ABSTRACT
This chapter reviews the fundamentals and their application to determine the positive-, negative-, and zero-sequence reactive impedances for overhead line circuits. Overhead or aerial lines are assumed to be long, straight conductors for the purpose of calculating the reactance. Equilateral spacing or transposing of the some conductors is necessary for symmetrical line impedances. To reduce the impedance many high-voltage and extra high-voltage lines use several conductors in parallel for each of the three phases. To calculate the impedance of the conductors with earth return, it is necessary to know the distribution of the current returning in the earth. When two three-phase lines are paralleled, usually on the same tower, the combined zero-sequence impedance can be determined as one value. The earth is a conductor of enormous dimensions and non-uniform conductivity. In zero-sequence line impedance calculations, the tower footing resistance is assumed zero, which is practical for fault calculations.
