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.

The characteristics and research methods of transformer interturn breakdown, detection and protection and characteristics of interturn fault were introduced in this paper, and the research direction of transformer interturn fault was prospected, which can provide reference for the academic research and operation and maintenance of transformer interturn fault.

In order to study the effect of mesoscale crystal morphology of XLPE material on its AC breakdown characteristics and analyze its mechanism, XLPE samples with different crystal morphologies were prepared by controlling the cooling rate of samples during cooling crystallization. At the same time, the crystalline structure and morphology of the samples were characterized and observed by scanning electron microscope (SEM) and X-ray diffraction (XRD), and its dielectric properties were tested by the broadband dielectric spectrometer, three electrode system, and AC breakdown system. Finally, the test results were verified and the mechanism was analyzed by means of simulation. The results show that decreasing the cooling rate can prolong the crystallization time, making the molecular chains regularly arrange and stack to form large-size spherulites with a relatively high crystal area and relatively perfect structure. The improvement of crystal structure makes the relative dielectric constant of the XLPE sample increase slightly, the conductivity decrease, and the breakdown strength and stability significantly improve. The simulation results are consistent with the test results. The perfect crystal morphology of the sample at mesoscale reduces the degree of electric field distortion between spherulites and inhibits the occurrence of partial discharge and breakdown.

A halogen-free flame retardant unsaturated polyester insulating impregnating resin was prepared by introducing DOPO into unsaturated polyester. The effect of adding flame retardant on the properties of the resin were analyzed by infrared spectroscopy, thermogravimetric analysis and flame retardancy experiment. The results show that the addition conversion rate of DOPO can be improved by using methyl tetrahydrophthalic anhydride (MTHPA) as the carrier to react with DOPO first and then with maleic anhydride (MA). The prepared resin is uniform, transparent after curing, and has good flame retardance, which can reach UL94 V0 level. With the increase of phosphorus content, the thermal stability of resin decreases, and the optimal phosphorus content is about 2.7%. When the molar ratio of unsaturated acid to saturated acid is 1∶1 to 1.5∶1 and using the compound initiation polymerization system, the resin has good reactivity and storage stability.

To investigate the possibility of using black shale as a filler in the plastic industry, the composition and morphology of black shale in Guilin area were studied. It was found that black shale has nano layered structure, and was mainly composed of silica, K-feldspar, and organic carbon. The black shale/HDPE composite were prepared by modifying black shale with different coupling agents and surfactants, and their mechanical properties, morphology, volume resistivity, and dielectric constant were studied. The results show that aluminate coupling agent and sodium dodecylbenzene sulfonate can improve the compatibility between shale and HDPE. When the shale filling amount is 50 phr, the tensile strength, impact strength, and volume resistivity of black shale/HDPE composite reduce. The tensile strength remains at 23.47 MPa, the maximum impact strength is 6.39 kJ/m², and the volume resistivity can also be maintained above 10¹⁴ Ω·cm, maintaining good mechanical properties and insulating properties.

In order to guide the selection of fluorocarbon resin film forming material cured at room temperature in the development of anti-pollution flashover coating, the structure and properties of fluorocarbon resin film forming materials were characterized by FT-IR, AFM, UV ageing, thermogravimetric analysis, contact angle test, volume resistivity and high-voltage capacitor bridge. The results show that the optimal mass fraction of curing agent for FEVE-based type I and type II fluorocarbon resins are 19% and 24%, respectively. Under the optimal curing agent content, the contact angle of FEVE-based type I and type II fluorocarbon resins are 91° and 104°, respectively. After UV ageing for 800 h, the appearance color, hydrophobicity, hardness, adhesion, thermal decomposition temperature, and molecular structure do not change. After 30 min of ultrasonic fog wetting, the AC wet lightning voltage of fluorocarbon resin is about 25 kV, indicating that the FEVE-based fluorocarbon resin has excellent electrical insulation properties and ageing resistance, and is a good base material for the development of antifouling flashover coatings.

