Two kinds of modified magnesium hydroxide (MH) were used as flame retardant, and then compounded with low density polyethylene (LDPE) to prepare LDPE/MH flame retardant materials. The effects of the flame retardants on the mechanical properties, flame retardant properties, thermal stability, and electrical properties of the materials were studied. The results show that the flame retardant properties of the materials increase significantly after adding the modified magnesium hydroxide flame retardant, but the mechanical properties, thermal stability, and electrical properties decrease. The flame retardant of the LDPE with amino silane coupling agent modified magnesium hydroxide is better than that of the LDPE with alkyl silane coupling agent modified magnesium hydroxide, but its adverse effects on mechanical properties and electrical properties of materials are more obvious. When the addition amount of alkyl silane coupling agent modified magnesium hydroxide is 70 phr, the comprehensive properties of the material are better.

In order to study the radial temperature field distribution of overhead conductor, firstly, on the basis of heat transfer theory, a 3D model of finite element simulation was established according to the physical structure of conductor, and a simulation experiment was designed. Then the simulation and experimental results were compared. The results show that under natural convection conditions, the maximum radial temperature difference of the conductor can reach 10.4℃, and the maximum surface temperature difference of different position on conductor is 3.4℃. The simulation results coincide with the measured values under natural convection conditions basically, and the relative error between each layer temperature of the conductor is within ±5%, which verifies the reliability of the simulation model. Under forced convection conditions, there are obvious difference between simulation results and measured values, which indicates that the axial heat transfer of the conductor caused by different heat dissipation conditions has significant effect on the radial temperature field distribution of the conductor. For conservative consideration, in practical applications, the core temperature of conductor can be calculated by multiplying the maximum surface temperature of conductor measured from different position of conductor with correction coefficient of 1.05‒1.10.

The effects of electric field and temperature on the diffusion behavior of water molecules in nano-SiO₂ modified insulating oil were studied by molecular simulation technology. The results show that the water molecules are polarized under electric field, and the water molecules would change from an original disordered arrangement to an ordered arrangement along the direction of electric field. Therefore, under the action of electric field, the Brownian motion of water molecules weakens, and the diffusion ability of water molecules in oil decreases. The electrostatic force between water molecules and oil medium was enhanced by electric field, which is 2‒3 times bigger than that without electric field. This is also the main reason for the increase of interaction energy between water molecules and oil medium under electric field. In addition, under the action of electric field, the free volume fraction of the model decreases, and the effect of temperature on the hydrogen bond between O and H atoms in the model weakens.

Taking the UHV DC transmission line insulators under four typical climatic conditions such as extremely arid, semi-arid, semi humid, and humid as research objects, we conducted natural pollution accumulation tests on insulators. The pollution accumulation characteristics of UHV DC insulators under different environmental conditions were obtained, and the pollution accumulation characteristics of insulators with different umbrella types and hydrophobic surface were described. The results show that from the extremely arid region to humid region, both the ratio of ESDD to NSDD and uneven pollution coefficient of the insulators decrease. The ESDD ratio of bell-type insulator to outer umbrella insulator in humid area is 0.82, and the ESDD ratio of composite surface insulator to hydrophilic surface insulator of tension string in extremely arid and semi-arid areas is 1.64 and 1.85, respectively. The research results can provide a reference for the differential design of external insulation for UHV DC transmission lines at different environmental areas.

Within tens of meters of offshore area in Fujian, a large number of insulation layer is ablated and even on fire for 10 kV overhead insulation line, which causes great security risks to line operation and social security. The ablation location and regional distribution characteristics of the insulation line were investigated, and the main cause was that the offshore lines occurred pollution flashover discharge. Then according to the ablated line samples obtained in the field, the insulating property variation of the line before and after ablation was analyzed. Taking a 10 kV overhead insulation line model as an example, the phenomena and mechanisms of pollution flashover discharge and insulation layer ablation were simulated by finite element analysis and artificial pollution test. At last, according to the mechanism of ablation phenomenon, some specific preventive measures were proposed.

Using ethyl acrylate (EA) and butyl acrylate (BA) as soft monomers, methyl methacrylate (MMA), styrene (St), and acrylonitrile as hard monomers, methyl Hydroxyethyl acrylate (HEMA) and methacrylic acid (MAA) as crosslinking monomers, sodium dodecyl sulfate (SDS) as emulsifiers, and ammonium persulfate (APS) as initiators, an acrylate base emulsion was prepared through semi-continuous seed emulsion polymerization. And then a modified acrylate adhesive for FPC was prepared by adding suitable amount of curing agent and vulcanizing agent to emulsion. The optimal formulation of the acrylate base emulsion was obtained by simple variable method and orthogonal experiment, that is as follow: m(soft monomer) : m(hard monomer) : m(crosslinking agent) : m(emulsifiers): m(initiators)= 65:30:4:3:0.3, w(SDS)=2%, w(APS)=0.3%. With this formulation, the peel strength of the encapsulation sample is 0.92 N/mm, the peel strength of the single panel is 2.15 N/mm, and the soldering resistance pass rate is 100%, the moisture absorption rate of the film is 3.11%, which can all meet the performance requirements of adhesivein the FPC substrate.

