Numerická analýza a simulace Rogowského cívky

This work illustrates an analysis of Rogowski coils for power applications, when operating under non ideal measurement conditions. The developed numerical model, validated by comparison with other methods and experiments, enables to investigate the effects of the geometrical and constructive parameters on the measurement behavior of the coil and we also study the behavior of Rogowski coils coupled with bar conductors under quasi-static conditions. Through a finite element (FEM) analysis, we estimate the current distribution across the bar and the flux linked by the transducer for various positions of the primary conductor and for various operating frequencies. Simulation and experimental results are reported in the text.Tato práce ilustruje analýzu rogowských cívek pro energetické aplikace při provozu v podmínkách bez ideálního měření. Vyvinutý numerický model, ověřený porovnáním s jinými metodami a experimenty, umožňuje zkoumat vliv geometrických a konstrukčních parametrů na chování měření cívky a také studujeme chování rogowských cívek spojených s tyčovými vodiči za kvazi-statických podmínek . Pomocí analýzy konečných prvků (FEM) odhadujeme rozložení proudu přes tyč a tok spojený snímačem pro různé polohy primárního vodiče a pro různé provozní frekvence. Simulační a experimentální výsledky jsou uvedeny v textu.410 - Katedra elektroenergetikydobř

Risk Analysis of Stochastic PERT Graph

Purpose of the article: The paper deals with a time and probability analysis of stochastic graph PERT. The paper focuses on the comparison of two different approaches calculation of probability analysis. Concretely the planning time of the project was calculated. A sample PERT network graph was examined, which comprised 18 nodes and 18 real activities and 6 fictions activities. For the purpose of the analysis, the basic characteristic times were calculated in accordance with traditional approaches related to the PERT method. Methodology/methods: The implementation of the PERT algorithm is based on the critical path method (CPM). It was calculated the basic time charactetistics of the project and identificed the critical path. For probability analysis was also calculated expected value, variance and standard deviance of the activities. For calculation of the planning time was used distribution function of standardized normal distribution. The PERT algorithm is realized by using spreadsheet in the MS Excel. Scientific aim: of the paper is comparison of two different approaches calculation of the probability analysis and their influence on the calculation of the planning time of the project. Findings: Two different approaches calculation of the probability analysis shows on different result of values of project planning time. Approach II better reflects the difference between the values of variances of project activities. The value of variance depends on the input values of three time durations s activity estimates (pessimistic, most likely, optimistic). For higher values of probability there is a bigger difference between the values of planned times that are calculated by two described approaches. Conclusions: The problem was solved using the example project whose model (network graph) contained 18 nodes and 24 activities. For each activity have been known three time estimates (pesimitic, most likely, optimistic). Based on these estimates were calculated expected values of the duration activities and their variances. Expected values of the duration activities were used as input values to calculate the time characteristics. Variances of the activities were used as input values to calculate the variance at the nodes. For these calculations two approaches was used. The expected value of project duration (value of earliest time in last node) was the same for both approaches. For the approach I is a value of the variance in the last node less than for the approach II. These values were used as input data for calculation of planning time of the project at various levels of probability according to the standardized normal distribution. From obtained results dependence between the probability and size of the differences in planned times were observed. This difference increases with a probability going to one. Based on the analysis a recommendation shows to use the approach II under conditions when there are large variations between optimistic (pessimistic) estimates of activity durations and the most likely estimate of activity duration. It causes great differences in values of the variances of the activities. The approach II better reflects this dissimilarity in the variances of the activities. This approach provides longer planning times of the project opposite the approach I

Financial health of agricultural enterprises in the organic sector

The present research was aimed at evaluating the economic performance of organic farm enterprises (legal entities) in the Czech Republic on the basis of their production base and financial health. The evaluation was carried out by means of specific financial indicators. The results recorded in the organic farming sector were confronted with those of the conventional agriculture. It stemmed from the analysis that conventionally farming legal entities, as opposed to the organically farming ones, tend to have higher average assets per hectare of farmland. Secondly, as for the structure of assets, fixed assets prevail substantially over current assets. Organic farms, on the contrary, have a significantly higher average value of external financial resources per hectare of farmland. In order to evaluate the financial health of organic farms, their economic results were used; firstly in absolute value (including per hectare calculation) and then within the individual ratios. The analysis showed that 84.4 % farms of the sample were profitable as long as subsidies were included in the yields. While excluding subsidies from the calculations, an overwhelming majority of enterprises (95.3 %) recorded a loss. Comparing the per hectare economic results, higher average profit rates were recorded for organic farms. Furthermore, financial health of the enterprises was analyzed by means of selected indicator ratios. Concrete results, including the respective commentaries, can be found in the present paper too

Analýza procesu zplyňování alternativního paliva (50% odpad, 50% plasty)

