Determination of space charge distributions in polyethylene samples submitted to 120 kV DC voltage

Charge distribution evolution was measured on polyethylene samples subjected to an applied voltage of up to 120 kV. Plates and cables made of the same polyethylene with identical electrodes were used. This makes it possible in the case of planar samples to look at the effect of the thickness for identical applied fields. The pressure wave propagation method was used for the measurements. The results indicate that increasing the thickness of the insulator does not increase the charge densities which develop in it under applied field. The observed space charge is localized in the vicinity of the electrodes, in a region extending over 0.7 mm, in which the diffusion of impurities from the semiconducting electrodes is very important. This confirms previous results showing the strong influence of additives diffusing from the electrodes on the behavior of insulating structures