X-ray computed tomography and serial block-face SEM have provided detailed threedimensional reconstructions of electrical trees for the first time. The application of finite element analysis (FEA) to the analysis of electrical fields in an epoxy block containing a tree is considered. Illustrations are provided by way of a number of case studies. It is shown that the limitations of FEA do not arise from the discrete nature of the meshing: rather uncertainties are more concerned with material properties in high fields on the micrometer scale, the limitations imposed by the pixel size of the imaging technique, and the discrete nature of the image reconstruction technique. For a dynamic model of tree growth space charge dynamics on the same physical scale need also to be modelled. A meshing strategy is used, calibrated against the charge simulation method, to ensure accurate but manageable computations in critical parts of a tree such as branch tips.Examples of field values are given using geometric constructs and low-field material characteristics as illustrative values. The field variation around a conducting tree structure, including the maximum field direction as a branch starts to bifurcate, is determined as an example. These yield values in excess of those expected if space charge movement was considered, but consistent with analytical calculations.

X-ray computed tomography and serial block-face SEM have provided detailed threedimensional reconstructions of electrical trees for the first time. The application of finite element analysis (FEA) to the analysis of electrical fields in an epoxy block containing a tree is considered. Illustrations are provided by way of a number of case studies. It is shown that the limitations of FEA do not arise from the discrete nature of the meshing: rather uncertainties are more concerned with material properties in high fields on the micrometer scale, the limitations imposed by the pixel size of the imaging technique, and the discrete nature of the image reconstruction technique. For a dynamic model of tree growth space charge dynamics on the same physical scale need also to be modelled. A meshing strategy is used, calibrated against the charge simulation method, to ensure accurate but manageable computations in critical parts of a tree such as branch tips. Examples of field values are given using geometric constructs and low-field material characteristics as illustrative values. The field variation around a conducting tree structure, including the maximum field direction as a branch starts to bifurcate, is determined as an example. These yield values in excess of those expected if space charge movement was considered, but consistent with analytical calculations. Index Terms -XCT, x-ray computed tomography, SBFSEM, Serial block-face SEM, FEA, finite element analysis, electrical tree, field, model, charge simulation method, CSM, image-based modeling. This work is licensed under a Creative Commons Attribution 3.0 License. For more information, see http://creativecommons.org/licenses/by/3.0/ Qi Li (aka Steven) was born in Hunan Province, China, in September 1984. He completed the B.Eng. degree in electrical and electronics engineering at

The effect of interface modification on electrical tree growth and breakdown of epoxy resin Abstract -This study investigates the effect of an interface on the lifetime of epoxy resin samples and the growth characteristics of electrical trees. Six sample types are presented; all having been prepared in the point-plane configuration using a needle -with a tip radius of 3μm-as the HV electrode. Most were molded in two parts producing an interface perpendicular to the field direction at the centre of the sample. Tests were carried out at 13 kV rms until sample breakdown occurred and sample images were taken at fixed one minute intervals during the test period. Results show that the interface modification affects electrical tree characteristics and improves the time to breakdown of the epoxy resin tested.

The effect of interface modification on electrical tree growth and breakdown of epoxy resin Abstract -This study investigates the effect of an interface on the lifetime of epoxy resin samples and the growth characteristics of electrical trees. Six sample types are presented; all having been prepared in the point-plane configuration using a needle -with a tip radius of 3μm-as the HV electrode. Most were molded in two parts producing an interface perpendicular to the field direction at the centre of the sample. Tests were carried out at 13 kV rms until sample breakdown occurred and sample images were taken at fixed one minute intervals during the test period. Results show that the interface modification affects electrical tree characteristics and improves the time to breakdown of the epoxy resin tested.