Application of the multilayer soil equivalence method in determining the normalized parameters of the grounding system

Abstract

Introduction. Normalized parameters of the grounding system, such as touch voltage and resistance, are critically important for ensuring electrical safety and reliability of power plants and substations. The complexity of the multi-layered soil structure makes it difficult to determine mentioned parameters. This is due to the fact that real soils on the territory of energy facilities of Ukraine have three or more layers, and the specified parameters are determined by software with two-layer calculation models. Therefore, the need to provide multilayer geoelectric structures into equivalence two-layer models for practical application is an urgent task. Goal. Determination of the application limits of the multilayer soils equivalence method based on the calculating results analysis of the grounding system normalized parameters. Methodology. The study considered a three-layer model for four soil types (A, H, Q, K) common in Ukraine. The calculations were performed using the LiGro software package, which is based on the method of integro-differential equations, applied to the analytical solution of the problem of the electric field potential of a point current source in a three-layer conducting half-space. As a criterion for the possibility of applying the equivalence method, a relative error value of 10 % was chosen when determining the normalized parameters of a grounding system of the given topology and soil type. When determining the error, the calculation results in the original three-layer soil structure for the given topology of the grounding system were taken as the true value. The results show that the effectiveness of equivalent technique significantly depends on the type of soil and the area of the grounding system. In particular, for soil type A, replacing the upper and middle layers with the equivalent first layer (the lower layer with the second) provides a smaller error in the calculations of the grounding resistance than representing the upper layer as the first, and the middle and lower layers as the second equivalent layer. At the same time, there is a tendency for the error to decrease with increasing area of the object: from 225 m² to 14400 m², for the first case, the error decreased from –14.6 % to –2.6 %, and for the second case, it changed from –9.3 % to 14.6 %, respectively. Originality. For the first time, the results of the methodical error evaluation of the equivalence techniques of multilayered soils of different types when calculating the normalized parameters of grounding system are presented. Practical value. Determination of the conditions and limits of the use of the equivalence method when calculating the normalized parameters of grounding system by software complexes can be used in the design of new or reconstruction of existing energy facilities of Ukraine. References 20, tables 5, figures 4.