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.

The thermal conductivity mechanism and common thermal conductive fillers of thermal conductive silicone composites for electronic packaging were presented, the preparation strategies and research progress of filled-type high thermal conductive silicone composites were reviewed, and the future research direction of thermal conductive silicone composites for electronic packaging was prospected.

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.

On the basis of the crystal structure of piezoelectric effect of polyvinylidene fluoride (PVDF) polymer, the effects of different annealing temperatures (60-160℃) on the surface crystal morphology, crystal size, crystallinity, and key dielectric parameters including polarization response curve and piezoelectric coefficient of PVDF film samples were studied. The results show that the sample crystal size and crystallinity increase with the increase of annealing temperature in the range of 60-140℃. The polarization curves show higher residual polarization intensity and hysteresis, and the piezoelectric coefficient increases from 11 pC/N to 27 pC/N with the increase of annealing temperature. When the annealing temperature reaches 160℃, cracks appear on the surface of sample, and consequently the breakdown is easy to occur in the polarization process, and the dispersity of piezoelectric coefficient is large.

A base gel was prepared with bisphenol A epoxy resin E124 as the main resin, polymercaptan as the curing agent, and imidazole as the accelerator. A single component high thermal conductive structural adhesive was prepared by adding different proportions and sizes of spherical alumina and irregular alumina into the base gel. The effects of different filling content and different particle sizes of alumina on the thermal conductivity, bonding strength, viscosity, and thixotropy of the single component high thermal conductive structural adhesive were studied. The results show that when the mass ratio of base gel to the three different particle sizes of alumina is m(base gel)∶m(40 μm Al₂O₃)∶m(2 μm Al₂O₃)∶m(0.5 μm Al₂O₃) =15∶59.5∶25.5∶6, m(base gel)∶m(40 μm Al₂O₃)∶m(5 μm Al₂O₃)∶m(0.5 μm Al₂O₃) =15∶59.5∶25.5∶8, m(base gel)∶m(40 μm Al₂O₃)∶m(10 μm Al₂O₃)∶m(0.5 μm Al₂O₃)=15∶68∶17∶8, three kinds of high thermal conductive structural adhesives cured at 90℃ for 15 min can be obtained, their thermal conductivity is 2.73, 3.05, 2.85 W/(m·K), their bonding strength is 5.49, 5.55 and 5.31 MPa, and their viscosity is 145 000, 127 467 and 118467 mPa·s, respectively. The volume resistivity of the three kinds of high thermal conductive structural adhesives is above 10¹⁴ Ω·m, and the adhesive survival rate after high temperature and humidity, cold and thermal shock is more than 70% and 90%, respectively. The performance of the high thermal conductive structural adhesive meets the basic performance requirements of screen printing and heat dissipation materials for chip packaging.

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 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.

In order to improve the insulation ability of the three media interaction area of basin insulator, the reasons of the accumulation of foreign body, and the flashover along the basin insulator surface induced by the structure design defect of the three media interaction area was analyzed from the composition of three media interaction area, the movement characteristics of foreign body and the typical discharge phenomenon. Through electric field simulation, the influence of grounding shielding electrode, the flange thickness of basin insulator, and the distance between the grounding shielding electrode and the busbar cylinder flange on the electric field intensity in the low potential three interaction area were studied, the variation law of electric field in the high potential three interaction area with tilting angle and three media interaction area width of basin insulator were given. The calculation method of the thickness of the high voltage side of grounding shield electrode to prevent resin through failure and the criterion of electric field check in the three media interaction area were presented. The results show that the reasonable structure design of three media interaction area with high and low potential can effectively inhibit the surface flashover induced by foreign matter accumulation.

In this paper, the physicochemical and electrical properties of oil-paper insulation in the process of surface discharge deterioration under static and flowing oil conditions were studied. The discharge product and moisture of oil-paper insulation were analyzed by infrared spectrometer and micro-water measuring instrument. The multilayer microstructure of oil-paper insulation was analyzed by viscosity tester, X-ray diffractometer, and scanning electron microscope. The conductivity, electric strength, and partial discharge of oil-paper insulation were analyzed by electrical measurement. The multi-type discharge deterioration characteristics of oil-paper insulation in static and flowing oil were compared and analyzed. The results show that the flow of oil slows down the surface discharge deterioration of oil-paper insulation, retards the rise of electrical conductivity and the decline of electric strength, and inhibits the occurrence and development of surface discharge. The surface conductivity determines the difficulty of surface discharge, and its increase results in the statistical distribution of surface discharge times showing a repetitive characteristic of "wave" gradually. Discharge frequency determines the surface discharge deterioration and destruction degree of oil-paper insulation, which is an efficient characteristic quantity to evaluate the deterioration state of oil-paper surface discharge.

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.

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.

In order to solve the prediction problem of water tree density of XLPE cable, an analysis method combining the macro detection data with the micro water tree profile of aged cable was proposed. Two new parameters (carbon and oxygen index and water content index) were proposed to quantitatively describe the changes of EDS and FTIR results in the water tree region. Firstly, the polarization and depolarization current method (PDC) was used to detect the water-tree ageing cables under different experimental conditions. A series of macroscopic parameters such as cable ageing factor, DC conductivity, and 0.1 Hz dielectric loss factor were obtained. Then, the micro parameters of water tree were obtained by microscopic observation of cable slice. The water tree growth model was established to calculate the water tree density of cable, and the correlation between the macroscopic parameters of cable and the microscopic water tree density was analyzed. The results show that the longer the ageing time, the greater the carbon oxygen index and water content index, and the faster the rate of increase. Based on the correlation coefficient, a new mathematical model for predicting the growth density of water tree inside XLPE cable is established, which realize the combination of microstructure of water tree inside cable and macro test parameters.

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.

The research on the correlation between the insulation strength and microscopic parameter of gas medium is beneficial to improve the development efficiency of SF₆ alternative gas. In this paper, based on density functional theory, the M06-2X functional and def2 series basis sets were used to establish the stable structures of 73 kinds of gas molecules. The Fukui function parameters that characterize the electron probability density difference were calculated, its correlation with insulation strength was analyzed, and the corresponding prediction model was established. The results show that the electrophilic index, local reduced electrophilic index minimum, local reduced nucleophilic index minimum, molecular volume, local surface electrophilic index maximum, local surface nucleophilic minimum have strong correlation with insulation strength. When the electron probability density in the prediction model is 0.000 05 a.u., the maximum determination coefficient is 0.812, and the mean square error is 0.094.

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 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.

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.