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In the electric power industry of Ukraine, the main system-forming objects are power transmission lines and substations with 330(220) kV switchgear. The most powerful sources of danger at substations are short circuits on the busbars, a direct lightning strike or the operation of overvoltage limiters and arresters.The purpose of the article is to develop a method for determining the resistance of the grounding system of substations with open switchgear 330(220) kV, aimed at increasing accuracy, taking into account the most influential independent factors. The provisions of the theory of experiment planning, the theory of electric circuits, mathematical modeling in the package Grounding 1.0, LiGro and Microsoft Excel were used to conduct the research. In the paper, a comparative analysis of the known formulas for determining the resistance of the grounding system is carried out: the formula of the GOST 12.1.30-81 standard, Ohlendorf-Laurant, Laurent and Neumann, Schwartz, Sverak formulas, as well as the formula of the international standard IEEE Std 80-2013. The results of multifactorial experiments to determine the dependence of the resistance of the grounding system on its area, the size of the grid cell, the perimeter of the cross-section of the grounding, the equivalent specific resistance of the soil, the short-circuit current and the depth of the grid location are given. A graphical comparison of the results of determining the resistance according to the considered formulas was carried out. In the paper, the method of determining the parameters of grounding system of 330(220) kV substations was further developed, aimed at ensuring standardized values of the resistance of the grounding system and the ground potential rise using formulas obtained from the results of multifactorial experiments. The results obtained in the work will make it possible to reduce the probability of damage to the insulation of 6- 10 kV cables, as well as cables of secondary circuits from low-frequency and high-frequency (pulse) voltages when large currents flow into the grounding system in the mode of a single-phase short-circuit to the ground in electrical grid with a grounded neutral. [ABSTRACT FROM AUTHOR]

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Purpose. Definition of the direction for further research to improve accuracy of the calculation of rated parameters of ground grids based on the analysis of statistical databases of electrophysical characteristics of the soil. Methodology. To solve this problem we compiled the statistical base of soil of Ukraine in the location of electrical substation, we performed the statistical analysis for the number of layers of geoelectric structure, and electrical characteristics. In the experiments implemented the comparing of accuracy calculation of the most typical three-layer soil in the Ukraine, by the new three-layer model of ground grids and the equivalent two-layer model, which used previously. Results. On the results of analysis the ranges of the electrical resistivity and statistical distribution for electro-physical characteristics of the soil are determined. The resulting distributions allow to develop criteria for instruments, installations and means of interpretation during the sounding of soil, as well as the requirements for mathematical models of ground grids. It was found that the most typical for places of locations the electrical substations in Ukraine are three-layer geoelectric structures. In the paper the statistical distribution for three-layer soil by type (Q, K, H, A) are described. The results of numerical experiments show that the use of methods to simplify of the multilayers soil does not allow the calculation of grounding grids with high accuracy. In the work recommendations for applicability the method equivalenting depending on the type of geoelectric structure are developed. Originality. For the first time, we obtained the statistical distribution of stratification of the soil in the location of power plant in Ukraine, determined the accuracy of the method to simplify a multi-layer soil in determining the rated parameters of grounding grids. In the paper the necessity to develop a mathematical model of the grounding device located in the three-layer soil is shown, as well as a new installation of soil sounding, which allows to increase the depth of sounding and new means of interpreting the results of sounding Wenner installing a four-layers geoelectric structure. Practical value The resulting recommendations for the applicability of equivalenting of multilayer soil, as well as research in specific work areas would help to reduce costs on materials and labours during the modernization and upgrade of grounding devices, moreover it will increase the electrical safety and reliable operation of electrical substation. [ABSTRACT FROM AUTHOR]