Analysis of Fault Potential Assessment under Typical Line-fault in a Real Urban Old Community

Electric shock is always an issue of concern in residential power system, especially in an old residential community with increasing electrical loads. The past literature usually reports calculated results based on a typical low-voltage distribution line system with a single building. In this study, the fault potential in multiple buildings of a real old residential community under specific phase-to-ground fault is investigated using the partial element equivalent circuit (PEEC) model with the buried conductors and overhead line systems, the actual wiring, grounding configurations, and protective earthing methods considered in the simulation. The main LV switch box, main distribution box, overhead lines, and each building are of concern in the assessment as both fault positions and observation positions. It is found that when a phase-to-ground fault occurs outside the residential buildings, e.g., sub-main distribution box, the fault potential could be easily transferred into most of the buildings with a PE wire connected with the N wire. The effective value would be more significant than 24V, a generally guided safe threshold value for human-body electric shock. For the line fault cases that occur in the buildings, the fault potential distribution and the threat to the other measured positions mainly depend on the protective earthing method, while the line topology outside the building has little effect on the fault potential distribution. Three typical grounding methods existing in the concerned urban villages are all discussed and compared in the study.