Serial block-face scanning electron microscopy for three-dimensional imaging of electrical trees

Electrical trees are defects that can grow in polymeric insulation and cause power equipment failure. They have been imaged mainly using two-dimensional approaches. Here we present the use of Serial Block-Face Scanning Electron Microscopy (SBFSEM) for three-dimensional (3-D) model reconstruction of electrical trees. SBFSEM is an automated process of serial sectioning combined with block-face imaging of the sample, inside a chamber of a low-vacuum SEM. Two polymeric samples with a bush and branch-type electrical trees were examined using SBFSEM. 3-D replicas of sections of the tree were created and tree characteristics quantified. Parameters such as diameter and number of tree channels, tree volume and proportion of volume degraded were obtained and compared, indicating that electrical trees can be classified through these parameters.