In order to reveal the influence of external electric field on the internal molecular structure characteristics of silicone rubber insulation materials at the micro level, this paper used molecular simulation and quantum chemistry methods to explore the changes in the microstructure and space charge characteristics of silicone rubber under the action of external electric field. The results show that with the increase of electric field strength, the total energy of the silicone rubber molecule system decreases, the dipole moment and polarizability increase, and the C-Si bond inside the molecule becomes longer when subjected to the stretching effect of external electric field, resulting in a decrease of the stability of silicone rubber structure and affecting its mechanical and electrical properties. Under a higher electric field strength , the energy gap of the frontier orbitals decreases, and the reactive active sites of the silicone rubber molecular chain change, it causes of trap energy levels for the electron traps and hole traps in the frontier orbitals of the molecular chain to form different degrees of trap energy level distribution, and enhances the ability of silicone rubber to capture free electrons or injected charges in insulating materials. When the electric field reaches the critical value of 12.75×10³ kV/mm, the molecular structure of silicone rubber is disrupted and causes changes in the infrared spectrum.

Interfacial discharge between XLPE and SIR in cable joints is one of the main causes of cable failure. In order to improve this phenomenon, the XLPE sample surface was treated by plasma silicon deposition with different time, and the micro-morphology and interface discharge tests were carried out. The results show that the plasma silicon deposition technology can effectively improve the voltage resistance of XLPE/SIR interface. With the increase of plasma silicon deposition treatment time, the surface roughness of XLPE sample decreases at first and then increases, and its change trend is the same as that of the initial discharge voltage, breakdown voltage, and voltage increase amplitude of XLPE/SIR interface, and is opposite to that of the surface resistivity. The XLPE sample after 3 min of plasma silicon deposition has the smallest surface roughness (R _a=41.8nm) and the largest surface resistivity (857×10¹² Ω). Under this treatment time, the XLPE/SIR interface has the largest actual contact area, the fewest micro-pores, and the largest increase in breakdown voltage. Among them, the breakdown voltage increases by 66.7% compared with the untreated XLPE/SIR interface.

The ternary copolymer of polyvinylidene fluoride, poly (vinylidene fluoride trifluoroethylene chlorofluoro-ethylene) (P(VDF-TrFE-CFE), abbreviated as PVTC) is expected to be used as a new type of capacitor film material due to its high relative dielectric constant. In this paper, the crystal phase structure of PVTC was regulated by optimizing the hot pressing process of thin film preparation, and the influence of different hot pressing temperatures on the crystal phase structure of PVTC thin films was discussed. Then, PVTC composite films doped with low content voltage stabilizer aromatic ketone small molecule 4-acryloxy-2-hydroxyphenylketone (ALRB) were prepared by solution casting method, and the influence law and mechanism of ALRB doping content on the electrical properties of the composite films were studied systematically. The results show that when the hot pressing temperature is 180℃, a multiphase structure coexisting with α phase, β phase, and γ phase is formed inside the PVTC film, which has significant improvement effect on its dielectric properties and energy storage properties. Appropriate amount of voltage stabilizer ALRB can dissipate high-energy electron energy and improve the insulation performance of PVTC films. When the mass fraction of ALRB is 0.5%, the electric strength of PVTC/ALRB composite film reaches 485.7 kV/mm, and the discharge energy density and charge discharge efficiency are 12.12 J/cm³ and 64.4%, respectively.

Polymer-based nanocomposites have received much attention for their application prospects in the development of capacitors with high energy storage density. In this paper, ultra-thin barium niobate (Ba₅Nb₄O₁₅, BNO) nanosheets were prepared by hydrothermal method, and were used as fillers to prepare nanocomposite films by combing with polyvinylidene fluoride trifluorochloroethylene (PVDF-CTFE) and polymethyl methacrylate (PMMA). The effects of ultra-thin BNO nanosheets on the delectric properties and energy storage properties of polymer composite films were studied. The results show that the dielectric constant and electric strength of polymer nanocomposite films increase significantly with a low BNO addition content, and thus the energy density increases. When the mass fraction of BNO is 0.5%, the maximum energy density of the nanocomposite film reaches 13.96 J/cm³, which is 2.6 times higher than that of pure P(VDF-CTFE)/PMMA polymer, and the energy storage efficiency reaches 67.4%.

Converter transformer is the key equipment in high-voltage direct current (HVDC) transmission system, and its valve-side windings are subjected to complex composite voltage waveforms during operation. The existing researches primarily focus on partial discharge characteristics under single voltage form or AC-DC composite voltages. However, due to the influence of power electronic devices such as converter valves, converter transformers also endure pulsating voltages. In this paper, the impact of positive polarity DC pulsating voltage on partial discharge of oil-paper insulation under actual operating conditions was studied, and the partial discharge characteristics of two typical oil-paper insulation defects, needle tips discharge in oil and surface discharges on oil-paper boards, were obtained under DC pulsating voltage. The results show that the DC component only changes the frequency and amplitude of partial discharge, and has same effect on the two types of defects. As the amplitude of the pulsating component increases, the discharge pulses of the two types of defects increase gradually, forming pulse clusters and exhibiting significant polarity effects. The pulse clusters for needle tips discharge in oil are concentrated on the rising edge, while those for surface discharges on oil-paper boards are concentrated on the falling edge.

