Concept of Pulsed Electroacoustic Imaging for Space Charge Detection in Dielectric Materials

The detection of space charge (SC) accumulation and transport in electrical insulation plays an important role in electrical engineering. In this article, the concept of the pulsed electroacoustic (PEA)-based imaging of SCs in dielectric materials was investigated. The main focus is on a visualization of SC distribution in all 3-D. Volumetric profiles of charge density distribution were obtained, i.e., in the direction of the elastic wave propagation as in the conventional method and, additionally, in the transversal plane. The discretization in this plane (which is dependent on the electrode's shape and pitch) was possible due to the application of a movable high-voltage electrode. The pivotal element was a step pulser that was responsible for charge excitation. The image-reconstruction approach yielded SC distribution in a transversal plane based on PEA signals that were acquired in the synchronized rotation of an electrode. Presented experiments were performed on double-layered polyethylene material that contained embedded homocahrge or heterocharge patterns that were deposited in corona mode with a mask shutter. Verification was carried out with the specimens being exposed to a sprinkled charge (either unipolar or bipolar) using a metallic mask shutter in corona mode, which allowed for the precise deposition of the charged pattern. The experimental results showed a good quantitative correspondence between a deposited charge density pattern in the analyzed specimen by surface mapping and reconstructed one by means of the PEA-imaging approach. The more precise localization of SC distribution (including charge polarity) is an important aspect in the dielectric research on new materials as well as in power, transportation, and industrial applications.