Event-Based Evaluation of Short-Term Wettability Degradation of RTV Nanocomposite-Coated 150 kV Ceramic Insulators Under Tropical Flashover Stress

Flashover events can induce rapid surface condition changes on outdoor ceramic insulators, while early-stage degradation is typically assessed indirectly through long-term ageing or electrical diagnostics. This study proposes an event-based, surface-focused evaluation framework to assess short-term flashover-induced surface degradation using normalized wettability indicators. A controlled experimental comparison was conducted on uncoated, TiO2-RTV-coated, and SiO2-RTV-coated 150 kV ceramic insulators subjected to a single flashover pre-stress under humid tropical conditions. Static contact angles decreased from 42.6° to 18.3° for uncoated ceramic, from 112.4° to 86.7° for TiO2-RTV, and from 115.8° to 92.6° for SiO2-RTV after flashover exposure. The corresponding relative wettability retention values were 43.0%, 77.1%, and 80.0%, while the wettability degradation index values were 0.57, 0.23, and 0.20, respectively. Surface morphology and elemental presence were qualitatively examined via SEM–EDS. The results show that both nanocomposite coatings effectively preserve post-flashover surface hydrophobicity compared with uncoated ceramics, with the SiO2-RTV system exhibiting the highest short-term wettability retention. By integrating static contact-angle measurements, qualitative surface morphology, and normalized wettability indicators, this study proposes an event-based evaluation framework for RTV-coated ceramic insulators. Flashover-voltage and leakage-current measurements were included only as supplementary validation to support the surface-based interpretation, without implying direct electrical performance modeling. This surface-focused, event-based approach provides an experimental basis for post-flashover condition assessment of ceramic insulators operating in humid outdoor environments.