Streamer inception and propagation in insulating liquids with inserted scavenger electrodes

This paper deals with inception and propagation of streamers in insulating oil with inserted free-potential electrodes (scavenger electrodes). Aim of the investigations was the experimental proof for the applicability of percolation theory concepts in streamer modeling. In percolation theory, allowed and prohibited regions within an insulating material are defined. The material properties being affected by the spatial distribution of allowed regions. Experimental proof of percolation processes could be found by introduction of allowed regions into the fluid. For this purpose, defined 'allowed' regions e.g. metal surfaces have to be integrated in the insulating liquid. The experiments were carried out in point-plane electrode configurations with metal-rings of defined diameter being inserted as free potential electrodes within the insulating liquid. Free potential electrodes in the liquid phase act as scavengers for electrons. Consequently, if electron conduction phenomena play a major role in prebreakdown phenomena, streamer inception and propagation should be affected with respect to streamer propagation direction. Positive and negative streamers show different behavior when reaching the free potential electrode. Negative streamers will always tend to reach the scavenger electrode whereas positive streamers are not strongly affected in propagation by free potentials. The results as well as it's significance for streamer modeling will be discussed.