Metal particles in gas insulated metal enclosed switchgear (GIS) and gas insulated enclosed transmission line (GIL) can bounce near the insulator under the electric field, which intensifies the charge accumulation and may cause surface flashover in serious cases. In this paper, a 126 kV real size disc insulator was selected as the test sample. A sealed chamber and coaxial structure electrodes were designed, and the effects of bouncing metal particles on the surface charge accumulation behaviors of insulator at different temperatures (23, 40 and 60℃) were studied by using Kelvin electrostatic probe. The results show that the charge accumulation on the nonplanar region is closely related to the motion mode of metal particles at room temperature. And the charge accumulation on the insulator surface is positively correlated with the temperature. As the temperature rise to 60℃, the metal particles moving to the vertical surface of the ground electrode are easy to cause surface flashover, and a large number of heteropolar charges would be accumulated on the non-plane region in the same radial direction as the flashover.

Three kinds of soluble polyimide (PI) resins were prepared from 4,4′-hexafluoroisopropylidene)bisphthalic anhydride (6FDA) and three kinds of romatic diamine monomer containing rigid-rod amide bonds in the molecular chains by one-step high temperature solution polycondensation reaction, respectively. And then three kinds of transparent PI films were prepared by the N,N-dimethylacetamide (DMAc) solution of the above resins. The films were tested by attenuated total reflection Fourier transform infrared spectroscopy, thermogravimetric analysis, dynamic mechanical analysis, thermomechanical analysis, and UV-visible spectrum, and their yellowness index was tested. The results show that the PI films exhibit good optical transparency, their ultraviolet cutoff wavelength is below 380 nm and the optical transmittance is over 80% at the wavelength of 500 nm. In addition, the PI films exhibit good thermal stability with the glass transition temperatures (T_g) higher than 320℃ and the 5% weight loss temperatures (T_5%) over 520℃. The linear thermal expansion coefficients (CTE) of the PI films are all lower than 50×10^-6/K, indicating that the introducing of rigid amide bonds can efficiently enhance the high-temperature dimensional stability of the solution-processable fluoro-containing PI films.

In order to improve the dispersion of carbon nanotubes (CNTs) in epoxy resin (EP) nanocomposites and the interface interaction between them, so as to prepare EP nanocomposites with excellent comprehensive properties, polyvinyl pyrrolidone (PVP) molecular chains were grafted to the surface of CNTs by covalent bonding under the action of Fenton reagent, and the dispersion of modified CNTs in ethanol and acetone was studied. Then the modified CNTs were compounded with EP to prepare nanocomposites, and their comprehensive properties were studied. The results show that the traditional physical coating modification of CNTs by PVP can be changed into chemical modification with covalent bond through the HO∙ with strong oxidation decomposed by Fenton reagent, and hydroxylation modification can be realized, which improves the grafting rate of PVP. After modification, the CNTs have good dispersion in ethanol and acetone. There is a strong interface interaction between the modified CNTs and EP, which can improve the mechanical properties of EP obviously. When the mass fraction of modified CNTs is 0.25%, the impact strength and flexural strength of the nanocomposites increase by 58.6% and 5.2%, respectively.

In this paper, we proposed an intelligent recognition method for composite insulator hydrophobicity on the basis of image processing. For the composite insulator images with different hydrophobicity levels, the images were performed histogram equalization and filtering treatments at first, then the water drop/water trace was separated from the background by the Otsu threshold segmentation method, so as to extract clear and complete water drop/water trace contour. The water drop/water trace coverage rate, the maximum water drop/water trace area ratio, and the water drop/water trace average size were used to quantify the water drop/water trace, and the support vector machine was used to establish the feature classification model, so as to realize the hydrophobicity intelligent recognition of composite insulators. The results show that the hydrophobicity intelligent identification method of composite insulator based on image processing can effectively identify seven kinds of hydrophobicity levels, and the average identification accuracy rate is above 80%.

In this paper, a multi-physics finite element model of actual 10 kV T-type cable terminal joint was established. The electric field and temperature field distribution characteristics of the T-type cable terminal joint with air gap defect at insulation interface were studied, and the change laws of electric field and temperature field amplitudes were analyzed, then the characteristic quantities reflecting the air gap defect of T-type cable terminal joints effectively and the monitored position were proposed. The results show that different degrees of air gap defects in T-type cable terminal joints have a certain impact on the electric field distribution characteristics at the interface, but the electric field and temperature field amplitudes at other typical positions do not change significantly. The air gap defect position would near breakdown under air gap damping condition, at this time, the increase of electric field amplitude on flange base and upper surface of box can reach 20%, and the temperature rise can reach 15℃. In actual engineering, the potential critical hazard of partial breakdown discharge in T-type cable terminal joint can be reflected by monitoring the increase of electric field amplitude and temperature rise of the flange base and the upper surface of box.

