Measurement of charge distributions in insulating materials for high voltage cables

Evolutions in time of charge distributions in thick dielectric insulators such as those used in high-voltage DC insulation are investigated. The pressure wave propagation (PWP) method has been applied to low-density, high-density, and cross-linked polyethylene under electric stress. It is shown that the impurities contained in carbon-loaded polyethylene electrodes play a very significant role in the development of a space charge distribution within the insulator. It is suggested that, by studying the evolution of the charge distributions, it is possible to determine whether a stabilization occurs and how much time is required to reach this stabilization, depending on the temperature and the applied voltage. Consequently, such a measurement made on samples having the same structure as the cables will help in defining tests and standard procedures for equipment evaluation