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Number of results: 25
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Abstract

Finding the most critical contingencies in a power system is a difficult task as multiple evaluations of load and generation scenarios are needed. This paper presents a mathematical formulation for selecting, ranking, and grouping the most critical N-1 network contingencies, based on the calculation of a Power Constraint Index (PCI) obtained from the Outage Transfer Distribution Factors (OTDF). The results show that the PCI is only affected by the impedance parameter of the transmission network, the topology, and the location of all generators. Other methods, such as the Performance Index (PI) and the Overload Index (OL) are affected by the power generation and demand variations. The proposed mathematical formulation can be useful to accelerate the calculation of other methods that evaluate contingencies in power system planning and operation. Furthermore, the fast calculation of indices makes it suitable for online evaluation and classification of multiple events considering the current topology. The results showed that the proposed al- gorithm easily selected and ranked the expected contingencies, with the highest values of the index corresponding to the most critical events. In the filtering process, the computa- tional calculation time improved without losing the robustness of the results.
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Abstract

Intensive modernization and reconstruction of the energy sector takes place throughout the world. The EU climate and energy policy will have a huge impact on the development of the energy sector in the coming years. The European Union has adopted ambitious goals of transforming towards a low-carbon economy and the integration of the energy market. In June 2015, the G7 countries announced that they will move away from coal fired energy generation. Germany, which has adopted one of the most ambitious energy transformation programs among all industrialized countries, is leading these transformations. The long-term strategy, which has been implemented for many years, allowed for planning the fundamental transformation of the energy sector; after the Fukushima Daiichi nuclear disaster, Germany opted for a total withdrawal from nuclear energy and coal in favor of renewable energy. The German energy transformation is mainly based on wind and solar energy. Germany is the fifth economic power in the world and the largest economy in Europe. Therefore, the German energy policy affects the energy policy of the neighboring countries. The article presents the main assumptions of the German energy policy (referred to as Energiewende). It also presents the impact of changes in the German energy sector on the development of energy systems in selected European countries.
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Abstract

A data logger has been built to record, for a month, the power consumption of various equipment and the temperature at different points inside and outside of a radio communication base station operated by Vodafone Portugal. Here we show how the concerns with measurement uncertainty led us to choose an analog system over a digital one for AC power measurement.
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Abstract

The paper presents a new method for simultaneous tracking of varying grid impedance and its uncertainty bounds. Impedance tracking consists of two stages. In the first stage, the actual noise estimate is obtained from least squares (LS) residua. In the second stage, the noise covariance matrix is approximated with the use of residual information. Then weighted least squares (WLS) method is applied in order to estimate impedance and background voltage. Finally uncertainty bounds for impedance estimation are computed. The robustness of the method has been verified using simulated signals. The proposed method has been compared to sliding LS. The results have shown, that the method performs much better than the LS for all considered cases, even in the presence of significant background voltage variations.
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Abstract

Fast and accurate grid signal frequency estimation is a very important issue in the control of renewable energy systems. Important factors that influence the estimation accuracy include the A/D converter parameters in the inverter control system. This paper presents the influence of the number of A/D converter bits b, the phase shift of the grid signal relative to the time window, the width of the time window relative to the grid signal period (expressed as a cycle in range (CiR) parameter) and the number of N samples obtained in this window with the A/D converter on the developed estimation method results. An increase in the number b by 8 decreases the estimation error by approximately 256 times. The largest estimation error occurs when the signal module maximum is in the time window center (for small values of CiR) or when the signal value is zero in the time window center (for large values of CiR). In practical applications, the dominant component of the frequency estimation error is the error caused by the quantization noise, and its range is from approximately 8×10-10 to 6×10-4.
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Abstract

The large variability and unpredictability of energy production from photovoltaic power microinstallations results from the dependence on the current weather conditions. These conditions depend on a number of factors and are variable over the time. Despite this specificity, photovoltaic micro-installations are becoming more and more popular in the world and in Poland. This is mainly due to the fact that the generation of energy from renewable sources has numerous advantages, the energy is free, renewable in time and ecological, and its production on its own gives partial independence from energy supplies from the power grid. In addition, the observed significant prices decrease of solar modules has further accelerated the development of the use of this energy source. Concern for this method of energy production among households has increased significantly in Poland after introducing the prosumer in the legal framework and the use of administrative and financial support. The implemented prosumer mechanisms allowed, for example, the net balancing of the energy consumed and produced by the micro-installation through storage in the power grid. The article describes the problem of balancing sources using solar energy, based on micro-installation used in the household (the so-called prosumer installation). The conducted analyses compared the load profile of a typical household and the energy generation profile from a photovoltaic installation, determining the real balancing formation level of such a system.
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Abstract

