
Simulation of earthing system resistance measurement
Pirochta, Josef ; Topolánek, David (referee) ; Vyčítal, Václav (advisor)
In this bachelor thesis, the effect of different soil models and random wire placed underground on the results of earth resistance measurements using the 4pole method was investigated. To determine this influence, simulations were performed in Ansys Electronics software, in which different soil models (with local inhomogeneity, horizontally divided soil and soil divided at an angle) were created. In these models, the measured earth was placed together with the measured random wire and its resistance was determined by simulating the measurements and with respect to the distant ground. The effect of the different soil models on the accuracy of the measurements was determined from the differences in the resistance of the earth random wire obtained by measurement and with respect to the distant ground. It was found by simulations that, of all the variants investigated, performing measurements in the presence of different soil models and a random wire can lead to a measurement error of up to 7,2 %.


Determination of electromagnetic field distribution around underground power cable
Gromotovič, Ivan ; Paar, Martin (referee) ; Vyčítal, Václav (advisor)
The thesis deals with the distribution of the electromagnetic field around the conductor in the way of laying the conductors. The paper describes the structure of the cables and their lettering. More detailed is described the underground cable and various ways of protecting the conductor against mechanical damage are shown. The functions of the locator of underground lines on the electromagnetic field principle are briefly described . In the practical part, in simulation software Ansys Maxwell has been designed models to simulate the layout of the underground line. The output of the thesis is the comparison of the results created by the simulations.


The measurements of earthing systems and the role of electrical soil resistivity
Capyk, Jan ; Jurák, Viktor (referee) ; Vyčítal, Václav (advisor)
The theoretical part of the thesis is focused on explaining the concept of soil resistivity, applicable methods of its measurement, comparison of two methods used to measure the resistance of the earth electrode and a description of the measuring device Metro PU 193 used for the practical part of the thesis. In the practical part, the reader is acquainted with the results of measuring soil resistivity and earth resistance in the field, with their evaluation with respect to various influencing factors and with designs of earth conductors for high voltage poles for which soil resistivity was measured. The thesis contains plotted graphs of various dependencies according to the results of measured values and compares them with theoretical assumptions.


Appropriateness of modelling the actual soil model as a uniform or horizontal twolayer soil model
Kuběna, Michael ; Topolánek, David (referee) ; Vyčítal, Václav (advisor)
The present thesis deals with soil resistivity and especially the suitability of replacing various soil models with a twolayer horizontal model. First, the factors that influence soil resistivity as well as the methodology of its measuring are described, and various soil models are introduced. Then, the Ansys program was used to create several soil models: a vertical model with perpendicular or oblique division, a model with a pronounced inhomogeneity and a threelayer model. In all of these models, a Wenner measurement simulation was performed, followed by a twolayer horizontal replacement model. Then the size of the error that was created by replacing the actual model with a twolayer horizontal model was examined.


Steady state and shortcircuit conditions in 110kV E.ON network fed from Sokolnice transformer station
Vyčítal, Václav ; Rampl, Martin (referee) ; Blažek, Vladimír (advisor)
This thesis can be divided into five main parts. The first part deals with theoretical analysis of power flow calculation in power network during steady state condition. Load flow calculation is presented here as a linear and nonlinear problem. Newton iteration method is proposed for solving power flow as nonlinear problem. The second part of this thesis deals with the analysis of shortcircuit calculation in accordance with valid International Standard IEC 60909. The equivalent voltage source method is adopted in case of the shortcircuit calculation. For the calculation of unbalanced shortcircuit currents, the symmetrical components method is also presented. The last three parts of this paper are focused on calculations of power flow and shortcircuit conditions in power grid Sokolnice. So in the third part is the description of nodal area Sokolnice with its substations and the calculation of load flow and shortcircuit conditions for two different power supply options. For each supply option is also considered an abnormal (fault) grid condition. (overall there are solved four different options) The fourth part of this thesis deals with the result analysis and also the results of different power supply options are compared. In the last part there are presented necessary technical improvements for faultfree operation of power grid Sokolnice based on the result of power flow and shortcircuit conditions in that grid.


