Comparison of PWM and SIN aging of insulating material subjected to surface discharges

The electric stress created on an insulation system depends on the type of applied voltage stimulus. Real insulating systems often contain defects of different types e.g. cavities, voids within dielectric materials or at boundaries between the dielectric and the conductor which are sources of PD at large enough electric field. These defects can arise in the technological manufacturing processes or due to exploitation stresses. The paper will present comparison of aging test of insulating material subjected to surface discharges at pulse-width modulated (PWM) and sinusoidal (SIN) waveforms. Special focus and novel research aspect will refer to the interface between insulating material and conductor, subjected to PWM or SIN like stimuli. The paper presents experimental results of interaction of conductor on the mechanism of surface discharges in the insulation system. The dedicated test setup will be designed to perform experiments with various dielectric materials. Cooper electrode will be investigated, within specially prepared insulation samples composed of ethylene propylene rubber (EPR) and cross linked polyethylene (XLPE). For obtaining the correlation between the electrical stresses due to surface discharges on the polymer surface and their morphological changes of structure the following investigations were performed on samples: optical microscopy surface analysis, microstructural analysis of polymer surface by Scanning Electron Microscopy (SEM), elemental analysis with Energy Dispersion Spectroscopy (EDS), microstructural surface roughness analysis. Comparison of those results for both PWM and SIN will reveal the impact of voltage stimuli in defined setup.