Relation between transmission lines coupling factor and over head earth wire length : its impacts on fault current distributions

High voltage (HV) transmission mains form important assets in electrical networks. The existence of this infrastructure within the community necessitates effective earthing design to ensure safety compliance. Overhead earth wire (OHEW) forms parts of the HV transmission mains, as such the OHEW plays an important role when it comes to fault current distributions. The existence of the OHEW introduces the coupling factor between the faulted phase and the OHEW. These coupling factor aides in further reducing the fault current percentage into the substation earth grid. If the OHEW is continuous and infinite between substations, 100% of the coupling factor applies. Under the condition where the OHEW is non-continuous and finite, the coupling factor will not be to the full effect. This study endeavours to provide information in regards to the coupling factor under substation faults for a continuous and non-continuous OHEW. Furthermore, the relation between the coupling factor and the length of the OHEW is established. For the finite condition, the impact on the pole grid current and the length of the OHEW is discussed. The study shows the advanced accuracy of the proposed new method with respect to the existing research methods. A case study is also included.