The local field distribution in the vicinity of needle tip under the existence of streamer

The structure of initial streamers in liquid dielectrics drastically changes with the tip curvature of the needle electrode and the applied voltage. In cyclohexane, a filamentary streamer appeared first, and then it changed to a sphere, hemisphere, pagoda-like and bush-like shape with increasing tip curvature or applied voltage. In this paper, the local electric field distribution for the existence of the streamer is calculated using FEM to consider the prebreakdown phenomena in dielectric liquids. The actual experimental values for the streamer size and the injected charge of each streamer are taken in to account in the calculation. From such calculations, the difference between the various streamer structures can be explained when streamers exist at the needle tip