The paper presents an analysis of the sustainable development of electricity generation sources in the National Power System (NPS). The criteria to be met by sustainable power systems were determined. The paper delineates the power balance of centrally dispatched power generation units (CDPGU), which is required for the secure work of the NPS until 2035. 19 prospective electricity generation technologies were defined. They were divided into the following three groups: system power plants, large and medium combined heat and power (CHP) plants, as well as small power plants and CHP plants (distributed sources). The quantities to characterize the energy effectiveness and CO2 emission of the energy generation technologies analyzed were determined. The unit electricity generation costs, discounted for 2018, including the costs of CO2 emission allowance, were determined for the particular technologies. The roadmap of the sustainable development of the generation sources in the NPS between 2020 and 2035 was proposed. The results of the calculations and analyses were presented in tables and figure
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Abstract

Power systems that are highly loaded, especially by a stochastic supply of renewables and the presence of storages, require dynamic measurements for their optimal control. Phasor measurement units (PMUs) can be used to capture electrical parameters of a power system. Standards on the PMU dynamic performance have been modified to incorporate their new dynamic mode of operation. This paper examines the PMU dynamic performance and proposes essential algorithms for measurement accuracy verification. Measurements of dynamic input signals, which vary in amplitude or frequency, were taken during automated tests of two PMUs. The test results are presented and expounded with further recommendation for the performance requirements. This paper also presents and examines applied testing procedures with relevance to the specifications of the IEEE Standard for Synchrophasor C37.118.1™-2011 and its amendment C37.118.1a™-2014.
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Abstract

A solar photovoltaic (PV) system has been emerging out as one of the greatest potential renewable energy sources and is contributing significantly in the energy sector. The PV system depends upon the solar irradiation and any changes in the incoming solar irradiation will affect badly on the output of the PV system. The solar irradiation is location specific and also the atmospheric conditions in the surroundings of the PV system contribute significantly to its performance. This paper presents the cumulative assessment of the four MPPT techniques during the partial shading conditions (PSCs) for different configurations of the PV array. The partial shading configurations like series-parallel, bridge link, total cross tied and honeycomb structure for an 8#2;4 PV array has been simulated to compare the maximum power point tracking (MPPT) techniques. The MPPT techniques like perturb and observe, incremental conductance, extremum seeking control and a fuzzy logic controller were implemented for different shading patterns. The results related to the maximum power tracked, tracking efficiency of each of the MPPT techniques were presented in order to assess the best MPPT technique and the best configuration of the PV array for yielding the maximum power during the PSCs.
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Abstract

An analysis of the power system functioning and the behaviors of the energy market participants allows the trends taking place within years to be identified, including these associated with the evolution of the electric energy and power demand profiles. The problems of balancing the peak power demand are of both a short and long term nature, which implies the need for changes in the electricity generation sector. Apart from the existing “silo-type” generation units, the construction of distributed energy sources implemented in the civic formula in the framework of self-sufficient energy communes and energy clusters is becoming increasingly important. Support for these programs is realized both at the legislative level, as well as within dedicated competitions and ministerial activities. The financial support carried out by the National Fund for Environmental Protection and Water Management and the Regional Operational Programs is also noticeable. One of the activities aimed at spreading the idea of clustering was the competition for certified energy clusters, conducted by the Ministry of Energy. The goal of the contest was the promotion and development of the distributed energy sector, which could be used for the improvement of energy security in the local manner and constitute a basis for the knowledge necessary in planning and developing the state’s energy policy. The paper presents a synthetic analysis of the results of the competition for a certified energy cluster from the perspective of planning and operational needs related to the functioning of the power system. Further, the information about the investment plans of new generation capacities, including their breakdown with respect to type, achievable power and costs has been provided. Also, the balancing of the demand for electric energy by own generation within the energy clusters has been characterized for three time perspectives
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Abstract

