The increasingly developed microelectronic devices have put forward higher requirements on thermal conductive and electrical insulating thermal interface materials, and the silicone rubber composites with high thermal conductivity and electrical insulating can be prepared through construction of micro-nano hybrid heat conduction network. First, a nano-alumina coated graphene oxide was prepared by a simple and green self-assembly strategy, and it was reduced into TRGO@Al₂O₃ nano-hybrid filler by high temperature treatment. Then it was mixed with micron alumina and filled into liquid silicone rubber. The influence of different nano alumina coated amounts on the thermal conductivity and volume resistance of the system was studied by adjusting the ratio of nano alumina to graphene oxide. The synergistic thermal conductive effect of the micro-nano hybrid system was studied by controlling the ratio of nano-hybrid filler to micron alumina. The results show that when the 3% of TRGO@Al₂O₃ and 54% of micron alumina are compounded, the thermal conductivity of the composite reaches about 2.5 W/(m·K), and the volume resistance is greater than or equal to 10⁹ Ω·cm.

The thermal conductivity of insulating varnish could be improved by adding inorganic oxide thermal conductive material into the epoxy modified unsaturated polyester resin. The effect of particle size and surface modification of fillers on the sedimentation of insulating varnish and effect of different filler content on the thermal conductivity and viscosity of insulating varnish were studied. A high thermal conductive and solvent-free insulating varnish was prepared, and its performance was characterized. The results show that the surface modification of filler could reduce its sedimentation rate. When the filler content is 40%, the viscosity of insulating varnish is 72 s, the thermal conductivity reaches 0.46 W/(m·K), and the insulating varnish exhibit no sedimentation at 40℃ after 6 days, which indicates that it has practical application value.

To investigate the key factors of design for thermo-expandable sheets, we made thermo-expandable sheets from two types of glass mat with different fiber diameter and PA thermoplastic film. Different thermo-expandable sheets were prepared by changing the fiber diameter, resin content and density, and their thermal expansion rate and effect were studied. The results show that the thermal expansion effect of thermo-expandable sheets is codetermined by the elastic potential energy of fiber and the viscous resistance of melting resin. Under the same composition and density condition, the thermal expansion rate of thermo-expandable sheets increases with the increase of fiber diameter. There is a critical resin content for thermo-expandable sheets. When the resin content is below the critical value, the thermal expansion rate increases with the increases of resin content. When the resin content is above the critical value, the thermal expansion rate decreases with the increase of resin content. The critical resin content decreases with the increase of fiber diameter. When the single fiber diameter and resin content is unchanged, the higher the density of thermo-expandable sheets, the greater the thermal expansion rate.

With the miniaturization and lightweight of electronic equipment, graphite film materials with high thermal conductivity were widely concerned recently. In this paper, the preparation of polyimide (PI) based graphite film was reviewed, and the influence factors of their performance, which included molecular structure, molecular orientation, and the inducement of other materials, were introduced in detail. The research and patent situation of graphite film composite materials were summarized, and the future research and development direction were suggested and prospected.

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.

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.

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.

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%.

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.

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.