What is a hydrophobic coating on polymer insulators and its purpose?

• A. A coating that prevents color fading; it has no electrical effect.
• B. A coating that increases surface roughness to trap moisture.
• C. A coating that enhances conductivity
• D. A hydrophobic coating repels water and reduces continuous leakage paths, delaying tracking and flashover.

Answer: (D)

A hydrophobic coating on a polymer insulator is a water-repellent layer that keeps the surface dry. Its purpose is to prevent rainwater and polluted moisture from forming a continuous conductive path across the insulator surface, which reduces leakage current. By making droplets bead up and roll off, it breaks up the wetting film that would otherwise enable tracking and flashover, delaying those failures. The other options don’t fit: coatings that only affect color have no electrical effect; increasing surface roughness would tend to hold moisture rather than repel it; and a coating that increases conductivity would defeat insulation.