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Impact of Pollution on Insulators

Insulators on transmission lines are subject to the deposition of pollutants from the environment.  The nature of the pollutants depends on the nature of the environment. 

In Coastal areas, the pollutants is usually sodium chloride which is deposited onto the the insulator surface.  If the humidity increases or if rainfall occurs, the sodium chloride gets moist and provides a conduction path which can result in a flash over. 

In industrial areas, the chemical salts deposited depend on the nature of the industry.  The moisture absorption by these deposits depend on the relative humidity and climatic conditions.  Some of these deposits can become acidic and can corrode the insulator surface.

The deposits on the insulator surface become conductive when they become and provide a path for the leakage current across the insulator.  When the temperature rises, dry bands form on the insulator surface.(See article on dry band formation). the voltage gradient across these bands increases until arcing occurs across the bands.  These arcs can develop into a flash over.