In order to solve the problem of transformer oil leakage caused by the ageing failure of rubber sealing rings, the rubber sealing rings was conducted life evaluation research. Since there is low oxygen content and a small amount of H₂S retained as an oxidation inhibitor in the transformer insulating oil, and the sealing rubber ages faster in a strong oxidizing medium, we choose H₂S+hot air and hot air environment to conduct ageing tests. The dynamic curve direct method was adopted. According to the relationship between the performance change of rubber and ageing time and the Arrhenius model, accelerated ageing tests were carried out at three different temperatures, and the compression set rate was used as the performance index. The relationship between the performance change rate constant k and the life estimation value t under two environment was obtained to estimate the service life. The results show that the performance of rubber sealing ring degrade in different degrees under hot air and H₂S+hot air environment. With the increase of ageing time and ageing temperature, its hardness increases, and the elastic recovery ability changes to be poor. According to the established life estimation formula, the service life of EPDM rubber sealing ring is predicted to be 33 years and 35 years under hot air and H₂S+hot air environment, respectively.

In this paper, the thermal conductivity mechanism of filled epoxy resins was firstly introduced, and then the research status of the modified epoxy resins doped with different dimensional inorganic thermal conductive fillers was summarized mainly. On the basis of design idea for building the thermal conductive paths, the effect of different dimensions of filler size, distribution orientation, mixed filling, surface functionalization and other factors on improving the thermal conductivity of epoxy resin composites were described emphatically, and a comparative analysis was given. Finally, a brief outlook on the future development of the filled epoxy resin research field was put forward.

Dopamine (DA) and 3-glycidoxypropyltrimethoxysilane (KH560) were used to double-layer surface modification of boron nitride nanosheet (BNNS), the effect of the modified BNNS on thermal stability of epoxy-based (EP) insulating materials was discussed combining FTIR, TGA, and SEM experimental test with reactive molecular dynamics simulation. The results show that both methods of grafting KH560 at the end of polydopamine (PDA) and grafting DA at the end of KH560 can modify the BNNS surface successfully, and the double-layer surface modified BNNSs have better dispersion in composites. Besides, the breakdown strength of double-layer surface modified BNNS/EP composites is higher than 31.2 kV/mm. The thermal stability of composites can be obviously improved by double-layer surface modification, the improving effect of grafting DA at the end of KH560 is optimal. The modification of double-layer covalent bond grafting long chains that grafting DA at the end of KH560 can improve the interfacial compatibility, which can enhance the interaction force between BNNN and EP matrix. Moreover, the long chain branch is beneficial to fill the void inside the materials, and so that the thermal stability of composites increases.

Natural ester insulating oil is a kind of environmentally-friendly liquid dielectrics with good insulation properties, and it has been generally applied in oil-filled electrical equipment. Investigating the types and contents of fatty acids in different natural ester insulating oils will be beneficial to grasp the physical and chemical properties of different insulating oils. In this paper, a method of determining the fatty acid composition in natural ester by ¹H-NMR was presented, and the results were compared with that of GC-MS. The results show that this simple and rapid determination of fatty acid content in natural ester insulating oil by ¹H-NMR is feasible and reliable. The maximum error absolute value of fatty acids content measured by ¹H-NMR spectroscopy and GC-MS is 2.95%, which is in the tolerance interval.

In this paper, the theoretical basis for ageing diagnosis of XLPE cables based on the electromagnetic wave velocity in cables was elaborated, and the calculating method of average wave velocity according to input impedance spectrum was introduced. Then the effect of uniform ageing and segmented ageing of cables on average wave velocity was studied by simulation, and a method to diagnose cable ageing on the basis of average wave velocity was proposed. Finally, cable models including uniform thermal ageing and segmented thermal ageing were built in the laboratory, and the effectiveness of the above diagnosing method was verified. The results show that the average wave velocity of the accelerated uniform ageing cable and the segmented ageing cable decreases from 166 m/μs to 139 m/μs and 152 m/μs, respectively. The more serious the ageing of cables, the lower the wave velocity in cables. The proposed method can provide more information for ageing diagnosis of XLPE cables.

