Efficient modeling of a combined overhead-cable line for grounding-system analysis

Simple compact models for combined overhead-cable lines supplying a substation are presented as an extension of a previous paper for grounding system analysis. The overhead line section can be equipped with uniform or combined ground wires, whereas the cable line section can consist of coated metal sheathed cables, with/without intermediate grounding, or uncoated metal sheathed cables in continuous contact with the earth. Besides the calculation of the earth current at the faulted substation, the proposed modeling method allows the evaluation of the leakage current at the transition station, where cables are connected to the overhead line, as well as at critical overhead line towers. In this manner, the effects of the so called ldquofault application transferrdquo phenomenon can be conveniently estimated at the design stage in order to assess the most appropriate safety conditions. Some numerical examples are given by applying a computer program based on the proposed methodology.