The aramid fiber (AF) reinforced composite has a wide application prospect in the field of electrical insulation, but the product performance is restricted by the poor adhesion between AF and resin matrix. In order to improve their interfacial performance, the plasma etching method and plasma grafting method were used to modify the AF surface. The influence of two methods on the interfacial properties of aramid fibers and AF/epoxy composites, as well as the mechanical properties of the AF/epoxy composites NOL ring were studied. The results show that both two methods improve the shear strength of the AF/epoxy interface. The plasma etching method reduces the tensile strength of the NOL rings, while the plasma grafting method increases the tensile strength of the NOL rings. Compared with the unmodified AF, the shear strength of the AF/epoxy interface which treated with 90 W air dielectric barrier discharge plasma followed by 1% 2,4-toluene diisocyanate increases from 31.7 MPa to 36.4 MPa, the tensile strength increases from 23.6 kN to 25.1 kN, and the correction coefficient K value of tensile strength increases from 62.8% to 72.1%, indicating that the mechanical properties of aramid fiber are made full use.

Silicone rubber composite insulators would produce powders on their surface after long-term operation in high humidity environment. In order to study the effect of water ingress into on-site aged silicone rubber on its properties, we used the composite insulator sheds which have operated over ten years in the southern coastal areas as research object. Deionized water immersion tests were conducted on the silicone rubber samples which have been removed their chalking layers to study the effect of water ingress into samples on their mass and physicochemical properties, and the influence of water ingress on the secondary chalking phenomenon of the silicone rubber was discussed. The results show that the silicone rubber samples which have removed their chalking layers could generate new chalking layers after deionized water immersion, whose microstructures and physicochemical properties were close to the naturally formed chalking layers. It is determined that water is the main influence factor which aged silicone rubbers produce powders on their surface again by changing the water temperature of tests, and high temperature can accelerate the generation of chalking layers.

The cable joint interface is easy to discharge along the surface, which would lead to insulation failure, making it become the weakest link in the power cable system. In this paper, the effects of different interface roughness, pressure, and temperature on the AC breakdown voltage of the silicone rubber/polyethylene double-layer dielectric interface were investigated, and the interface discharge channels after breakdown were analyzed. The results show that the interface breakdown voltage at room temperature is related to the interface roughness. The higher the interface smooth degree, the higher the interface breakdown voltage, and the smaller the interface carbonization area. The bigger the interface pressure, the higher the interface breakdown voltage, while the interface carbonization area increases at first and then decreases. With the increase of temperature, the interface breakdown voltage decreases, but the breakdown voltage at higher temperature does not decrease significantly. In addition, the interface carbonization area increases at first and then decreases with the increase of temperature, and the change of interface contact state at different temperatures is one of the main reasons affecting its properties. The interface state of cable accessories has a significant impact on their interface breakdown characteristics, which should be paid attention to during cable operation and maintenance.

Epoxy composite insulating materials doped with 0%, 1%, and 10% of modified nano Al₂O₃ were prepared and conducted thermal ageing tests at 150℃, and their thermal ageing characteristics and mechanism were studied through dynamic thermal mechanical testing, scanning electron microscopy testing, and linear thermal expansion testing. The results show that an inhomogeneous ageing structure is formed in epoxy composite insulating material during thermal ageing, and the thickness of surface ageing layer is related to the content of nano Al₂O₃. When the doping mass fraction of nano Al₂O₃ is 1%, the thickness of surface ageing layer is the smallest, and the nanoparticles are well dispersed and closely embedded in the epoxy matrix. According to the free volume theory of glass transition, it is found that the free volume fraction of sample is the smallest when the doping mass fraction is 1%, the corresponding α main relaxation time of the epoxy matrix is the longest, and the molecular chain activity is the lowest. Adding an appropriate amount of modified nano Al₂O₃ into the epoxy resin can improve the cross-linking degree of molecular chain and reduce the free volume of system. Thereby the diffusion of oxygen in the material is weakened, and finally the inhomogeneous thermal ageing degree of the epoxy composite insulating material is reduced.

In the long-term operation process, due to the ageing of transformer oil for offshore wind power, the moisture and other impurities will be produced, which may cause transformer insulation failure, resulting in economic losses and safety accidents. Thus, it is urgent to propose an effective method of transformer oil filteration and judgment to improve the transformer oil performance and evaluate its ageing status. In this paper, the oil filter film was conducted superhydrophobic modification, and the effects of the number of oil filtration, the type of film, and the superhydrophobic modification on the properties of oil before and after filtration were investigated. The health classification model of transformer oil was established by support vector machine algorithm. In addition, a new method based on machine learning was proposed to evaluate the oil filtering effect of superhydrophobic film. The results show that the oil filtering performance of the film after superhydrophobic treatment is improved greatly. Especially after three times of modified organic film filtration, the comprehensive performance of transformer oil has significantly improved, meeting the applicable standard of transformer oil. Compared with several algorithms, the model built by support vector algorithm has the highest accuracy of 84.8%.

