Incorporating inorganic nanoparticles (NPs) into polymer matrices provides a promising solution for suppressing space charge effects that can lead to premature failure of electrical insulation used in high voltage direct current engineering. However, realizing homogeneous NP dispersion is a great challenge especially in high-molecular-weight polymers. Here, we address this issue in crosslinked polyethylene by grafting matrix-compatible polymer brushes onto spherical colloidal SiO 2 NPs (10-15 nm diameter) to obtain a uniform NP dispersion, thus achieving enhanced space charge suppression, improved DC breakdown strength, and restricted internal field distortion (10.6%) over a wide range of external DC fields from À30 kV/mm to À100 kV/mm at room temperature. The NP dispersion state is the key to ensuring an optimized distribution of deep trapping sites. A well-dispersed system provides sufficient charge trapping sites and shows better performance compared to ones with large aggregates. This surface ligand strategy is attractive for future nano-modification of many engineering insulating polymers. Published by AIP Publishing.
This paper focuses on the effect of nanoparticle surface modification on the charge transport characteristics in XLPE/SiO 2 nanocomposites. A titanate coupling agent (TC9) and a 3-(Methacryloyloxy)propyltrimethoxysilane (KH570) were used for the surface modification of SiO 2 nanoparticles. It was found that both KH570 and TC9 coupling agents improve the nanoparticle dispersion compared with unmodified SiO 2 nanoparticles. The improvement in dispersion was found to be due to increased surface hydrophobicity of the treated SiO 2 nanoparticles. In addition, it was found that the surface modification improved the DC conductivity, dielectric characteristics, and space charge properties as compared to XLPE or XLPE/SiO 2 nanocomposites without surface modification. The results of the TSC measurements showed that the introduction of SiO 2 nanoparticles into XLPE increased the trap density and produced more trap energy levels. Improving the nanoparticle dispersion was found to further increase the corresponding trap depth and trap density. The trapped homocharge formed an independent electric field and reduced the effective electric field, which reduced charge injection and increased the charge injection barrier height. Therefore, the space charge formation in the material bulk was suppressed.
Power cables operate at high temperatures over long periods of time, and the electrical behavior of silicone rubber (SIR) in the new types of extra-high-voltage prefabricated cable accessories would change as a result of thermal aging. In this study, tests were conducted to reveal the effects of thermal aging (1000 h at 60-180°C) on the electrical treeing behavior. It was found that with increasing thermal aging time, the average electrical tree initiation voltage (ATIV) of SIR initially increases to a peak value and then decreases, finally becoming stable within 1000 h. Meanwhile, the probability of pine-like trees decreases at first and then increases, whereas the probability of bush-like trees initially increases and then decreases. The thermal aging temperature affects the rate of ATIV following the Arrhenius equation. These results strongly imply the existence of a thermal aging process that greatly influences the treeing degradation process. The results obtained using differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS) indicate that thermal oxidation plays a major role in the initial thermal aging process and facilitates additional crosslinking, which enhances ATIV. With increasing thermal aging time, thermal degradation and thermal crack reactions play leading roles, resulting in decreased crystallinity and ATIV. Microcracks are present after long-term thermal aging, and they are the dominant factor in ATIV stability. ATIV stability also provides a theoretical basis for the electrical strength design margin for insulating materials.
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