A simple qualitative model for the different types of streamers in dielectric liquids

Abstract

A new qualitative model is presented which describes why there are different types of streamers, under what circumstances they are found and when one type can switch to another one. The approach combines different ideas and models that have been presented before. It is shown that rather than to distinguish between positive and negative streamers it is more advantageous to distinguish between slow and fast streamers. The physical conditions necessary to obtain these two streamer types, and also the very fast streamer, are described. Especially, a new propagation condition for the fast streamer is identified which states that the voltage at the streamer tip has to be larger than a critical value. The presented approach naturally leads to a more systematic classification of the different streamers types than before. It is shown graphically in the plane of the parameters electrode curvature radius and applied voltage in which regions the different types of streamers are located. The influence of rise time and polarity of the applied voltage, of pressure and temperature, and of the chemical purity of the liquid on both slow and fast streamers is also studied. Most predictions of the new qualitative model are in agreement with experiments.