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Structure Analysis of Streamers in Transformer Liquids under Impulse Voltages

It is well known that the performance of streamers in transformer liquids are closely related to the test conditions, e.g. liquid nature, voltage polarity, voltage level and field configuration. The differences in streamer phenomena under various test conditions can be reflected by the evolution of streamer shapes. However, the conventional parameters such as stopping length, average propagation velocity and apparent area cannot quantitatively describe the degree of structural complexity of streamers. In this paper, multi-fractal analyses were performed for 2-D projected streamer images captured in a mineral oil under impulse voltages. The multifractal spectrum shape, spectrum shift alone vertical axis and maximum value on the spectrum curve were estimated in order to describe the changing trend of streamer main branches and side branches, the distribution of streamer branches and the complexity of overall streamer morphology, respectively. Variations of these parameters with changes in test conditions including voltage polarity and voltage level were evaluated.