Thermally Stimulated Depolarization Currents on Silicone Rubber with Nanofillers

High voltage direct current (HVDC) power transmission is becoming more and more competitive to high voltage alternate current (HVAC) power transmission, especially for bulk power transmission over long distances. For crossing wide metropolitan areas or long distances in the open sea, especially HVDC cable lines are attractive. Regarding the insulation, extruded XLPE HVDC cables offer significant advantages over those with other types of insulation, e.g. oil-paper insulated cables. In addition to higher permissible conductor temperatures also jointing of extruded cables is simpler. Nevertheless, the electric field distribution is much more complex in HVDC insulation systems because it strongly depends on the conductivities of the insulation. Especially the presence of space charges can lead to increased electric field stress up to failure of the device. These challenges require development of new insulating materials that are suitable for HVDC applications. The purpose of this paper is to present the method of Thermally Stimulated Depolarization Currents (TSDC), which allows investigating and evaluating insulating materials. First, the general test procedure of a TSDC measurement is introduced, and then all significant TSDC parameters are described. A test setup has been developed to perform TSDC measurements, which is presented in this paper. Furthermore, the challenges of a TSDC measurement are outlined and solutions are introduced. The investigations are performed on a liquid silicone rubber (LSR) to be used as an insulating material, e.g. for the insulation of a cable joint. In addition, TSDC measurements are performed on LSR samples with different concentrations of nanofillers to evaluate their electrical properties. The final approach is to present the scope of the TSDC method with regard to HVDC applications.