Combining with the relationships among the DC submarine selection, voltage level, and transmission capacity of HVDC submarine cable projects in China, taking the raw material input of DC submarine cable required per unit transmission capacity as a typical economic index, we find that with the increase of voltage level and current capacity of the single loop DC submarine cable, the economy of DC submarine cable increases. By comparing the materials consumable variation of different routes after improving the voltage level and transmission capacity, we find that it is more effective to improve the economy of DC submarine cable by increasing the electrical level of DC submarine cable insulation and the maximum operating temperature of conductor to improve the voltage level and transmission capacity, respectively. In addition, a ±525 kV DC submarine cable with the highest conductor operating temperature of 70℃ was selected as the typical specification, and its insulation field strength distribution variations were analyzed through finite element simulation when the applied voltage and conductor operating temperature increased to 972 kV and 90℃, respectively. The results show that the increase of voltage level and conductor operating temperature will both cause a further increase of field strength close to insulation shield after the insulation field strength reversal, and there is a synergism effect between them. On this basis, a semicircular protuberance with 0.125 mm of depth was set on the interface of insulation shield into insulation, and the finite element simulation results show that the field strength at the protuberance increased by 35.4% compared with the case without protuberance.

In this paper, the effect of DC-temperature composite field on the electrical tree growth characteristics was introduced. The effect mechanism of charge transport on the electrical tree deterioration under temperature and electric field coupling conditions and the research progress in electrical properties of epoxy nanocomposite dielectrics were reviewed.

PI nano composite films were conducted long-term multiple ageing at 270℃, 70℃ and 90%RH, and 320℃, and their thickness, dielectric spectra, conductivity, partial discharge initiation voltage, and insulation life at different ageing stages were tested. The results show that the insulating properties of the PI film has no obvious change after ageing at 270℃. The high humidity environment has a significant impact on the dielectric spectra, conductivity, and partial discharge initiation voltage of the PI film, but it does not shorten its insulation life. The internal structure of PI film would change under the high temperature of 320℃, which will shorten its insulation life by about 30%.

PTC resistance device, which made by positive temperature coefficient (PTC) material, can be used as a passive component to prevent overcurrent fault. In this paper, four kinds of polymer-based PTC materials were prepared by melting blending method, and the effects of conductive filler concentration, coupling agent, and supplementary conductive filler on their properties were studied. According to the temperature-resistance characteristics and heat transfer equation of polymer PTC composite, its current limiting process was simulated. The experimental results show that increasing the concentration of conductive filler will lead to the decrease of the resistivity of composite at room temperature. The PTC properties of the composites can be improved by using silane coupling agent to modify CB and adjusted by the interaction of various fillers. The simulation results show that under certain assumptions, the PTC resis-tor, as a passive component to prevent overcurrent fault, can limit the short-circuit current of power system in a short time.

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.

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.

DGEBA/OSC cross-linked epoxy resin blend systems with different proportions were constructed by molecular dynamics (MD) simulation using methyl tetrahydrophthalic anhydride (MTHPA) as curing agent, and the blend system samples were prepared. The thermodynamic properties of the blending systems were studied by simulation and experiment. The simulation and test results show that with the increase of the OSC proportion, the glass transition temperature (T_g) of the blend systems increases, when the molar ratio of DGEBA to OSC is 6∶4, the T_g increases by 30.7 K. The elastic modulus and strength of the systems increase at first and then decrease, and reach the optimum at 8∶2 of molar ratio. The addition of OSC can reduce the fractional free volume (FFV) and mean square displacement (MSD) of the systems, and weak the molecular segment movement ability. The calculation results of synergy rotational energy barrier and cohesive energy density (CED) show that the blend system with stronger molecular segment rigidity and larger interaction force between segments has better thermodynamic properties.

In this paper, the current fire protection standards of transformer oil for rail transit were introduced in detail. The necessity of synthetic ester as transformer oil for rail transit was described mainly from the aspects of fire safety, environmental protection, moisture resistance, and later oil change maintenance.

