According to the structure of cable buffer layer, a partial discharge test platform with controllable humidity environment for buffer layer was established. Three typical defect models were designed and conducted partial discharge tests by pulse current method. The results show that the variation of relative humidity has little effect on the geometric shape of partial discharge pattern, while has large effect on the characteristic parameters of partial discharge. With the increase of humidity, the discharge amplitude of three models decreases at first and then increases. Under constant humidity and voltage, the partial discharge activity in the needle-plate system is higher than that in the other models. Under 180 V of voltage and 90% of humidity, the maximum pulse amplitude reaches 770 mV.

In order to research the influence of processing temperature of master-batch on the properties of HVDC cable insulation, three kinds of master-batch were prepared at different processing temperatures, and then the insulating properties of HVDC cable insulation manufactured by the master-batch were studied. Impurity detection was carried out at first, and then the chemical structure of crystal points detected by impurity detection was analyzed by attenuated total reflectance infrared spectroscopy (ATR-IR). At last, the electrical and mechanical properties of three HVDC cable insulation were compared. The results show that there are more crystal points detected in the HVDC cable insulation prepared by the master-batch under an excessive processing temperature, and part crystal points are light yellow. Compared with semitransparent crystal points, there is no strong absorption peaks in the infrared spectra of light yellow crystal points, but the excessive processing temperature has a greater negative effect on the electrical properties of HVDC cable insulation, while has a smaller effect on its mechanical properties.

In order to investigate the optical properties of epoxy-mica insulation in ageing process, we conducted multi-factor accelerated ageing treatment on epoxy-mica main insulation of generator stator bars. The blue whiteness of the samples at different voltage and temperature was measured, and the effect of ageing on the optical refractive index and absorption ratio of epoxy-mica insulation material was analyzed. The equation relationship between blue whiteness and ageing time was determined by regression analysis, and the validity of equation was proved by t test. Finally, the insulation life of epoxy- mica main insulation was fitted and analyzed by the variation characteristics of blue whiteness combining with Fallou model. The results show that the blue whiteness value of epoxy-mica insulation decreases constantly with the increase of ageing degree of insulation. Combining Weibull distribution probability with Fallou model, we can realize the life assessment of epoxy-mica insulation.

The traditional insulation reliability evaluation method based on failure life data for solid dielectric need long test time, and the failure data is little and difficult to obtain. In view of this issue, a reliability assessment method based on the test data of accelerated performance degradation was studied in this paper. Firstly, the average charge density was used as the characteristic parameter of performance degradation, and accelerated performance degradation tests were conducted to obtain performance degradation data under 140 kV/mm, 160 kV/mm, and 180 kV/mm of field strength, respectively. Secondly, the pseudo-failure life of XLPE insulation material under different field strengths was calculated, and its statistical distribution was determined. Finally, the pseudo-failure life data was expanded in combination with the virtual augmentation theory, and the expanded data was analyzed by statistical analysis methods. The results show that the performance reliability indicators such as sample reliability, failure distribution density function, and average life can be obtained through using accelerated performance degradation test method to assess the reliability of XLPE insulation. In combination with the accelerated life model theory, the life expectancy of the XLPE insulating material is 15.3 years under 20 kV/mm of stable field strength, and the reliability when reaching the expected life is 0.445 1.

In order to obtain a silicone rubber composite with both good resistivity nonlinear characteristics and high electric breakdown characteristics, a copper calcium titanate (CCTO) ceramic powder was prepared, and the CCTO was mixed with two-component liquid silicone rubber to prepare CCTO/silicone rubber composite (the volume fraction of CCTO ceramic powder was 3%, 5%, and 10%, respectively). Their microstructure, dielectric spectrum characteristics, DC breakdown performance, and DC nonlinear resistivity were tested, and their application performance was compared by establishing a high-voltage DC cable terminal simulation model. The results show that the CCTO ceramic powder has obvious characteristic diffraction peaks, and the powder particle size is about 500 nm; with the increase of CCTO ceramic powder content, the dielectric constant of the CCTO/silicone rubber composite increases, the DC breakdown strength decreases, and the non-linear characteristics of resistivity are significantly enhanced. With the enhancement of the nonlinear characteristics of resistivity, the electric field strength in the reinforced insulation of cable terminal stress cone decreases significantly. When the volume fraction of CCTO ceramic powder in the composite is 5% or 10%, the composite can be used as a reinforced insulating material of stress cone for high voltage DC cable accessory.

