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Number of results: 191
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Abstract

Polychlorinated biphenyls (PCBs) are one group of persistent organic pollutants (POPs) that are of international concern because of global distribution, persistence, and toxicity. Removal of these compounds from the environment remains a very difficult challenge because the compounds are highly hydrophobic and have very low solubility in water. A 900 W domestic microwave oven, pyrex vessel reactor, pyrex tube connector and condensing system were used in this experiment. Radiation was discontinuous and ray powers were 540, 720 and 900 W. The PCBS were analyzed by GC-ECD. The application of microwave radiation and H2O2/TiO2 agents for the degradation of polychlorinated biphenyl contaminated oil was explored in this study. PCB – contaminated oil was treated in a pyrex reactor by microwave irradiation at 2450 MHz with the addition of H2O2/TiO2. A novel grain TiO2 (GT01) was used. The determination of PCB residues in oil by gas chromatography (GC) revealed that rates of PCB decomposition were highly dependent on microwave power, exposure time, ratio to solvent with transformer oil in 3:1, the optimal amount of GT01 (0.2 g) and 0.116 mol of H2O2 were used in the study. It was suggested that microwave irradiation with the assistance of H2O2/TiO2 might be a potential technology for the degradation of PCB – contaminated oil. The experiments show that MW irradiation, H2O2 oxidant and TiO2 catalyst lead to a degradation efficiency of PCBs only in the presence of ethanol. The results showed that the addition of ethanol significantly enhanced degradation efficiency of PCBs.

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Authors and Affiliations

Reza Tajik
Hasan Asilian Mohabadi
Ali Khavanin
Ahmad Jonidi Jafari
Babak Eshrati
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Abstract

An acoustic emission method (AE) is widespread and often applied for partial discharge (PD) diagnostics, mainly due to its ease of application as well as noninvasiveness and relatively high sensitivity. This paper presents comparative analysis of AE signals measurement results archived under laboratory conditions as well as on-site actual AE signals generated by inside PDs in electrical power transformer during its normal service. Three different PD model sources are applied for laboratory research: point to point, multipoint to plate and surface type. A typical measuring set up commonly used for on-site transformer PD diagnostics is provided for the laboratory tasks: piezoelectric joint transducer, preamplifier, amplifier and measuring PC interface. During the on-site research there are three measuring tracks applied simultaneously. Time domain, time-frequency domain and statistical tools are used for registered AE signals analysis. A number of descriptors are proposed as a result of the analysis. In the paper, at- tempt of AE signals descriptors, archived under laboratory condition application possibilities for on-site PD diagnostics of power transformers during normal service is made.
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Authors and Affiliations

Michał Kunicki
Andrzej Cichoń
Sebastian Borucki
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Abstract

This paper deals with a three-phase power system with hybrid transformer (HT) installed between two AC sources. The main aim of this paper is analyze the basic properties of HT with active load and ability to bidirectional energy flow. The HT contains two main units – a conventional transformer with electromagnetic coupling and PWM AC line chopper connected with secondary windings with electric coupling. The HT is located between the distribution system and a Local Balancing Area (LBA) with low power local energy sources. After describing the HT circuit and three-phase, twosources power system, the mathematical and circuit models of the AC source with HT are presented. These models are verified by means of the simulation and experimental test results obtained for a three-phase HT of about 3 kVA rated power.

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Authors and Affiliations

J. Kaniewski
Z. Fedyczak
P. Szcześniak
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Abstract

The new topology of three-winding welding transformer is proposed. Each secondary winding is connected in parallel through the separate bridge rectifier to the welding arc. The main feature of the proposed device is parallel working of two secondary windings with different rated voltage. The advantage is nonlinear transformation ratio of current that provides unprecedented power efficiency. The self- and mutual leakage inductances, which are important in power conversion, are calculated by 2D FEA model. The operational current of the device is modelled numerically via P-Spice simulator. The proposed topology is up to 30% more power effective than conventional welding transformer provided that the leakage inductances of primary and secondary windings are correctly fitted. This transformer is used for manual arc welding.

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Authors and Affiliations

Lyudmila Sakhno
Olga Sakhno
Simon Dubitsky
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Abstract

The subject presented in this paper refers to measurements and assessment of the corrected sound pressure level values (noise) occurring around a medium-power transformer. The paper presents the values of noise accompanying the operation of the power object before and after its modernization, which consisted in repeated core pressing and replacement of the cooling system. The main aim of the research work was the assessment of the influence of the repair work on the noise level emitted into the environment.

