The effect of graphene as a hydrophobic additive on the pollution performance and accelerated ageing of coatings when applied to ac high voltage ceramic insulator materials.

Abstract

This study focuses on the development and pre-testing of a modified insulator coating. The study aims to investigate and evaluate the performance of Pristine Graphene (PG) and Nanoplatelet Graphene (NPG) doped Room-Temperature Vulcanising Silicone Rubber (RTV SR) coatings at different weight percentages (wt%). Key properties such as surface resistivity, hydrophobicity, hydrophobicity transfer/recovery, tracking resistance, and erosion resistance were analysed to assess the effectiveness of the modified coating. From an electrical insulation resistance perspective, NPG doped RTV SR coatings with over 3 wt% demonstrated more than twice the reduction in surface resistivity compared to the reference RTV SR coating. Furthermore, the Inclined Plane Tests (IPT) confirmed that the addition of NPG particles to the RTV SR mixture lowers the combustion temperature of the ATH (Aluminium-Trihydrate) filler, resulting in faster ignition during electrical discharging or DBA (Dry Band Arcing) events. However, the project presented promising performance in terms of hydrophobicity, recovery, and transfer properties. A 10 wt% NPG weight fraction led to an approximate 10% increase in static contact angle measurements compared to the unfilled RTV SR coating. The presence of NPG did not hinder the hydrophobicity recovery and transfer mechanisms within the RTV SR matrix. After pollution application, similar large static contact angles were measured as those observed on a clean 10 wt% NPG doped RTV SR coating surface. This observation led to a hypothesis that physical entanglement and/or interfacial interaction between Low-Molecular-Weight (LMW) silicones and the free-floating NPG sheets within the bulk layer of the modified coating material could result in the transfer of NPG sheets to the surface during polluted surface conditions. Consequently, this encapsulation of pollution particles would develop a pollution layer with a hydrophobicity level comparable to that of a clean NPG doped RTV SR coating surface over time. Several recommendations are proposed for future research, including the setup of an inclined plane tester to evaluate hydrophobicity resistance and transfer principles, exploration of alternative fillers which do not decrease combustion temperature when adding to virgin RTV SR material, implementation of thermogravimetric analysis to study the modified coating’s chemical and physical phenomena, and conducting outdoor pollution performance and ageing tests in severe marine environments. Additionally, further investigation of the LMW silicones and NPG hydrophobicity transfer "package" hypothesis, accurate measurement of pollution layer thickness and homogeneity, Scanning Electron Microscopy (SEM) studies to determine morphological characteristics, and improvement of NPG mixing and dispersion quality are recommended. Furthermore, evaluation and comparison of PG doped RTV SR samples as well as corona activity analysis between different PG/NPG doped RTV SR weight percentages is also recommended. The study concludes by emphasising the need for standardised tests and procedures to evaluate the long-term durability of superhydrophobic coatings and highlights the potential of semiconductive coatings, enhanced by graphene, to prevent flashovers, by governing small leakage currents. The reason for the study is to see if RTV SR coating can be modified to be superhydrophobic.