Increasing the share of energy production from renewable sources (RES) plays a key role in the sustainable and more competitive development of the energy sector. Among the renewable energy sources, the greatest increase can be observed in the case of solar and wind power generation. It should be noted that RES are an increasingly important elements of the power systems and that their share in energy production will continue to rise. On the other hand the development of variable generation sources (wind and solar energy) poses a serious challenge for power systems as operators of unconventional power plants are unable to provide information about the forecasted production level and the energy generated in a given period is sometimes higher than the demand for energy in all of the power systems. Therefore, with the development of RES, a considerable amount of the generated energy is wasted. The solution is energy storage, which makes it possible to improve the management of power systems. The objective of this article is to present the concept of electricity storage in the form of the chemical energy of hydrogen (Power to Gas) in order to improve the functioning of the power system in Poland. The expected growth in the installed capacity of wind power plants will result in more periods in which excess energy will be produced. In order to avoid wasting large amounts of energy, the introduction of storage systems is necessary. An analysis of the development of wind power plants demonstrates that the Power to Gas concept can be developed in Poland, as indicated by the estimated installed capacity and the potential amount of energy to be generated. In view of the above, the excess electricity will be available for storage in the form of chemical energy of hydrogen, which
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Abstract

In renewable systems, there may be conditions that can be either network error or power transmission line and environmental conditions such as when the wind speed is unbalanced and the wind turbine is connected to the grid. In this case, the control system is not damaged and will remain stable in the power transmission system. Voltage stability studies on an independent wind turbine at fault time and after fixing the error is one of the topics that can strengthen the future of independent collections. At the time of the fault, the network current increases dramatically, resulting in a higher voltage drop. Hence the talk of fast voltage recovery during error and after fixing the error and protection of rotor and grid side converters against the fault current and also protection against rising DC voltage (which sharply increases during error) is highly regarded. So, several improvements have been made to the construction of a doubly-fed induction generator (DFIG) turbine such as: a) error detection system, b) DC link protection, c) crow bar circuit, d) block of the rotor and stator side converters, e) injecting reactive power during error, f) nonlinear control design for turbine blades, g) tuning and harmonization of controllers used to keep up the power quality and to stabilize the system output voltage in the power grid. First, the dynamic models of a wind turbine, gearbox, and DFIG are presented. Then the controllers are modeled. The results of the simulation have been validated in MATLAB/Simulink.
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Abstract

Due to unfavorable factors, dangerous conditions occurred in the delivery of electric energy in Poland. This was the most serious incident of its kind since the 1980’s. Such a serious incident raised concern about the safety of the electric power system in the summer and led to the formulation of conclusions for the future. In this article, the author analyses the conditions, which caused that situation. Poland was experiencing a doubt in August 2015, which along with an extremely high maximum daily temperature created remarkably unfavorable conditions for power plants and decreased the capacity of overhead power lines. Such unfavorable metrological conditions occurred not only in Poland, but also in Central-Eastern and Western Europe. It is worth emphasizing that the safety of electric energy delivery was endangered only in Poland. The improper renovation and upkeep policies, as well as unplanned outages in power plants caused a significant decrease of available power in the National Electric Power System. Unscheduled flows between Germany and Poland ruled out the possibility of importing electric energy at such a critical time. The author presents the correlation between the maximum daily air temperature in the sweltering heat and an increase in the demand for electric energy. Overall, unfavorable conditions posed a threat in the delivery of electric energy in Poland. In this article, the author draws attention to the report from the Supreme Audit Office (Najwyższa Izba Kontroli – NIK) from 2014, which predicted such a dangerous situation. Unfortunately, that report remained unnoticed. The author formulated appropriate solutions in order to increase the safety of electric energy delivery in the summer and to prevent such occurrences in the future.
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Abstract

