An experimental study was conducted to improve the electrical insulation of epoxy resin. The effects of boehmite, γ-alumina and α-alumina nanoparticles on the volume resistivity, dielectric strength and glass transition temperature of epoxy nanocomposites were investigated. The results showed that α-alumina nanoparticles displayed obvious advantages in enhancing electrical insulation performance of epoxy nanocomposites, compared to boehmite and γ-alumina nanoparticles. The direct current volume resistivity and breakdown strength of epoxy nanocomposite with 2.0 wt% α-alumina nanoparticles was improved to 2.2 à 1018 Ω cm and 76.1 kV mmâ1 respectively. And these improved values of electrical insulation properties are much higher than these of epoxy nanocomposites reported in previous studies. The main reason of these improvements may be that the epoxy/α-alumina interaction zone was enhanced by crosslink. Keywords: Nanocomposite, Epoxy resin, Insulation, α-alumin

Atmospheric corrosion is ubiquitous in China but varies a lot among different regions covering the cold, temperate, and tropical zones. Categorizing the atmospheric corrosivity and plotting precise atmospheric corrosion map remain key interest for a variety of industries. The present work proposed an atmospheric corrosion map of China for hot-dip galvanized steels, which was constructed by inverse distance weighting (IDW) interpolation algorithm based on both the measured corrosion rates of coupons exposed at 2393 inland test stations and calculated corrosion rates from a prevalent dose-response function in 2918 sites in coastal regions. When the corrosion category was used as the criterion, the IDW interpolation algorithm of power 2 performed best. Cross-validation results confirmed that the prediction accuracy of IDW interpolation reached 85.6%. Based on the corrosion map, the categories of atmospheric corrosivity in China could be determined.

The bird-streamer caused failures have become one of the major causes of transmission line outages. It is more common and widespread than generally believed, and greatly threatens the reliability of transmission lines. The laboratory study of such failures mechanism is seldom reported especially for long gaps such as 500 kV insulators. Presented in this paper are the results of long air gaps bird streamer flashover experiments conducted on 500 kV and 220 kV transmission line insulators. The experimental results demonstrated that bird-streamer caused surface flashover can happen in 500 kV insulators, however space flashover, because the bird streamer will split into different jets under high electric field cannot short circuit the long air gaps. The high risk areas of flashover for 220 kV and 500 kV insulators were defined in this paper: an elliptical area for 220 kV I string insulator and a symmetrical area beside the central line for 500 kV V string insulator. The influence of some main factors on flashover processes is also elucidated, such as volume, conductivity and viscosity of the streamer, and the insulator type and configuration. The paper has significant value in understanding the bird caused failure mechanisms and designing remedies.

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.

Silicone rubber (SIR) has been widely used in electrical insulation fields, and the introduction of new materials is very important for the performance improvement of SIR composites. In this work, four different fillers, including aluminium hydroxide (ATH), yimonite (YMT), boron nitride (BN) and mica-filled SIR composites were prepared, and the vulcanization behavior, mechanical properties, insulation performance and hydrophobicity of the SIR composites were investigated and compared. Both BN- and mica-filled SIR composites showed excellent insulation performance, while the ATH-filled SIR composite exhibited the best mechanical properties with an elongation at break of 230% and a tensile strength of 2.9 MPa. The SIR/BN composite showed a breakdown strength of 29.2 kV/mm with a 5% failure rate. The addition of YMT deteriorated the insulation performance of SIR but improved the elongation at break and hydrophobicity, with an elongation at break increasing from 115% to 410% and the static contact angle improving from 109.8° to 115.6°.