Abstract
The PEA method has been used to study the evolutionof electrode interface charge and space charge in 2 mmthick XLPE samples at ±40 kV and room temperature.The voltage polarity is switched and the transition to asteady-state at each polarity is followed. The samplesare intended to be symmetric except for the electricalboundary conditions, however the measured spacecharge distribution is more or less unsymmetrical for allcases studied. Gold leaf, aluminium foil and graphitepaint have been used as electrode materials, and theobtained results are different for the three electrodematerials. Measurements with gold electrodes on threesamples having different storage conditions prior to themeasurements also provided significant differencesbetween the samples.
Highlights
The pulsed electro acoustic method, PEA, is a tool to study how charge at the electrode interfaces and space charge inside insulation samples develop with time
The data from the PEA measurements are presented as the time evolution of interface electric field ratios and as individual scans of the pressure signal for selected times during the measurements, see Figs. 1 to 12
The space charge within the sample is characterized by zero charge in the middle of the sample and a slight gradient extending through the sample
Summary
The pulsed electro acoustic method, PEA, is a tool to study how charge at the electrode interfaces and space charge inside insulation samples develop with time. Making measurements close in time with and without voltage on, more information can be obtained since the interface charge is changing immediately when the voltage is switched off whereas the space charge is slowly decaying. Concentration gradients will cause conductivity gradients, so when DC voltage is applied the electric field will become nonuniform, and space charge will appear due to the nonuniform polarization. The insulation samples are intended to have uniform distribution of by-products, and care is taken to prevent concentration gradients to arise due to diffusion. In this situation, it is possible to study if any other parameters or processes cause the electric field to become non-uniform. There seems to be no statistically significant conclusions drawn, so more attention to repeated measurements and improvements in the sample handling seems to be needed
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