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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.
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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.
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Development of the tool for application of the method for localization of unsymmetrical faults
Pospíšil, Tomáš ; Vyčítal, Václav (referee) ; Topolánek, David (advisor)
In resonant earthed distribution systems, the capacitive current of the system is compensated by grounding via a arc suppression coil. The level of fault current is then very small and independent on the fault location which greatly complicates the rapid finding of the fault site. At this moment there is no method to be used to directly locate the site of a single-phase fault in the distribution network, new methods and solutions are being constantly sought to address the shortcomings of the existent localization methods. The diploma thesis deals with the design of a universal software tool that allows to apply a new method of locating an asymmetric fault in the distribution network. The tool is created in a MATLAB environment and utilizes the negative sequence voltage measured on the low-voltage sides of the distribution transformers and the negative sequence current measured behind the power transformer. By using the proposed tool, it is possible to read the parameters of any part of the distribution system that the user enters together with the measured values of the voltage and current into the initialization file. After the specified network parameters are loaded, a numerical model is created, which is then used for the method. In the work is described in detail the way of entering the parameters of the network into the initialization file, the method of automatic assembling of the numerical model based on the entered data and the possibility of customizing the calculation parameters. At the end of the thesis, the functionality of the proposed software tool is verified on data from simulation of the test network.
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Testing of the admitance principle of the fault indicator
Musil, Milan ; Vyčítal, Václav (referee) ; Topolánek, David (advisor)
The thesis deals with the proposal, implementation and evaluation of test for fault condition indicators. Thesis focusing on earth fault indicators based on admittance principles. These indicators must be able to evaluate earth faults in compensated, compensated with auxiliary resistor, unearthed and high-resistance earthed networks. The proposed tests verify the current and voltage measurement errors in inputs including monitored characteristic variables such as conductance and susceptance. The proposed test are applied to a selected ample of the fault indicator. As part of the tests, the indicator is subjected to secondary test using the Omicron CMC256plus tester as well as test on fault records that have been converted to COMTRADE for this purpose. The last series of tests carried out uses the physical model of the medium voltage system, where the tested equipment is subjected to fault states in the compensated whit auxiliary resistor system and isolated system. Furthermore, part of the thesis is research of new methods of earth fault detection, including their principles and function description. Also included in the thesis is an overview of manufacturers of indicators, or protection, who are involved in the production of earth fault protection.
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The framework for application of phase allocation of consumers
Franěk, Vít ; Koudelka, Jan (referee) ; Vyčítal, Václav (advisor)
The aim of this work is to introduce the issue of the smart grids concept, as well as the issue of phase identification sorting from implementation smart grids. The issue of phase identification sorting is described by several possible methods. The work continues by calculating the theoretical network and processing the values measured from the low voltage network and applying the phase identification method based on voltage events. Based on the results, a laboratory task proposal is prepared.
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Probabilistic approach for evaluation of the safety of earthing systems
Klíč, Tomáš ; Vyčítal, Václav (referee) ; Topolánek, David (advisor)
This thesis deals with the grounding systems, namely their evaluation in terms of safety. The introduction describes the grounding theory, the principle reason for their use, and the difference between the current evaluation method of grounding systems in terms of security against electric shock and a new approach. Another part is devoted to describing the assessment of grounding systems in terms of safety, respectively. permissible touch and step voltages using currently based ČSN and PNE. Another essential part of the theoretical description of how to assess safety of grounding systems in terms of probabilities, consisting in determining the probability of death of a person, including the probability of failure and the probability of a man close to the rated grounding system during the disturbances, and classify the probability tolerable, moderately tolerable or intolerable and if necessary, assign the risk group appropriate solutions to mitigate the risks. The work, of course, the practical part. Designed for probabilistic approach will be processed illustrative example of evaluation chosen grounding system, which would be the basis for the negotiation of an international group CIRED / CIGRE focused on this issue.
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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
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Unsymmetrical power flow calculation with the help of software applications
Ermolenko, Ilya ; Koudelka, Jan (referee) ; Vyčítal, Václav (advisor)
This work consists of four parts. The first part of the thesis provides a theoretical introduction to the power flow calculation problem. Furthermore, the analysis of power flow calculation as a linear and as a nonlinear problem is performed. In this thesis, Newton’s iteration method is used in the calculation of the nonlinear problem. The following describes possibilities for improving the power flow calculation by improving the Newton's iteration method and using non-standard methods. The second part describes the possibilities of power flow calculation using various software applications, such as Pandapower, Matpower, OpenDSS and PSS Sincal. In the third part of the thesis the selected software applications tool is used to test the possibility of unsymmetrical power flow calculation in the LV network for the state with and without the PEN conductor, and the calculation of the ground fault in the compensated network. In the fourth part of the work, the unsymmetrical power flow calculation is tested for a larger LV network, further is performed the evaluation of the influence of PEN conductor modeling on the calculation results compared to the calculations of a network without this conductor.
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Measurement of electrical soil resistivity
Matyska, Stanislav ; Topolánek, David (referee) ; Vyčítal, Václav (advisor)
This master’s thesis deals with the measurement of the electrical soil resistivity. In the theoretical part there are described the methods by which the soil resistivity is measured – especially the Wenner’s method, which was used for the practical measurements. Then there is also described the one-layered and the two-layered model of this method. Furthermore, there is described the procedure for the measurement of soil resistivity using the OMICRON CPC 100 and PU 193 instruments used in the measurement. To verify the modeling of a two-layered soil model, the theoretical part of the thesis describes the soil modeling process using the program Ansys. As for the practical part of the thesis, the measurements were carried out in three localities: Brno – Královo Pole; Hrušovany nad Jevišovkou – Pravice; Hustopeče nad Bečvou – Vysoká. The measured values were processed using the Matlab’s graphical user interface (GUI) that was developed within this thesis. From these values, at least one two-layered soil model was created for each location and both meters – a total of 12 models were created. For these models, measurements were simulated in Ansys. The results of the simulations were then compared with the measured values. The aim of this thesis is to compare the measured data with the data obtained by the simulations and subsequently to describe the suitability / unsuitability of the substitution of the one-layered soil model for the two-layered one for given measurements.
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