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The location mismatch of power production and consumption makes the large capacity energy transmission rather necessary. Overhead transmission line has always been the major approach to power delivery, where insulators are essential. Large-scale pollution flashover of insulators used to be the greatest threat to power system. Therefore, silicone rubber (SR) based insulator was introduced due to its hydrophobicity and now gets increasingly popular. However, the hydrophobicity degradation of SR during operation has been widely reported, significantly affecting the long-term performance. Therefore, super-hydrophobic SR was proposed for enhancement. In this paper, the recent progresses towards the fabrication techniques of super-hydrophobic SR are reviewed, including etching, moulding, and coating. The simplicity of fabrication procedure and the hydrophobicity of sample are paid most attention to. As a consequence, fabricating super hydrophobic insulator by coating is most likely to be used, and coating of nano-SiO2 with PDMS/epoxy resin transition layer is recommended. No rigorous condition is needed during the fabrication process, and the cost of coating is only around 1 $/m2. Besides, the durability of coating under multiple stresses was illustrated, which confirms its feasibility for actual service. Moreover, based on the current research, several prospects are proposed towards the investigation on super-hydrophobic coating. [Display omitted] • The basis and scope of different theories on wettability are summarized. • Advanced techniques for fabricating super-hydrophobic silicone rubber are investigated. • Coating method for the actual manufacture of super-hydrophobic insulator is recommended. • Prospects for the research on super-hydrophobic silicone rubber are proposed. [ABSTRACT FROM AUTHOR]

The dielectric response of a nano-ATH (Aluminium Tri-hydrate) filled silicone rubber is investigated over the frequency range 10 −4 to 10 3  Hz and compared with that of the micro-ATH composite. An equivalent circuit has been used to decompose the dielectric response into: a loss peak process, a quasi-dc (Q-DC) process, a dc-conductance and constant high frequency capacitance. It was found that the Q-DC and loss peak were a result of the ATH filler with the loss peak more clearly resolved in the nano-ATH filled material than in the micro-ATH material where it is weaker and partly obscured by the Q-DC process. In contrast to the micro-ATH material the characteristic frequencies of all the dielectric responses in the nano-ATH filled samples have the same activation energy. The physical mechanisms of the Q-DC process and loss peak are discussed in terms of long range transport between nano-ATH clusters and the dipolar behaviour of isolated clusters respectively. [ABSTRACT FROM AUTHOR]

The effect of electrical stress on glass fiber reinforced polymer under wet condition has been investigated in the present study. A specially designed and fabricated test setup was used through which the current passing through the GFRP rod during the test was recorded. Based on the changes in morphology of GFRP rod surface and development trend of current, the degradation process of GFRP rod caused by electrical stress under wet condition was divided into four consecutive stages, namely degradation inception stage, hydrolysis stage, carbonization stage and breakdown stage. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA) and X-ray Photoelectron Spectroscopy (XPS) analyses were employed to provide the physical and chemical properties of GFRP at different stages. The results showed that the degradation process of GFRP caused by electrical stress under wet condition progressively developed in the form of degraded channel, in which the epoxy resin matrix deteriorated significantly. The occurrences of hydrolysis, oxidation, pyrolysis and carbonization of epoxy resin matrix could be observed sequentially in the degradation process of GFRP during the test. With the development of the degradation process of GFRP, the content of epoxy resin matrix continued to decrease and the relative content of highly oxidized carbons (C-O, C=O and O-C=O) in epoxy resin matrix on GFRP surface increased before the carbonization process and then decreased in the carbonization process. The present study is helpful for better understanding of the electrical performance of GFRP used in high voltage composite insulator as well as in other electrical applications. [ABSTRACT FROM AUTHOR]

Polymer dielectrics are indispensable in electrical and electronic systems, being used as insulation, capacitors, gate dielectric, etc. However, a lot of polymer materials show unsatisfactory efficiency at high temperature and low frequencies, which has been found to be closely related to polarization processes. In this paper, the dielectric spectroscopy of poly (vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) films is investigated over a broad frequency range from 10 mHz to 1 MHz and temperature range from −130 °C to 130 °C based on the Dissado-Hill model. The processes in the entire response are identified and characterized quantitatively. The temperature dependence of major processes contributing to energy storage and dielectric loss are revealed. It is found that the variations of both β polarization and DC conductance coincide with Arrhenius equation, while both α polarization and quasi-DC polarization show Vogel−Fulcher−Tammann (VFT) features. Moreover, α polarization and quasi-DC polarization share the same form parameter of VFT equation, indicating that they have a common origin of microstructure. The origin and correlation of polarization processes could be used to develop a paradigm for rational design of polymer dielectrics to enhance or suppress specific processes for certain purposes. [Display omitted] • An approach to retrieve the contributions of individual processes is developed. • K–K transform dedicated to the actual dielectric response is introduced. • The temperature dependences of several key processes in P(VDF-HFP) are obtained. • α polarization and QDC process are found to have the same activation energy. [ABSTRACT FROM AUTHOR]