As the weakest insulation link of gas insulated substation (GIS), the surface defects of basin-type insulator are the key problems in the research of improving the insulation strength of GIS. This paper firstly introduced the generation and development mechanism of common surface defects of basin-type insulator, such as bubble defects, impurity defects, dirty surface, and crack defects. Secondly, the mechanism of flashover induced by surface defects of basin-type insulator was analyzed and summarized, it is explicit that the surface electric field distribution and surface charge accumulation of basin-type insulator are the important factors affecting the flashover of insulator; In addition, the advantages and disadvantages of the existing diagnosis methods of basin-type insulator surface defects were summarized. Finally, In view of the shortcomings of partial discharge detection methods for basin-type insulator surface defects under power frequency voltage excitation, starting with the voltage mode of partial discharge excitation, the current situation of partial discharge detection methods for basin-type insulator surface defects under different voltage excitation was studied and summarized.

In order to solve the problem that the cable capacity much lower than the design standard due to the high thermal resistant environment in the running process of duct cable laying, this paper developed the cable pipe materials that graphene microchip and graphite flake modified HDPE (PG-GNPs-HDPE) with high thermal conductivity, then established a simulation model and verified the improving effect of using the high thermal conductive pipeline of PG-GNPs-HDPE under the common duct laying condition of the current urban distribution network. The results show that compared with the ordinary HDPE pipe, the carrying capacity of 110kV 500mm² cable group with 2×4 laying is increased by 9.32% after using PG-GNPs-HDPE high thermal conductivity pipe; for 10 kV 3×400 mm² cable group with 3×4 laying, the carrying capacity increases by 7.42%.

In order to compare the properties of domestic and imported meta-aramid paper for traction motor, we tested and analyzed the structure, mechanical properties, and dielectric properties of domestic paper A and B and imported paper. The electrical properties of stator models using the three kinds of paper were tested. The results show that the structure of paper A is relatively loose, and its tensile strength is slightly lower than that of paper B and imported paper; The elongation at break of the three meta-aramid papers is stably maintained at 17%‒19%. The edge tear strength of paper A and B is generally higher than that of imported paper. The breakdown voltage of paper A is slightly lower than that of paper B and imported paper, but the breakdown voltage of paper A is higher than that of paper B and imported paper after impregnation. This is due to the loose structure of paper A, which is conducive to the entry of insulating paint into the paper to fill the gap. The dielectric loss factor, resistance, capacitance, and withstand voltage performance of the stator models are normal, which shows that the two kinds of domestic meta-aramid paper can replace the imported one as slot insulation and filler strip.

In order to improve the heat resistance of the water-soluble silicon steel sheet paint, we prepared water-soluble silicon steel sheets with excellent heat resistance, by adding composite inorganic fillers made of different proportions of precipitated BaSO₄ and inorganic adhesives into water-soluble polyester resin matrix. The mechanical properties, electric strength, and heat resistance of the paint were analyzed. The results show that when the composite inorganic filler disperse in the matrix resin evenly, the pencil hardness reaches to 9H, and the adhesion achieves level 1. With the increase of the proportion of BaSO₄ in the composite inorganic filler, the electrical strength, volume resistivity, and heat resistance increase at first and then decrease. When the mass fraction of BaSO₄ and inorganic adhesive is 5:2, the electrical strength of the paint film reaches a maximum of about 280 kV/mm, and the volume resistivity is as high as 1.5×10¹⁶ Ω·m. The maximum initial thermal decomposition temperature is about 273℃, and the final residual rate is 77%. The performance of the paint is basically unchanged after irradiation, it has stable dimensions and surface resistance after Flinklin burning, it is indicated that the insulating performance is still maintained at high temperature.

In order to explore the influence of high voltage cable oil filled terminal grounding system defects such as lack of copper net and lead seal defects of on the voltage and current of oil filled terminal, we built an RLC equivalent model of oil filled terminal. On the basis of capacitance parameters and test parameters computed by COMSOL, the change of terminal voltage and current characteristic under the defects was analyzed, and then it was verified by actual fault cases. The results show that the loss of copper net leads to the grounding failure of the outer semi-conductive layer, and the voltage of the outer semi-conductive layer increases significantly, results in the discharge. The lead seal fracture leads to the unreliability of the connection between the aluminum sheath and the tail pipe, results in the voltage suspension of terminal aluminum sheath, and causes the discharge between the aluminum sheath and the buffer layer under long-term operation. Defects between the lead seals reduce the contact area between the aluminum sheath and the lead seal, the minimum allowable contact area at the lead seal is about 10%.