Evaluation and Calculation of Overhead Line Impedance in Distribution Networks

Abstract: The determination of the impedance for overhead lines is a critical step before the analysis of distribution feeder such as load flow and short circuit calculation can begin. Because distribution systems consist of single-phase, two-phase, and untransposed three-phase lines serving unbalanced loads, it is necessary to retain the identity of the self and mutual impedance terms of conductors and take into account the ground return path for the unbalanced currents. In this paper, Carson’s equations are developed by Kirchhoff’s voltage and current lows. This developing that use a suitable impedance model of distribution systems is novel and easy to understand. Due to the aforementioned equations, a computer program by Matlab software has been developed to calculate the impedance of overhead distribution lines. Comparison of the results shows the validity of the proposed program and ATP software. Then, some effective parameters such as power frequency, skin effect, type of conductor and spacing distance between the phase conductors on impedance calculation are obtained and studied.