Development of automatic measurement system for growth and shape of tree by image processing

A system to automatically measure the tree degradation phenomenon in organic insulating materials using an optical microscope is discussed. Cross-linked polyethylene was used as the sample material. A video-graphic processing method made it possible to examine the initialization period of the treeing phenomenon and to measure the tree length, surface area, and form of propagation using serial video images. As a result, it was possible in a long-time breakdown test, to demonstrate characteristic difference in tree length and surface area according to the size of the applied voltages in the period immediately after initialization. When the voltage was low the tree shape resembled the branches of a tree. As the voltage increased, the shape of the breakdown area formed a round chestnut-like tree. In a short-time breakdown test, it was shown that length and surface area were greatly influenced by the radius of curvature of the needle electrode. This difference was evident 20 s after the initialization of the tree. When the radius of the needle electrode tip was large, the tree took on a bushlike shape. When the radius was small the tree went from a tree-branch shape to a bushlike shape