Zero-sequence representation of nonuniform overhead lines

A mathematical model and equivalent schemes for zero-sequence components are suggested for overhead transmission lines with nonuniform span lengths and nonuniform tower resistances to ground. Besides the nonuniformity, the model takes into account the voltage drops in the grounding system formed by the line's ground wires and the ground electrodes of the terminal substations, avoiding the simplifying assumption, made in available line models, that the ground fault current magnitude does not depend on grounding system impedances. The analysis of a typical example is carried out in the paper; it shows that to ignore these two effects might lead to inadequate line ground wire and substation ground electrode sizing.