By means of small wind turbines, it is possible to create distributed sources of electricity useful in areas with good wind conditions. Sometimes, however, it is possible to use small wind turbines also in areas characterized by lower average wind speeds during the year. At the small wind turbine design stage, various types of technical solutions to increase the speed of the wind stream, as well as to optimally orientate it, can be applied. The methods for increasing the efficiency of wind energy conversion into electricity in the case of a wind turbine include: the use of a diffuser shielding the turbine rotor and the optimization of blades mounted on the turbine rotor. In the paper, the influence of the diffuser and rotor blades geometry on the efficiency of an exemplary wind turbine for exploitation in the West Pomeranian Province is investigated. The analyses are performed for three types of the diffuser and for three types of rotor blades. Based on them, the most optimal shapes of the diffuser and blades are selected due to the efficiency of the wind turbine. For the turbine with the designed diffuser, calculations of the output power for the assumed different values of the average annual wind speed and the constant Betz power factor and the specified generator efficiency are made. In all the analyzed cases, the amount of energy that can be generated by the turbine during the year is also estimated. Important practical conclusions are formulated on the basis of these calculations. In the final part of the paper, a 3D model of the wind turbine with the diffuser and rotor blades chosen based on earlier analyses is presented. As a material for the diffuser and rotor blades, glass fiber type A is applied. By means of calculations using the finite element method, the limit displacement of the turbine structure under the influence of a hurricane wind are determined. Based on these calculations, the correctness of the modelled small wind turbine structure has been demonstrated.
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Abstract

The article deals with the issue of the meaning of the Polish early education coursebooks for conservation/change in educational practices. It is the liberal and constructivist discourse to which the coursebook authors should refer (especially in the context of the present time and democracy) if these books are to become a tool of the prodevelopmental and emancipatory interest of both students and society. However, the research on Polish coursebooks for early education (grades I – III), show that this very condition has not been ful3 lled. In such a situation it is the German school coursebooks that might be inspiring because of their discursive background as well as of the methodological proposals and the range of content present in them. The article is also an attempt to reconstruct “the image of school” present in German early education coursebooks. It is possible to name and describe the key dimensions in this image such as: the democratic nature of teacher-student relations, the focus on the activation of students’ personal knowledge as well as on their ethical and cognitive autonomy, realistic vision of the world, trust in students’ competences, and creating the sphere of the nearest development.
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Abstract

In order to improve the efficiency and ensure the security of power supply used in a mine, this paper mainly studies the quasi-resonant flyback secondary power supply and analyzes its operational principles based on the requirements of soft-switching technology. In accordance with the maximum energy of a short-circuit and the request of maximum output voltage ripple, this paper calculates the spectrum value of the output filter capacitor and provides its design and procedures to determine the parameters of the main circuit of power supply. The correctness and availability of this theory are eventually validated by experiments.
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Abstract

Our purpose in this paper is to show how the output of academic student-writers demonstrates the different ways in which they react to the discipline’s discoursal demands and how that, in turn, forms their writer identity. We also argue that the current Second Language Acquisition (SLA) theory fails to adequately integrate notions of second language (L2) academic writer identity and the social contexts in which L2 writers produce their texts.
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Abstract

An embedded time interval data acquisition system (DAS) is developed for zero power reactor (ZPR) noise experiments. The system is capable of measuring the correlation or probability distribution of a random process. The design is totally implemented on a single Field Programmable Gate Array (FPGA). The architecture is tested on different FPGA platforms with different speed grades and hardware resources. Generic experimental values for time resolution and inter-event dead time of the system are 2.22 ns and 6.67 ns respectively. The DAS can record around 48-bit x 790 kS/s utilizing its built-in fast memory. The system can measure very long time intervals due to its 48-bit timing structure design. As the architecture can work on a typical FPGA, this is a low cost experimental tool and needs little time to be established. In addition, revisions are easily possible through its reprogramming capability. The performance of the system is checked and verified experimentally.
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Abstract

Blockchain is a technology, which could revolutionize many industries in the future. A system like that is based on a chain of blocks that is used for storing and transferring various data, forming a decentralized ledger. Although various fundamental projects based on the blockchain system in the energy industry are in their early stage of development, as well as other solutions, applications of blockchain technology in the broadly understood power engineering sector are considered to have a very large potential. This paper presents a brief description of the blockchain technology, its general operating principle and the possibilities it brings. The next section of the article contains a characterization of two exemplary and possible blockchain technology applications, which in the perspective of time may have a significant impact on the power engineering sector. The first solution is related to carrying out energy transactions, which could be conducted in an easy way directly between energy producers and consumers. Thanks to blockchain technology, this could lead to a partial decentralization in that area. The second proposed example concerns energy resources origin tracking, which would allow fixed origin attributes and parameters affecting the environment to be assigned to the generated energy. By implementing that solution, it would be possible to construct a fuel footprint of individual generating units. The article also mentions examples of other potential applications of blockchain technology in the power engineering sector.
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Abstract

