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.

Electrical Trees and Their Growth in Silicone Rubber at Various Voltage Frequencies

“…Owing to the harsh working conditions of power electrical equipment, there have been many investigations to determine the influence of temperature, voltage type, voltage frequency, thermal aging, and moisture on electrical treeing characteristics [8][9][10][11][12][13][14][15]. Partial discharge characteristics, treeing imaging technology, and channel characteristics have also been studied in order to better understanding the initiation and growth mechanisms of electrical treeing [2,7,[16][17][18].…”

Three dimensional imaging of electrical trees in multiple stages

“…More recently, three high-resolution systems for visualization and generation of 3D electrical trees have been developed exploiting developments in X-ray techniques and electron microscopy [7,8]. Serial Block-Face Scanning Electron Microscopy (SBFSEM) has the same basic mechanism as the serial sectioning method (SSM) in [6] but can provide an improved resolution (~50 nm).…”

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

“…Imaging methods are a common tool for studying electrical treeing phenomena [5]. Electrical trees created in translucent materials are analysed using conventional optical methods.…”

“…Recently, the authors have deployed X-ray computed tomography (XCT) and serial-block-face scanning electron microscopy (SBFSEM) techniques for 3D imaging of electrical trees in unfilled polymers [5,8]. In the past, 3D images of electrical trees in translucent XLPE have been generated using computed tomography and serial-sectioning methods combined with optical microscopy [9].…”