Abstract: This paper analyzes the subjective and objective reasons for the high resistance of the substation grounding grid, and discusses in depth the resistance reduction measures of the substation grounding grid from design to construction, operation and maintenance. It also elaborates on the characteristics and existing problems of various widely used resistance reduction methods. Keywords: Grounding resistance, substation grounding grid, resistance reduction measures 1 Introduction The substation grounding grid plays an important role in the reliable operation of the power system and the personal safety of substation staff. Its grounding resistance, step voltage and contact voltage are important technical indicators of the substation grounding system, and are important parameters for measuring the effectiveness and safety of the grounding system and for determining whether the grounding system meets the requirements. However, some substations, due to geographical constraints, must be built in areas with high soil resistivity. This results in higher design calculations for grounding resistance, step voltage, and contact voltage, failing to meet current standards. In recent years, with the increase in power system short-circuit capacity, accidents caused by poor grounding have become increasingly frequent, thus grounding issues have received increasing attention. How to rationally determine the design scheme of the grounding device and reduce grounding resistance during the design and construction process is one of the key points of substation electrical design and construction. 2. Reasons for High Grounding Grid Resistance in Substations There are several reasons for high grounding grid resistance in substations, which can be summarized as follows: 2.1 Objective Conditions: First, high soil resistivity. Especially in mountainous areas, high soil resistivity has a significant impact on system grounding resistance. Second, dry soil. Arid regions and sandy/pebble soil layers are quite dry, and since the earth's conductivity is mainly based on ion conduction, dry soil has higher resistivity. 2.2 Exploration and Design Aspects: In substations located in mountainous and complex terrain, the uneven soil and significant variations in soil resistivity necessitate thorough exploration and measurement of each grounding grid location. Based on the terrain, topography, and geological conditions, a practical grounding device must be designed. If the grounding device is not rationally designed and its grounding resistance calculated according to the terrain and topography of each grounding grid location, but instead existing drawings or typical designs are applied, then inherent deficiencies will exist in the design, resulting in excessively high grounding resistance. 2.3 Construction Aspects: For substation grounding in different regions, careful design is important, but strict construction is even more crucial. For substations in complex terrain, especially those located in rocky areas, the excavation of horizontal grounding trenches and the driving of vertical grounding electrodes are extremely difficult. Furthermore, grounding engineering is a concealed project. If full-process technical supervision and necessary oversight are not implemented during construction, the following problems may arise: First, construction may not follow the drawings. Especially in mountainous areas where construction is difficult, there are frequent instances of insufficient length of horizontal grounding electrodes and incomplete installation of vertical grounding electrodes; second, the burial depth of the grounding electrodes may be insufficient. In mountainous and rocky areas, the burial depth of grounding electrodes is often insufficient due to excavation difficulties, directly affecting the grounding resistance value. Thirdly, there's the issue of backfill soil. Regulations require fine soil for backfilling, with layered compaction, which is often difficult to achieve in actual construction, especially in rocky areas where soil extraction is inconvenient. Often, excavated gravel and construction waste are used for backfilling, further accelerating the corrosion of the grounding electrode. Fourthly, using charcoal or salt to reduce resistance is the most common practice. While this provides short-term resistance reduction, it's unstable. These resistance-reducing agents are washed away by rainwater, accelerating the corrosion of the grounding electrode and shortening the lifespan of the grounding device. 2.4 Operational aspects Some grounding devices are qualified in the early stage of construction, but after a certain operating cycle, the grounding resistance will increase. In addition to the hidden dangers left during construction mentioned above, the following issues also deserve attention: First, due to the corrosion of the grounding body, the contact resistance between the grounding body and the surrounding soil increases. Especially in the acidic soil of mountainous areas, the corrosion rate of the grounding body is quite fast, which will cause some grounding bodies to detach from the grounding device; Second, the resistance of the connection between the grounding down conductor and the grounding device increases due to corrosion or forms an open circuit; Third, the grounding electrode of the grounding down conductor is damaged by external force, etc. 3 Grounding