In high-voltage insulated gate bipolar transistor (IGBT) devices, traditional Si-based semiconductor chips are gradually replaced by emerging wide-bandgap semiconductor chips. High-power-density wide-bandgap semiconductors lead to a sharp rise of operating temperature in power electronic modules. Silicone gel is used as an insulating material for the packaging of high-voltage IGBT devices, and its insulating performance faces the challenges of high temperature and thermal ageing. In order to study the effects of high temperature and thermal ageing on the thermal stability and insulating properties of silicone gel, we studied the effects of high temperature and long-term thermal stress on the dielectric properties, volume conductivity, and breakdown strength of silicone gel by high temperature experiments and thermal ageing experiments of silicone gel materials, and analyzed the high temperature characteristics and thermal ageing characteristics of the silicone gel. The results show that with the increase of temperature, the real part of complex permittivity and breakdown strength of silicone gel decreases, and the dielectric loss and DC conductivity increases. With the increase of thermal ageing time, the real part of complex permittivity of silicone gel increases, the dielectric loss decreases at first and then increases, the DC conductivity increases at first and then decreases, and the breakdown strength decreases.

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.

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 transformer fault diagnosis technique based on a single detection method is difficult to identify the same type of defects of oil-paper insulation in detail, which cannot meet the requirements of power system on equipment operation reliability under the background of rapid development of deep offshore wind power. Therefore, an oil-paper insulation defect identification method based on information fusion of phase-resolved partial discharge (PRPD) spectrum and dissolved gas analysis (DGA) data was proposed. Six kinds of electrode models were designed and made to simulate the typical defects of surface discharge in transformers with different electric field inhomogeneity coefficients, and PRPD and DGA data were collected. Then convolutional neural network (CNN) and back propagation neural network (BPNN) were adopted to recognize the patterns of PRPD spectrum and DGA feature vector of six kinds of defects, respectively. Finally, the CNN-BPNN information fusion model based on D-S evidence theory was proposed to realize joint diagnosis based on PRPD spectrum and DGA data. The results show that the CNN-BPNN model based on the D-S evidence theory can effectively correct the wrong output of the single criterion model and reduce the uncertainty of the classification results. When the input dimensions of PRPD spectrum are 8×8, 16×16, and 32×32, the recognition accuracy of the model integrated with the DGA feature vector is 93.21%, 97.53%, and 99.17%, respectively, which is 4.81%, 2.78%, and 0.84% higher than that of PRPD single criterion model. The CNN-BPNN model can effectively integrate the electrical physical information and chemical product information of partial discharge, which not only improves the accuracy of defect identification, but also enhances the confidence of the output results, and reduces the data storage requirements, providing accurate, reliable, and lightweight defect identification methods for intelligent operation and maintenance of transformers.

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 flexible low-frequency transmission system is superior in enhancing transmission capacity, reducing line charging reactive power, and improving voltage quality at the end of transmission channels, which can effectively meet the urgent demand for efficient aggregation and transmission of medium- and long-distance offshore wind power. In order to study the operating characteristics of submarine cables under low frequency condition, an electric-magnetic-thermal-flow coupled finite element simulation model of 220 kV cross-linked polyethylene was built considering the influence of external laying environment, and the steady-state ampacity and temperature field distribution of submarine cables operating at 50 Hz and 20 Hz in different laying sections were analyzed. The finite element simulation was verified by building a steady-state thermal path model of submarine cable on the basis of IEC 60287:1995 and previous simulation results of thermal field distributions in submarine cable under low frequency. The results show that under different laying environments of land section, sea section, and submarine section, the relative errors between the ampacity and temperature field distribution calculation results of simulation model and the analytical equation of IEC are within 3%, indicating that the temperature field simulation model of 220 kV cross-linked cable proposed in this paper has good accuracy and high efficiency. Meanwhile, it is found that the frequency reduction can reduce the AC resistance of cable conductor, improve the current distribution in the cable conductor, and reduce the operating loss of each part of cable, thereby the overall operating temperature of cable is reduced eventually and the cable transmission capacity is improved favorably.

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 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.

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%.

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.