Computer Aided Design of Transformer Station Grounding System Using CDEGS Software

S Nikolovski,T Barić

doi:10.14311/552

Abstract

This paper presents a computer-aided design of a transformer station grounding system. Fault conditions in a transformer station can produce huge damage to transformer station equipment if the grounding system is not designed properly. A well designed grounding system is a very important part of the project for transformer station design as a whole. This paper analyses a procedure for transformer grounding system design and spatial distribution of touch and step voltage on the ground surface level, using the CDEGS (Current Distribution Electromagnetic Interference Grounding and Soil Structure Analysis) software. Spatial distribution is needed for checking and finding dangerous step and touch voltages above and around the transformer station. Apparent earth resistivity data is measured and analyzed using the RESAP module of the CDEGS software. Because of the very high current flow into the grounding system during a single line to ground fault or a three phase fault in the transformer station, very high and dangerous potentials can be induced on the metallic structures including the fence, which can cause dangerous situations for people and animals near the station and for the personnel inside the station. The PLOT module of CDEGS is used to view the results of the scalar potential, step and touch voltage on the surface. Graphic displays include equipotent contour lines and potential profiles (gradients) in 3D and 2D perspective and apparent soil resistivity (Wm) versus inter electrode spacing (m). The results of alternative grid designs may be displayed simultaneously for the purpose of comparison.

Highlights

With ever increasing fault current levels in today’s interconnected power systems it is necessary to ensure very low grounding resistance of transformer stations
The safety criteria in this paper are based on IEEE Std. 80, 188 editions and IEC 479-1, 1984 and some Croatian safety requirements
Described and verified for several (110/35/10 kV) transformer substations: “TS Našice”, “TS Osijek”, and “TS Valpovo”. These transformer substations are in the eastern part of the Croatian power system

Summary

Introduction

With ever increasing fault current levels in today’s interconnected power systems it is necessary to ensure very low grounding resistance of transformer stations. The safety criteria in this paper are based on IEEE Std. 80, 188 editions and IEC 479-1, 1984 and some Croatian safety requirements Another task is to check some existing grounding grids for an increased fault current level, i.e., to determine the fault current level which satisfies the safety criteria. These transformer substations are in the eastern part of the Croatian power system Due to their operational time, TS are exposed to potential fault conditions. In this sample case a single line to ground fault is relevant for the grounding design.

Mathematical expression of the electromagnetic field

Example of transformer station grounding design

Conclusion