AAU logo

Ghomi, Mohammad

Ghomi, Mohammad

PROJECT TITLE:  Measurement of the Transient Impedance of the Grounding System (Vertical Electrode) Buried in the Multi-Layer Stratified Soil Using Small-Scale Setup

PhD period: 2019.01.01 – 2021.12.31.
Section: Electric Power Systems 
Research Programme: Modern Power Transmission Systems
Supervisor: Claus Leth Bak
Co-Supervisor: Filipe Faria da Silva
Contact Information

Collaborator: To be announced later.
Funding: Self-financing.


The appropriate design of grounding systems impersonates a principal role in the precise operation of electrical systems in terms of transient analysis, insulation coordination, electromagnetic compatibility (EMC), power system protection, and human safety. Meanwhile, lightning strikes a transmission line, then high lightning current will flow into the grounding system and dissipate into the soil. Therefore, in the low-frequency range (0 to 150kHz), the characteristic of the grounding system subject to lightning current is dramatically different. Hence, these challenges are considered as common challenges in the modeling of the grounding system. However, the principal complex issue in the modeling of the grounding system is the modeling verification of precise grounding system (input harmonic impedance) at the wide-band frequency, especially at high frequencies.

This Proposal first presents an overview of the challenges in grounding system modeling by considering the frequency and time domain of the power system transient analysis. Accordingly, the impact of the high-frequency ranges of lightning, electrical and geometrical parameters will be considered. Hence, the size and structure of the grounding device, the electrical parameters of the soil, impulse current parameters (first stroke and subsequent stroke), and the feed point of the lightning will be considered during studies on the phenomena.

In the second stage, the full-wave approach to achieve tower–footing grounding system in the wideband range of frequency will be proposed. Moreover, remarkable issues like the frequency dependence of soil electrical parameter, length of electrode effects, and a layer of soil will be considered during the study in this stage. These issues will be referenced because they lead us to the real condition of phenomena. Furthermore, overvoltage analysis becomes more realistic, which can reduce the costs of commissioning and maintenances of power transmission lines (TLs) and wind turbines (WT).

The typical high voltage transmission line will be implemented in EMTP tools. Additionally, the proposal will consider two grounding system models during research and studies. These two models called, the simple resistive model and the precise model. The proposed precise model will be developed in the time domain based on state-space equations for back flashovers evaluation.

At the final stage, the proposal will focus on the laboratory setup. During the Laboratory tests, the transient impedance of tower-footing grounding system will be measured in different types (e.t uniform and two-layers). Additionally, multilayers soil in the high voltage laboratory will be addressed as the main challenges in grounding system modeling. However, comparing the simulation and laboratory test will lead us to verify our obtained results. 


Publications in journals and conference papers may be found at VBN.