In this paper, the oil resistance reliability of impregnated resin, enameled flat wire, and aramid fiber paper for oil-cooled motors was studied, and the performance changes of insulating materials after long-term contact with automatic transmission fluid (ATF) under high temperature conditions were investigated. The results show that the insulating materials are greatly affected by the moisture in ATF in the oil resistance test, water and air can promote the hot oxygen ageing of ATF to generate acidic substances, which can accelerate the hydrolysis of material. After conducting high-temperature oil resistance test for 2 000 h, the two impregnating resins, enameled flat wire D and two aramid papers show excellent oil resistance and good reliability.

Furan molecule is one of the important characteristic products of insulating paper pyrolysis during local thermal failure of oil-immersed transformer, and the detection of furan molecules content in transformer oil is an important off-line testing method to assess the operating condition of transformer. In order to clarify the diffusion process of furan molecules from insulating paper to insulating oil and its correlation with temperature labels of local overheating fault, molecular dynamics methods were used to study the diffusion process of furan molecules from insulating paper to vegetable oil based on nanoscale oil-paper interface models under room temperature (300 K), low temperature overheating (500 K), medium temperature overheating (750 K), and high temperature overheating (1 000 K). The results show that with the increase of temperature, the diffusion coefficient of furan molecules in oil-paper insulation increases gradually, and the number of furan molecules diffusing from insulation paper to vegetable oil changes closely with temperature. There are few furan molecules diffuse into vegetable oil under 300 K and 500 K. Under the temperature of 750 K and 1 000 K, some of furan molecules diffuse into vegetable oil, and the molecule number increases with temperature. The above simulation results are consistent with the empirical basis that furan compounds can be detected in local overheating fault of medium and high temperature in oil-immersed transformers.

In this paper, the effects of properties of chopped fiber on the breakdown strength, conductivity, trap characteristics, and mechanical properties of meta-aramid paper were studied. The results show that based on the reference sample of which the fiber diameter is 25 μm, fiber length is 6 mm, crystallization temperature is 300℃, and the ratio of precipitated fibrids and chopped fibers is 7:3, when the fiber diameter increases to 45 μm, the embedding degree of chopped fibers decreases, interface pores appear, and the breakdown and tensile strength of aramid paper can decrease by 16% and 24%, respectively. When the length of fiber increases to 18 mm, chopped fiber morphology shows coiling-type thus forming the "hard-form" interface, the breakdown strength of aramid paper decreases by 63%, while the tensile strength shows little change. When the crystallization temperature decreases to 230℃, the structural stability of chopped fibers reduces, which causes their melting under hot-pressing process, and the breakdown strength and tensile strength decreases by 36% and 50%, respectively. With the increase of proportion of chopped fiber, the breakdown strength of aramid paper increases at first and then decreases, which is along with the change of paper compactness, while the tensile strength of aramid paper increases monotonically with the increase of chopped fiber content, which reflects the necessity of chopped fibers for the stable molding of aramid paper and the weakening effect of excessive chopped fibers on electrical insulation. In addition, the aramid papers with low breakdown strength show a higher conductivity and a shallower trap depth, which can be regarded as reference indexes for the insulation performance of meta-aramid papers.

In this paper, the research status and future developing trends of polyimide (PI) film carrier materials for flexible solar cells was reviewed. The basic structure of flexible solar cells, the property requirements of substrate materials and the research and application status of PI flexible substrate were introduced. Emphatically, the research and application progress of high temperature resistant PI films for the substrate-types flexible solar cells and the colorless and transparent PI films for the superstrate-types flexible solar cells were reviewed. At last, the future developing trends of PI film substrate materials for advanced flexible solar cells were prospected.

By using organic-inorganic composite technology, the high temperature resistant insulation layer was prepared by coating quartz fiber wrap cladding with silicone nano alumina sol. The micro morphology and structure of the organic silicon-nano alumina sol coating were analyzed by SEM, FTIR, XRD and other characterization techniques. The thermal stability of the organic silicon-nano alumina sol composite insulating paint was analyzed by TG-DSC. The insulation performance and breakdown voltage performance of high-temperature wire were tested at room temperature and high temperature. The results show that the organic silicon-nano alumina sol composite insulating paint has good thermal stability, and it can significantly improve the temperature resistance level of the glass fiber wrap cladding. The high-temperature wire shows good high temperature insulation and high voltage resistance. At 800℃, the electrical resistance is greater than 1 MΩ·m, and the normal temperature breakdown voltage is greater than 2 000 V. It is suitable for special environments such as high temperature and high voltage in the aviation and aerospace fields.