A thermochromic microcapsule epoxy resin composite insulation material (TEP) was prepared, and its power frequency permittivity (ε_r), dielectric loss factor (tanδ), and DC conductivity (σ) were analyzed in this paper. The results show that the temperature characteristic of dielectric constant of composite insulation material has an infelction point at 70℃. When the temperature is lower than 70℃, εr increases rapidly with the increase of temperature. When the temperature is higher than 70℃, the change rate of εr with temperature decreases significantly. The tanδ decreases significantly when the temperature is 50-70℃. The addition of thermochromic microcapsules can effectively reduce the DC conductivity of composite insulation material. In the thermochromic temperature range of 50-70℃, the solid-liquid phase transition occurs inside thermochromic microcapsules, which is the main reason for the special temperature characteristics of ε_r and tanδ. In the solid-liquid phase transition process, the molecular activity of the core material in microcapsule increases gradually, and the resistance that it needs to overcome in the orientation polarization with the external electric field decreases, resulting in the rapidly increase of ε_r and the significant decrease of tanδ with the increase of temperature. When the core materials of microcapsule are fully transformed to liquid state, its molecular activity decreases with temperature, leading to the significant decrease of ε_r with temperature.

In order to study the effect of antioxidant types in transformer oil on the thermal ageing performance of insulating paper, antioxidants T501, T531, and DBP were added to the insulation system composed of naphthenic mineral oil and insulating paper, and the antioxidant mass fraction was 0.4%. The heat ageing test was carried out at 130℃ for 600 h. The moisture and furfural content in the insulating oil, the moisture content and polymerization degree in the insulating paper were determined every 120 h. At the same time, the aged insulating paper was characterized by FTIR, XRD, SEM, and EDS. The results show that the addition of antioxidant T501 and T531 have little effect on the deterioration of insulating paper, and the deterioration of insulating paper in the oil with antioxidant DBP is aggravate in the late ageing stage. Since the antioxidant T531 has a combination of neutralization and hydrolysis, it inhibits the degradation process of cellulose, and the ageing degree of T351 insulating paper is the lightest.

In order to study the influence of humid environment on the insulating performance of traction motor stator, we took the newly manufactured and overhauled stator winding of traction motor with silicone insulation system as the research object. The damp heat tests were carried out on the stator winding and its end, the insulating performance of the insulation system before and after moisture absorption were tested, and the main ways of moisture penetration into the insulation system were analyzed. The results show that the insulation resistance of the stator winding insulation system decreases after the damp heat test. The weakest part in the wet environment is the connection welding part of the end winding insulation, which is the main way of moisture to penetrate into the insulation system. Once this moisture channel is formed, it is easy to dry, but in the humid environment, the moisture will enter the channel and cause the insulation resistance decrease. After long term operation, the insulation performance of stator winding will decrease due to humidity.

The nanomolecular model of TiO₂/vegetable oil interface structures before and after modification of two silane coupling agents (KH570 and KH792) were established by molecular dynamics simulation, and the effect of TiO₂ interface before and after modification with silane coupling agents on the diffusion behavior of water molecules in oil were further investigated by dynamics simulation. The results show that compared with the untreated TiO₂, the modified TiO₂ interface has stronger adsorption of water molecules, which inhibits the migration behavior of water molecules in the oil, resulting in the significant reduction of their diffusion coefficient, thus reducing the formation of “small bridges” of water molecule impurities in the oil, and improving the insulating properties of vegetable insulating oil. Among them, the modification effect of KH792 is more significant. Further, by calculating the interaction energy between water molecules and TiO₂ interface system, the number of hydrogen bonds form and the free volume fraction, the causes and physical mechanisms of above phenomena are explain, which provides theoretical support for the study of nanoparticle doping to improve the insulating properties of vegetable insulating oil.