In order to obtain the temperature rise characteristics of a new environmentally friendly gas HFO-1336mzz(E) applied in gas insulated transmission line (GIL), a multi-physics coupled model of magnetic-heat-fluid field was established based on the finite element method. The internal temperature distribution of GIL under rated operating conditions was simulated and analyzed, and the effects of the type of buffer gas, filling gas pressure, mixing ratio, and operating current on the temperature rise of GIL were studied. The results show that the temperature field inside the GIL shows a temperature gradient distribution of upper high and lower low under rated working conditions. The temperature rise of the A-phase conductor is only 0.70℃ greater than that of the B-phase conductor, and the temperature rise of grounded enclosure is the smallest. Under the same conditions, the temperature rise of conductor in HFO-1336mzz(E)/CO₂ mixture is only 0.38℃ lower than that in HFO-1336mzz(E)/N₂ mixture. Considering the impact of solid deposition from the decomposition of HFO-1336mzz(E), CO₂ is more suitable as a buffer gas than N₂. Increasing the filling gas pressure and mixing ratio can reduce the temperature rise of conductor, and the temperature rise of conductor in 10%HFO-1336mzz(E)/90%CO₂ mixture at 0.70 MPa is only 5.02℃ higher than that in pure SF₆ at 0.50 MPa. The temperature rise of GIL conductor and grounded enclosure increases with the operating current, and the effect of filling gas pressure on the current-carrying capacity of GIL is greater than the mixing ratio. When the operating current exceeds 3.0 kA, the temperature rise of GIL would exceed the temperature rise limit.

The difference of laying methods in different sections of marine transmission line has a great impact on the ampacity of submarine cable, so it is of great significance to study the ampacity under typical laying methods in transmission section. In this paper, an electric-heat-current coupling model of submarine cable in landing section and submarine section of submarine cable line in ±160 kV DC transmission project was established. On the basis of finite element method, the influence of air domain size, position of angle steel support, seawater and soil factor on the steady ampacity of submarine cable were studied under four typical laying methods, which is the submarine cable laid at the bottom of cable trench and laid on the angle steel support in landing section and the submarine cable laid and directly buried in submarine section. The results show that the submarine cable laid at the bottom of cable trench is greatly affected by the air domain size, and increasing the convection area can effectively improve the steady ampacity of submarine cable. The semi-closed area between the support and the inner wall of trench should be taken into account in calculating the ampacity of cable laid on the angle steel support. The temperature of submarine cable laid at the shallow depth of support is lower and its ampacity is larger. In the submarine section, the submarine cable temperature changes in the same direction with the rise and fall of sea water temperature, which is opposite to the increase and decrease trend of sea water velocity. The increase of soil temperature results in the decrease of buried submarine cable ampacity. The landing section is the bottleneck section of ampacity calculation, and the ampacity can be improved effectively by using the water filling cable trench when the submarine cable is laid at the bottom of cable trench. When the submarine cable is laid on the support, the ampacity can meet the engineering requirements by installing cooling water pipe.

Epoxy impregnated paper is one of the main insulation materials of valve-side bushing, and its performance is affected by curing process. In order to explore the effect of curing temperature on the electrical properties of epoxy impregnated paper, we prepared epoxy impregnated papers at 120℃, 130℃, 140℃ and 145℃ of post-curing temperature, respectively, and their glass transition temperature, dielectric properties, and DC breakdown strength were tested. The results show that with the increase of post-curing temperature, the glass transition temperature increases, the DC breakdown strength increases at first and then decreases, and the dielectric loss factor decreases at first and then increases. The analysis shows that the addition of hydroxyl-rich wrinkle paper will increase the curing rate in interface area of epoxy impregnated paper, leading to the frequency of interface relaxation peak decrease at first and increase, which affects the insulation properties of epoxy impregnated paper.

The power frequency breakdown voltages of a new eco-friendly insulation CF₃SO₂F/N₂ and CF₃SO₂F/CO₂ mixtures were measured under sphere-sphere and needle-plate electrodes. The effects of pressure, electrode spacing, and electric field non-uniformity on the power frequency breakdown characteristics of the CF₃SO₂F mixtures were analyzed and compared with SF₆. The results show that under slightly non-uniform electric field, the power frequency breakdown voltage of CF₃SO₂F mixtures is linearly related to pressure, and the breakdown voltage show weak saturation trend with the increase of electrode spacing. Under extremely non-uniform electric field, the power frequency breakdown voltages of CF₃SO₂Fmixtures exhibits "hump" curves of "rising-falling-rising" as the pressure increases, and the corresponding pressure of "hump" peak is between 0.2 MPa and 0.35 MPa. The overall power frequency breakdown strength of the CF₃SO₂F/N₂ mixture is greater than that of the CF₃SO₂F/CO₂ mixture. At 0.3 MPa and above, CF₃SO₂F/N₂ mixtures can maintain a highly insulation level relative to SF₆ under extremely non-uniform electric fields, which has good application potential.

The performance of insulating paper determines the reliability and life of power transformers. In order to ensure the safe and reliable operation of transformers, we combined with domestic and foreign literature and related research results, described the current research status of physical modification technology to improve the performance of insulating paper from the nanoparticle modification and thermal stabilizer modification, analyzed the advantages and disadvantages of the two modification methods, and explored the economic and feasible modification method of cellulose insulating paper for power transformers to essentially improve the reliability of transformer operation.