Improved circuit-based grounding electrode model considering frequency dependency of soil parameters

Abstract

A lightning protection system (LPS) provides protection against possible losses in human lives, services to the public, cultural heritages, and economic values. Good performance of a grounding system, which is a crucial part in the LPS, is vital for the overall performance of the LPS. Various attempts have previously been made to improve the grounding performance by means of experimental and simulation work, including the continuous improvement made to achieve a better grounding electrode model. The circuit-based grounding electrode model is known for its simplicity, computational efficiency, and compatibility with many leading software. However, previous circuit-based models neglect the frequency dependence effect due to difficulties in computation and overall formulation. This work aimed to improve the circuit-based model of grounding electrodes by taking frequency dependent soil into consideration. Two main equations, as proposed by Dwight and Sunde and by Scott, were used to model a horizontally laid grounding electrode. The frequency domain approach was chosen for the simulation of the transient performance of the grounding electrode using Current Distribution, Electromagnetic Fields, Grounding and Soil Structure Analysis (CDEGS), while Matrix Laboratory (MATLAB) was used to solve the frequency dependent equations. The performance of the developed frequency dependent soil model was compared to that of the frequency independent model. For the case of high soil resistivity (2000 Qm), the frequency dependent model gave a 75.2% lower ground potential rise (GPR) than that of the frequency independent model. Analyses were also carried out to determine the effects of the current front time on the grounding electrode voltage response using both models. Again, for a soil resistivity of 2000 Om and current front time of 1 ^s, a 75.2% difference was recorded between the two models. The differences were lower for the case of 10 |is and 20 |is current front times. The consideration of soil frequency dependence on the effects of other parameters such as electrode length, burial depth, and soil profile, was also studied. It was found that the GPR at the grounding electrode experienced a reduction in value as the frequency was considered compared to that of when the frequency was not considered. In short, this work has successfully developed an improved and reliable circuit-based grounding electrode model with the effect of frequency taken into consideration and hence it is more suitable for accurate transient analysis.