Fundamental Aspects Determination Of Substation Grounding Characteristics Under Transient Phenomena For Different Soil Conditions

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Muhamad Saufi Bin Hussain
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Designing a grounding system for the distribution substation could be very difficult due to many factors that need to be considered especially when there is a fault occur at that particular grid. While a fault may be from within the system itself or from natural phenomena like lightning events. This fault current strikes may cause a total failure of the substation if it is not given extra safety measure. Thus, proper grounding system exist to yield the pathway for high fault current during transient event or even at normal condition to dissipate into the earth without damaging electrical equipment in the substation. Besides, different soil condition can be a major determinant in designing a grounding system. Therefore, this project evaluates the substation grounding system based on lightning event under different cases of soil conditions which comes in uniform and 2-layered soil. The simulation of the grid design was done by using 3 modules from the Current Distribution Electromagnetic Field Grounding Soil Structure Analysis Software (CDEGS) which is MALT, FFTSES, and HIFREQ. The grounding grids were evaluated by examine its individual grid resistance and impedance, GPR, touch voltage and step voltage. The influence of different soil models and lightning strikes on the grounding resistance, GPR at the surface, touch and step voltages are clearly presented in this project. In addition to that, these grid design evaluations were compared between under lightning transient and normal power frequency condition. Results indicated a major increase in grid resistance, touch and step voltages with respect to increasing soil resistivity in uniform model under power frequency condition as well as under lightning transient. In addition to that, results show that increase in size of the grid could decrease the touch and step voltages. All characteristic values for safety assessment are provided and plotted in 3D and spot-2D presentation. The results were then used to provide recommendations on the optimum substation grounding grid design based on the factors that were discussed.
FYP 2 SEM 2 2019/2020
Lightning , Power Frequency , Soil Resistivity , Touch And Step Voltages