FRACTAL ANALYSIS OF THE TREEING PROCESS FROM LUMINOUS DISCHARGE IMAGEAND MEASUREMENT OF DISCHARGE MAGNITUDE

The purpose of this study is to analyze the growth of trees generated in PMMA from the apex of a void created by a needle tip. The analysis was based on fractal theory. In the measurement system, PMMA blocks we re used with electrodes consisting of a needle and a plate. One cycle of an applied ac voltage was divided into twenty successive phase angl e sections, labeled phi 1, phi 2, ..., phi 20, from one negative peak to the next negative peak of the applied voltage. The quantitative eva luation of the fractal dimension D of the luminous discharge pattern w as performed for each section, particularly, for the sections phi 7, 8 , 9, 17, 18 and 19 where the discharge luminescence reached around the tip of the tree. It was noted that some samples revealed substantiall y different tree patterns even under the same measurement conditions. The reasons for the different trees have been investigated by determin ing D and attempting to correlate tree growth and the change of tree l ength with aging. When D of the discharge luminescence at phi 7, 8, 9, 17, 18 and 19 were large, luminescence with complex branches were gen erated. The present results indicate that tree growth and branching de pend on the discharge at phi 7, 8, 9, 17, 18 and 19.