In order to investigate the effects of degassing treatment on the electrical tree growth and discharge evolution in DC cable insulation, and to clarify the affecting mechanism of degassing treatment in the critical breakdown process of electrical tree, taking cross-linked polyethylene (XLPE) samples with different degassing time as research objects, on the basis of partial discharge (PD) experiment data, the dynamic evolution processes of electrical tree growth rate and discharge magnitude were quantified by combining derivative analysis and adaptive threshold method, and the critical breakdown characteristics were identified by counting mutation point. The results show that degassing treatment can significantly delay electrical tree growth, reduce discharge activity, and increase the breakdown threshold. In short-time degassed samples, charges tend to accumulate more rapidly and trigger electrical tree expansion immediately, and the electrical tree growth and the discharge evolution are synchronous. However, when degassing is sufficient, the processes of trap capturing charges and energy accumulation become more prominent, and the discharge shows significant lag in driving electrical tree propagation, and drives the rapid evolution close to breakdown through phased accumulation–release mode. The proposed analytical method can effectively improve the identification accuracy of breakdown point, providing a theoretical basis for the insulation optimization and health monitoring of DC cables.

This paper investigated the generation laws of characteristics gases at the cross-linked polyethylene-silicone rubber insulation interface of cable accessories under different types of discharge faults, and proposed gas diagnostic criteria for discharge fault types at the cable accessory interface based on this. Firstly, a gas generation experimental platform for insulation interface discharge of cable accessories was established, different types of discharge faults were distinguished by the high-frequency current transformer method, and the characteristics of the escaping gases from insulation interface discharge faults were analyzed by gas chromatography. Then, a real-type discharge fault gas generation platform of cable accessory was built to experimentally verify the generation laws of characteristic gases under interface discharge faults. Finally, the diagnostic criteria for discharge faults in cable accessories were proposed based on characteristic gas formation laws. The results show that the insulation interface mainly generates H₂, CO₂, CO, CH₄, and C₂H₆ under low-energy discharges (partial discharges), while additionally produces C₂H₄ and C₂H₂ under high-energy discharges (arc discharges). Based on this, a comprehensive gas diagnostic criteria is proposed: when the concentration ratio of CO to CO₂ is between 0.10 and 0.69, it is considered as low-energy discharge; when it is greater than 0.70, it is considered as high-energy discharge. Only the first five gases are present in the gas composition, it is considered as low-energy discharge; while both C₂H₄ and C₂H₂ are detected, it is considered as high-energy discharge. Quantitative indicators show that the proportion of unsaturated hydrocarbons in high-energy discharges ranges from 0.07 to 0.16, and the concentration ratio of unsaturated hydrocarbons to H₂ ranges from 0.08 to 0.30.

As offshore wind power expands into deep sea, the precise calculation of steady-state ampacity for high-voltage direct current (HVDC) submarine cable is of critical importance. Existing studies often neglect the influences of ocean currents on the heat transfer in seabed porous media and submarine cable laying conditions, leading to deviation in ampacity assessment. This study established a three-dimensional thermo-electro-hydrodynamic coupled model based on COMSOL multiphysics to systematically investigate the influencing mechanisms of sediment permeability, porosities, and submarine cable laying conditions on the temperature field and ampacity of HVDC XLPE submarine cable under vertical ocean currents. The results show that seawater flow velocity is the decisive factor influencing ampacity. Setting the sediment porosities to 0.4 and the permeability to 10³ d, when the flow velocity increases from 2 cm/s to 50 cm/s, the ampacity increases by 35.2%, which is mainly attributed to the significant enhancement of convective heat transfer efficiency in the sediment layer. Setting the sediment permeability to 10³ d and the seawater flow velocity to 50 cm/s, when the sediment porosities increases from 0.2 to 0.6, the ampacity increases by 5.6%, which attributes to expanded pore networks enhancing the equivalent thermal conductivity. Sediment permeability and flow velocity exhibit a significant synergistic effect, when the permeability exceeds 10² d, secondary convective heat transfer can be induced in high-speed flow fields. Setting the sediment porosities to 0.4 and seawater flow velocity to 50 cm/s, compared to 10² d of sediment permeability, the flowing fluid can additionally contribute 1.6% of the ampacity gain when the sediment permeability is 10³ d. The bipolar system exhibits a significant thermal coupling effect under ocean currents, causing the temperature difference between the two poles to increase with the increase of flow velocity. Setting the sediment porosities to 0.6 and the permeability to 10³ d, when the flow velocity is 50 cm/s, the temperature difference between the two poles increases by 1 283.3%, resulting in an ampacity difference up to 136 A. Among the laying parameters, the laying spacing has a greater impact on the ampacity than the laying depth.