Design and optimization of laboratory HV models
Kočí, Zbyněk ; Vyčítal, Václav (referee) ; Varmuža, Jan (advisor)
Bachelor's thesis is focuses on the operation of the distribution system in the Czech Republic and the use of new types of cables in the world. It describes the characteristics, division and use of overhead lines and cable lines. This work also deals the division and control DC networks, their advantages and disadvantages. In superconducting cables is engaged in their development, advantages and disadvantages. Describes their application and use in the future. It also describes the parameters affecting the properties of the ropes and the cables of the AC and DC wiring and ways to mitigate the negative effects on the ropes and on the surrounding environment. Work deals with measurement and counting of the laboratory models for their optimization. Finally, the work describes a proposal of new laboratory model for the measurement and stating components, which are needed for optimization models and the production of a new model


The calculation of the shortcircuit currents and voltages of given distribution network
Vyčítal, Václav ; Vaculík, Petr (referee) ; Toman, Petr (advisor)
This thesis deals with the transient phenomena in electric power systems especially short circuits. Than short circuit is classified to other types of faults in electric power system. The study also describes short circuit current as a function of time. However to complete a basic theory of short circuits, separate chapters are devoted to the causes of short circuits and to hazards connected with short circuit currents. The main part of this paper is devoted to the derivation of the formulas for calculation of short circuit currents using symetrical components and to calculation method presented in IEC 60909. In the end of this part there is a example of a simple network with calculation of symetrical and asymetrical short circuit current. In the last part of this thesis there is an example of 110 kV network with calculation of short circuits currents on busbars. The topology of the network and elekctrical equipment data are based on real part of a distribution network situated in the Czech Republic.


Creation of a laboratory model of the earth system
Moliš, Martin ; Vyčítal, Václav (referee) ; Topolánek, David (advisor)
This work deals with designing of grounding system model. This model might be used for potential distribution, step and touch voltage measuring, depending on particular grounding system. Moreover measuring transferred potential into another grounding system and the influence of foreign grounding system’s presence on the overall earth resistance. The aim of this work is to create a simulation on the model of whole system’s behavior during a fault on the power line. This model also might be used for laboratory classes.


Deficiencies and inaccuracies in measurement of MV distribution network laboratory model
Němec, Jiří ; Vyčítal, Václav (referee) ; Ptáček, Michal (advisor)
The paper analyzes the deficiencies and inaccuracies in measurement of medium voltage distribution network laboratory model. The aim is to propose solution to these problems. In the second chapter, basics of the theory of medium voltage network and the operating parameters of distribution grids are described. The theoretical part is mainly based on the Czech technical standards. The third chapter focuses on description of the laboratory model and it contains its label values. The fourth chapter deals with executed measurements and mathematical models created in the program PSCad. Comparison of the measurements and the computer simulations is included. Description of the measurements contains its purpose, the measured parameters and results of the measurements. Input parameters for creating computer simulations are listed and their results are processed. In response to measurements, yet unknown parameters of the laboratory model and its behavior in various operational states are clarified. On the basis of the findings, which this paper brings, it is possible to modify the laboratory exercise and thus reach more accurate results.


Probabilistic Approach for Assessment of Earthing System Design
Vyčítal, Václav ; Gurecký, Jiří (referee) ; Procházka, Karel (referee) ; Toman, Petr (advisor)
This dissertation thesis deals with application of probabilistic approach to assessment of earthing system safety in distribution networks, especially for cases with common earthing of high and low voltage side of distribution transformers HV/LV. In these cases, the increased potential during fault might be transferred from high voltage to low voltage network and thus the individuals from public can be exposed to increased risk. Thus, for these cases were in this thesis defined expectable touch scenarios together with the resulting risk imposed on individuals from the public. Based on the results it seems that adoption of probabilistic approach for these cases of earthing systems might be more suitable compared to the conventional deterministic worst case approach. In accordance to the aims of the thesis, a thorough analysis of currently adopted probabilistic approaches was carried out as well and it was pointed out to some new possible simplifications in the adopted probabilistic based methodologies. For example, it seems that appropriate modelling of human body resistance by the full lognormal distribution is not completely necessary and similar results can be obtained when only the resistance for 50 % of population together with c3 and c4 fibrillation curves are used. Much of the work was also devoted to the determination of possible uncertainty of calculated risk of evaluated earthing system, especially due to inappropriate modelling of earthing system. The appropriateness of different earthing system modelling methods together with other parameters on the value of calculated risk was investigated through conducting sensitivity analysis. Based on the analysis results it seems, that due to using more, or less simplified modelling method, a possible underrating in the resulting risk of about 40 % (about half an order/decade) is expectable. On the other hand, the change of parameters related directly to calculation of fibrillation probability seems to exhibit greater change in calculated risk by up to units of orders/decades.
