Evaluation of Dynamic Hydrophobicity Behavior of Silicone Rubber Insulators Filled With 2D Nanosheets Using a Direct Current Dynamic Drop Test

The growing use of composite polymer insulators in high-voltage direct current (HVDC) transmission systems requires a thorough understanding of their dynamic hydrophobicity characteristics to ensure long-term reliability. This study investigates the retention, recovery, and transfer of hydrophobicity in silicone rubber (SiR) composites filled with two-dimensional (2D) nanosheets, specifically molybdenum disulfide (MoS2) and tungsten disulfide (WS2), under DC Dynamic Drop Test (DDT) conditions. The efficacy of these fillers is evaluated against traditional alumina trihydrate (ATH) and fumed silica (SiO2) fillers. The Weibull probability analysis of the hydrophobicity retention test indicates that MoS2-filled composites achieved the highest hydrophobicity retention time (773.4 min), representing a 324.3% increase compared to the unfilled sample (185.4 min), while WS2 composites showed a 223.1% increase (609.7 min). In terms of hydrophobic recovery after 24 hours, MoS2 composites demonstrated a 282.6% improvement (125.6 min), followed by WS2 with a 160.4% improvement ( $\eta =87.1$ min) relative to the unfilled reference (33.9 min). The hydrophobicity transfer test showed that fumed silica promoted faster low molecular weight (LMW) migration, while MoS2 and WS2 slowed LMW diffusion due to stronger filler-matrix interactions. Experimental improvements-such as optimized sample preparation, electrolyte control, and voltage ramping-significantly reduced test variability, improving DDT reproducibility. The findings confirm that MoS2 and WS2 nanosheets substantially enhance the long-term hydrophobic stability of SiR composites under HVDC stress, highlighting their suitability for outdoor insulation applications.