Aiming to improving the insulator resistance in the polluted media, a new proposed model consisting of an insulating surface coated by a non-linear conductive film has been studied.
There are two important roles of the non-linear film.
At low voltage gradient, a very small current passes. This low leakage current tends to raise the surface temperatures slightly above the ambient and retards dew deposition, which contributes to many flashovers. At high voltage gradient, i.e. the condition of dry zones formation; the leakage current increases sharply under the discharge across the dry zones, so this discharge diminishes.
To investigate the effect of this non-linear film on the surface diacharge and flashover, the electrical characteristics of non-linear film has been studied, and both theoretical model and experimental work, which has been carried out with simple model are discussed.
It has been found that the chance of the formation of local surface discharges, and the critical flashover voltage has increased due to the existence of this non linear film. The mathematical expressions of the electric field in the discharge column and pollution layer were deduced for computing the critical flashover voltage.