This paper aims to investigate the application effect of two-component polyurea materials in enhancing the insulation strength of transmission line conductor gaps. Firstly, the physicochemical and electrical properties of the two-component polyurea materials were characterized systematically. On this basis, an experimental platform simulating transmission line conductor gaps was constructed, and the effects of coating thickness and gap distance on the breakdown characteristics of the conductor gaps under 50 Hz AC voltage were analyzed systematically. The results show that the glass transition temperature of the two-component polyurea materials is 152℃, exhibiting good thermal stability, the characteristic electric strength reaches 26.21 kV/mm, the tensile strength is 20.2 MPa, and the elongation at break is 515.2%, and it also shows excellent resistance to UV ageing. When the coating thickness is thin (1 mm and 2 mm), the enhancement effect of polyurea materials on the breakdown voltage of transmission line conductor gaps is limited. However, as the coating thickness increases to 3-5 mm, the breakdown voltage of conductor gap increases significantly. In particular, when the gap distance is 20 cm, as the polyurea coating thickness increases from 0 mm to 4 mm, the characteristic breakdown voltage of conductor gap increases from 138.43 kV to 160.94 kV, showing a significant improvement. When the coating thickness reaches 4 mm or more, even if the minimum withstand gap distance shorten to below 3 cm, the polyurea coating still does not breakdown, demonstrating excellent voltage resistance.

Regarding the issue of metal suspended particle defects in basin insulators, based on the electroluminescence principles, a ZnS:Cu/epoxy resin luminescent composite coating was prepared by doping sulfurized zinc-based material (ZnS:Cu) into epoxy resin (EP), and its properties were characterized. The luminescence pattern of the coating was investigated using rod-plate electrodes, and a defect experiment was simulated on basin-type insulator to explore the feasibility of the ZnS:Cu/epoxy resin coating in defect self-diagnosis. The results show that with the increase of ZnS:Cu content, the surface flashover voltage of the ZnS:Cu/epoxy resin composite coating rises, and the dielectric loss factor increases. The composite coating has a certain luminous threshold, when the mass fraction of ZnS:Cu is 10%-30% and the coating thickness is 0.1-0.3 mm, its luminous intensity increases with the increase of electric field strength, ZnS:Cu content, and coating thickness. Moreover, after spraying the ZnS:Cu/epoxy resin coating on the basin insulator, the defect location can be determined through the luminescence, achieving the purpose of defect diagnosis, which provides a new idea for the defect identification and diagnosis of power insulation equipment.

To study the interface ageing characteristics of hybrid porcelain insulator, the hybrid porcelain insulators, type A and type B composite porcelain insulator were conducted 1 000 h water-boiling ageing test, and the leakage current, infrared temperature rise, and bonding property of the aged samples were measured. The interface bonding mechanism of the hybrid porcelain insulator was analyzed through porcelain block simulation. The results show that during the water-boiling process, the leakage current of the hybrid porcelain insulator changes slightly and no temperature rise occurs, the bonding property is CC-5 level, and the anti-ageing performance of the interface is good. The simulation test show that after coating the silane coupling agent, the surface roughness of the porcelain increases by 821.4%, and the formation of Ti-O-Si chemical bond enhances its physical interlocking with the silicone rubber. At the same time, more -OH groups appear on the surface of porcelain block, which can better chemically bond with silicone rubber, achieving good interface bonding effect.

