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, 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 study, EPDM seal ring commonly used in gas insulated switchgear (GIS) equipment was treated at -55℃, and the effects of low temperature on its surface morphology, structure, glass transition temperature, and mechanical properties (tensile and compression permanent deformation) were investigated. The results show that the low temperature treatment cannot damage the macromolecular chain structure in the seal ring, but it is easy to cause frosting, and the glass transition temperature shows an increasing trend. The mechanical properties of the seal ring change greatly after low temperature treatment, the hardness and breaking strength decrease, while the elongation at break and compression permanent deformation increase. The degree of change in tensile property is related to the amplitude of alternating temperature difference in alpine environment, the greater the amplitude, the greater the breaking strength loss of the seal ring.

In the preparation of tetragonal nano-barium titanate powder by traditional solid-phase method, the dispersion and particle size of the BaCO₃ precursors play a crucial role in the morphology, particle size, and dielectric properties of the obtained tetragonal BaTiO₃ nanoparticles. In this paper, nano BaCO₃ powders were prepared by controlling the concentration of the Ba(OH)₂ using Ba(OH)₂ and drikold as raw materials. Then, BaTiO₃ powders and ceramic were prepared using the BaCO₃ powders, and the dielectric properties of BaTiO₃ ceramic was studied. The results show that the short rod-shaped nano BaCO₃ powders with a particle size of 180 nm and the highly dispersed, highly uniform and pure tetragonal BaTiO₃ powders with a particle size of 400 nm were prepared. The dielectric constant and dielectric loss factor of the BaTiO₃ ceramic obtained by calcination at 1 250℃ is 4 885 and 0.018 9, respectively.

In this paper, a test platform for partial discharge characteristics and flashover characteristics of insulation molding parts for power transformer was built, and the distribution laws of partial discharge initial field strength, partial discharge initial discharge quantity, partial discharge extinguishing field strength, and surface flashover field strength of different insulation molding parts were obtained. The results show that the partial discharge initial field strength of insulation molding parts decreases with the increase of electrode spacing. When the electrode spacing increases from 10 mm to 25 mm under parallel components, the partial discharge initial field strength decreases by about 40.6%. The partial discharge initial discharge quantity under different components is 8.51-13.70 pC. Under the parallel component, the partial discharge initial field strength of insulating strip and insulating spacer is 2.55-2.85 kV/mm and 1.43-1.78 kV/mm, respectively. Under the vertical component, the partial discharge initial field strength of insulating strip and insulating spacer is 2.65-3.35 kV/mm and 4.31-5.49 kV/mm, respectively. The surface morphology of different insulation molding parts has a significant impact on their surface flashover characteristics. The denser and larger the surface embossed grooves, the better the effect of hindering the development of surface discharge. On the basis of test sample database, a comprehensive performance evaluation method for insulation molding parts based on entropy weight method is proposed. The weight of different performance indicators, which is determined by using four indicators of discharge characteristics of insulation molding parts, as well as the dispersion degree of apparent density and size deviation, is used to evaluate the comprehensive performance of different insulation parts, and the rationality of this evaluation method is verified.

In view of the voltage dip/swell in the power system, a programmable power supply was used to modulate the applied voltage, and the effect of voltage fluctuation on the internal partial discharge characteristics of epoxy resin was analyzed. The results show that the voltage fluctuation will lead to the change of partial discharge pattern of air gap, which exhibits asymmetry in positive and negative half cycles. The greater the applied voltage fluctuation, the more significant the asymmetry of partial discharge. The reason for the change of partial discharge pattern is due to the combined effect of external electric fields and surface charges accumulated inside the air gap. On the one hand, the electric field generated by surface charges can overlap the applied electric field to adjust the total electric field in air gap. On the other hand, as the discharge continues, the dissipation and neutralization of surface charges can also affect the total electric field in air gap, resulting in the partial discharge exhibit asymmetry in positive and negative half-cycle of the applied voltage.

In order to improve the reliability of interlayer gap discharge faults diagnosis in winding, taking a hydrogenerator stator winding as the experimental object, the influencing factors of diagnosing interlayer gap discharge through partial discharge were studied. Firstly, the characteristics of interlayer gap discharge in winding under the superposition of multiple discharge sources were obtained through offline test, online test, and simulation test. Then, by simulating the electrical conduction attenuation of bar and combined with the generator winding structure and detection distance, the effect of detection distance on the detection results was analyzed. The results show that the winding interlayer gap discharge has independent characteristics, the pulse distribution is suspended in PRPD pattern and has symmetrical positive and negative polarities. The pulse peak values are located around 45° and 225°. In one phase, the positive and negative polarity pulse peak values simultaneously deviate to the right of 45° and 225°, while in the other phase, the positive and negative polarity pulse peak values simultaneously deviate to the left of 45° and 225°. When the winding structure is different, the distribution of discharge gaps and the length of lead ring are also different, resulting in significant differences in detection distance, which has great effect on the amplitude detection results of partial discharge signals. If only electrical conduction is considered, for every one meter increase in detection distance, the average attenuation of partial discharge amplitude is approximately 10%. When only one closer phase can detect gap discharge, the interphase analysis method fails. Even there are multiple discharge sources and gap discharge simultaneously in winding, the interlayer gap discharge can be identified through the suspended characteristics of gap discharge PRPD pattern. The detection range has an impact on the identification of partial discharge patterns. When the global spectra with large range is complete, while the local patterns overlap with each other, the specific faults cannot be identified. When the global spectra with small range is incomplete, while the local patterns are clear, the specific faults can be identified.

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, 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%.