films is in the range of 289-297℃, and the thermal decomposition temperature at 5% is higher than 508℃. The thermal expansion coefficient of 40%PTFE/FPI is as low as 59.67×10^-6 K^-1. The tensile strength of 20%PTFE/FPI is 70 MPa, the tensile modulus is 1.59 GPa, and the elongation at break is 7.7%.

Bushing is an important component of oil-immersed transformers, and its internal insulation moisture, ageing, and development of some defects after long-term operation will cause distortion of local electric field, which seriously threatens the safe operation of bushing. In this paper, the variation patterns of dielectric parameters of the aged and damped oil-immersed paper under different test temperature environment were obtained, and a dynamic dielectric parameter calculation model was established. Meanwhile, a simulation model was established on the basis of actual structure of a 252 kV/1 250 A bushing. Electro-magnetic-thermal coupling multiphysics were used to conduct simulation analysis, and the transient electric field distribution and distortion severity inside the bushing under three typical defect conditions were obtained. The results indicate that when the end screen of bushing is unreliable grounding (resulting in floating potential), electric field distortion occurs at the contact side of bushing and end screen, and the voltage grading effectiveness of capacitive core is weakened. When there is wrinkle on the capacitance screen of bushing, the maximum electric field intensity at the wrinkle regions increases proportionally with the bending curvature. Notably, the field strength inversion phenomena are observed at the distortion zones when the capacitance screen reach specific bending curvature. The bubbles attached on the end screen surface have greater influence on the electric field distribution than bubbles dispersed in transformer oil. Such surface-attached bubbles are prone to produce partial discharge.

Photosensitive polyimide (PSPI) has a unique role in semiconductor packaging, among them, ester-type PSPIs containing acrylic acid derivatives are widely used in industry. Generally, the PSPIs are synthesized by the well-established chloride method, but chloride ions are introduced during the synthesis process, which negatively affects the reaction apparatus, resin purification, and the environment. For the development of green and reliable synthesis methods, we explored the reaction process for the preparation of hydroxyethyl methacrylate PSPI by polyisoimide using 4,4′-diaminodiphenyl ether (ODA) and 4,4′-biphenyl ether dianhydride (ODPA) as the polymerized monomers. The effect of solid content, solvent, and reaction temperature on the gel formation during the synthesis process of PSPI was discussed. The photolithographic and thermo-mechanical properties of PSPI prepared by the polyisoimide method were investigated. The results demonstrate that the PSPI prepared by this method has good photolithographic patterning ability (for a film with thickness of 4.5 μm, circular holes can be opened at a diameter of 15 μm, and the film retention rate is ≥90%) and excellent thermal properties and mechanical properties (T_d5%=471℃, T_g=297℃, and tensile strength is 127.5 MPa). There are no Cl-ions introduction during synthsis process, and the process is green and friendly, and simplified with a short reaction cycle. The method was extended to the preparation of other four PSPI systems, and the isomerization method is found to be universal, and this efficient and green synthesis method provides theoretical guidance for the preparation of high-performance PSPI photoresists in laboratories and enterprises.