Experimental results and analysis about the behavior of ethylene propylene diene monomer (EPDM) class 15 kV type suspension insulators exposed to an acid environment and an altitude of 2240 mas1 are reported. An aqueous solution with the principals ions present in the most acid rain registered in the Valley of Mexico was used. The fog clean method developed for non ceramic insulators (IEC-507) was utilized, but with the difference in the manner of applying the pollutant mixture on the surface of insulators. For evaluate the loss of hydrophobicity the technique of contact angle was used. The flashover voltages and the behavior of accumulated charge are analyzed. The results show a strong reduction of the hydrophobicity on insulators previously exposed to acid rain.

The humidity correction factors specified by IEC Publication 60-1 (1989) and IEEE Std.4 (1995) for impulse voltages are restricted to 1 2 h/6 < 15. However, values of h/S 2 15 g/m3 in many regions of the world are present. The IEC-60 and the IEEE Std.4 procedures are based on the macroscopic observation that the atmospheric correction factors are larger when the discharge is governed mainly by positive streamers;while they tend to be lower when leaders or negative streamers are present. A better atmospheric correction factor implies to study the influence of atmospheric parameters on each discharge mechanism of the breakdown process. In this paper for standard lightning impulse voltages an analysis of the influence of absolute humidity divided by relative air density (his) greater than 15 gr/m3 on the positive streamer predischarges is reported.

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The amount of data regarding the fractal analysis of experimental discharge patterns is very scarce. Results on topological and on fractal analysis in 2-D patterns of real electrical breakdown tracks in atmospheric air are reported. It was evaluated the degree of randomness of the path upon calculating the fractal dimension and the influence of the polarity on the fractal dimension, using R/S analysis and Wavelets methods.

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