Space charge distribution measurements in polyethylene aged in dry and wet environments using the thermal step method

The paper presents space charge distribution measurements in various types of polyethylene subjected to accelerated electrical aging in wet and dry environments. It is shown that dry aging, which produced partial discharges of picocoulombs magnitude, introduced significantly more charge into the material than wet aging, during which partial discharges were not present. Space charge distributions in wet-aged insulation gave good correlation with the length of vented water trees and thus could be used to assess the extent of water treeing more easily than by microscopic observations and tree length measurements.