DC Characterization of Liquid Silicon Insulation Material

Increasing use of Direct Current (DC) in medium and high voltage electrical networks is demanding new research in the existing as well as new insulating materials. The electric field under DC is complex because it is dependent on the conductivity and temperature, which leads to formation of space and surface charges in the insulation material. The formation of space and surface charges in the insulation material can lead to premature breakdown of the insulation material. Several studies are being carried out around the world to use the existing alternating current (AC) infrastructure under DC conditions. To study the feasibility of using any equipment under DC conditions, it is therefore important to investigate the conductivity and space charge behavior of the insulation material and their dependence on the temperature and the electric field, which are not predictable yet. In this study, an attempt has been made to study the conductivity and its dependence on temperature and the electric field of liquid silicon insulation material. This liquid insulation material has a unique property of turning into solid state once exposed to moisture. In this paper, conduction Current measurements has been performed in liquid as well as solid state to investigate their conductivity values and study its dependence on the temperature and the electric field. From the results obtained, an indication of the electric field threshold value, above which space charge starts accumulating in the solid silicon insulation material is found out. These parameters then were used for performing simulations using finite element analysis software to study the behavior of insulation material under DC conditions. Due to the complex conduction phenomenon observed and the complexity in the measurement set up, it was not possible to study the electric field threshold values in liquid silicon insulation. A comparison between XLPE and solid silicon insulation under DC conditions is then studied. The electric field inversion is observed in both the insulation materials. In addition to this, it is observed that, because of the high electric field dependency on the conductivity a solid silicon insulation equalizes the inverted electric field distribution and thus reducing the magnitude of maximum electric field.