Electric Field Regulation at the Cable Accessories Using One New Numerical Approach

The problem of electric field grading in cable components, having both theoretical and technological implications, can be framed in more general topic of field control in HV equipment. A solution may be obtained by two possible approaches: using geometric field control [11, 13, 14, 15, 17, 18], in which the field distribution depends on the arrangement of main and auxiliary electrodes or using resistive-capacitive (RC) field control [2, 4, 6, 10, 12 ], where the field distribution relies mainly on the electrical characteristics of stress grading materials. The above considerations are applicable to a wide class of MV and HV electrical devices such as insulators, bushings, spacers, voltage deviders, cable accessories (joints and terminations), etc. In the following, paper attention will be focused on the cable terminations and joints. At the places of cable connections and endings exterior cover is removed, and the radial character of electric field is disturbed. Because of high voltage, the inhomogeneous electric field exists on those parts of the cable, having the highest intensity at the ends of the covers, or screen. Cable joints and terminations represent the weakest part of a HV cable power line because of the electric field enhancement at the edge of the truncated conductors and dielectrics. The results for electric field and potential distribution at the coaxial cable terminations and joints, having exponential or ellipsoidal form, obtained by the Equivalent electrodes method (EEM), are presented in this paper. The EEM and Finite elements method (FEM) are compared. Equivalent electrodes (EE) are appointed on the end of coaxial cable, where the edge effect exists. At the great distance from terminations and joints, inside the cable, it may be considered that the field is approximately homogeneous and the charge distribution is continuous. At the cable splice, it is possible to solve the problem (electric field and electric potential distribution) as superposition of two components: the first one originates from continuous distribution of the electrical charge, and the second one from equivalent electrodes.