Dimensioning of creepage distances under humidity conditions - water adsorption test

The quick progress in the development of new electrical insulating materials allows significant miniaturization of electric and electronic components. At present, many dielectric materials with very high performance are available. However, long-term experience about the influence of humidity on the insulating characteristics of small creepage distances (d < 10 mm) does not exist for such new materials. Because of this lack of information we will describe the water adsorption characteristics of different insulation materials in this paper. For this purpose we will present a test procedure called "Water Adsorption Test", which allows the classification of various insulation materials into so-called water adsorption groups. With the exact knowledge about the allocation of each insulation material to these groups it is possible to dimension small creepage distances with respect of their withstand capability under humidity conditions. Within the scope of this paper the investigated samples are consisting of a glass fibre reinforced epoxy resin as well as a resin-impregnated polyester fleece. We found out, that the resin-impregnated polyester fleece is the most porous material and therefore it shows the lowest withstand characteristics under humidity conditions.