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.

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.

Composite insulators have gradually become the preferred approach for electrical insulation in power systems, especially in polluted areas. Composite insulators consist of three main components: the shed, rod, and end fitting. Insulators withstand mechanical stresses via rods that are composed of glass-fiber-reinforced epoxy (GFRE). However, regardless of the high tensile strength of GFRE rods, in real-life operation, abnormal fractures have frequently been reported all over the world, which substantially increase the risk of major accidents in power systems. Fractural accidents mainly consist of brittle and decay-like fractures, which exhibit rather different morphologies at the cross sections. Brittle fracture has been effectively eliminated, while the mechanism of decay-like fracture has still not been clearly revealed. In this study, surface discharge tests were applied to investigate the discharge influence on the degradation of GFRE. The test successfully simulated the composition variation of the rods in real-life composite insulators with decay-like fractures. Moreover, it confirmed that the distinction between the characteristics of brittle fracture and decay-like fracture stems from epoxy degradation due to hydrolysis and carbonization. In addition, the respective influences of the resin type, glass fiber type, and acid liquid immersion on the degradation process were probed, and the degradation mechanism proposed in this research was verified. Based on the results, measures for preventing the development of decay-like fractures in real-life operations were determined.

Capacitors and sensors based on polymer dielectric materials are key components in electrical systems and electronic devices. Considering the temperature rise during operation, an effective evaluation method for the thermal ageing of polymer matrix is urgently needed. P (VDF‐HFP) film with a thickness of 20 μm is manufactured by solution casting and a thermal ageing experiment up to 1000 h is conducted. Dielectric responses of wide ranges of temperatures and frequencies are measured for samples with different ageing durations. The universal relaxation law and Dissado–Hill dielectric response model are applied to further investigate the results. The characteristics of individual processes are obtained, which demonstrate that the main chain relaxation following the Vogel−Fulcher−Tammann equation and side chain relaxation following the Arrhenius equation both remain unchanged after thermal ageing. However, the activation energies of those two processes change significantly during the process and show different variation trends. The activation energy of the side chain relaxation gets larger monotonically due to the influence of annealing and the breaking of crystalline region. As a result, a non‐destructive evaluation method for the thermal ageing of P (VDF‐HFP) is proposed accordingly.