A two-dimensional fluid-solid coupling model of 110 kV power transformer was established, the winding temperature rise characteristics of natural ester insulating oil power transformer and mineral insulating oil power transformer were compared and analyzed by finite-volume method, and the correctness of the calculating method was verified through experiments. At the same time, the winding overload characteristics for the same transformer with two insulating oils were compared. The results show that the winding temperature rise of the natural ester insulating oil transformer is slightly higher than that of the mineral insulating oil transformer, and the difference of their hot spot temperature rise is 4.7℃, but the natural ester insulating oil can improve the transformer temperature rise limit by 10 K. Thus, the winding temperature rise characteristics of natural ester insulating oil transformer is better than that of mineral insulating oil transformer. The overload capacity of natural ester insulating oil transformer is better than that of the mineral insulating oil transformer, and the difference between their overload performances expands further as the overload multiplier increases.

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 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.

The surface of meta-aramid paper was coated with poly(m-phthaloyl-m-phenylenediamine) (PMIA) slurry with different solid contents, and the coated meta-aramid paper was dried. The morphology, mechanical properties, dielectric properties, and electric strength of the modified meta-aramid paper were characterized by cold field emission scanning electron microscope, universal testing machine, broadband dielectric impedance spectrometer, and electric strength testing instrument. The results show that the PMIA slurry can change the structure of aramid paper and decrease the internal void of aramid paper. When the solid content of PMIA slurry is 10%, the transverse and longitudinal tensile strength of meta-aramid paper increases to 51.3 MPa and 94.4 MPa, respectively, the dielectric constant of meta-aramid paper is 2.07, and the electric strength of meta-aramid paper increases to 29.83 kV/mm. The mechanical properties and electric strength of the meta-aramid paper coated with PMIA slurry are better than those of original aramid paper. After treated at 180℃, the mechanical properties and electric strength of the modified meta-aramid paper are still better than those of original meta aramid paper, which can meet the applications of aramid paper in higher electric field environment and further broaden the applications field of aramid paper.

In this paper, an evaluation method based on polarization and depolarization currents (PDC) multi feature weight for cable insulation ageing state was proposed. Firstly, on the basis of PDC method, several ageing characteristic quantities reflecting insulation state were extracted. Secondly, the ordered binary comparison quantization method and principal component analysis method were used to determine the weight of feature quantity from subjective and objective aspects, and on the basis of DS (Dempster/Shafer) evidence theory, the subjective weight and objective weight were fused effectively to get the fusion weight. Thirdly, on the basis of the fuzzy comprehensive evaluation method, the effective evaluation of cable insulation ageing state was realized by combining with the fusion weight. Finally, the effectiveness of the evaluation method was verified by an example. The results show that the proposed method can evaluate the cable insulation ageing status effectively and accurately, which can provide a new direction for the evaluation of cable insulation ageing status.

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.

The oil-paper insulation systems, composed of insulating paper and monoester insulating oil or mineral insulating oil, were conducted thermal ageing tests, the ageing temperature was 130℃ and 140℃, and the ageing atmosphere was nitrogen and air, respectively. The thermal ageing characteristics of two insulation systems were compared. The results show that after the ageing of oil-paper insulation, the acid value and water content of monoester insulating oil are higher than that of the mineral insulating oil. Under the nitrogen atmosphere, the monoester insulating oil can prolong the ageing life of insulating paper significantly compared with mineral insulating oil, but at 130℃, the monoester insulating oil only prolong the ageing life of insulating paper slightly compared with mineral insulating oil. There is little difference between the thermal ageing life of insulating papers in the two insulating oils under air atmosphere.

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.

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.

In order to compare the discharge characteristics difference of metal particles and bubbles in flowing transformer oil, the flowing oils containing impurities were conducted partial discharge (PD) and breakdown experiments on a simulating experiment discharge platform. The waveforms of discharge signals were compared, and the phase resolved partial discharge (PRPD) maps were established. The results show that there are significant differences between the discharge characteristics of two defects in flowing oil. The metal particle PD can excite ultra high frequency signals, while the bubble PD can only excite very high frequency signals. The metal particle PD covers all the power frequency cycle, and the bubble PD distributes in the power frequency negative half cycle (236°-305°) mainly. Compared with metal particles, the effect of bubbles on the breakdown voltage of transformer oil is more serious.