With the long-term operation of transformers, microorganisms will be produced in transformer oil, and the microbial metabolites can affect the quality of transformer oil. In this paper, the changes of the content, composition, and structure of extracellular polymeric substances (EPS) produced by microorganisms in the transformer oil were analyzed by using three-dimensional fluorescence spectroscopy (3D-EEM), ultraviolet spectroscopy, and Fourier transform infrared spectroscopy (FTIR). The types of organic compounds in new oil and fault oil were compared and analyzed, and the effect of EPS on the quality of transformer oil was investigated. The results show that C=C and C=O characteristic functional groups generate in the transformer oil after long-term operation. The color of the oil in darkened, and the absorbance increases significantly in the near ultraviolet region with the wave length of 190 nm-400 nm. The content of protein (PN) in new oil, running oil, and fault oil is always higher than that of polysaccharide (PS), and PN is the main component of EPS. The number of fluorescent emission contour rings of EPS in fault oil decreases, mainly including O-H, C-H, C=O and unsaturated bond. Compared with new oil, the water content of faulty oil increases by up to 5 times, and the acid value is 40 times higher than that of new oil.

Epoxy molding compounds (EMC) play important roles in packaging of chips for electrically controlling systems of electric vehicles (EV). The increasing working temperature of EV controlling system puts forward higher and higher requirements for the thermal stability of traditional EMC materials. In this paper, the progress on the high temperature resistant molding compounds at home and abroad in recent years was reviewed, and the development status of high temperature resistant resins and the progress of high temperature resistant resins modified traditional epoxy resin based EMC materials were described. Especially, the development status of high temperature resistant EMC materials modified by bismaleimide (BMI), cyanate ester (CE), and polybenzoxazine (PBZ) and phthalonitrile (PN) based molding compounds were reviewed. Finally, the future development trend of high temperature resistant molding compounds for packaging of electronic control chip in EV was prospected.

Polarization-depolarization current (PDC) method is widely used to evaluate the insulation status of cross-linked polyethylene (XLPE) cables. However, the existing studies tend to use a single dielectric characteristic parameter to reflect the ageing condition of insulation, which does not make full use of the rich dielectric response information in PDC results, and a single dielectric parameter is difficult to apply to different ageing types. To solve the above problems, an improved radar spectroscopy evaluation method was proposed to evaluate the insulation condition of XLPE cable by comprehensively utilizing multidimensional dielectric parameters. To verify the effectiveness of the proposed method, PDC test was conducted on short XLPE cable specimens after being artificially accelerated thermal and water tree ageing. Then the PDC results were analyzed by the proposed multidimensional dielectric parameter radar spectroscopy method. The results show that the area parameter of polygon in radar chart can effectively reflect the degree of ageing in both types of aged XLPE cables.

In order to analyze the influence of natural ester insulating oil on the insulation performance of high-voltage transformer, in this study, a 220 kV power transformer was taken as the research object, the wave process calculation was carried out on it to obtain the node potential and oil channel gradient voltage under the full wave of lightning impact. And the electric field distribution under power frequency and full wave voltage of lightning was obtained by establishing a calculation model of transformer main insulation electric field, and then the insulation margin was calculated. The results show that the main insulation margin of natural ester insulating oil transformer is large at power frequency, while it is small at full wave of lightning. By improving the insulation structure of natural ester insulating oil transformer, the main insulation distance between medium voltage and high voltage windings of the natural ester insulating oil transformer is reduced by about 6%; the minimum insulation margin under the full wave of lightning can be increased by 15% by increasing the insulation thickness and radius of the winding turn, and the cost is saved effectively.

In order to investigate the ageing mechanism of composite insulators in extreme cold regions, the influence of ageing time on the physicochemical, mechanical, and electrical properties of composite insulator skirts were studied by an improved multi-factor ageing method. The results show that with the increase of the ageing time, cracks, holes and particle accumulation appear on the surface of the silicone rubber material, that leads to the significant decrease of its hydrophobicity. At the same time, the overall hardness of the silicone rubber material increases, the elongation at break decreases rapidly, and the mechanical properties decrease significantly. In addition, with the increase of ageing time, the dielectric constant increases significantly, the dielectric loss keeps increasing, the density of deep trap energy level gets lower, the density of shallow trap energy level increases, the surface conductivity increases significantly, and the flashover voltage decreases sharply.