How does humidity influence leakage current on insulators?

• A. Humidity reduces the risk of flashover.
• B. Humidity has no effect on leakage current.
• C. Humidity lowers surface resistance, increasing leakage current and the risk of flashover.
• D. Humidity increases surface resistance, reducing leakage current.

Answer: (C)

Humidity changes how easily current can flow along the surface of an insulator. When the surface is dry, its resistance is very high, so only a small leakage current passes. As moisture increases, a thin water film forms on the surface and dissolves some pollutants, creating ions that can move under the electric field. This greatly lowers the surface resistance, allowing more leakage current to travel along the surface. The higher leakage current can heat the surface and promote tracking, raising the risk of flashover, especially under high voltage or contaminated conditions. So humidity increases leakage current by reducing surface resistance, which is why this option is the best choice.