Orderly arranged Silicon carbide (SiC)/epoxy (EP) composites were fabricated. SiC was made magnetically responsive by decorating the surface with iron oxide (Fe₃O₄) nanoparticles. Three treatment methods, including without magnetization, pre-magnetization and curing magnetization, were used to prepare SiC/EP composites with different filler distributions. Compared with unmodified SiC, magnetic SiC with core-shell structure was conducive to improve the breakdown strength of SiC/EP composites and the maximum enhancement rate was 20.86%. Among the three treatment methods, SiC/EP composites prepared in the curing-magnetization case had better comprehensive properties. Under the action of magnetic field, magnetic SiC were orderly oriented along the direction of an external field, thereby forming SiC chains. The magnetic alignment of SiC restricted the movement of EP macromolecules or polar groups to some extent, resulting in the decrease in the dielectric constant and dielectric loss. The SiC chains are equivalent to heat flow channels, which can improve the heat transfer efficiency, and the maximum improvement rate was 23.6%. The results prove that the orderly arrangement of SiC had a favorable effect on dielectric properties and thermal conductivity of SiC/EP composites. For future applications, the orderly arranged SiC/EP composites have potential for fabricating insulation materials in the power electronic device packaging field.

Adaptive material can alleviate the local high electric field in electrical devices, due to its nonlinear conductivity characteristics. To solve the deterioration problem caused by the high doping of large-diameter fillers in adaptive material, CNT (carbon nanotube) was used as the second filler. And the effect of CNT doping amount on the conductivity of SiC/SR (silicone rubber) composites was explored. Experiments showed that CNT doping can improve the nonlinear conductivity. The threshold field of the material doped with 0.7 vol % CNT decreased by 97%, and the nonlinear coefficient was increased by 83.7%. With the increase of CNT doping content, the decay rate of surface potential increased, which was attributed to the increase of the carrier mobility and ratio of shallow-to-deep trap density. A new field grading material (FGM) coating structure was proposed, which was compared with the traditional structure. Through finite element simulation, the field grading effect of the two structures can be analyzed. The results showed that, the field grading effects of the two coating structures were almost the same. But considering the influence of surface charge dissipation, the new coating structure was selected. The electric field of insulator surface and interface can be reduced by more than 30% with the best CNT doping ratio. It was verified that, the interface charge and leakage current of the insulator coated with the best FGM were at the compliance level.

Nanocrystalline (NC) alloy may confront saturation problems with different high-frequency operation circumstances, which are summarized as two typical situations in this paper. One case is “dynamic saturation (DS)” where the alternating magnetic field contains the weak dc biasing field. Another situation is “static saturation (SS)” where the hybrid field comprises not only the weak time-varying field but also the strong dc biasing field. The external and internal factors that affect the saturation magnetization process for the NC alloys were analyzed, under two types of saturation magnetic fields. Two parameters including the saturation time and the rotational velocity of magnetic moment were employed. The external factors, which determine the working condition of the NC alloys, are the dc biasing field and the frequency of the alternating field. The effects of the above two factors are related to the type of saturated magnetic field. In the DS field, the promoting effect of frequency increase on the magnetization process is greater than that of the biasing field, while in the SS field, the opposite is true. The internal factor, which is the grain size, is essential to the soft magnetic properties of the NC alloys. The effects of this factor are independent of the type of saturation field. Increasing the grain size of the NC alloys will delay the magnetization process.

The suitable filling scheme is an important factor that affects the thermal conductivity of composites used for heat dissipation. In this study, the separation axis theorem (SAT) is conducted to study the prediction model of the effective thermal conductivity (ETC) of SiC/silicone rubber composites. Based on the representative volume element (RVE) model, a series of cubic units with built-in cubic particles of log-normal distributed size are developed for the SiC/silicone rubber composites. Combined with SAT for contact detection and thermal resistance network theory, a general solution for the ETC of a typical RVE is then derived. Furthermore, ETC prediction models of SiC/silicone rubber composites with filling particles of three typical connection mechanisms are obtained by comparing the experimental data and finite element simulation results. Finally, the thermal conductivity prediction model from this study demonstrated an average reliability of 96.8% which is better than that of the commonly used Maxwell prediction model. This model could be used to predict the ETC and guide the preparation of SiC/silicone rubber composites.

When passing through complex terrain, overhead bare wires may come into contact with tree branches, residential buildings, masts, or other obstacles, potentially leading to phase-to-phase or single phase-to-ground short circuits. To address the electric field distortion at the insulation-bare conductor junction in overhead hybrid wires, this study proposes a novel functionally graded insulation (FGI) structure design coupled with nonlinear conductivity materials for electric field regulation. An axisymmetric finite element model of the proposed structure at a 220 kV AC line junction was established. Comparative simulations of scenarios with no insulation enhancement and with a neat silicone rubber structure verified its preliminary field-regulating effectiveness. To further enhance adaptive field control, five different SiC/silicone rubber (SiC/SR) composites were introduced into the reinforced insulation layer. Simulations were conducted to analyze the influence of filler content and particle size on the field-regulation characteristics. Results show that the 10% vol-1.5 μm SiC/SR composite demonstrates9 optimal field homogenization, notably reducing the maximum junction field by 27.96% and the cone surface field by 65.02%, while optimizing the non-uniformity coefficient to 1.22. This synergistic design effectively suppresses field distortion, providing a theoretical and practical basis for insulating overhead hybrid transmission lines.