According to International Energy Agency (IEA) energy security is the continuous supply of energy at acceptable prices. National energy is based primarily on its own energy resources such as hard coal and brown coal. The 88% of electric energy production from these minerals gives us full energy independence. Additionally, the energy production costs from these raw materials are the lowest compared to other technologies. Of these two, the energy produced from brown coal is characterized by the lowest unit technical generating cost. Poland has the resources of these minerals for decades to come, the experience related to mining and processing them, scientific and design facilities and technical facilities and factories producing machines and equipment for their own needs, as well as for export. Coal is and should remain an important source of electricity and heat supply in Poland for the next 25–50 years. It is one of the most reliable and profitable energy sources. This policy may be difficult in the next decades due to the exhaustion of the available resources of hard and brown coal. The conditions for the construction of new mines, and thus for the development of coal mining in Poland, are very interdisciplinary in legal, environmental, economic and reputational terms. Germany has similar problems. Despite the fact that it is an image of a country investing in renewable energy sources, which are pioneers of energy production from RES, in reality hard and brown coal are still the primary sources utilized to produce electric energy.
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Abstract

A transformer is an important part of power transmission and transformation equipment. Once a fault occurs, it may cause a large-scale power outage. The safety of the transformer is related to the safe and stable operation of the power system. Aiming at the problem that the diagnosis result of transformer fault diagnosis method is not ideal and the model is unstable, a transformer fault diagnosis model based on improved particle swarm optimization online sequence extreme learning machine (IPSO-OS-ELM) algorithm is proposed. The improved particle swarmoptimization algorithm is applied to the transformer fault diagnosis model based on the OS-ELM, and the problems of randomly selecting parameters in the hidden layer of the OS-ELM and its network output not stable enough, are solved by optimization. Finally, the effectiveness of the improved fault diagnosis model in improving the accuracy is verified by simulation experiments.
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Abstract

When the machine is at high speed, serious problems occur, such as high frequency loss, difficult thermal management, and the rotor structural strength insufficiency. In this paper, the performances of two high-speed permanent magnet generators (HSP- MGs) with different rotational speeds and the same torque are compared and analyzed. The two-dimensional finite element model (FEM) of the 117 kW, 60 000 rpm HSPMG is established. By comparing a calculation result and test data, the accuracy of the model is verified. On this basis, the 40 kW, 20 000 rpm HSPMG is designed and the FEM is established. The relationship between the voltage regulation sensitivity and power factor of the two HSPMGs is determined. The influence mechanism of the voltage regulation sensitivity is further revealed. In addition, the air-gap flux density is decomposed by the Fourier transform principle, and the influence degree of different harmonic orders on the HSPMG performance is determined. The method to reduce the harmonic content is further proposed. Finally, the method to improve the HSPMG overload capacity is obtained by studying the maximum power. The research showed that the HSPMG at low speed (20 000 rpm) has high sensitivity of the voltage regulation, while the HSPMG at high speed (60 000 rpm) is superior to the HSPMG at low speed in reducing the harmonic content and increasing the overload capacity.
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Abstract

The national power industry is based primarily on its own energy mineral resources such as hard and brown coal. Approximately 80% of electrical energy production from these minerals gives us complete energy independence and the cost of its production from coal is the lowest in comparison to other sources. Poland has, for many decades had vast resources of these minerals, the experience of their extraction and processing, the scientific-design facilities and technical factories manufacturing machines and equipment for own needs, as well as for export. Nowadays coal is and should be an important source of electrical energy and heat for the next 25–50 years, because it is one of the most reliable and price acceptable energy sources. This policy may be disturbed over the coming decades due to the depletion of active resources of hard and brown coal. The conditions for new mines development as well as for all coal mining sector development in Poland are very complicated in terms of legislation, environment, economy and image. The authors propose a set of strategic changes in the formal conditions for acquiring mining licenses. The article gives a signal to institutions responsible for national security that without proposed changes implementation in the legal and formal process it, will probably not be possible to build next brown coal, hard coal, zinc and lead ore or other minerals new mines.
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