Acoustic Wave Behavior in a Specimen Containing an Air Void Defect

The PEA method is the most used technique for the space charge measurements. As is well known, this method uses pressure waves to detect the charges accumulated in solid dielectrics. Based on its working principle, the generated acoustic waves travel within PEA cell and the specimen under test in order to be finally detected by the piezoelectric sensor. For a multilayer specimen and, in particular, in case of different materials that make up the specimen, the acoustic wave reflection is inevitable. Considering that, in several cases, the reflected waves could be detected by the piezoelectric sensor before than the main signals, the PEA cell output profile could results distorted. Based on the above considerations, the aim of the proposed work is to evaluate the acoustic waves behavior in a three layers specimen which has been used in a previous published paper. The specimen under test, realized to simultaneously measure the space charge and the partial discharges, was composed by three layers of Kapton foils in which an air void has been created. The previously obtained space charge distribution is reported again in this work. Mathematical calculations and simulation results shown that the PEA cell output signals found in the previous work are not correct due to the multiple acoustic waves reflection within the specimen.