The dielectric spectrum experimental data of epoxy resin material for ultra high voltage (UHV) power equipment was fitted by Havriliak Negami (HN) equation, and the HN mathematical model parameters of epoxy resin material were established. In the frequency range of 10^-1-10⁶ Hz and temperature range of -40-200℃, the frequency spectra and temperature spectra of epoxy resin were measured using broadband dielectric spectrometer. Then the experimental data was fitted by the improved HN equation, and the characteristic parameters of dielectric spectrum mathematical model were obtained. The results show that the uniqueness and accuracy of the fitting parameters can be guaranteed combining with genetic algorithm and least square method. The characteristic parameters of dielectric spectra, including direct current conductivity and relaxation polarization time, have significant temperature dependence, which basically accords with Arrhenius formula.

Vegetable insulating oil is easy to oxidate during operation and it will affect the service life of transformer. In this study, 2,6-di-tert-butyl-p-cresol (BHT) was chosen as antioxidant, and the characteristic parameters of the vegetable insulating oil were compared by the ageing tests. The effect of BHT antioxidant was analyzed by measuring the acid value, peroxide value, and moisture content. The effect of BTH antioxidant on the insulating properties was studied by detecting the dielectric loss factor, breakdown voltage, and FDS curves. The results show that BHT antioxidant can effectively improve the dielectric constant of vegetable insulating oil. Through the molecular formula analysis on the reaction mechanism between BHT reagent and unsaturated oil in natural ester insulating oil, the oxidation resistance process of BHT in natural ester insulating oil can be reflected more intuitively. When the addition amount of BHT is 0.20%, it has a better effect on improving the insulation performance of vegetable insulating oil.

In the electrical test and operation of generator, the hypotenuse electric field at the end of stator winding is very high, which is a weak part that corona discharge often occurs. In this study, an analytical model and a finite element model of the hypotenuse electric field at the end of stator winding were established. The influencing factors and laws of the hypotenuse electric field were studied, and the influence of the hypotenuse clearance, rotating angle, and dielectric constant of the filling medium on the maximum electric field was analyzed. An effective method to optimize the electric field at the end was presented. The results show that under the in-phase winding, the hypotenuse electric field can be optimized by decreasing the surface electric field of stator bar, the width of bar, and the rotating angle of bar or increasing the hypotenuse clearance; Under the out-of-phase winding, the hypotenuse electric field can be optimized by increasing the dielectric constant of filling medium and the hypotenuse clearance of winding. The finite element model of hypotenuse electric field can accurately analyze the maximum electric field and the distribution trend at the end of winding. The correctness of the model is verified by corona test of UV imaging equipment, which indicate that that the model has good engineering application value.

In order to find out the effect of adding nano-SiO₂ on the relative permittivity and conduction characteristic of ethylene propylene diene monomer (EPDM) insulation, we prepared EPDM composite dielectrics with different mass fractions of nano-SiO₂ by melt-blending method. The dispersion of nanoparticles in the EPDM matrix and the bonding properties between nanoparticles and EPDM matrix were analyzed. The relative permittivity and the steady-state current of the EPDM nanocomposite dielectrics at different temperatures and electric fields were measured, and the conductance characteristic were analyzed. The results show that when the mass fraction of nano-SiO₂ is 0.5%, the dispersion of nano-SiO₂ is the best in EPDM. The steric hindrance, which formed by doping of low content, reduces the mobility of the EPDM molecular segments and its side groups, and the interface effect is obvious in the nanocomposite dielectrics, making the relative permittivity and conductance decrease, the threshold electric field strength of space charge injection enhance, the insulating performance improve significantly. With the increase of the mass fraction, the interface effect between nanoparticles and EPDM matrix is weakened. When the mass fraction of nano-SiO₂ is 2.5% or 5.0%, the agglomeration caused by doping makes the relative permittivity and the conductance increase, and the threshold electric field strength of space charge injection decreases. The interface effect caused by the addition of nano-SiO₂ is a key factor affecting the properties of EPDM nanocomposite dielectrics.