A numerical analysis of the harmonic impedance seen along a transmission overhead line

This paper presents general relations for calculation of harmonic impedance seen along an AC transmission overhead line. This is modeled by a chain of two symmetrical passive quadripoles corresponding to the segments that are on either side of the section of interest. Chain matrices of the two quadripoles are written by considering uniformly distributed line parameters and on their base, the expressions for the input impedances of the two quadripoles fed in the common section are obtained. The equivalent impedance seen in the section of the line, obtained by placing in parallel the two impedances mentioned above, depends on both the position along the line and the frequency. The expression for its calculation is applied to the numerical study realized for overhead lines having a nominal voltage of 220 kV. The results allow the identification of line areas and the frequencies where the risk of parallel resonance occurrence is greatest..