Silicone rubber composites filled with nano-silica are currently widely used as high voltage insulating materials in power transmission and substation systems. We present a systematic study on the dielectric and mechanical performance of silicone rubber filled with surface modified and unmodified fumed nano-silica. The results indicate that the different interfaces between the silicone rubber and the two types of nano-silica introduce changes in their dielectric response when electrically stressed by a sinusoidal excitation in the frequency range of 10⁻⁴–1 Hz. The responses of pure silicone rubber and the composite filled with modified silica can be characterized by a paralleled combination of Maxwell-Wagner-Sillars interface polarization and DC conduction. In contrast, the silicone rubber composite with the unmodified nano-silica exhibits a quasi-DC (Q-DC) transport process. The mechanical properties of the composites (represented by their stress-strain characteristics) reveal an improvement in the mechanical strength with increasing filler content. Moreover, the strain level of the composite with a modified filler is improved.

In the present work, a field brittle fracture composite insulator was collected and examined with the purpose of obtaining a better understanding of the failure features. Firstly, the macroscopic and microscopic fractography of this fractured composite insulator was observed confirming that the classical brittle fracture morphology features appeared in this field failed composite insulator. Secondly, the X‐ray photoelectron spectroscopy (XPS) analysis was performed on the fracture surface of the glass‐fibre‐reinforced polymer rod. By examining the XPS survey spectra and high‐resolution XPS spectra for nitrogen, sulphur, silicon, calcium, aluminium, boron and carbon elements, the type of the glass fibre and the acid source responsible for this brittle fracture composite insulator were confirmed. Furthermore, the oxidation of the silicate network of glass fibre at the fracture surface was first observed, meanwhile, the oxidation of the epoxy resin matrix was also observed. The leaching of non‐silicate constituents leading to a high‐silica glass fibre was also observed; moreover, in comparison with the calcium and aluminium elements, the boron element resides in the silicate network was more preferential to be leached. The present work provides an insight into the brittle fracture in high voltage composite insulator from chemical properties point of view.

Long‐term liquids diffusion tests were performed on glass fibre reinforced polymer (GFRP) used in high voltage composite insulator. The plate‐shaped GFRP specimens were immersed in three types of liquids, which high voltage composite insulator would encounter in practice, including deionised water, NaCl solution and nitric acid solution for a period of 4000 h. Chemical reaction and physical dissolution complicated the diffusion processes, which could be divided into three types based on the features of diffusion curves. Fourier transform infrared spectroscopy, scanning electron microscopy and optical interferometry were employed to investigate the chemical property, two‐dimensional (2D) and 3D surface morphologies of GFRP. The results revealed that the surface layer of GFRP was destroyed to some extent depending on the type and concentration of the liquid, the maximum of profile height deviation of GFRP surface was proposed to evaluate the extent of the corrosion of GFRP, the greater the profile height deviation, the more serious the corrosion of GFRP. The present work is helpful for a better understanding of the diffusion behaviour of liquids into GFRP used in high voltage composite insulator as well as in other industry applications.

High‐temperature vulcanised (HTV) silicone rubber composite insulator has been widely used in extra‐high and ultra‐high transmission lines due to its excellent electrical and mechanical performance. In practice use, liquids may encounter the composite insulator intermittently and can lead to the degradation and deterioration of silicone rubber. In the present research, the effects of liquids immersion and subsequent drying on the surface properties of HTV silicone rubber were investigated by means of the contact angle measurement and surface physical morphology measurement which was further analysed in terms of the discrete wavelet transform method, multiresolution signal decomposition algorithm, and three‐dimensional fractal dimension calculation. Based on the experimental results, the mechanism of the loss and recovery of the hydrophobicity of HTV silicone rubber surface during the liquids immersion and subsequent drying processes were further explained by taking into consideration the embedded water molecules (and/or hydrated ions) on the HTV silicone rubber surface and the synergy of the increase in roughness/fractal dimension and low molecular weight siloxanes diffusion. This study is helpful for better understanding of the change of surface properties of HTV silicone rubber caused by environmental and electrical stresses.

Composite polymer dielectrics have strong electrical, mechanical, thermal and environmental properties but experience both high electric fields and harsh environmental conditions as outdoor insulation. The present investigation of the stress‐strain characteristics and morphology of the fracture cross‐section reveal the risk of a weakly bonded interface between the aluminium hydroxide (ATH) filler and silicone rubber used for insulators in transmission lines and substations. Dielectric response measurements are proposed as a non‐destructive probe of the interface quality. An analysis, based on the Dissado–Hill model, indicated that the introduction of ATH interfaces gave rise to a quasi‐DC process, in which charge transport is in the form of hopping along the weakly bonded interfaces. A schematic plan is proposed that would allow such an analysis to be used to obtain quantitative information correlated to the status of the weakly bonded interface for the diagnosis of micro‐interface quality in ATH‐filled silicone rubber and dielectric composites in general.