Optimum Design And Retrofit Of Grounding Grid Of Large Substation

Along with the development of electric power system capacity, the value of failure current flowing into ground has been increased greatly. In order to control ground potential rise, the area of the grid may be very large and maximum diagonal of the grid can be above a kilometer. Because the area of large substation is big, grounding grid is unequipotential. The gradient of earth surface potential above the large equidistant substation is big, and the leakage current of their conductors are not uniform. It is very important to the optimum design of grounding grid of large substation on the unequipotential model for application of engineering.Based on method of field-circuit coupling theory, nodal method of analysis is applied to the power parameter calculation of grounding grid. The self-resistance and self-inductance of conductors, mutual inductance between conductors are taken into account. The methods are able to compute the power ground impedance, touch and step voltage, potential distribution on the soils.The grounding grid is designed according to the method of unequal spacing provided by DL/T621-1997 under equipotential model, which is verified by numerical calculation. Because the grounding grid of large substation is not equipotential,the above method can not decrease the difference of voltage in grounding grid effectively. Therefore the optimum design is proposed on the unequipotential model, in which the object function is the maximum difference of contact voltage in grounding grid. The software of optimum design using MATLAB language is compiled in uniform and nonuniform soil, by which the optimization results are obtained and analyzed in different grounding area and different grounding conducts number.Because of the long time and the corrosion effects of grounding grid, grounding impedance of the large substation is less than 0.5 ohm and it is necessary to reform the grounding grid. The soil resistivity around the substation is measured,the measured data can be inversed and obtained the soils structure .The grounding grid is designed and reformed.