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Design and Analysis of Transformer Stations Grounding System Using CDEGS Software

In this paper the single phase to ground fault conditions in transformer station have been simulated in order to get spatial distribution of touch and step voltage on the ground surface. Spatial distribution is needed for checking and finding dangerous step and touch voltages. The field theory approach is used. The frequency domain analysis is performed using HIFREQ (High Frequency) modules of CDEGS (Current Distribution Electromagnetic Interference Grounding and Soil Structure Analysis) software. It is useful to know that CDEGS allows calculation for multiple frequencies, but for this presentation we will use only 50 Hz frequency. Because of a very high current flow into the grounding system there are high potentials dangerous to people near the station and the personnel inside the station. So, the main task is to get the resistance of the grounding system as small as possible in order to keep the step and touch potentials on an acceptable level. The PLOT module is used to view the results of scalar potential on the surface. Graphic outputs allow examination of the performance of grid areas by inspecting them on the screen. Graphic displays include equipotential contour lines and potential profiles (gradients). Results of alternative grid designs may be displayed simultaneously for the purpose of comparison. A typical grounding grid is generated in the HIFREQ module and placed 0.8 meter below the transformer station surface.

substation; grounding grid; fault current; safety; touch and step voltage; ground potentials

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