Three dimensional imaging of electrical trees in micro and nano-filled epoxy resin

2019 2nd International Conference on Electrical Materials and Power Equipment (ICEMPE)

Chen

Zheng

et al. 2019

Electrical trees are artifacts resulting from aging of polymeric insulation in high electrical fields. Whilst there is some debate concerning the mechanism by which they grow, there is no doubt that their growth can lead to the ultimate failure of the host insulation. Studying electrical trees is mainly confined to measurement of associated partial discharges and observing the physical growth of the tree structure optically. This paper reviews developments in observations of the growth of trees in the laboratory. In particular, consideration is given to the benefits of generating three-dimensional replicas of real trees from X-ray computed tomography (XCT) and serial block face scanning electron microscopy (SBFSEM), and how these can facilitate better understanding of tree development mechanisms. It is concluded that both two-and three-dimensional imaging are required, and these need correlating with partial discharge measurements to develop models of tree growth and effective asset management tools.

Section: Imaging In Filled Polymersmentioning

confidence: 99%

Lessons from Three-Dimensional Imaging of Electrical Trees

2019 2nd International Conference on Electrical Materials and Power Equipment (ICEMPE)

Chen

Zheng

et al. 2019

“…However, optical tomography cannot resolve complex trees and optical microscopy is limited in resolution. In contrast, XCT and SBFSEM can provide sub-micrometer resolution and be applied to optically-opaque materials [18]. The general methodology for electrical tree 3D model creation consists in experimental sample preparation, electrical tree formation, machining the sample to prepare it for the scan, image acquisition and post-processing of the data which includes image segmentation and surface generation.…”

Section: Geometric Three-dimensional Tree Reconstructionmentioning

confidence: 99%

Application of FEA to image-based models of electrical trees with uniform conductivity

IEEE Trans. Dielect. Electr. Insul.

Schurch

Pattouras

et al. 2015

Self Cite

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

“…Samples 1 and 2 have been reported previously [1,6,7], but are reexamined here from a technique comparison viewpoint. Recorded videos of tree growth, animations of cross-section slices along the progression of the tree and animations of virtual replicas generated are provided in [23].…”

Section: Case Studiesmentioning

confidence: 99%

Comparison and combination of imaging techniques for three dimensional analysis of electrical trees

Schurch

IEEE Trans. Dielect. Electr. Insul.

Bradley

et al. 2015

Imaging of electrical trees has been an important tool for studying the phenomenon. The authors have previously shown that electrical trees can be three-dimensionally (3D) imaged and virtual replicas generated using X-ray Computed Tomography (XCT) or Serial Block-Face Scanning Electron Microscopy (SBFSEM). Here these techniques are evaluated and compared for 3D analysis of electrical trees along with conventional optical methods. A number of types of laboratory created trees showing range of morphologies were grown and examined to delineate the capabilities of each technique. Cross-sectional images and virtual replicas of the electrical trees from XCT and SBFSEM techniques were compared both qualitatively and quantitatively. SBFSEM provides greater detail than XCT, evidenced by imaging smaller sub-branches and when comparing parameters such as the number of tree channels, tree length or tree volume captured. On average, SBFSEM captures almost double the number of tree channels per slice than XCT, and virtual replicas in most of the cases have larger volumes. However, SBFSEM is a destructive technique, which makes the imaging process less reliable than XCT and not suitable for multi-stage of tree growth experiments. For full analysis, a combination of imaging techniques is proposed. Optical methods are used first to monitor tree growth. Then, micro-XCT which provides pixel size down to ~0.4 µm with a field of view of around 1 mm × 1 mm, can be used to reveal the overall 3D structure of a normal/mature electrical tree. Nano-XCT can be used to explore in more detail regions of interest, with a pixel size of ~65 nm, but a limited field of view of 65 µm. Finally, sections of the tree can be analyzed in even greater detail using SBFSEM, which can provide resolutions below 50 nm. Using this approach, a deeper and more complete analysis of the structure of electrical trees can be achieved.