High temperature liquid nuclear magnetic resonance (¹³CNMR), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC) were used to study three kinds of polypropylene resins for DC capacitors at home and abroad with different temperature resistance grades, and analyze the effect of microstructure on electrical properties. The results show that the isotactic index, intermolecular chain defect distribution, and molecular weight characteristics jointly affect the crystallization characteristics of polypropylene, and thus affect the final high temperature dielectric properties of materials. The isotactic index of 5 units of imported polypropylene resin is greater than 97%, and the intermolecular chain stereodefect distribution is narrow (I=1.075), the weight average molecular weight is higher and the molecular weight distribution index is larger (PDI>5.6), showing excellent high temperature insulation properties (the electric strength α=533 kV/mm). While the molecular weight distribution of domestic polypropylene resin is narrow (PDI<5), the weight average molecular weight is lower, the isotactic index of 5 units is less than 97%, and the intermolecular chain stereodefect distribution is wider (I=1.106), which leads to its poor high temperature insulation performance and low electric strength (α=497 kV/mm).

The cable joint is the weakest link in the cable line, and the contact resistance between the conductor and the connecting pipe at the aluminum alloy conductor cable joint is the key factor affecting the temperature distribution and failure rate of the cable joint. In order to study the influence of different crimping processes on the temperature distribution characteristics of cable joints, a 35 kV aluminum alloy conductor was used as the research object, and the contact resistance between conductor samples with different crimping percentages and connecting tubes were measured through the contact resistance measurement circuit. The quantitative relationshipes between contact resistance and crimping percentage under two crimping processes of pit pressure and confining pressure were obtained. The electro-thermal coupling model of a cable joint with conductor cross-sectional area of 400 mm² was established by COMSOL finite element simulation software, and the corresponding relationship between contact resistance and temperature distribution characteristics of cable joint under different crimping processes was studied. The results show that the contact resistance increases with the increase of the crimping percentage. Under the premise of ensuring that the maximum temperature of the long-term operation of the cable does not exceed 90℃ and meeting the mechanical performance requirements, the crimping percentage under the pit pressing process should be controlled at 27.86%-35.44%, and the crimping percentage under the confining pressure process should be controlled at 16.01%-22.21%. The temperature rise curves of the two crimping processes have the same change trend. The highest temperature of the cable core appears at the position of the connecting pipe, and gradually decreases along the axial direction. The temperature of the outer surface of the joint shows a downward trend as a whole, but the temperature of the connecting pipe increases in a small range due to the existence of contact resistance.

In order to ensure the safe and stable operation of capacitor voltage transformer (CVT), improve its insulation reliability, the insulation state of CVT was evaluated based on improved criteria importance through intercriteria correlation (CRITIC) method. Firstly, the CVT was conducted the artificially accelerated thermal ageing, and its capacitance and dielectric loss factor, polarization and depolarization current, voltage and current were tested under different ageing cycles. The results show that after ageing, the total capacitance of CVT increases from 10.106 nF to 10.155 nF, the time constant of the third branch increases from 62.35 s to 82.80 s, the current and voltage phase difference increases from 96.3° to 97.8°, and only the primary side apparent impedance value decreases among the insulation characteristic parameters. Subsequently, the CRITIC method was improved by residual expectation coefficient and activation entropy, and the improved CRITIC method was used to weight and score the CVT insulation characteristic parameters. In the empowerment results, the weight of 0.1 Hz low frequency dielectric loss factor is the largest, which is 0.323 3, and the weight of C1 dielectric loss factor is the smallest, which is 0.091 2, and the improved CRITIC method solves the problem of information incompleteness. Finally, the insulation score of CVT was correlated with the operating time under actual working condition, and its insulation status was evaluated. When the insulation score is 0 points, the corresponding operating time under working condition is 29.88 years, which is consistent with the actual project. According to CVT insulation score, the internal insulation state can be judged.

Aiming at the problem that the energy storage characteristics of polypropylene (PP) capacitor films reduce greatly under high temperature and high electric field, the polypropylene was modified by melt grafting with maleic anhydride (MAH) at the molecular level, and the effects of grafting monomer content, initiator mass fraction, and reaction temperature on the high-temperature energy storage characteristics of the films were investigated. Then a maleic anhydride grafted polypropylene (PP-g-MAH) biaxially oriented capacitor film with superior high-temperature energy storage characteristics was prepared, and its structure and performances were characterized and tested. The results show that with the increase of monomer content, initiator mass fraction, and reaction temperature, the charge and discharge efficiency of the grafted sample increases at first and then decreases. The graft modification promotes the increase of crystal nuclei and the reduce of spherulite size in PP, which increases the trap depth and trap density of the film effectively, reduces the carrier mobility, and enhances the electric strength and energy storage characteristics at high temperature.

As a key device in ultra-high voltage and extra-high-voltage transmission projects, the deflagrate accidents of bushings seriously threaten the safe and stable operation of the power system. Adhesive impregnated paper bushing is an alternative to oil-impregnated paper bushings with deflagration risks, while there is relatively little research on the thermodynamic behavior of its core insulating material of epoxy resin impregnated paper during arc faults and the risk of bushing deflagration. In this paper, the thermogravimetric experiments and differential scanning calorimetry analysis at different heating rates were conducted on epoxy resin impregnated paper, and its thermal decomposition process was analyzed. Flynn-Wall-Ozawa (FWO) method and Coast-Redfern (CR) method were used to obtain the pyrolysis kinetic models of epoxy resin impregnated paper at high temperature in an oxygen-free environment. The results show that the thermal decomposition process of epoxy resin impregnated paper in adhesive impregnated paper bushing can be divided into three stages: epoxy melting, endothermic reactions, and decomposition gasification, and the first two stages conform to three-dimensional diffusion model, random nucleation and subsequent growth model, respectively. After an arc breakdown fault occurs in bushing cores, the thermal decomposition mass loss of epoxy resin impregnated paper is as high as 90% under the effect of high temperature. The high temperatures and gas expansion produce high amplitude internal stress inside the core, which leads to core cracking and even explosion.