Comparative Study of the Behavior of Two Polyethylene Types under DC Voltage by the Pressure Wave Method.

In order to develop extruded high voltage dc cables it is necessary to improve the understanding of charge storage and transport phenomena occurring in insulants such as polymer materials, when they are submitted to high dc voltages. A comparison of the behavior of two types of polyethylene, LDPE and XLPE, is presented. This study is based on the measurement, using the pressure wave propagation method, of the evolution of charge distribution in samples under electric stress. Important characteristics of these two materials are obtained, such as the internal field distribution, its distortion as compared to the applied field, and the localization of the charges responsible for these effects. For the materials under test, some regions of the samples are submitted to a field exceeding the applied one by 80%. Nevertheless, the localization of the space charges observed in some situations indicates that there is no particular risk during a reversal of the polarity of the applied voltage.