A series of polypropylene/ethylene propylene copolymer (PP/EPC) cable materials were prepared by blending polypropylene (PP) with two kinds of ethylene propylene copolymer (EPC) with different ethylene content. The effects of EPC types and contents on the mechanical, thermal, and electrical properties of PP were investigated. The results show that the addition of EPC improves the toughness of PP significantly on the basis of maintaining the original excellent thermal and electrical properties of PP, and the toughening effect is more obvious by increasing the amount of EPC and the ethylene content in EPC.

In order to study the thermal conductivity of high thermal conductive (HTC) mica tape, the micro structure of different high thermal conductive VPI dry mica tapes were analyzed, and a thermal conductivity test method of HTC dry mica tape was proposed. A comprehensive evaluation method of thermal conductivity was discussed. The results show that under the existing VPI system, the thermal conductivity of the main insulation with high thermal conductive mica tape increase by up to 45% compared with the main insulation with conventional mica tape. Using the comprehensive thermal conductivity λ_s to measure the contribution of high thermal conductive mica tape is more objective and comprehensive, and the comprehensive thermal conductivity of the main insulation with high thermal conductive mica tape increase by up to 33% compared with the main insulation with conventional mica tape.

A silicon-containing propargyl ether of bisphenol A (PSPE-A) was synthesized by the polycondensation of bisphenol A dipropargyl ether and chlorosilane, and a diacetylenic benzene end-capped silicon-containing propargyl ether of bisphenol A (DPSPE-A) was synthesized by two step method. Then the bis(triphenylphosphine) nickel dicarbonyl, octacarbonyl dicobalt, and bis(cyclopentadiene) cobalt were used to catalyze the curing of the PSPE-A and DPSPE-A resins, respectively, and a carbon fabric (T300CF) reinforced silicon-containing propargyl ether of bisphenol A resins was prepared. The thermal curing and thermal properties of PSPE-A and DPSPE-A were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic thermomechanical analysis (DMA), and the mechanical properties of the PSPE-A based composites were studied. The results show that end capping with diethynyl benzene can increase the thermal properties of PSPE-A resin. The three catalysts can all decrease the curing temperature of PSPE-A resin, and the initial curing temperature of PSAPE-A and DPSPE-A decreases by about 130℃ and 60℃ after using bis(cyclopentadiene) cobalt, respectively. The flexural strength of the cured PSPE-A and DPSPE-A is 35.8 MPa and 27.8 MPa, respectively. The flexural strength of T300 carbon fabric reinforced PSPE-A and DPSPE-A composites is 458.2 MPa and 287.6 MPa, respectively.

The effects of doping micro-SiO₂ on the electrical tree resistance, thermal stability, thermal conductivity, and trap characteristics of epoxy resin under repetitive frequency bipolar square wave voltage were investigated. The results show that the electrical tree breakdown time of epoxy resin is prolonged by doping micro-SiO₂, and the prolong effect is the most obvious at 10 kHz, the electrical tree breakdown time is prolonged from 6 min to 44 min. Doping micro-SiO₂ can also increase the thermal conductivity of the epoxy resin and reduce the degradation of epoxy molecular chain at high temperature. The micro-SiO₂ filler can introduce more deep level traps, hinder the development of electrical tree channels, extend and even block the development path of electrical tree, which decreases the damage degree of molecular chain. Therefore, doping micro-SiO₂ can effectively improve the electrical tree resistance of epoxy resin under repetitive frequency bipolar square wave voltage.

A medium-density aramid pressboard was prepared by using meta-aramid chopped fiber and precipitated fiber as raw materials, the effects of chopped fiber length, grammage of single pulp layer, and moisture content of paper billet on the properties of the aramid pressboard were studied. The conventional properties, compatibility, and processing performance of the aramid pressboard were studied. The results show that when the chopped fiber length is 7 mm, the grammage of single pulp layer is 64 g/m², and the moisture content of paper billet is 63%, the aramid pressboard has excellent electrical and mechanical properties, good compatibility with synthetic ester transformer oil and silicone transformer oil, and good processing performance, which meets the application requirements of traction transformer and offshore wind power oil-immersed transformer.