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Literature review reveals that steel grounding system is widely used and readily accepted in many other countries worldwide, where copper is very expensive. It is also used in many occasions by the utilities (nuclear and fossil fuel power plants), industrial plants (petroleum refinery, chemical plants, cement plants, steel plants, etc.) and REA’s (or Rural Electric Coops) substations as the ground grid material in USA. Such installations usually require great amounts of sub-surface steel piping, tanks and pilings so that there are major advantages in minimizing the extent of underground copper for grounding or other purposes.
Based on the National Bureau of Standards [presently called The National Institute of Standards and Technology or “NIST”] statistical data on corrosion of steel, an equation is introduced to estimate the corrosion rate of underground steel. The variables include the major soil characteristics (parameters), namely: resistivity, pH value, moisture content and aeration. This formula, together with the IEEE Standard No. 80-2000 , is used in the design of steel grounding. Also discussed, in detail, the design procedures for cathodic protection scheme to minimize corrosion of steel grounding. Numerical examples are included in the paper to enhance the understanding of steel grounding design for high voltage AC substations.
Overall corrosion protection then becomes easier to achieve either for coated or bare steel pipes, tanks and steel grounding structures underground.
Unfortunately, there is no simple, concise and practical design guide available for the use of steel as ground grid material and how to design the cathodic protection system. The main focus of this paper is to develop a practical design guide for steel
It is the unfamiliarity of using steel, lack of experience data, unavailability of any design standard and guide, and the fear of ground grid integrity due to corrosion, that steel is not commonly used. Also the IEEE standard provides limited information about the design procedure of the grounding system with materials other than copper.
|Steel Grounding Design Guide and Application Notes|