Adnan Mujezinovic

Application of finite element method in calculation of large and complex grounding systems

Grounding systems have the most important role in safety of staff and substation equipment and therefore they require detailed analysis of relevant parameters. This paper discusses the possibility of application of software packages based on finite element method (FEM), when conducting analysis of grounding systems. Firstly the paper describes a mathematical model with assumptions on which is based. Complex grounding grids buried in both single-layer and double-layer soil where analyzed. In order to verify the presented model, calculation results are compared with results of various analytical and numerical methods, as well as with measured results. Finally to show the practical application of this approach, an example of a real grounding grid is calculated.

Modelling of the cathodic protection system with dynamic non-linear polarization characteristics

Cathodic protection (CP) is a technique that is used for protection of underground and underwater metallic structures from corrosion. Design of cathodic protection system requires defining of protection current density and potential. These parameters must meet given criterions during the exploitation of cathodic protection system. This paper deals with problem of modelling of the cathodic protection systems with dynamic non-linear polarization characteristics. Firstly, paper describes dynamic non-linear polarization characteristics. Mathematical model based on combined Boundary Element Method and Finite Difference Time Domain Method with assumptions on which is based are explained in the following part. Finally, application of the presented mathematical model was done on one geometrically simple example.

Application of coupled 1D and 2D isoparametric discontinuous boundary elements in the calculation of large grounding systems

This paper presents the application of coupled 1D and 2D isoparametric discontinuous boundary elements for calculation of large grounding systems. Indirect method of boundary elements was applied. Parts of long thin grounding conductor (e.g., tapes, grids, mashes or rods) are discretization with a 1D linear isoparametric discontinuous boundary elements. Boundary surfaces of solid grounding conductor (e.g., large diameter pipelines) are discretization with 2D bilinear isoparametric discontinuous boundary elements. Computer program “EARTH” was developed. Examples for grounding calculations of 1D and 2D were particularly tested, as well as coupled examples of 1D-2D.

Electric Field Calculation on Surface of High-Voltage Transmission Line Conductors

This paper presents a calculation of the value of the electric field on the surface of the conductors and in the immediate vicinity of the high voltage transmission line of 400 kV level. For the calculation of the values of the electric field, the CSM method is used. Verifying the established model was carried out by comparing the calculation results with results of measurements of the electric field at a height of 1 m above ground level. Measurements of the value of electric field lines below the height of 1 m above ground were carried out over the years in Bosnia and Herzegovina. The measurements and calculations were carried out on 400 kV lines of standard dimensions and reduced dimensions. Using the established model, values of the electric field on the surface of the conductors and in their immediate vicinity were calculated. The calculated values of the electric fields are used to determine the corona onset voltage gradients.

Calculation of the corona onset voltage gradient under variable atmospheric correction factors

Corona phenomena on conductors are of importance for high voltage transmission lines. In this paper a calculation of the corona onset voltage gradient of AC conductors has been performed for taking into account the effects of atmospheric conditions. Corona characteristic on overhead transmission lines (OHTL) are influenced by a several factors. The conductor surface roughness and atmospheric conditions have a direct influence on the corona onset voltage gradient. Atmospheric conditions have the largest influence on the value of the air density. The air density is function of the ambient temperature and pressure. Ambient temperature at any given location is subject to daily and seasonal variable. The transmission line crossing a high humidity area and thus humidity should be taken into account in evaluating of the corona onset voltage gradient. Increased voltages in the 400 kV electric power network of Bosnia and Herzegovina are increasing the value of the voltage gradient and higher power losses due to AC corona. Therefore, it is important to determine the value of the voltage gradient on conductor surface as well as corona onset voltage gradient to accurate determined power losses due to AC corona.

Computer aided design of the substation grounding system

This paper deals with design of the substation grounding system by using computer. As it is well known, proper design of the grounding system is most important part of the whole project of the substation, from safety point of view. Procedure of the measurement of the soil resistivity and interpretation of the measured results is given. Interpretation of the soil resistivity data and results of interpretation are explained. Also, calculation procedure of potential distribution of the complex grounding system, grounding system resistance, distribution of touch and step voltage by using a computer are presented. Whole procedure was implemented on the real substation grounding system. Results of the potential distribution on the ground surface of substation touch voltages and step voltages are calculated in the paper. Finally, analysis of the capacitor banks underground steel construction influence on all relevant parameters of the grounding system is given in this paper.

Application of the coupled BEM/FEM method for calculation of cathodic protection system parameters

Cathodic protection (CP) is a technique that prevents corrosion of underground metallic structures. Design of any CP system first requires defining the protection of current density and potential distribution, which should meet the given criterion. It also needs to provide, as uniform as possible, current density distribution on the protected object surface. Determination of current density and potential distribution of CP system is based on solving the Laplace partial differential equation. Mathematical model, along with the Laplace equation, is represented by two additional equations that define boundary conditions. These two equations are non-linear and they represent the polarization curves that define the relationship between current density and potential on electrode surfaces. Nowadays, the only reliable way to determine current density and potential distribution is by applying numerical techniques. This paper presents efficient numerical techniques for the calculation of current density and potential distribution of CP system based on the coupled boundary element method (BEM) and finite element method (FEM).

Software Tool for Grounding System Design

The purpose of the grounding systems is to ensure safety of substations equipment and personnel in and outside of substation at the maximum fault cur-rents. In order to properly perform their function, grounding system should have low resistance, thus limiting the potential values at the ground surface during the highest values of fault currents. This paper presents mathematical models on which developed software tool for calculation of the grounding system parameters is based. Modules of the developed software tool were used to conduct some calculations which are typical for designing of the grounding systems.

Power Transformer Modeling from Differential Protection Aspect

Differential protection have the most important role in protection of power transformers from internal faults. This paper discusses the power transformer modeling from differential protection aspect. Firstly the paper describes a low frequency transient model of power transformer and parameters of given model. Cases of inrush current, short circuit in protection zone and over—excitation were simulated. Finally, in all cases the harmonic content of the differential current is analyzed and appropriate conclusions are given regarding the performance of differential protection on the basis of these analyzes.

On the Use of Boundary Element Method for Cathodic Protection System Modeling

Metallic installations placed in the soil or sea water (such as metallic pipelines) are submissive to the processes of corrosion. Corrosion is the destruction of the metal which is placed in electrolytes. One of the most often used technique for protection of underground or underwater metallic infrastructures against corrosion is cathodic protection systems. Design of any cathodic protection system requires determination of the electric potential and current density distribution on the electrode surfaces. This paper presents numerical method based on the direct boundary element method for calculation of distribution of electric potential and current density on electrode surfaces with nonlinear polarization characteristics. Presented numerical method was used to calculate parameters of one illustrative example of cathodic protection system.