The paper presents analysis of alternative fuel gasification with use of flue gas as a gasifying agent. As a result of a process syngas with combustible components (CO, H2, CH4, CnHm) was obtained. Laboratory tests were carried out to determine usability of selected alternative fuel to low-temperature gasification process. Tests were conducted in a laboratory reactor allowing to gasify a fuel sample of appx. 1 g. The experimental stand enables recording of a sample weight loss and syngas composition. The process takes place for fuel samples of a constant weight and different granulation and with a set composition of flue gas used as a gasifying agent. The aim of the laboratory research was to determine the usability of RDF fuel for indirect co-firing in power boilers and to build a knowledge base for industrial-size process by defining the process parameters: kinetics (time for fuel to remain in the reactor), recommended fuel granulation and process temperature.Článek prezentuje analýzu zplyňování alternativního paliva s využitím spalin jako zplyňovacího prostředku. Jako výsledek zplyńovacího procesu “syngas” byly definovány hořlavé složky (CO, H2, CH4, CnHm). Byly provedeny laboratorní testy pro určení použitelnosti vybraného alternativního paliva pro proces zplyňování při nízkých teplotách. Testy byly prováděny v laboratorním reaktoru, který umožnil zplyňovat vzorek paliva o hmotnosti cca. 1 g. Experimentální zařízení umožňuje zaznamenat úbytek hmotnosti vzorku a jeho složení. Proces probíhá u vzorků paliva s konstantní hmotností a s různou granulometrii a se stanoveným složením spalin použitým jako zplyňovací medium. Cílem laboratorního výzkumu bylo zjistit použitelnost paliva RDF pro nepřímé spolu-spalování v energetických kotlích a vytvořit znalostní základnu pro reálný průmyslový proces definováním parametrů procesu: kinetiky (doby setrvání paliva v reaktoru), doporučená granulometrie paliva a teploty procesu

The evaluation of a risk degree for the process of a brown coal spontaneous ignition on dumps with using of modern numeric methods

The article is a summary of information about evaluation of a risk degree for a brown coal spontaneous ignition which is realized on the base of a database analysis of information about the development of stative quantities and desorbated gases in the stored bodies of the brown coal. The data were gained from the long term complex measurements which were realized at chosen companies during the coal mining in the previous parts of the project. In the last part of the project, we examined results of temperature models from thermographs with results of gasses and coal samples from the mines. Then, the influence of atmospheric conditions (insolation, water downfall, changes of barometric pressure etc.), the influence of coal mass degradation, the influence of physical and chemical factors, and the influence of other defective factors on the process of the coal spontaneous ignition. The gasmetry was assess with gas in-situ samples and laboratory gas models of indicative gasses for the spontaneous ignition, which were taken from the method of the thermic oxidation with the aim of the correlation finding for an epicentre of temperature within the spontaneous ignition.Web of Science262757

Sustainable growth rate in the strategic analysis of brewery industry

An analysis of sustainable growth rate could considerably improve an assessment of Strategic Business Unit’s potential. The sustainable growth rate analysis enabled us to compare a possible growth rate within the brewery industry with a growth rate that firms had achieved. To demonstrate this in more depth, we presented a case study of the brewery industry in Poland and Czech Republic.Growth, strategic analysis, seer industry, corporate growth, Research and Development/Tech Change/Emerging Technologies, GA, IN,

Globalization tendencies in the Czech SME'S - Historical Approach (1997-2004)

The main purpose of this paper is to present historical development of SME’s in the Czech Republic between years 1997-2004. It covers sections about changing strategy approach to prepare SME’s to EU entry and nearly two years in the European Union. The Czech economy made big changes especially in SME field, because before year 1989 in the state managed economy were used only big companies forms. SME’s sector in Czech Republic is now a dynamic growing phenomenon, which has influence on regional labour market, foreign trade and investment possibilities. It is the purpose of making year-to-year research, which has as a main goal to map changes in a SME structure, adaptability and influence of changing factors in our business environment. Research section presents a part of final doctoral thesis about finding main factors, which make impulses to change strategy to be innovative and on the way to knowledge society after the EU accession. As a conclusion is SME suggested to use some development strategies or support cooperation way to be more adaptable on wide European market. Reason is - SME’s have to change their point of view – to think European not only local market orientation. It is the way to continue their business by the innovative direction. Paper covers not only historical data, but also some experience with SME preparation process on strategy changes in time of globalization from management point of view.integration, globalization, innovation tendencies, SME

Analysis of factors influencing Czech SMEs after EU accession

The main goal of this paper is to present current research findings in three fields - business environment as a source of innovations, education needs and dynamics of SMEs units. The conclusion is made as some recommendations and useful strategies to support this very important part of national economy. The research was financially supported by Internal Grants IGS SU Nr. 18/2005 and Nr. 41/2006.globalization, SME, education, development strategies

The application for a prediction of the coal spontaneous ignition – Predisam

The article follows the research of the project number TA01020351 called "The research of possibilities when predicting steam origin and consequent spontaneous ignition of brown coal fuels" which was researched with the support of the Technological Agency in the Czech Republic in 2011-2014 in the connection with a realized technical research. Therefore, it gives a summary information about the evaluation of the risk degree for the origin of spontaneous ignitions of the brown coal. The presented way of evaluation is based on a numeric expression of a value for MHU criteria - the point load of particular indicators is added together with other results gained from this research project. Then, more information is taken from companies running the dumps of brown coal products - both for suppliers (mining companies) and big consumers (power engineering). The complex knowledge about prediction of the origin of the spontaneous ignition enables to make an early response to eliminate a threat of mining fire in open pit mines or on the dumps of coal products. Consequently, it reduces the risk of fire and breakdowns of transportation means DPD, heavy machines and preparation plants. The working injuries are reduced as well - burns by coal in fire or inhalation of gas products from imperfect combustion.Web of Science252878