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.

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.

The research status and development tendency of semi-alicyclic colorless and transparent polyimide(CPI) film was reviewed from several aspects, including its developing history, important monomers, resins synthesis technology, film production technology, and the practical applications of CPI films in advanced optoelectronic fields. Emphatically, the current hot-topics in the development of semi-alicyclic CPI films were presented, and the future developing trends of semi-alicyclic CPI films were prospected.

In this paper, a photoelectric joint detection system composed of a photomultiplier tube and an electric field sensor was used to carry out the discharge tests of ball-plate electrode gap with burr of different gap distances under positive switching impulse voltage. Compared with the discharge tests of the rod-plate and that of ball plate, the 50% discharge voltage(U_50%) and the physical characteristic parameters under the initial streamer were obtained and compared. The results show that in the ball-plate electrode gap with burr defects, the initial delay, the field strength jump value, and the light power jump value of the initial streamer are positively correlated; in the initial stage of streamer, the burr can shorten the initial delay of discharge, especially for short gap. After the initial streamer developing, the development law of initial streamer of ball-plate electrode with burr is similar to that of rod-plate electrode gap, and the burr aggravates the development of discharge. For the whole discharge process, the burr defect will greatly reduce the discharge voltage of the ball-plate electrode, so that it is close to the discharge voltage of the rod-plate electrode gap under the same clearance.

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.

During the normal operation of converter transformer, moisture will cause the decline of the electrical performance of oil-paper insulation and accelerate its ageing, resulting in a decrease of life and insulation breakdown. In order to study the influence of moisture on the space charge characteristics and breakdown characteristics of oil-paper insulation under AC and DC composite voltage, we prepared oil-paper insulation samples with different water content, then we used space charge measurement under AC and DC composite voltage to get the influence of moisture content on the space charge characteristics of oil-paper insulation under the voltage forms of AC, DC, and AC and DC composite voltage, and studied the breakdown characteristics of samples with different moisture contents under different voltage types. The results show that the electric field distortion rate of oil-paper insulation under AC and DC composite voltage is greater than that under DC and under AC electric field; as the DC component increases, the increase amplitude of breakdown voltage of the samples with higher water content is significantly lower than that of samples with lower water content, and the electric strength of samples with low water content is more affected by the DC voltage component than that of samples with high water content.

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 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.

The electret effect can improve the adsorption capacity of the filter membrane for polar impurities. In this paper, BaTiO₃ doped composite nanofiber filter membrane for transformer insulating oil was prepared by combining electret technology with electrospinning process. The electrospinning conditions for preparing PVDF nanofiber membranes with small diameters and pores without beading were obtained by system study on the relationship between electrospinning parameters and the morphology of fiber membrane. And then the regeneration experiment for transformer insulating oil was carried out. The results show that the filter membrane can remove polar substances, and has high specific surface area and high porosity. After doping BaTiO₃ and corona discharge treatment, the filter membrane can be stably charged. The dielectric loss factor and breakdown voltage of the aged insulating oil are significantly optimized after filtering by the BaTiO₃ doped composite nanofiber filter membrane. Compared with other filter membrane electret-doped composite nanofiber membranes, it has better regeneration effect on transformer insulation oil.

From the perspective of the particle size of pollution particles, the particle size characteristics of the insulator surface pollution under two typical dust pollution sources of nickel plants (metal) and chemical plants were tested and analyzed, and the influence mechanism of the pollution particle size on the pollution accumulation was studied by establishing a pollution particle deposition model. The results show that the average particle size of pollution particles on insulator surface in chemical plant area is only 6.67 μm, while the average particle size of pollution particles on insulator surface in nickel plant area attains 24.5 μm. The deposition rate is the largest when the particle size of pollution particles is 20‒30 μm, therefore the surface of insulator in nickel plant area is polluted seriously. The simulation results based on the pollution particle deposition model can confirm with the on-site pollution accumulation phenomena, which explains the influence of pollution particle size on the insulator pollution accumulation.