An Extension in Cable Modeling for Grounding System Analysis

The building blocks of the equivalent circuit of a complex grounding system are individual equivalent circuits of all system elements, which are represented with their equivalent π circuits. In this paper, we focus on underground single-core cable lines with a ground return wire, which are very common elements in distribution networks. We model the cable line as a four-phase distributed parameter line and take into account all self-impedance and mutual impedance of three cable sheaths and the ground return wire. In the model, we allow for variable earth resistivity along the cable path and cases with the ground return wire placed in full cable length or in a portion of it. The developed π-equivalent circuit is nonsymmetric, which is a step forward in cable modeling for grounding systems analysis. We have analyzed a simple distribution system where we have shown that, with the use of π-equivalent circuits, we can easily calculate voltages in grounding systems. The proposed methodology offers a possibility to calculate voltage and current distribution along the cable line in all four conductors. The results show that costs savings are possible if the ground return wire is not laid in full cable length. The length of the ground return wire is determined so that the voltage magnitude safety levels are not violated.