Surface Tracking of MgO/Epoxy Nanocomposites: Effect of Surface Hydrophobicity

Abstract

Surface tracking has been one of the challenges for outdoor organic insulations, in electronic and electrical devices. In this paper, surface tracking behavior of nano-MgO/epoxy composite samples were measured according to the standard IEC 60112. Improved tracking resistance was obtained in nanocomposites with an 18.75% uplift in the comparative tracking index, and a decrease of 58.20% in the surface ablation area at a fixed 425 V. It was observed that the tracking resistance and surface hydrophobicity shared the same tendency—both, the comparative tracking index and surface contact angle increased with an increase of the nanofiller content. Samples with better hydrophobicity exhibited a higher tracking resistance. It could be the case that the conductive pathway of contamination was harder to form, as a result there were fewer discharging processes. With the development of surface tracking, the surface contact angle abruptly decreased, at first, and tended to be constant, which was also accomplished with the failure of samples. In addition, reduced surface resistivity was also found in the nanocomposites, which was beneficial for releasing surface charges and inhibiting distortions in the electric fields.

Effect of Filler Concentration on Tracking Resistance of ATH-Filled Silicone Rubber Nanocomposites

“…In fact, the effect of nano-sized fillers on the surface charge transport dynamics has also been demonstrated in previous studies on surface resistivity [7] and flashover voltage [29] of polymeric nanocomposites. In [7], an increase of surface resistivity with higher filler loadings was found for MgO/epoxy nanocomposites. A similar trend in the increase of surface resistivity was also reported in [7].…”

“…This hydrophobic nature contributes to improved tracking resistance performance by preventing the surface from being wet by contamination. For example, it has been shown that degradation of tracking resistance is related to the decrease in the SCA for MgO/epoxy nanocomposites [7]. The results of Figure 6 also demonstrate that the difference in the SCA caused by different filler loading seems to be negligible for the considered micro-sized SiO2 and nano-sized ATH fillers.…”

“…The results of Figure 4 illustrate that the tracking resistance performance of ATH/SiR nanocomposites improves as the concentration of nano-sized ATH fillers increases. As discussed in [7,8], the process of surface tracking failure involves various development stages, such as surface contamination, heat generation, heat accumulation, and thermal decomposition. The relationship between measurement results of material properties and factors that affect development stages of tracking failure is shown in Table 1.…”

“…As surface contamination is a main cause for tracking failures in polymeric insulators [7], quantitative characterization of surface hydrophobicity for different filler loadings is necessary. In this study, the effect of different filler concentrations on surface hydrophobicity of SiR micro-and nanocomposites was characterized based on measurement of the surface contact angle (SCA) [3,7]. In order to achieve repeatability, 9 droplets were applied to different areas for each specimen.…”

“…Representative failure modes that have been reported in outdoor insulation applications are surface tracking and erosion. The occurrence of surface tracking, which is characterized by the formation of an irreversible carbonized conduction pathway [2,7], involves various development stages and factors, such as surface wetting, leakage current flow, dry-band zone formation, and local heat accumulation. [7][8][9].…”