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Instruments / Technical Area	Publication Details	Published
I13-2-Diamond Manchester Imaging	The importance of particle dispersion in electrical treeing and breakdown in nano-filled epoxy resin Siyuan Chen , Simon Rowland , James Carr , Malte Storm , Kwang-Leong Choy , Adam J. Clancy International Journal Of Electrical Power & Energy Systems 129 DOI: 10.1016/j.ijepes.2021.106838 Diamond Proposal Number(s): [18215] Show Abstract ▼ Abstract: The addition of nano-fillers has been widely proposed as a method to enhance the dielectric properties of high voltage polymeric insulation, though there are mixed reports in the literature. Here the potential of silica nano-particles to extend the time to failure specifically through resistance to electrical tree growth in epoxy resin is determined. The benefit of silane treating the nano-particles before compounding is clearly established with regard to slowing tree growth and subsequent time to failure. The growth of trees in needle-plane samples is measured in the laboratory with loadings of 1, 3 and 5 wt% nano-filler. In all cases the average times to failure are extended, but silane treatment of the nano-particles prior to compounding yields much superior results. The emergence of a pronounced inception time before tree growth is also noted for the higher-filled, silane-treated cases. The average time to failure of silane-treated 5 wt% filled material was 28 times that of the unfilled resin. The improvement in performance between the nanocomposites with untreated and treated fillers is attributed to fewer agglomerations and improved dispersion of the filler in the treated cases. Measurements of Partial Discharge (PD) indicated significant differences in PD patterns during the growth of trees in the treated and untreated cases. This distinction may provide a quality control method for monitoring materials. In particular, long periods in which PDs were not measured were observed in the silane-treated cases. Visual imaging of tree growth in the unfilled material allowed the changing nature of the tree from fine to tree to dark tree to be observed as it grew. Corresponding PD measurements suggest the dark tree is gradually becoming conductive, and that growth of maximum PD measured is dependent on the relative rates of the growth of the tree and its carbonization. X-ray computer tomography identified significant differences in average tree channel diameters (a reduction from 2.8 µm to 2.0 µm for 1 wt% and 3 wt% cases). This implies that in addition to tree length changes, evaporated tree volumes also change and may explain the change in partial discharge characteristics observed.	Jul 2021
I13-2-Diamond Manchester Imaging	Electrical tree growth in microsilica-filled epoxy resin Siyuan Chen , Zepeng Lv , James Carr , Malte Storm , Simon M. Rowland Ieee Transactions On Dielectrics And Electrical Insulation 27, 820 - 828 DOI: 10.1109/TDEI.2020.008671 Diamond Proposal Number(s): [18215] Show Abstract ▼ Abstract: Epoxy resin is widely deployed as a high voltage electrical insulation material when compounded with inorganic fillers. However, in the laboratory, the filler prevents visual observation of the long-term degradation known as electrical treeing. To date therefore, much laboratory testing has been conducted on unrepresentative unfilled materials. Here, the impact of micro-sized fillers on the treeing phenomenon in an epoxy system has been explored. Sub-micrometre resolution 3D reconstructions of electrical trees are reported from X-ray computed tomography (XCT) using an advanced ‘pink beam’ synchrotron light source imaging system. The role of filler particles between 1 and 10 μm in size on tree channel propagation is reported. In highly filled materials (30% by weight) a radical change in tree growth behavior is seen, leading to bush tree rather than branch tree growth. The dielectric breakdown time at constant stress was also found to increase as the square root of the filler level. The change in geometry of tree growth may explain the extended life of filled materials in high voltage applications.	May 2020
I13-2-Diamond Manchester Imaging	3D XCT imaging of electrical tree growth in epoxy resin Zepeng Lv , Siyuan Chen , Simon M. Rowland , James Carr , Timothy Burnett Ieee Transactions On Dielectrics And Electrical Insulation 27, 631 - 639 DOI: 10.1109/TDEI.2019.008450 Diamond Proposal Number(s): [18215] Show Abstract ▼ Abstract: This paper reports observations of electrical tree growth by X-ray computed tomography (XCT) in multiple steps. Growth between times of observation has been obtained by subtraction of an image from the subsequent one. Partial discharge (PD) signals were also recorded during tree growth. It is determined that not all PDs support tree extension. By comparing the energy released by PD and the vaporization energy of newly grown tree channels, it is found that only the PDs that reach the tree tips can contribute to the growth of tree length. In such cases, the efficiency of energy conversion was very high, whereas PD resulting in increases in tree channel diameter had a much lower conversion efficiency. Nano XCT images reveal many finer branches along the trunk of the main tree and in the front of the main channel tree tips. It seems that those finer branches led to tree growth, but were not directly associated with local PD. The new imaging techniques have shown great value in resolving the relationship between partial discharge activity and electrical tree growth, providing a platform for deeper understanding of the tree growth process, and interpretation of partial discharge measurements.	Mar 2020
