In order to study the failure mechanism of water-blocking buffer layer in high voltage power cable, especially the electrochemical corrosion characteristics, we analyzed the composition of the white powders from failed cables, and confirmed the production mechanism of different composition in the white powders combining with theoretical analysis and simulation experiments. The moisture absorption characteristics of the buffer layer was tested, and the influence of the water content and current density of the buffer layer on its electrochemical corrosion characteristics was studied. Finally, based on electrochemical impedance spectroscopy, the influence of electrochemical corrosion on the electrical characteristics of the buffer layer was identified, and the evolution rule of the buffer layer from electrochemical corrosion to final ablation was determined. The results show that moisture ingress due to dampness or mechanical damage of the cable sheath causes electrochemical corrosion of the buffer layer and leads to the generation of white powder (consisting of NaHCO₃ and Al(OH)₃) and results in the final failure of the cable. The corrosion rate is closely related to the current density, while the final corrosion degree mainly depends on the moisture content of the buffer layer.

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%.

During the operation of high-voltage DC cables, space charge generates in the insulation layer, it leads to electric field distortion and even insulation breakdown. In order to study the effect of space charge in the actual operation of cable, we obtained the temperature field of high-voltage direct current submarine-land composite cable under the conditions of rated current, maximum steady-state current, and short-term overload current, respectively. According to the simulation results, the temperature difference in the space charge test was set as 10℃, 20℃, and 40℃, respectively, and then the temperature field of 400 kV high-voltage DC cable under different condition was simulated. The results show that the temperature difference between the two sides of XLPE insulation layer is 8.1℃ and 18.7℃under rated current and the maximum steady-state current, respectively; while the temperature difference is 61.1℃ under the short-term overload for 1 hour; and that is 41.1℃ under short-term overload for 36 hours. The experimental results show that the temperature gradient enhances the accumulation of heteropolar charge at the low temperature side of positive pole of XLPE, which leads to the distortion of electric field. Through the correction computation of the electric field distortion rate, it is found that the maximum electric field distortion rate has a linear relationship with the average electric field strength. With the increase of temperature gradient, the electric field distortion rate also increases. The maximum electric field distortion rate is 1.68 under the temperature gradient of 40℃ with the applied electric field of 50 kV/mm.

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.

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.

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.

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.

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%.

Under the sinusoidal, bipolar square wave, and bipolar short impulsive voltage with 50 Hz of frequency, three typical corona-resistant turn-to-turn insulated twisted pairs for new energy vehicles were used to experiment, and the influences of three voltages on their partial discharge inception voltage (PDIV) characteristics were studied. The results show that within the effective bandwidth after frequency domain filtering, the discharge frequency domain energies under bipolar repetitive short pulse and square wave voltage distribute in 0.5‒0.9 GHz mainly. Keeping other test environments unchanged, the PDIVs under sinusoidal and bipolar repetitive square wave voltage are almost equal. The PDIVs under sinusoidal and square wave are about 20% lower than under bipolar repetitive short pulse voltage, and with the increase of pulse width, the PDIV decreases under bipolar repetitive short pulse voltage. According to the research results, when conducting PDIV test on turn-to-turn insulation, the sinusoidal and square wave voltage are more conservative test voltages for evaluating the PDIV of inverter-fed motor turn-to-turn insulation. When conducting PDIV test on capacitive sample of twisted pairs, the sinusoidal voltage can be considered to replace pulse voltage.