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Hocine HADI
Samir FLAZI
Amel OUIS

Abstract

The study of flashover phenomenon of the outdoors insulators showed that the flashover evolution is a progressive breakdown of the air, between the electric discharge and the wet pollution deposit on the insulator surface. To understand the mechanism of this evolution, an experimental study was carried out, in positive and negative polarity, in order to measure the dielectric rigidity represented by the critical distance of an air interval between the discharge and wet pollution, according to the following parameters: Electrolyte resistivity, nature of the electrode opposite to the discharge and initial discharge current. Next to that, a simulation study was then carried out to assess the electric-field distribution in the interval between the electric discharge and the electrolyte surface, and to determine the maximum field value in the vicinity of the discharge that corresponds to the experimental breakdown conditions.
The obtained results show that the discharge current acts directly on the breakdown voltage, with a relatively weak electric field strength and a significant time lag to breakdown. We found that the initiation and the evolution of the streamer to the vicinity of the discharge compared to a metal electrode necessitate a feebler field strength, which is explained by the means of heat near the discharge, of photo-ionization and space charge caused by the discharge.

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