Study On The Grounding Optimum Design And Resistance Reduction Measures Of Substations In The High Soil Resistivity Region

With the increasing of the electric power system capacity, the numerical values of ground short-circuit current, touch voltage and step voltage will be magnified, and lead to great threats to the safety of persons and equipments. Especially, in high soil resistivity regions, the security parameters of grounding grid are even harder to meet the standards. This paper originates from the project'Reforming of XXX communication building', which is part of'PLA Communication System Reforming Project'. Achievements in this paper have been applied in practice and received satisfied results. To solve these problems, methods of optimizing the design of the grounding system and reducing resistance are proposed in this paper.To equalize the earth surface potential and decrease touch voltage and step voltage, an optimum design of grounding grids is proposed. For grounding grids of small and medium substations, according to DL/T621-1997, the method of unequal spacing provided based on equipotential model is commended in this paper. However, for big substations, a new method for optimum design is given. The key of this method is employing unequipotential model, taking the maximum difference of contact voltage in grounding grid as the object function, and using curve fitting method to arrange the level conductors of grounding system exponentially. At last, apply the proposed method to the ground grid of a 220kV transformer substation, and employ the CDEGS software package to simulate grounding parameters.This paper analyzes some different resistance reduction methods, and summarizes their characteristics and applicable scope. Considering the characters of high soil resistivity regions, analyze the influences of three different methods (vertical grounding rods measure, resistance reducing material measure and electrolysis polar measure) on adjusting the grounding parameters. And, receive the best operating method for each measure of the three. Vertical grounding rods measure: employ the grounding parameters calculating program to calculate the effect of different position, quantity, length and other factors of vertical grounding rods on resistance reduction; and calculate the effect of various parameters of vertical top-layer soil on resistance reduction. At last, analyze the influences of vertical grounding rods on reducing touch voltage, step voltage, seasonal factors and so on. Resistance reducing material measure: analyze the principle of resistance reducing material. Based on the current situation of the resistance reducing material market and some problems in application, this paper elaborates basic requirements on choosing resistance reducing material. And, show the effects of different resistance reducing materials via the experimental data. Electrolysis polar measure: analyze the resistance reducing principle of electrolysis polar. Study the layout method, and the dosage calculating.Based on all the above findings, propose the choosing rules on optimum designing and resistance reducing reforming of substations in high soil resistivity region. Moreover, apply the rules in this paper to other substations grounding projects, and verify the validity and applicability of the methods which were proposed in this paper by analyzing the results. Achievements in this paper will be the foundation of some deeper investigations in this field.