Space charge phenomena in laminated HVDC insulation

In non-energy high voltage DC applications often a combination of solid and liquid insulating materials is used. Despite this fact, investigations into the space charge behavior of such laminates are scarce. In this paper tests on samples made of polycarbonates (PC) and transformer oil are discussed. The results were reproducible and showed exclusively homocharge. At each interface between the different dielectrics a surface charge layer was detected in accordance with theory. Modifications of PCs showed different amounts of space charge and consequently, different field enhancements in the dielectric bulk. Prior to the interpretation of space charge measurements on acoustically and electrically nonhomogeneous laminates, special attention has to be paid to charge calibration procedures as well as reflections of acoustic waves. Methods for solving these problems have been developed.