Considering the heat transfer and charge accumulation process in DC GIL comprehensively, we established an electro-thermal multi-physics field coupling model of DC GIL. On the basis of this model, the effect of the volume conductivity of insulating materials on the surface charge accumulation of basin type insulator was simulated and calculated under the coupling action of DC electric stress and thermal stress. The results show that the surface charge accumulation of insulator can be inhibited effectively by decreasing the volume conductivity of typical insulating materials for current AC basin type insulator by two orders of magnitude. However, if the volume conductivity of insulating materials decreases excessively, the surface charge accumulation of basin insulator will be aggravated.

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.

A series of accelerated thermal ageing tests were conducted on some nuclear cables. On the basis of Arrhenius model, the apparent activation energy of nuclear cable materials was obtained using the elongation at break method and the dielectric loss spectrum method, and the effect of activation energy variation on the ageing life evaluation of nuclear cable materials was studied. Then the thermal ageing reference curves of nuclear cable materials were developed on the basis of fixed activation energy and varying activation energy, respectively, and verified by experiments. The results show that the apparent activation energy decreases gradually with the ageing of cable materials. A small change of apparent activation energy will have great impact on the life evaluation of cable materials. The thermal ageing reference curve on the basis of varying activation energy is more consistent with the actual ageing trend of cable materials, which can be used for the ageing life evaluation of nuclear cable materials.

Aiming at the lack of metal passivator in oil for 22 transformers in a power grid company, a self-developed metal passivator adding device was used to add metal passivator, and the adding effect of metal passivator was verified by sampling and detecting the metal passivator content and corrosive sulfur regularly. The results show that adding metal passivator can alleviate the corrosion of corrosive sulfur to transformer effectively, and the key problems during the adding process of metal passivator are pointed out, which are preventing oil leakage, preventing air mixing in, controlling injection flow, and preventing pollutants mixing in.

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.

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 epoxy resin samples for dry type insulation equipment were conducted ageing test. The electric strength and dielectric spectrum of the samples with different ageing degree were tested, and their activation energy were calculated. It is found that with the increase of ageing degree, the activation energy of the epoxy resin shows a change trend of decreasing-increasing-slightly decreasing-increasing, and the electric strength shows a zigzag downward trend. The accelerated ageing time at high temperature can be converted into operating time at working temperature by the accelerated ageing factor (AF) obtained by Arrhenius equation. Taking that the electric strength decreases to 50% of the initial value as a sign of life end for material, we could obtain the activation energy corresponding to the life end of epoxy resin material, which is 209.7 kJ/mol. The judging method of the insulation state and life for epoxy resin dry type insulation based on activation energy is established, and the connection mode and test method of dielectric spectrum measurement for dry type insulation equipment are proposed by taking dry type transformer as an example. The life prediction method is applied to an actual dry type transformer in the project, it is obtained that the activation energy of the dry-type transformer is 69.4 kJ/mol, and the its minimum residual life is predicted to be 36.5 years.

The discharge characteristics of column-plate electrode structure under high frequency excitation were studied by combining experiment and simulation under different solution concentrations. The discharge characteristics of gas-liquid two-phase dielectric barrier discharge (DBD) were measured through experiment, and the electrical and luminescent characteristics under different solution concentrations and applied voltage amplitudes were obtained. On this basis, the equivalent circuit model corresponding to this experiment was established by combining with the physical process of gas-liquid two-phase discharge. The model parameters were determined by combining the experiment with the electric field simulation, and the circuit simulation model was established in Simulink. The voltage and current waveform, and Lissajous graph under different concentration and voltage amplitude were obtained through simulation. The correctness of the simulation model was verified by comparing simulation and experimental results. The discharge parameters, such as air gap voltage, liquid phase voltage, discharge channel current, and energy ratio, which could not be obtained in the experiment directly, were further extracted by the above model. The results show that the solution concentration has no significant influence on the voltage and current waveform and luminescence characteristics of the loop obtained by experiment. However, it is found through simulation that the proportion of energy consumed by gas phase and liquid phase are affected by it greatly. With the increase of solution concentration, although both liquid power and gas power increase, the liquid power increases faster, resulting in that the energy ratio of liquid phase increases obviously. The energy ratio of gas phase can be improved by increasing the excitation source voltage, which can inhibit the energy obtained by liquid phase to a certain extent.