IMPROVED DESIGN OF EARTHING SYSTEM

Abstract

Grounding system is an important element of electrical systems. In a very simplified way, its basic function could be considered to provide a conductive connection between electrical plant and soil. In electricity supply systems it is a common practice to connect the system to -"earth" at suitable location, the idea being that in the event of a fault, sufficient current will flow through the fault path so that the protective gear will operate and isolate the faulty circuit. Proper installation will facilitate the protective device operation, removing hazardous fault current from flowing uncontrolled over the earth until the protective device operates. Grounding is critically important to achieve equipment and personnel protection in Small Hydropower (SHP) station. It is one of the most important designs for the power house and switchyard. Grounding of the electrical system has to limit voltage stress on personnel and equipment within predictable limits. With the rapid growth in the magnitude and interconnection of the power system, difficulties are encountered for satisfying various earthing criteria. In such conditions if existing infrastructure available in the form of civil structures is used, then not only it can lead to satisfying the criteria but can also provide economic benefits. The wide spread use of steel reinforcing bars in concrete foundations and footings of structures can provide a ready-made supply of grounding electrodes. In low resistivity soils, the concrete or cement covering on the steel will protect it from corrosion while in high resistivity soils, the low resistivity of concrete as compared to that of the soil would increase the effectiveness of the electrode. This dissertation report describes in detail basic earthing system including various factors affecting soil, earthing electrode, corrosion etc., reasons and the procedure for including civil structures in the design of earthing system and software programme which can be used to optimize the requirement of conventional earthing system by using civil structures of the power house. Analysis of the results proving the effectiveness of concrete encased electrodes is also included.