High Voltage Grounding Systems
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Minimization of Construction Costs of Substation Grounding Grids: In every electrical installation, one of the most important aspects is adequate grounding; in particular, the grounding of high-voltage substations to protect people and equipment in the event of an electrical fault. Well-designed grounding systems ensure the performance of power systems and safety of personnel. It is desirable that the substation grounding provides a near zero resistance to remote earth. The prevailing practice of most utilities is to install a grid of horizontal ground electrodes (buried bare copper conductors) supplemented by a number of vertical ground rods connected to the grid, and by a number of equipment grounding mats and interconnecting cables. The grounding grid provides a common ground for the electrical equipment and for all metallic structures at the station. It also limits the surface potential gradient. Currently the IEEE 80-2000 standard for substations grounding limits the determination of the grounding parameters (namely step, touch and ground potential rise) to that of a uniform soil model unless the Sunde graphical method is used. With the Sunde graphical method, it relies on interpretation to obtain a two layer soil model. Without the use of the graphical method, the IEEE 81-1983 has several empirical equations that can be used for the two layer model; however, these equations rely on the use of images which retard the speed of calculations to the point where the overall optimization of the grounding grid (with respect to size and shape) has yet to be determined. The goal of the thesis was to improve upon the current restrictions for the grounding grid design, while minimizing the material (i.e., copper conductors) and installation costs of a grid. The first part of the research examined previous work through a combination of literature review, mathematical computations, and field measurements to validate the theoretical aspects of grid design. The thesis introduces an optimized uniform and two-layer soil with fast accurate calculations directly from soil measurements without the use of graphical methods or the use of complex image theory. Next, the thesis develops enhanced grounding parameter equations using Simpson’s Rule of integration. The final part of the thesis demonstrates how it is possible to optimize the configuration of the grounding grid itself, minimizing costs, and yet still achieving a safe installation. This is the first time such an optimization is possible, and it is made possible by the techniques developed in this thesis. The techniques are applied to existing real-world grid designs, and the results obtained show the effectiveness of the method in reducing construction costs. This thesis shows how these construction and material savings are realized by utilizing a process whereby the grounding design minimizes the overall cost. The overall contribution of this thesis is the optimization of the grounding grid design by eliminating the current restrictions found in the IEEE standards 80 and 81, respectively, and offering an optimized grounding system design, starting from the soil model to the actual grounding design itself.