Epoxy resin impregnated crepe paper (ERICP) insulating materials are widely used in power equipment insulation, and moisture is an important reason affecting their insulation state. In this paper, the frequency domain spectroscopy (FDS) technology was used for insulation condition evaluation. Firstly, ERICP samples with different moisture content were prepared and carried out FDS tests. Then, according to the FDS spectrum curves, the variation law of FDS characteristic parameters with moisture content was analyzed. Finally, the dielectric modulus spectrum and modulus factor were introduced, and the insulation condition evaluation method of ERICP was proposed. The results show that the change of moisture content affects the overall change law of FDS curves. The dielectric modulus can effectively suppress the influence of DC conductivity to characterize the internal relaxation process. The dielectric modulus spectrum of ERICP samples has obvious relaxation peak in the low-frequency range, and the characteristic frequency of relaxation peak increases with the increase of moisture content. The integral area of the imaginary part of dielectric modulus can be used as a characteristic parameter to characterize the insulation condition of ERICP. The relationship between the modulus factor and moisture content has 0.997 5 of goodness of fit with the exponential function.

The domestic and imported 220 kV cross-linked polyethylene (XLPE) cable insulation were carried out accelerated thermal ageing tests at 90℃ and 135℃, and the effects of thermal ageing with different temperature and different time on the physical and chemical properties, mechanical properties, and electrical properties of XLPE insulation were investigated. The thermal ageing life of domestic and imported XLPE insulation were evaluated. The results show that the oxidation reaction induced by thermal ageing leads to the appearance of carbonyl peak in the XLPE sample, and the higher the ageing temperature, the more obvious the carbonyl peak. After ageing, the cross-linking degree of XLPE samples increases, which damages the crystal structure in the crystallization zone and decreases the crystallinity, resulting in the overall deterioration of mechanical properties. The molecular chain of the aged sample is broken and degraded, and the movement of carrier is intensified under the action of electric field, resulting in the decline of AC electric strength. The thermal ageing life evaluation shows that the thermal ageing life of domestic XLPE insulation material is greater than that of imported XLPE insualtion material. The comprehensive comparison of various properties shows that the level of domestic XLPE insulation material is equivalent to that of imported XLPE insulation material.

In order to study the surface properties of different materials of insulators, epoxy resin and polytetrafluoroethylene (PTFE) were used as research objects. Firstly, the adhesion characteristics of insulators made of different materials were obtained through surface energy test. Then, the influence of different particle sizes of metal patticles on the surface flashover characteristics of insulators under natural adhesion conditions was studied through test. The results show that the surface energy of PTFE insulators is 30.44 mJ/m², which is lower than that of epoxy resin insulators, and the viscosity of PTFE is smaller. As the particle size of metal particles attached on the insulator surface decreases, the surface flashover voltage of epoxy resin and PTFE insulators increases gradually, and the surface flashover performance of the two materials of insulators is similar. The insulation failures caused by metal particles can be reduced by replacing the original epoxy resin interface with PTFE.

The dissolved gas monitoring method in oil is an important method for transformer fault diagnosis and operational status evaluation. A spectral analysis method of gas in transformer oil based on single gas chamber vacuum degassing was presented in this paper, and the principle and structure of the dissolved gas monitoring device in transformer oil based on this method were introduced. Due to the different temperature and pressure in the gas chamber during each detection, temperature and pressure compensation experiments were required, which verified the effectiveness of the temperature and pressure compensation method. Finally, the mixed gas was analyzed quantitatively by the designed device. The results show that the spectral analysis method of gas in oil based on single chamber vacuum degassing designed in this paper has a good effect, which verifies the feasibility of the design scheme. Compared with the common infrared spectroscopy methods for monitoring gas content, this scheme does not require nitrogen as the background gas, reducing the operating costs and improving the automation level of device.

In view of the degradation of insulating properties of ethylene propylene diene monomer (EPDM) cables caused by mechanical, electrical, and thermal stresses during operation, the dielectric spectrum of EPDM used for power cable insulation in tensile state was studied. Firstly, a tensile force applying fixture was designed, and a multi-stress dielectric spectrum testing system was built. The dielectric spectrum of EPDM under the joint action of tensile force and thermal stress was measured. The influence of tensile ratio on the dielectric loss factor of EPDM was analyzed emphatically. Then, the characteristic parameters of dielectric spectrum and their variation with tensile ratio were obtained by Cole-Cole model. The change of chemical groups of EPDM was analyzed by Fourier transform infrared spectroscopy (FTIR) from the microscopic view. Finally, the properties change mechanism of EPDM after tensile was summarized combining with carrier apparent mobility. The results show that the tensile ratio has significant influence on the complex dielectric constant and dielectric loss factor of EPDM, especially when the frequency is low, the dielectric loss factor decreases at first and then increases with the increase of tensile ratio. The analysis based on Cole-Cole model shows that the DC conductivity, relaxation strength, and relaxation peak frequency of EPDM decrease at first and then increase with the increase of tensile ratio. Combining with Fourier infrared spectroscopy, it is concluded that the EPDM molecular chain will break when the tensile ratio reaches a certain value, and the carrier mobility extracted from the depolarization current decreases at first and then increases with the increase of tensile ratio.

