Analysis of Droplet Motion Characteristics on the Surface of Silicone Rubber Sample Based on Ellipsoidal-Notch Droplet Model

Abstract

The morphology of water droplets on silicone rubber insulators plays a critical role in local electric-field distortion and flashover initiation. Flashover tests on smooth and rough specimens show that larger droplets exhibit stronger stretching, faster contact-angle reduction, and lower flashover voltage under increasing voltage, with these effects being more pronounced on rough surfaces. An inversion method for droplet geometric parameters was developed based on the ellipsoidal-notch model, and a coupled electric-field–two-phase-flow model was established accordingly. The results reveal that increasing droplet volume enhances the maximum electric field on the droplet surface, and that the ellipsoidal-notch model more accurately reproduces the experimentally observed symmetric stretching and convergence toward the droplet center. The evolution trends of the normalized stretching ratio $\lambda $ (t) in simulations agree well with experiments, while deviations on rough surfaces mainly arise from contact-line pinning and transient wetting behavior. The study further demonstrates that electric-field-induced droplet stretching acts as an important flashover risk-amplification mechanism by significantly enhancing local electric fields even on hydrophobic surfaces. These findings provide a physical basis for assessing early-stage wet-flashover risk in silicone rubber insulators.