Safety Performance of Large Grounding Grid With Fault Current Injected from Multiple Grounding Points

Due to the overhead ground wires of transmission lines or the transformer's neutral point connected to a substation grounding grid, it looks like that there are many currents injected into or drawn out of the grounding grid from different grounding points when fault occurs. As the grounding grid is becoming larger and larger in area, the potential difference within the grounding grid may become obvious, and the assumption that the grounding points can be regarded as one point may not be suitable. This paper proposes a method to analyze the non-equipotential grounding grids with the fault current injected from multiple grounding points due to the overhead ground wires of transmission lines or the transformer's grounded neutral point. With the method, the influences of the grid area, soil resistivity, material of the grid conductor, and relative position of the grounding points on the performance of the grounding grid are thoroughly analyzed.

I. Introduction

As more and more substations with high-voltage classes are going to be constructed, the area of the grounding grid is becoming larger and larger. Meanwhile, due to the high price of copper, steel is often used as the grounding conductor in China, which has much higher resistivity and permeability than copper. Thus, the feature of unequal potential of the grounding grid will become more and more distinct, which means that the location of the fault current injected point may affect the grounding impedance, touch voltage, and step voltage [1] –[4]. As the fault position cannot be manually controlled, the engineers should always consider the worst case scenario.