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

The measurements of charge distribution evolutions in polyethylene samples subjected to an applied voltage of <or=120 kV are discussed. To apply significant voltage gradients to plates or cables having an insulator thicknesses ranging from 5 to 10 mm, the large applied voltage was necessary. The possibilities offered by this equipment are illustrated by results obtained with 6-mm-thick plates. A comparison of the behaviors of 2-mm-thick plates and 6 mm thick plates made of the same materials and submitted to the same field is presented. The results indicate that increasing the thickness of the insulator does not increase the charge densities which develop under the applied field and that the observed space charge is localized at 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.<<ETX>>