Imaging and analysis techniques for electrical trees using X-ray computed tomography

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 threedimensional (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.

Effect of Polycyclic Compounds Fillers on Electrical Treeing Characteristics in XLPE with DC-Impulse Voltage

“…The energy level and deep trap density are the largest in XLPE-A composite, leading to a decrease in the charge transportation and resulting in the suppression of electrical treeing growth. Experimental results reveal that the polycyclic compound A has great application prospects in high voltage direct current (HVDC) cables.Energies 2019, 12, 2767 2 of 15 microscope (SEM), or X-ray computed tomography (XCT) were used to reveal the more complete representation of the electrical treeing phenomenon [13]. Electrical treeing is a kind of cumulative breakdown which is also associated with the charge movement and trap distribution [14,15].…”

Untitled

“…6 shows how the divergence in the entropy values operates as a strong indicator of the deterioration process. It is observed that as the fault evolves locally deteriorating the insulating medium [10,11,19], different pulses with different entropic characteristics are manifested. The evolution of this deterioration has a correlation with the appearance of a greater number of pulses, whose entropy values diverge from average value (close to 2), as Fig.…”

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

“…Three-dimensional models (or 'virtual replicas') from 'real' (rather than simulated) electrical trees have been generated using the imaging techniques of X-ray computed tomography (XCT) and serial block-face scanning electron microscopy (SBFSEM) [15,16]. In the past, optical microscopy combined with either computed tomography or serial sectioning methods were used to reconstruct the structure of trees [17].…”

“…Recent research has allowed complete three dimension (3D) replicas of trees to be generated using both X-ray computed tomography (XCT) and serial block-face scanning electron microscopy (SBSEM) [15,16]. The use of these methods enables the measurement and calculation of many quantities which characterize the tree: for example, parameters such as the diameter of tree channels, tree volume and surface area, and 3D fractal dimension [17].…”