resistance reduction methods In order to achieve the purpose of reducing the grounding resistance of the grounding grid, it is first necessary to study the methods of reducing the grounding resistance theoretically [1]. It can be seen from formula (1) that there are two ways to reduce the grounding resistance: one is to increase the geometric size of the grounding body to increase the capacitance of the grounding body; the other is to improve the geoelectric properties and reduce the resistivity and dielectric constant of the ground. The grounding grid is the foundation of the grounding system, consisting of grounding rings (grids), grounding electrodes (body), and down conductors. There is a common misconception that grounding rings are the main body of grounding, and grounding bodies are rarely used. In cases where grounding requirements are not high or geological conditions are quite favorable, grounding rings can also play a grounding role. However, this is usually not feasible. Grounding rings can play an auxiliary role in grounding, while the main role is played by grounding bodies. Many factors determine the magnitude of grounding resistance. Below, we will analyze the grounding formula of the traditional grounding grid with the grounding ring as the main body of grounding: Where: Equation (2) shows that in the traditional grounding method, when the soil resistivity is determined, sufficient grounding area is required to achieve the design resistance. To reduce the grounding resistance, the grounding area must be increased. For every four times the grounding area, the grounding resistance will be reduced by half. Equations (3) and (4) show that in the above-mentioned grounding grid, another way to reduce the grounding resistance is to increase the size of the grounding material, but the material consumption is too large and the effect is not ideal. To address the issue of high grounding grid resistance in substations, a thorough analysis of its causes is essential, followed by a careful on-site investigation. This, combined with relevant theoretical foundations and technical standards, requires the development of practical resistance reduction measures. 3.1 Technical Measures: The inherent characteristics of grounding engineering dictate that the surrounding environment has a decisive influence on the project's effectiveness. Designing a grounding project without considering the specific conditions of the project site is infeasible. The quality of the design depends on a comprehensive consideration of numerous factors related to the local soil environment. Soil resistivity, soil structure, water content, seasonal factors, climate, and available construction area, among others, determine the shape, size, and material selection of the grounding grid, providing crucial first-hand data for grounding design. Therefore, before design and construction, the following tasks must be completed: (1) Careful exploration and measurement are required. The topography, terrain and geological conditions of each remote sensing point grounding network location must be accurately explored. The soil resistivity and its distribution around the grounding electrode burial point must be measured to find the usable geological structure. (2) The lightning activity and patterns of the location must be investigated to determine the lightning protection measures to be taken and the requirements for grounding resistance. (3) The annual corrosion of the steel grounding electrode by the soil in the location and the acidity and alkalinity of the soil must be investigated. (4) Calculation and design must be carried out based on the above items to formulate practical resistance reduction measures and construction plans. 3.2 Resistance reduction methods (1) Laying horizontal extended grounding. Because the construction cost of horizontal laying is low, it can not only reduce the power frequency grounding resistance, but also effectively reduce the impulse grounding resistance. (2) Deep buried grounding electrode. In places where the ground resistivity decreases rapidly with the increase of stratum depth, the method of deep burial grounding electrode can be used to reduce the grounding resistance[5]. Therefore, by utilizing the properties of the earth, after burying the grounding electrode deeply, the grounding electrode is made to penetrate into the stratum with low ground resistivity, so as to reduce the grounding resistance through the low ground resistivity. When selecting the burial site, the following should be considered: choose a place with abundant groundwater and a high groundwater level; if there is a metal ore body near the grounding grid, the grounding electrode can be inserted into the ore body, and the ore body can be used to extend or expand the geometric size of the artificial grounding electrode; the spacing of the deeply buried grounding electrodes should be greater than 20m, and the mutual shielding effect can be ignored. However, the construction is difficult, the earthwork volume is large, the cost is high, and the difficulty is even greater in rocky areas. (3) Using grounding resistance reducing agent [2]. After laying the resistance reducing agent around the grounding electrode, it can increase the outer size of the grounding electrode and reduce the contact resistance. The resistance reducing agent is a chemical resistance reducing agent made of several