Effects of Vacuum Conditioning on PDC Measurements in Liquid Silicone Rubber

This study explores the impact of vacuum conditioning on the dielectric properties of Liquid Silicone Rubber (LSR) using Polarization and Depolarization Current (PDC) measurements, a critical consideration for the material's application in High Voltage Direct Current (HVDC) cable joints. The experimental procedure involved subjecting LSR samples to thermal conditioning at 120<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∘</sup>C with and without subsequent vacuum treatment, followed by a series of PDC measurements to assess changes in the dielectric behavior. Initial findings indicated that thermal conditioning alone led to reproducible measurements of material's electrical properties, likely due to the drying of the LSR and the homogenization of charge carrier distribution, without significantly altering the chemical structure of the silicone. However, subsequent vacuum conditioning introduced marked changes in the polarization mechanisms and electrical conductivity of the samples, suggesting accelerated aging processes induced by the vacuum environment. The results underline the importance of appropriate sample preparation in PDC measurements to obtain reliable data on the dielectric properties of insulation materials. Specifically, the study advises against the use of vacuum conditioning prior to PDC measurements to avoid introducing artificial aging effects that could skew the material's electrical behavior. Additionally, the research cautions against the interpretation of aging studies conducted under vacuum conditions for the exclusion of oxidative stress as fully representative of the in-situ environment of cable joints, given the distinct absence of high vacuum conditions in actual HVDC applications.