The working principle of composite insulators mainly involves the variation of their insulating performance under different environmental conditions, especially the increase in surface leakage current in wet weather, which may lead to partial arc and flashover phenomena.

Specifically, composite insulators maintain a high insulation level in dry conditions, but in wet weather such as fog, dew and drizzle, the contaminants on the surface absorb moisture, causing the electrolytes in the contaminated layer to dissolve and ionize, which leads to an increase in the conductivity of the contaminated layer and a corresponding rise in the surface leakage current. Due to the influence of shape and structural dimensions, as well as the uneven distribution of the contaminated layer and different degrees of wetting, the current density varies at different parts of the composite insulator surface, forming dry bands. The formation of dry bands further exacerbates the unevenness of the surface voltage distribution, with the dry bands bearing a higher voltage. When the electric field strength is sufficiently high, glow discharge will occur; as the leakage current increases, the glow discharge may transform into a partial arc. The partial arc may either extinguish or develop, and its thermal effect will expand the dry areas. The partial arc will propagate along the dry areas and continuously adjust its own length. The pollution flashover of composite insulators depends on the occurrence and development of four stages: the surface contamination process, the contaminated layer wetting process, the dry band formation and partial arc process, and the process of partial arc development penetrating the two poles.

In addition, the contamination accumulation on the surface of composite insulators is affected by factors such as the atmospheric environment, the structure and surface performance of the insulators themselves, and the scouring effect of atmospheric conditions (e.g., wind and rain). Long-term operational experience shows that the contamination accumulation on the surface of composite insulators is significant in urban industrial areas and regions with severe atmospheric pollution. Meteorological conditions such as fog, dew and drizzle are prone to induce pollution discharge of composite insulators, because they can fully wet the contaminated layer and completely dissolve the electrolytes in it without washing the contaminated layer away, thus maximizing the conductivity of the contaminated layer and minimizing the pollution flashover voltage.