substances, which is a strong electrolyte and water with good conductivity. These strong electrolytes and water are surrounded by a network colloid, and the gaps in the network colloid are filled by partially hydrolyzed colloid, so that it will not be lost with groundwater and rainwater, and thus can maintain good conductivity for a long time. The main function of the resistance-reducing agent is to reduce the local soil resistivity in contact with the grounding grid. In other words, it reduces the contact resistance between the grounding grid and the soil, rather than reducing the grounding resistance of the grounding grid itself. This is a relatively new and actively promoted method. Resistance-reducing agents have been used in engineering for more than 20 years. After continuous practice and improvement, they are now quite mature products in terms of both performance and construction technology. (4) Using the electrolytic ion grounding system (Ionic Earthing Array, abbreviated as IEA). IEA has been widely used in newly built substations in recent years and has achieved certain results. Research and practice have shown that the direct cause of excessive soil resistivity is the lack of free ions in the soil to assist in conduction. IEA can provide a large number of free ions in the soil, thereby effectively solving the grounding problem. IEA is composed of advanced ceramic composite materials, alloy electrodes, and neutral ion compounds to ensure that it can provide stable and reliable grounding protection. The main body of IEA is a copper alloy tube to ensure high conductivity and long service life. It contains special non-toxic electrolytic ion compounds that can absorb moisture in the air and release active electrolytic ions into the surrounding soil through deliquescence. It is precisely because IEA continuously releases active electrolytic ions that the conductivity of the surrounding soil can always be kept at a high level, so the fault current can spread smoothly into the surrounding soil, thereby giving full play to the protective role of the grounding system. In addition, the special backfill material contained in IEA has very good expansion, water absorption and ion permeability, so that IEA and the surrounding soil maintain a good contact interface. No matter how the weather or the surrounding environment changes, IEA can maintain the best grounding protection effect. However, the investment is relatively large. (5) Other methods. How to reduce grounding resistance has become one of the difficulties in engineering construction. In addition to the above methods, increasing the burial depth of the grounding grid, using deep hole blasting grounding technology [3], natural grounding body, local soil replacement, deep well grounding, expanding the grounding area and using two layers of horizontal grounding grid [4] are also feasible. Depending on the specific circumstances of each project, appropriate resistance reduction measures can be selected. These methods are not isolated but can be combined to achieve better practical results. 3.3 Careful Construction and Operation/Maintenance Careful construction is essential for achieving good design implementation. Seemingly unimportant implementation details often lead to serious consequences. Because grounding grid engineering is a concealed project, errors may not be immediately detected after construction, and even if problems are discovered, remediation is very troublesome, especially regarding corrosion prevention details. Therefore, after the design drawings and construction plan are finalized, on-site construction must be carefully organized. The arrangement of horizontal and vertical grounding electrodes must strictly adhere to design requirements, and strict control must be exercised over every aspect, including the quality of each weld joint, the use of resistance-reducing agents, and backfilling. Of course, after the project is completed, operation and maintenance must be strengthened. For problems that are prone to occur during the operation of the grounding device in the grounding grid project, operation, maintenance, and inspection should be strengthened, and defects should be addressed promptly. Grounding resistance and loop resistance should be measured regularly to ensure that the grounding is always in good condition. 4 Conclusion The design of the substation grounding grid should be based on actual conditions. Whether the grounding device can play its due role depends on the design, construction, and operation stages. First, design is a prerequisite for ensuring the effectiveness of grounding devices. Second, construction, operation, and maintenance are crucial; the quality and craftsmanship of construction are the foundation for ensuring the effectiveness of grounding devices and the means to realize the design objectives, while maintenance extends the service life and ensures long-term upkeep. Therefore, in the design and construction of substations in areas with high soil resistivity, it is essential to focus on optimized design and comprehensive management to fully improve the economic efficiency of grounding grid construction and the reliability of safe operation. Meanwhile, new resistance-reducing materials with high resistance-reducing efficiency, good corrosion resistance, stable composition, and low price will become the mainstream of grounding grid resistance reduction research.