With the large-scale construction of UHV long-distance power transmission, vegetable insulating oil instead of mineral insulating oil may become the future development trend. In order to analyze the differences and reasons of DC breakdown characteristics of LDPE (low density Polyethylene) under different environments, the DC breakdown experiments of LDPE were conducted in vegetable insulating oil and mineral insulating oil, and the impacts of insulating oil discharge process on the breakdown of LDPE samples were analyzed through simulation. The results show that the electric strength of LDPE in vegetable insulating oil is significantly higher than that in mineral insulating oil. The surface flashover characteristics and breakdown points of the two insulating oils are also different. The field intensity generated by discharge of vegetable insulating oil is small, so the breakdown field of LDPE in vegetable insulating oil is higher. The difference of discharge process of insulating oil is also the reason for the difference of flashover characteristics and breakdown point.

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.

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.

In order to quickly detect the overheating defects of wire insulation materials by using the key parameters of gas derivatives, the relationship curves between the concentration of gas derivatives and the temperature wire insulation materials were obtained through experiments. A thermoelectric coupling simulation model was established to simulate the effects of wire parameters, wire laying mode and ambient temperature on wire insulation temperature. A heat-flow coupling simulation model was established to simulate the effects of overheating defect location, threading tube horizontal length, and gas class on the sensor response time of escaped gas derivatives in the fluid field. The weight of influence degree was determined by orthogonal test. The results show that CH₄, C₂H₂, and CO are the main gases escaping from overheating defects of PVC insulation material. The selection of wire parameters has the greatest influence on insulation material temperature. The type of detected gas has the greatest influence on the response time of sensors.

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 characteristics of high-frequency copper clad laminates were summarized, the dielectric properties of their base resins were compared, and the research progresses of hydrocarbon resin (PCH) high-frequency copper clad laminates were mainly introduced. By summarizing the current researches on hydrocarbon resin based high-frequency copper clad laminates, the existing problems were pointed out, and their future development trends were prospected.

In this paper, the basic research and application progress of high temperature resistant epoxy molding compound (EMC) at home and abroad in recent years were reviewed. The property requirements of advanced power electronics on the molding compound, the high temperature degradation mechanism of traditional EMC, the relationship between structure and thermal stability of EMC, and the modification pathways for improving the thermal stability of EMC were presented. Especially, the development status of multi-aromatic ring (MAR) and naphthalene-containing EMC were reviewed. At last, the future development trends of high temperature resistant EMC for power electronic packaging were prospected.

In this paper, the developing history of polyesterimide (PEsI) materials, key monomers for synthesis, synthesis techniques of PEsI resins and their applications in electrical insulation, microelectronic packaging, flexible printing circuit board, liquid crystal display, flexible display, and wireless telecommunication fields were introduced. The development status of colorless and transparent PEsI film and low dielectric PEsI film were mainly reviewed. At last, the future developing trends of PEsI materials were prospected.

Three brands of commercial cross-linked polyethylene insulating materials for high-voltage cables were selected as the research objects. At first, the scorching resistance of three insulating materials was compared and analyzed by the change rule of melt torque of insulating materials with temperature under the action of high temperature shearing, and the scorching degree of the scorched sample was characterized by the gel content. Then, the method of using the torque change rate of insulating material melt under high temperature as the characteristic quantity to characterize the scorching resistance of insulating material was proposed, and the effectiveness of this method was verified by characterizing the scorching degree of different brands of commercial insulating materials. In addition, the crosslinking agent content and antioxidant content in the three insulating materials were compared and analyzed by infrared spectrum, and the correlations between the additive content of insulating material, the molecular weight of base material, and its scorch resistance were established on the basis of molecular weight of insulating material base material measured by gel permeation chromatography. The results show that the scorching resistance of different commercial insulating materials can be effectively distinguished by the torque analysis on insulating materials under the action of high temperature shearing. It is found that the high content of crosslinking agent is the main reason for the poor scorching resistance of insulating materials, and the scorching resistance of insulating materials can be improved by appropriately reducing the crosslinking agent content, increasing the antioxidant content, and reducing the weight average molecular weight.

A series of HFBAPP/6FDA/BPADA fluorinated phenyl ether-containing polyimide films were prepared using 2,2-bis [4-(4-aminophenoxy)phenyl] hexafluoropropane (HFBAPP) as the diamine monomer, 2,2′-bis (3,4-dicarboxylic acid) hexafluoropropane dianhydride (6FDA) and bisphenol A-type diether dianhydride (BPADA) as the dianhydride monomer. The effects of ether bond and trifluoromethyl on the comprehensive performance of polyimide films were analyzed and compared by changing the ratio of dianhydride monomer. The results show that with the increase of trifluoromethyl content and the decrease of ether bond content, the optical and thermal properties of the HFBAPP/6FDA/BPADA fluorophenyl ether-containing polyimide films increase, while the mechanical properties decrease, the glass transition temperature can reach 247.3℃, the residual carbon rate at 800℃ can reach 56.3%, the maximum transmittance in the visible range is 88.2%, and the maximum tensile strength is 84.7 MPa.