Influence of Electrode Material and Coupling on Space Charge Accumulation and Time-Dependent Current Curves in Silicone Rubber Plate Specimens

Inhalt:
Space charge and current measurements are important tools when evaluating the suitability of HVDC-cable system insulation materials. In addition, the measurement results can be used as input parameters for numerical simulations to calculate the electric field strength distribution in HVDC cable systems. Charge injection and extraction processes are dependent on the combination of electrode and insulation materials and their coupling influences the space charge accumulation and the current. When measuring space charges and currents in plate specimens metallic and/or semiconductive materials are often used. Whereby in real cable systems chemically bonded semi-conductive electrodes are used. In this paper, the influence of the electrode coupling and electrode material on the space charge accumulation and timedependent current curves is investigated. Specimens of 1 mm thick silicone rubber plate specimens with metal electrodes and coated polymer electrodes are used. Space charges and currents are measured simultaneously at 20 °C and 15 kV/mm. The measurements results show that the specimens with a direct contact to the brass electrodes lead to a seeming movement of the electrode charge peaks into the specimen. Possible reasons for this behaviour are assumed to be the influence of surface roughness or an influence of the silicone oil used as coupling medium. The results with the specimens with coated polymer electrodes prevent the charge peak movement but lead to an increase of the current. The significance of the usage of electrode material and coupling comparable to practical applications for electrical characterization in terms of space charges and apparent conductivity is shown.