Abstract: Micro-cracks with a depth of 30–40μm are formed on the surface of glass-fiber reinforced plastics (GFRP) rod, which could lead to the stress corrosion crack propagation along the original direction and developing dominant influence on the stress corrosion cracking (SCC) performance of the composite material. Micro-cracks with different depth and angles were simulated on the surface of GFRP rod. The strain response histories around the micro-crack during the whole stress corrosion test of the GFRP rod were obtained. The effects of depth and angle of micro-crack on SCC of GFRP rod were analyzed. The stress corrosion fracture times of GFRP rod with micro-cracks of different depth and angle were obtained. [Copyright &y& Elsevier]

• The breakdown rule of coated inorganic insulators under impulse is illustrated. • Flashover processes under steep-front impulses are recorded. • The breakdown mechanism under steep-front impulse is demonstrated. • Optimization approaches for coating insulators are proposed. Insulators play the vital role in the power transmission, including traditional porcelain/glass insulator and silicone rubber based polymeric insulator. By coating the glass/porcelain insulators with silicone rubber, the advantages of organic and inorganic dielectrics are integrated. However, it was found that the breakdown probability of coated insulators under steep-front impulse increases significantly. It suggests the possible degradation of insulator material and might become the hidden danger of power system. Therefore, in this research, a great deal of steep-front impulse voltage tests are carried out over various types of insulators. It demonstrates that the performance degradation is introduced by RTV coating instead of intrinsic defects. Then, based on the analysis of flashover paths and breakdown locations, the breakdown mechanism of coated insulator under steep-front impulse is illustrated. Also, numerical simulation of electric field distribution is performed for verification, taking the surface arc development into account. It indicates that the development of surface arc is distorted by the coating which results in the intense local field and dielectric breakdown. Next, different controlled experiments are designed and conducted to validate the theory. Besides, the corresponding modification towards the current coating method is proposed. [ABSTRACT FROM AUTHOR]

Composite insulators are of great significance in power systems due to their excellent electrical and mechanical properties. The mechanical load of insulator is borne by the rod made of glass fiber reinforced polymer (GFRP). Despite the considerable load margin, abnormal fractures have been reported continuously during actual operation. Among them, the evolution of decay-like fracture has still not been illustrated, which is why no effective preventive measures can be proposed. Liquid permeation, especially nitric acid, is supposed to play a vital role in the fracture. Thus, in this paper, the characteristics of glass fiber, fiber-epoxy interface, and GFRP-sheath interface immersed in different liquids are investigated. Based on the results, the significant role of boron element in the stress corrosion of glass fiber is illustrated. Therefore, the application of glass fiber without B is rather necessary. Also, the failure of fiber-epoxy interface by acid is identified by broadband dielectric response, which forms the channels of current concentration. It is key for the development of decay-fracture. Moreover, the degradation of GFRP-sheath interface after immersion is recognized by the measurement of interfacial resistivity. Consequently, coupling agents with good resistance to acid should be adopted, in order to avoid further liquid permeation into the GFRP rod. [Display omitted] • The element variation of glass fiber during liquid immersion is characterized. • The failure of fiber-epoxy interface is characterized by dielectric response analysis. • The failure of GFRP-sheath interface is characterized by interfacial resistivity. • Preventive measures towards the decay-fracture of composite insulators are proposed. [ABSTRACT FROM AUTHOR]

• Superhydrophobic and self-cleaning properties on insulators are achieved via coating. • Icing time is delayed, and ice adhesion is weakened after the coating. • Fast dissipation of surface charge is realized by introducing shallow traps. • Wet flashover voltage is increased by inhibiting electrical distortion. Composite insulator is an important component of outdoor insulation systems. It works in complex environments and faces a series of problems such as surface contamination, loss of hydrophobicity, and accumulation of surface charges, which may eventually lead to flashover. Aiming to solve these problems in a simple and scalable method, we propose a multifunctional nano-coating based on SiO 2 /PDMS/EP. By the combination of multiscale structure and low surface energy modification, this coating shows excellent water-repellency performance, a large contact angle greater than 160° and a small rolling angle near 0° are achieved on coated silicone rubber, which enables the surface with excellent self-cleaning performance. Benefiting from the multiscale roughness, the heat transfer is inhibited by the reduced contact area, which further slows down the icing process on coated silicone rubber. The de-icing force on coated silicone rubber is also smaller than that on pristine silicone rubber. This coating also introduces many shallow traps to the surface, which is beneficial to the fast surface charge dissipation in a short time. Besides, the high water-repelling ability can promote the droplet to roll away under the action of electrical field force, which alleviates the electrical distortion caused by the droplets. As a result, the wet flashover voltage of coated silicone rubber is 60% higher than that of pristine silicone rubber. This multifunctional coating is a facile, scalable, and effective approach to improving the comprehensive surface performance of insulators. [ABSTRACT FROM AUTHOR]