Aiming at the problem of electric field distortion and abnormal temperature rise caused by insulator degradation in DC transmission system, a distributed conductance matrix was constructed based on the multi-conductor system theory, and the distributed conductance characteristics and electric field distribution of U550BP/240T porcelain insulator string under DC voltage were studied by electric field simulation. The heating mechanism of insulator string was revealed by thermal-electric coupling model and DC live test. The results show that the distributed conductance between normal insulators is basically equal, about 15×10^-10 S/m, while the conductance between the fittings of zero-value insulators increases sharply to about 108×10^-10 S/m. The distributed conductance between fittings and conductors, as well as between fittings and ground, decreases with the increase of spatial distance. The voltage along the insulator string shows a U-shaped distribution. For the zero-value insulator, the partial voltage drops to 1.4%-1.6% of the total voltage, and the peak value of axial field strength attenuates to 5.5%-7.1% of the normal value, resulting in a significant rise in the field strength and partial voltage of the adjacent insulator. Through the 120 kV DC live test, it is verified that the heating curve along the string is similar to the U-shaped distribution curve of voltage, which verifies that the voltage plays a leading role in the heating of insulator. The iron caps of zero-value insulators exhibit uniform heat generation, while those of normal insulators show a significant temperature rise in the middle and lower parts. The correlation coefficient between the heat generation characteristic curves of the insulator string obtained from simulation and experiment is greater than 0.95%, with a maximum error of 12.38%, which verifies the decisive role of distributed conductance in the electric field distribution and heating of insulator, and can provide theoretical basis for the state monitoring of insulators in DC system.

The 1 100 kV bushing at the grid side of converter transformer in the converter station commonly adopts oil-impregnated paper capacitive bushing technology, which has prominent issues with abnormal gas production, prone to oil leakage and internal discharge failures. In order to improve the safety and reliability of 1 100 kV grid side bushings, we designed an epoxy resin impregnated paper capacitive bushing at the grid side of converter transformer. Firstly, the insulating materials, insulation structure, insulation coordination, and manufacturing processes of the bushing were studied. Secondly, the theoretical design of the bushing capacitive core was completed, and the designed product was simulated and analyzed using the finite element method. Finally, the prototype was produced and type tests were conducted. The results show that the simulation results of electric field distribution, hot-spot temperature, and mechanical stress of the newly developed 1 100 kV epoxy resin impregnated paper capacitive bushing all meet the application requirements, with an improvement of 3% in electric field safety margin. This bushing has successfully passed the type tests according to domestic and international standards, and all assessment indicators meet expectations.

First, the dimensions and material properties of imported hot sticks were measured and characterized to determine their mechanical and electrical performance parameters. Then, based on the parameters of the imported products and the existing manufacturing process of hot sticks, simulation design and process optimization were conducted. Finally, a hot stick was fabricated using pultrusion process, and its mechanical and electrical performance were tested. The results show that on the basis of mechanical and electrical physical fields simulations and systematic experimental validation, a domestic lightweight hot stick is successfully developed, and its maximum deflection difference does not exceed 13.2 mm. After 9 times of withstand voltage test under dry conditions, no breakdown, flashover or overheating occur in the hot stick. Moreover, compared with the ordinary domestic hot stick, the prepared hot stick has reduced its unit weight by 29.9%.

Aiming at the problem that the transformer life prediction model has low fit and ignores the influence of the operating state, a residual life prediction model (POA-RF model) based on pelican algorithm (POA) optimized random forest (RF) model was proposed. Taking preventive tests, online monitoring, defect reports, and account data as research objects, a transformer health index system consisting of transformer body, oil quality, and dissolved gas in oil health indices was constructed. Considering the corrective effect of operating status on residual life, with relevant parameters of the health index system as inputs, the POA was used to optimize the RF model to solve its overfitting problem and improve prediction accuracy. Experiments are conducted with the collected transformer instance data to verify the accuracy of the model. The results show that for the 8 groups of scrapped samples in the test samples, the average absolute error of the residual life predicted by the POA-RF model is 1.187 0 years, which is 20.52% and 49.02% lower than the predicted value of the RF model and the calculated value of the health index theory, respectively. For all the test samples, compared with other commonly used machine learning algorithms, the relevant performance indicators of the POA-RF model are all the best, and the optimization effect is obvious, which can better predict the residual life of transformer.