According to the special requirement of all glass fiber reinforced resin matrix composite (GFRP) transmission tower head on the fastening strength and insulation performance of connecting parts, GFRP insulated fasteners were developed. A medium-high temperature curing epoxy bulk molding compound (BMC) was designed and developed, and its initial viscosity decreases through blending modification of bisphenol A and bisphenol F epoxy resin. The mechanical properties and water absorption of samples with different ratio of Al(OH)₃, talcum powder, and SiO₂ fillers were tested to determine the material system that meets the requirements of molding process. Non-isothermal DSC measurement was conducted on the optimized material system, and T-β extrapolation and orthogonal tests were applied to evaluate, optimize, and determine the forming process parameters. The results show that the failure load, shear strength, and electrical properties of the product prepared by the optimal material system and forming process parameters meet the design requirements, which indicates this material system is suitable for the manufacture of GFRP fasteners with higher electrical performance.

The fault type recognition and condition assessment play the crucial roles in fault diagnosis and maintenance. Different defects will produce partial discharge signals with difference, and the partial discharge signal also changes with the defect severity and the evolution of partial discharge. This situation can be regarded as pattern recognition of different severity levels and evolution stages, and the pattern recognition is a typical classification problem. In this paper, classification problems such as pattern recognition and state assessment were reviewed. Compared to classification results based on mathematical statistics, artificial intelligence has achieved nearly 100% of recognition accuracy. However, there are still some shortcomings in current research, this paper gives some solution strategies and prospects future research direction.

A detection platform of insulation partial discharge (PD) under pulse voltage was constructed by using electromagnetic detection method with the help of a high-voltage pulse power source with adjustable voltage parameters of repetitive pulse. The influence law of frequency variation of repetitive square wave voltage on the PD statistical characteristics of single point and multipoint interturn insulation discharge model for inverter-fed motor was studied. The results show that with the increase of frequency, the amplitude of both insulation single point and multipoint discharge decrease significantly. This may be caused by composite factors such as the change of residual charge distribution on insulation surface, the increase of the excitation probability of initial electron, and the increase of surface temperature after discharge. According to the research results, the influence of square wave pulse voltage frequency on the PD pulse should be carefully considered in the PD detection of motor insulation, and the appropriate voltage frequency should be selected to improve the sensitivity and test accuracy.

In order to study the influence of insulation ageing of cable joint on the electric field distribution at the typical defects of XLPE/silicone rubber interface, we built a simulation model of 10 kV cable joint by COMSOL Multiphysics simulation software. The electric field distribution in the composite interface with defect of conductive impurities, scratches, moisture, respectively was calculated before and after ageing of insulation. And the growth change of water tree in the cable insulation was analyzed combining with the simulation results. The results show that three kinds of defects can lead to obvious electric field distortion at the defect of composite interface, and the ageing of insulation can increase the electric field strength at the interface, and increase the effect of defects on the electric field distribution at the same time. The electric field distortion at the end of water tree is serious after initiation, with the growth and development of water branches, the electric field strength in the area close to each other decreases, but the local electric field concentration still exists.

A MWCNTs/T-ZnOw/PVB composite was prepared via solution blending method by using multi-walled carbon nanotubes (MWCNTs) and zinc oxide whisker (T-ZnOw) as fillers and polyvinyl butyral (PVB) as matrix. The thermal diffusivity of the composite was measured by transient electro-thermal technique (TET). The effects of different mass fraction ratio of fillers, heat treatment time and temperature, and ultraviolet accelerated ageing on the thermal conductivity of the composite were investigated. The results show that under the same mass fraction of fillers, the thermal conductivity of the composite increases at first and then decreases with the increase of MWCNTs content. When the heat treatment time is 1 h, with the increase of the heat treatment temperature from 80℃ to 140℃, the thermal conductivity of the composite decreases at first and then increases. When the heat treatment temperature is 140℃, the thermal conductivity increases after heating for 1 h, but it decreases with the extension of heating time. When the composite is accelerated aged by ultraviolet irradiation, the thermal conductivity of the composite decreases with the increase of irradiation time.