A study of three-dimensional measurement of pre-breakdown streamer in dielectric liquids

This paper presents a new method which visualizes the high-speed three-dimensional (3-D) images of the pre-breakdown streamers in dielectric liquids. A new optical system, having two crossed light axes to observe the needle tip at different directions was designed. The shadowgraphic images from these two directions were combined through a beam splitter and focused on the photo-cathode of an image converter camera (ICC). The photograph taken by this highspeed shadowgraph system was reconstructed into the 3-D images of each frame using an image scanner and a computer. The growth and the decay processes of the streamer in cyclohexane were investigated by using this optical system. A random propagation of a filamentary streamer and actual movements of the bubbles produced by streamer were clearly shown as 3-D figures.