This paper presents a new method which visualizes the high-speed three-dimensional images of the pre-breakdown streamers in dielectric liquids.A new optical system, having two crossed light axes to observe the needle tip from different directions was designed. The shadowgraphic images from these two directions were combined through a beam splitter and focused on the photo-cathode of image converter camera. The photograph taken by this high-speed shadowgraph system was reconstructed to the three-dimensional images using an image scanner and a computer. Using this system, the growth and the decay processes of the streamer in cyclohexane was investigated.
In our previous work, we have observed that the structure of initial streamers in liquid dielectrics drastically changes by the tip curvature of the needle electrode and the applied voltage. In the present work, we have extended our FEM calculations by taking in the charge injected during the streamer inception, to make considerations about the prebreakdown phenomena in liquids. The local field distribution in vicinity of the streamer head and the needle tip is evaluated. The difference between the various streamer structures can be explained from the calculation results when an initial filamentary streamer is generated on the needle tip.
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