Abstract :
The phenomenon of skirting of the polluted insulators results in fact from the
combination from several constraints: deposit of a solid layer of material,
humidification of this deposit and the existence of a tension applied.
The modeling of Obenaus enabled us to determine these various parameters by a
mathematical function gathering the following parameters: resistance of
pollution, length of escape and supply voltage.
The action on one of these parameters enables us to analyze the tension of
skirting.
The theoretical approach makes it possible to connect these parameters with
those of the natural conditions sometimes characterized by empirical formulas.
The analysis of internal and external overpressures enables us to carry out a
technico-economic compromise between coordination of insulation and plan of
protection.
The analysis of internal overpressures (Ferranti Effect, effect of commutation)
and those external (atmospheric overpressures) enabled us to see that
overpressures have a harmful effect on insulation and for consequent on
longevity of the electric installations.
The atmospheric attenuation of overpressures under the influence of the effect
crowns has a beneficial effect on skirting.
For this, and in all the cases that one can consider, the wave of overpressure
penetrating in a station will be characterized dice that the distance from the
impact of the station is higher than 2 or 3 km, by a very flattened face, and an
amplitude definitely lower than the behaviour of shock of the material of the
station. It is also noted that, except in the case of a direct thunderbolt very near
to the station, atmospheric overpressures appear completely inoffensive when
they reach the station, which makes it possible to coordinate the insulation and
protection.