In this paper, the effect of electrical parameters of the semi-conductive layer on the surface electric field distribution of post insulator used in substation was calculated and analyzed by COMSOL. The results show that the semi-conductive layer can weaken the maximum electric field caused by water droplets, wet pollution, and dry pollution to different degrees, and the wet pollution is the most significant, with the electric field decreasing amplitude of 41.58%. Coating semi-conductive layer at the high voltage terminal has a significant improvement effect on the electric field, and the maximum decreasing amplitude of surface maximum electric field is 14.5% compared with not coating semi-conductive layer. When the high and low voltage terminals are coated by semi-conductive layer with the best relative dielectric constant, the comprehensive balance of electric field improvement is better. In the normal range of porcelain electrical parameters, the optimal electrical parameters of semi-conductive layer are universal, the relative dielectric constant of the optimal semi-conductive layer at high voltage terminal is 22, and the relative dielectric constant of that at low voltage terminal is 12. In addition, the resistivity of the semi-conductive layer at high and low voltage terminals should be at least greater than 1×10⁷ Ω·m and 6×10⁷ Ω·m, respectively, and the maximum electric field will be less than the case without semi-conductive layer.

In order to solve the problem of interface breakdown and surface discharge caused by uneven distribution of electric field of power cable and its terminal insulation, the structural parameters of 35 kV cold shrinkable power cable terminal were optimized to improve its insulation level in this paper. Firstly, the influence of axial length and end radius of stress cone on the terminal electric field distribution was analyzed based on COMSOL simulation software, and the optimal combination of terminal structural parameters was obtained. Then the power cable terminal samples were prepared, and the performance indexes were verified by power frequency AC voltage resistance and partial discharge tests. The results show that the axial length of the power cable terminal stress cone is the main factor affecting the change and distribution of interfacial electric field, and the change of terminal radius has little effect on the terminal electric field. The increase of axial length of stress cone alleviates the interfacial electric field intensity, but it is easy to cause discharge along the surface. The optimal axial length and upper radius of stress cone are 25 mm and 2.5 mm, respectively.

The study on the gas production law of stator bar for hydrogenerator under high temperature and partial discharge can provide a basis for insulation ageing monitoring of hydrogenerator on the basis of decomposition gas method. Aiming at the stator bar used in hydropower station, a high temperature pyrolysis experimental platform was built to study the pyrolysis gas of stator bar at 100, 120, 150 and 250℃. A partial discharge experimental platform of stator bar was established to study the ozone generation law of stator bar under partial discharge. The results show that CO and CO₂ are suitable used as the early characteristic gases of stator bar with high temperature fault. When there is partial discharge on the stator bar surface, the ozone concentration is related to discharge voltage and time. Under the same discharge condition, the ozone concentration rate generated by semi-conductive silica gel is higher and it has stronger corona resistance. Filling stator slot with semi-conductive silica gel is beneficial to the safe operation and on-line monitoring of stator bar.

C₆F₁₂O is a potential substitute gas for SF₆. To explore the decomposition characteristics of C₆F₁₂O/CO₂ mixed gas under floating electrode defect and different partial discharge intensity, a partial discharge decomposition test platform was built, and 96 h partial discharge decomposition experiments were conducted on C₆F₁₂O/CO₂ mixed gas under different applied voltages. The decomposition components were quantitatively analyzed by gas chromatography. The relationship between the decomposition components content, gas production rate, characteristic gas ratio and partial discharge intensity was studied respectively. The results show that the change rule of concentration, gas production rate of four typical products (CF₄, C₂F₆, C₃F₈, C₃F₇H) are different, which can be used as the characteristic component to judge the partial discharge intensity. The concentration relationship of characteristic components is c(CF₄)>c(C₂F₆)≈c(C₃F₈)>c(C₃F₇H), and the gas production rate relationship is similar. The concentration of characteristic components shows a “linear-saturated” growth with the increase of discharge intensity. It is preliminarily suggested that using c(CF₄)/c(C₃F₇H) as the auxiliary basis, and c(CF₄+C₂F₆+C₃F₈)²/c(C₃F₇H)² as the main basis, the PD intensity and defect severity can be judged combined with component content and gas production rate, which provide reference for finding out the operation and maintenance monitoring methods applicable to C₆F₁₂O/CO₂ mixed gas insulation equipment.

