Study of electric field at a zero-angle contact point between three dielectrics

Abstract

Overhead distribution systems in Thailand widely utilize space aerial cables (SAC) in many areas for improving system reliability. A common issue that has often been encountered in SAC systems is the damage of the insulation of the core conductor at spacer positions. One of the possible causes of this problem may be the occurrence of the partial discharge due to high electric field stress at the contact point between the cable and spacer. This thesis studies the electric field intensification near a contact point, at which the contact angle is zero, in a configuration of an insulated cylindrical conductor lying on a dielectric solid. In this configuration, the insulated conductor and the dielectric solid represent the SAC and spacer, respectively. The objectives of this thesis are first to determine the relationships between the degree of field intensification and the configuration parameters. In particular, the parameters are the geometric ratio of the thickness of the dielectric solid to the outer radius of the conductor insulation and the mismatch between the dielectric constants of the media involved. Then, the variation of the electric field at the contact point will be investigated in configurations in which a dielectric or conducting layer is inserted between the insulated conductor and the dielectric solid in order to mitigate the electric field intensification. In the analysis, the electric field is calculated analytically by using the method of multipole images in two dimensions to realize high accuracy.