The effects of temperature and DC electric field on the diffusion characteristics of water molecules in nano-SiO₂ modified vegetable insulating oil were analyzed by molecular simulation. The results show that the water molecules in the model is polarized under the influence of strong electric field, and the initial disordered arrangement is rapidly transformed into an ordered arrangement along the electric field. When water molecules are bounded by electric field, the Brownian motion intensity of water molecules becomes weak, and the diffusion strength of water molecules in vegetable oil is weaken. At the same time, the electric field increase the interaction energy between water molecules and vegetable oil molecules, which makes the combination between them more closely, and weakens the influence of temperature on the interaction energy. In addition, the free volume of model is smaller after the application of electric filed, and the peak value of radial distribution is lower in the radial distribution diagram.

In view of the high concentration of industrial dust pollution in some areas of Ningxia at present, considering the actual situation of uneven roughness of insulator surface in Ningxia power grid, the pollution particle deposition model of insulator surface under high pollution coverage was obtained based on the principle of energy conservation. The multiple physical field coupling insulator natural pollution simulation model was built by using COMSOL simulation software. Taking porcelain insulators of 110 kV AC transmission line near an industrial park in Wuzhong, Ningxia as the research object, the coupling effects of wind speed, particle size, pollution composition, and voltage type on the natural contamination characteristics of insulator surface were simulated. The results show that the pollution adhesion rate in the AC field shows irregular "M" shape along the shed, and the adhesion rate of silica is the highest. In the DC field, the pollution adhesion rate shows "U" shape along the shed, and the adhesion rate of iron oxide is the highest. Compared with the simulation model of insulator contamination on uniform rough surface, the model proposed in this paper can effectively improve the accuracy of simulation results and better reflect the contamination distribution of each shed of insulator string in the high-pollution industrial dust environment.

In order to analyze the breakdown discharge characteristics of air gap at micrometer scale, a microgap discharge experimental platform was built to study the change of breakdown characteristics of air gap with the air pressure and electrode spacing in the range of electrode spacing between 1-100 μm. When the air pressure or electrode spacing was adjusted to make the breakdown voltage reach the lowest point, it was found that the breakdown voltage curve appeared a plateau, and corresponding to different external conditions, the length range of plateau was different. Through the simulation of microscale electric field, it was found that the electric field at the edge of electrodes was still in a higher range, within the range the self-sustaining discharge can still achieve. The collisional ionization process can reach breakdown between the electrodes through a longer path rather than the shortest distance, so that the breakdown voltage maintained at the lowest point, thus the plateau period was formed. When the electrode spacing was less than 10 μm, the ion-enhanced field emission mechanism was involved in the breakdown, and the lowest point of breakdown voltage continued to decrease from the plateau period. The number density of cathode ions was not only sensitive to the electrode spacing, but also influenced by the external air pressure, and the generated ion-enhanced field would enhance the intensity of field emission and further reduce the breakdown voltage. Combined with the analysis of air pressure and electrode spacing, the traditional Paschen’s law is no longer applicable in the micro-scale range, and the breakdown voltage is no longer determined by the product of the electrode distance d and the pressure p.

In this paper, the modification methods of polypropylene, the development and operation of polypropylene cables, and the existing regulations and specifications of polypropylene cables were reviewed. According to the research and development status of polypropylene cables, the problems that may be encountered in the future operation of polypropylene cables were summarized and research suggestions were put forward, which can provide reference for the subsequent research and commercial application of polypropylene cable.

As a kind of environment friendly liquid dielectric with high ignition point and degradability, natural ester insulating oil is widely considered as a good substitute of mineral oil in power transformers. In order to improve the electrical and thermal ageing properties of natural ester-paper insulation system, the surface of cellulose insulation paper was modified by silane coupling agent, and the oil-paper composite insulation combinations of natural ester, traditional mineral oil, ordinary insulation paper, and silane modified insulation paper were conducted accelerated thermal ageing tests. The ageing characteristic paremeters of oil-paper during the thermal ageing of four combinations were compared and analyzed. The results show that the insulating paper modified by silane can maintain a relatively complete three-dimensional network structure of cellulose during thermal ageing, and improve the ageing resistance and electrical performance of the natural ester-paper system.