The silicone rubber composite insulators operating in humid and hot areas has the problem of microbial contamination caused by mold adhesion, and the effect of mold as a special biological pollution on the performance of silicone rubber insulators is still unclear. In this paper, the suspended insulator strings were contaminated by mold, and their surface flashover characteristics were analyzed under different pollution levels. The influence of mold contamination on the surface flashover properties of insulator was studied by hydrophobicity analysis, scanning electron microscopy, and infrared spectroscopy. The results show that for the insulators with the same pollution level, when there is mold pollution, the mold would damage the surface structure of silicone rubber compared with insulators without mold pollution, resulting in a significant decrease in the hydrophobicity of silicone rubber, and thus the flashover voltage is reduced significantly. Compared with the control group, the surface flashover voltage can be reduced to 76% of the original level at the lowest. However, under the same pollution level, when the mold concentration reaches 107 pcs/cm², there is an inflection point for the decrease of surface flashover voltage, and the decline rate slows down and tends to saturation. In summary, the synergistic effect of mold adhesion behavior and natural ageing of silicone rubber makes the mold mycelium form micro holes on the surface of insulator, resulting in the breakage of silicone rubber molecular chain, reducing the flashover voltage of insulator, and affecting the stable operation of silicone rubber insulators.

In order to develop an on-line monitoring technology for cable insulation status, we analyzed the harmonic components of resistive current by simulating the metal spike in XLPE cable insulation, which provided theoretical and experimental support for cable insulation diagnosis based on the harmonic components of resistive current. Firstly, the conductivity characteristics of XLPE were simulated and theoretically analyzed based on the jump conductivity model of polymer. Then, a simulation model of metal spike defect in XLPE was established, and the harmonic components of resistive current density under different needle curvature radius and needle plate spacing were simulated and analyzed. Finally, three kinds of XLPE metal spike defect samples with different specifications were made, and confirmatory experiments were conducted under the conditions of 30 μm of needle tip curvature radius and 2 mm of needle plate spacing, 90 μm of needle tip curvature radius and 3 mm of needle plate spacing, and 30 μm of needle tip curvature radius and 3 mm of needle plate spacing. The results show that there is metal spike defect in XLPE insulation, due to the sharp increase of local electric field strength, the conductivity characteristics of the insulation material will repeat between the Ohmic and non Ohmic regions with the change of AC voltage waveform, resulting in the distortion of resistive current waveform and the addition of higher-order harmonic components. When there is metal spike defect in XLPE insulation, there are obvious 3rd and 5th harmonic components in the resistive current, which constitutes the main components of resistive current harmonic component. As the severity of metal spike defect increases, the harmonic distortion rate of resistive current and conductivity distortion rate increase significantly, and the harmonic distortion rate can be used as a characteristic quantity to judge the severity of defect.

In the process of transportation and laying, the submarine cable will inevitably be twisted. If the twisting angle is too large, it will cause irreparable damage for the submarine cable. In this paper, a torsion model of submarine cable was established by finite element method, and the characteristic parameters that can effectively reflect the mechanical characteristics of submarine cable were determined by analyzing the temporal and spatial distribution characteristics of stress and strain. The threshold values of each characteristic parameter when torsion failure occured were established, and the mechanical parameter system that can represent the torsion behavior of submarine cable was established. The results show that the axial stress distribution of the submarine cable is more uniform at the initial stage of torsion. With the increase of torsion angle, the axial stress distribution of cable body will fluctuate. A parametric system including copper conductor stress, XLPE insulating layer stress, lead alloy stress, armor layer stress, and torsion angle can be established for parametric evaluation of submarine cable torsion behavior.