A review of methods for grounding grid analysis

This paper presents a brief review of the most important methods available for the grounding grid analysis. This includes numerical methods intended for the grounding grid direct current, time-harmonic current and transient current energization. Emphasis will be given to the methods involving transient grounding grid analysis. Available numerical methods will be surveyed according to the implemented soil model, e.g. homogenous soil, horizontally and vertically stratified multilayer soil as well as exceptionally heterogeneous soil. In that regard, various possible treatments of the boundary between soil layers are discussed. Here, image methods feature prominently in a solution to this problem. Whence, several possible image methods are reviewed. Additionally, numerical methods are surveyed according to the theoretical background approach. Here, one can make a clear distinction between circuit approach, transmission line approach, electromagnetic theory approach and hybrid approach. Numerical methods for the transient analysis of grounding grids are also reviewed in regards to the domain of the solution. Therefore, they could be regarded as frequency domain and time domain methods. Fast Fourier transform algorithm is seen as a conventional way of crossing between frequency and time domains. Major advantages and disadvantages of both approaches are pointed out as well.

1. Introduction

Grounding grid analysis has been a major concern of electrical engineers from the very beginning of high voltage power station development. From the historical perspective, grounding grid analysis started from the experimental and/or theoretical analysis upon which various authors presented approximative expressions. These expressions stemmed from the experimental and theoretical investigations carried out on a single horizontal or vertical grounding rod [1], [2]. With the knowledge obtained from the behavior of single horizontal or vertical grounding rod, various authors proposed additional empirical or approximate analytical expressions for the grounding grids [2]–[4]. Proposed analytical expressions had various constrains regarding dimensions and geometry of the grounding grid. It became obvious that all these empirical expressions have significant drawbacks when applied to the complex geometry grounding grid.