In a composite insulator, which combination best resists pollution and tracking?

• A. A metal core with no protective surface coating.
• B. Plain ceramic exterior with no geometry.
• C. A simple glass body without polymer.
• D. Optimized shed geometry, hydrophobic surface or coatings, and longer creepage paths.

Answer: (D)

Design features that resist pollution and tracking in composite insulators rely on combining geometry, surface properties, and creepage distance. Optimized shed geometry helps water and polluted films shed off the surface rather than forming continuous conductive paths, acting like a series of steps that break up spreading moisture. A hydrophobic surface or coating further reduces wetting, keeping the surface less conductive by preventing a stable conductive film from forming. Longer creepage paths increase the physical distance that leakage current must travel along the surface, lowering the likelihood of a flashover under polluted or humid conditions. When these elements are integrated—carefully shaped sheds, hydrophobic surfaces or coatings, and extended creepage distance—the insulator better resists pollution-induced leakage and tracking. The other options miss one or more of these crucial features, leading to poorer performance in polluted environments.