I13-2-Diamond Manchester Imaging	Application of FEA to image-based models of electrical trees with uniform conductivity Simon M. Rowland , Roger Schurch , Michalis Pattouras , Qi Li Ieee Transactions On Dielectrics And Electrical Insulation 22, 1537 - 1546 DOI: 10.1109/TDEI.2015.7116349 Diamond Proposal Number(s): [8935] Open Access Show Abstract ▼ Abstract: X-ray computed tomography and serial block-face SEM have provided detailed three-dimensional 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.	Jun 2015
I13-2-Diamond Manchester Imaging	Comparison and combination of imaging techniques for three dimensional analysis of electrical trees Roger Schurch , Simon Rowland , Robert Bradley , Philip Withers Ieee Transactions On Dielectrics And Electrical Insulation 22 (2), 709 - 719 DOI: 10.1109/TDEI.2014.004730 Open Access Show Abstract ▼ Abstract: 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 x 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.	Apr 2015
I13-2-Diamond Manchester Imaging	Three dimensional imaging of electrical trees in micro and nano-filled epoxy resin Roger Schurch , Simon Rowland , Robert Bradley , Teruo Hashimoto , George Thompson , Philip Withers 2014 Annual Report Conference on Electrical Insulation and Dielectric Phenomena DOI: 10.1109/CEIDP.2014.6995882 Diamond Proposal Number(s): [8935] Show Abstract ▼ Abstract: The authors have previously shown that electrical trees in unfilled polymers can be three-dimensionally (3D) imaged using X-ray computed tomography (XCT) or serial blockface scanning electron microscopy (SBFSEM). Here, we present the results of 3D imaging and analysis of electrical trees in filled epoxy systems for the first time. Electrical trees created in unfilled, micro silica-filled and nano silica-filled epoxy resin were scanned using XCT at the Diamond Light Source synchrotron and then also imaged using SBFSEM. 3D virtual replicas of the trees have been generated and their structures characterised.Imaging in micro-filled epoxy is more challenging than in nanofilled epoxy. It was found that trees in samples filled up to 20 wt% with micro silica can be imaged using either XCT or SBFSEM. In the case considered, the mean diameter of tree channels in micro-filled epoxy was found to be considerably smaller (0.6 microns) than in unfilled or nano-filled epoxies (3 microns).	Oct 2014
I13-2-Diamond Manchester Imaging	Imaging and analysis techniques for electrical trees using x-ray computed tomography Roger Schurch , Simon M. Rowland , Robert S. Bradley , Philip J. Withers Ieee Transactions On Dielectrics And Electrical Insulation 21, 53 - 63 DOI: 10.1109/TDEI.2014.6740725 Diamond Proposal Number(s): [5898] Open Access Show Abstract ▼ Abstract: Electrical treeing is one of the main mechanisms of degradation in polymeric high voltage insulation, a precursor of power equipment failure. Electrical trees have been previously imaged mostly using two-dimensional imaging techniques; thereby loosing valuable information. Here we review the techniques that have been previously used and present the novel application of X-ray computed tomography (XCT) for electrical tree imaging. This non-destructive technique is able to reveal electrical trees, providing a three-dimensional (3-D) view and therefore, a more complete representation of the phenomenon can be achieved. Moreover, taking virtual slices through the replica so created brings the possibility of internal exploration of the electrical tree, without the destruction of the specimen. Here, laboratory created electrical trees have been scanned using XCT with phase contrast enhancement, and 3-D virtual replicas created through which the trees are analyzed. Serial Block-Face scanning electron microscopy (SBFSEM) is shown to be a successful complementary technique. Computed tomography enables quantification of electrical tree characteristics that previously were not available. Characteristics such as the diameter and tortuosity of tree channels, as well as the overall tree volume can be calculated. Through the cross-section analysis, the progression of the number of tree channels and the area covered by them can be investigated. Using this approach it is expected that a better understanding of electrical treeing phenomenon will be developed.	Feb 2014
I13-2-Diamond Manchester Imaging	Three dimensional characterisation of electrical trees Roger Schurch , Simon M. Rowland , Robert S. Bradley , Philip J. Withers Conference On Electrical Insuation And Dielectric Phenomena 2013 Annual Report Conference on Electrical Insulation and Dielectric Phenomena DOI: 10.1109/CEIDP.2013.6748152 Diamond Proposal Number(s): [5898] Show Abstract ▼ Abstract: Most of the geometric analysis of the structure of electrical trees has been performed using a two-dimensional (2-D) approach. However, electrical trees grow three-dimensionally (3-D). We have recently shown that electrical trees can be 3-D imaged. A 3-D virtual replica can be created and through it, the tree characteristics analysed. Laboratory created electrical trees in polymeric insulation were scanned using X-ray computed tomography (XCT) for 3-D model reconstructions. Global parameters such as diameter of tree channels, tree surface and volume were determined. The fractal dimension from 2-D projected patterns resulted to be lower than the fractal dimension from the entire 3-D model for bush and branch-type trees. Local parameters such as numbers of channels, area covered by them and proportion of area degraded at a given cross-section were also calculated. Using the skeleton for analysing the tree structure, indexes such as number of vertices, segment length, vertex density, tortuosity and branch angle were calculated. Among them, vertex density provided a marked difference in value between a bush and a branch-type electrical tree. It is pointed out that using this 3-D approach for analysis, a more real and complete insight of the structure of electrical trees is achieved.	Oct 2013

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