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 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.

With a high voltage grade and large transmission capacity, ultra-high voltage (UHV) gas insulated metal enclosed transmission line (GIL) needs insulator with higher resistance to the comprehensive effect from electric, heat, and force. In this paper, epoxy composite materials were prepared by doping micro-Al₂O₃, micro-SiO₂, and micro-Al₂O₃-SiO₂ blend fillers, respectively. The mechanical, thermal, and electrical properties of the blend system were tested and analyzed. The results show that with the increase of the volume proportion of Al₂O₃, the comprehensive mechanical properties of the composites are improved, and pure micro-Al₂O₃/epoxy composite exhibits the best mechanical properties. Doping two fillers improves the thermal conductivity and arc resistance of the composites, but slightly reduces the glass transition temperature and increases the thermal expansion coefficient. When the volume ratio of Al₂O₃ and SiO₂ in composites is 1:1, the arc resistance duration and the thermal conductivity of the composite reaches 1.198 W/(m·K） and 186.63 s, respectively. With the increase of the volume proportion of SiO₂, the dielectric constant of the composites decreases, while the breakdown strength increases. The power frequency breakdown strength of the pure micro-SiO₂/epoxy composites is the highest, reaching 36.63 kV/mm.

In order to analyze the effects of rutile nano-TiO₂ doping on the properties of polyethylene (PE) materials from the microscopic perspective, PE and TiO₂/PE composite models with different mass fractions of water molecular were constructed by using molecular dynamics simulation method. And then taking temperature as a variable, the thermodynamic properties and microstructure of PE before and after being modified by nano-TiO₂ and the diffusion ability of water molecules in the composite system were analyzed. The results show that after doping with nano-TiO₂, the glass transition temperature of PE system increases by 33 K, the Young's modulus increases by 428.17%, and the shear modulus increases by 338.62%. Nano-TiO₂ greatly inhibits the movement of PE molecular chain and the diffusion of water molecules, which increases the stability of the composite system. The addition of water molecular and the increase of temperature decrease the thermodynamic properties of the composite system, both of which destroy the stability of the composite system.

Simulation calculations were conducted on the stator bars and windings of generator in a high altitude area by establishing a simulation model, and the rationality of the anti-corona design of the stator bar and winding was explored. According to the design, the stator bars and windings were manufactured and the reliability of the anti-corona structure was further verified through experiments. The simulation calculation results show that when the altitude is 3 000 m, the maximum field strength of the stator bar during the operation voltage, anti-corona assessment voltage, and voltage withstand process is 0.32, 0.44, and 0.53 kV/mm, respectively, and the maximum loss is 2.19×10⁵, 1.46×10⁶, and 6.34×10⁶ W/m³, respectively. The maximum electronic density between the layers of the generator winding is 1.32×10¹⁷ m^-3. After the modification of the oblique clearance of the stator winding, the maximum field strength of the stator bar during the operation voltage, anti-corona assessment voltage, and voltage withstand process is 0.78, 1.50, and 2.14 kV/mm, respectively, and the maximum loss is 3.01×10⁵, 6.8×10⁵, and 3.23×10⁶ W/m³, respectively. The experimental results show that the stator bars can pass the corona test under 40.7 kV and the withstand voltage test under 73.5 kV for 1 minute. With the increase of altitude, the ultraviolet photon number of the winding at 1.1U_n increases gradually, while that number is less than 1 000 when the altitude is below 3500 m. The anti-corona performance of the designed winding meets the design and operation requirements of the unit.

In this paper, a multi-source partial discharge diagnosis method based on joint detection of pulse current method and ultraviolet pulse method was presented. A multi-source partial discharge experimental platform of switchgear was constructed for four basic defect models. The characteristics of partial discharge information obtained by joint detection were extracted and a database was constructed, and then the discharge types were identified by k-nearest neighbor (KNN) algorithm and directed acyclic graph SVMs (DAG-SVMs) algorithm. The results show that the change of discharge number and discharge quantity in discharge pattern measured by pulse current method are related to the defect type in model. The existence of void and surface defects will increase the discharge quantity and pattern symmetry, and the existence of corona defect will increase the discharge number. The discharge pulse number measured by ultraviolet pulse method is related to the defect number in multisource discharge model and the ratio of ultraviolet to visible light. The higher the number of defects and the ratio of ultraviolet to visible light, the larger the discharge pulse number. The recognition accuracy of the KNN algorithm can reach up to 99.67%.

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.

Electron irradiation in the Geosynchronous orbit (GEO) will cause charge accumulation in aerospace insulating materials, which may cause electrostatic discharge of dielectric, while the electrostatic discharge will also affect the charge accumulation. In this paper, the joint measurement experiment of potential distribution and electrostatic discharge current was carried out on polyimide film materials under electron irradiation, and the surface charging and discharging process of polyimide film materials under the electronic irradiation of harsh GEO environment were studied. The results show that the surface potential of polyimide film is negative polarity under the electronic environment of 15 keV, 0.33 nA/cm², the distribution patterns include unimodal type, multimodal type, crater type, and flat top type, and the unimodal type and multimodal type have the highest discharge number. Short-term multiple discharges will change the potential distribution pattern and make the transformed distribution pattern maintain for a long time. The potential distribution pattern will affect the wavefront time of discharge current signal, while the potential level will affect the half peak time of discharge current signal, and the half peak time of the current signal at low potential level is about 28% higher than that at high potential level.

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.

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.