Influence of Potential Difference Within Large Grounding Grid on Fault Current Division Factor

The fault current division factor describes the shunting ability of the ground wires of the transmission lines or that of the neutral conductors connected to a substation ground. As the power system capacity grows rapidly in China, more substations with higher voltage classes are constructed, and the grounding grid is becoming larger and larger in area. As a result, the potential difference within the grounding grid may become more obvious and, hence, its influence on the fault current division factor cannot be ignored. This paper proposes a multiport circuit model for grounding grids with multiple grounding points to take into account the potential difference. With the help of commercially available tools for power system simulation, the model can be easily used to calculate the fault current distribution and the fault current division factor. The main factors that affect the potential difference within the grounding grid as well as the fault current division factor are analyzed. As an application, the fault current division factor of a 1000-kV ultra-high voltage substation is further calculated.