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Authors and Affiliations

Sebastian Borucki
Andrzej Cichoń
Tomasz Boczar
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Abstract

On-load tap changers (OLTC) are some of the main transformer elements that make voltage adjustment in a power network possible. Their failures often cause shutdowns of distribution transformers. The paper presents research work aimed at the assessment of the technical condition of OLTCs by the acoustic emission method (EA). This method makes the OLTC diagnosis possible without the need of disconnecting the transformer from the system. The measurements were taken in laboratory conditions. The influence on the operation non-concurrence of the power tap changer contacts on the AE registered signals has been investigated. The signals registered were subjected to analyses in the time and time-frequency domains. The result analysis in the time domain was carried out using the Hilbert transform and calculating characteristic times for the particular runs. A short-time Fourier transform was used for the assessment of results in the time-frequency domain.

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Authors and Affiliations

Andrzej Cichoń
Sebastian Borucki
Tomasz Boczar
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Abstract

An alternative method for analysis of acoustic emission (AE) signals generated by partial discharges (PD), based on a correlation between voltage phase run and AE pulses, so called phase resolved PD pattern (PRPD), is presented in the paper. PRPD pattern is a well-known analysis tool commonly used in such PD diagnostic methods as conventional electrical and UHF ones. Moreover, it yields various signal analysis abilities and allows a direct correlation indication between measurement results achieved using different methods. An original PRPD measurement methodology applied for AE method as well as some exemplary measurement results and further data analysis capabilities are presented in the paper. Also a comparative analysis of PRPD patterns achieved using various measurement methods and different PD source configurations have been investigated. All presented experiments were done under laboratory conditions using PD model sources immersed in the insulation oil. The main purpose of the presented research is to indicate an all-embracing analytical tool that yields an ability to direct comparison (qualitative as well as quantitative) of the AE measurement results with other commonly applied PD measurement methods. The presented results give a solid fundamental for further research work concerning a direct correlation method for AE and other described in the paper diagnostic techniques, mainly in order to continue PD phenomena analysis and assessment in real life high voltage apparatus insulation systems under normal onsite operation conditions.
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Authors and Affiliations

Michał Kunicki
Andrzej Cichoń
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Abstract

The article presents the results concerning the use of clustering methods to identify signals of acoustic emission (AE) generated by partial discharge (PD) in oil-paper insulation. The conducted testing featured qualitative analysis of the following clustering methods: single linkage, complete linkage, average linkage, centroid linkage and Ward linkage. The purpose of the analysis was to search the tested series of AE signal measurements, deriving from three various PD forms, for elements of grouping (clusters), which are most similar to one another and maximally different than in other groups in terms of a specific feature or adopted criteria. Then, the conducted clustering was used as a basis for attempting to assess the effectiveness of identification of particular PD forms that modelled exemplary defects of the power transformer’s oil-paper insulation system. The relevant analyses and simulations were conducted using the Matlab estimation environment and the clustering procedures available in it. The conducted tests featured analyses of the results of the series of measurements of acoustic emissions generated by the basic PD forms, which were obtained in laboratory conditions using spark gap systems that modelled the defects of the power transformer’s oil-paper insulation.
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Authors and Affiliations

Sebastian Borucki
Jacek Łuczak
Dariusz Zmarzły
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Abstract

In this paper, the power factor correction system consisted of: bridge converter, parallel resonant circuit, high frequency transformer, diode rectifier and LFCF filter is presented. This system is controlled by a pulse density modulation method and the principle of its operation is based on the boost technique. The modeling approach is illustrated by an example using AC/HF/DC converter. Verification of the derived model is provided, which demonstrated the validity of the proposed approach.
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Authors and Affiliations

Antoni Bogdan
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Abstract

This paper aims to present a new equivalent scheme of multi-windings traction transformers, based on multiport purely inductive circuit. The mathematical background of this equivalent scheme is described. The determination of the different scheme elements is made through a finite-elements calculation of both main and leakage inductances, for the case of a four-winding transformer. A procedure is defined, which allows to estimate the values of these elements from some measurements on the transformer at no-load and short-circuit operations. A specific strategy of short-circuit tests is described, allowing to determine all parameters in a rather simple way.

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Authors and Affiliations

Tadeusz J. Sobczyk
Joseph El Hayek
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Abstract

Since a few years ago, there is an increasing interest for utilization of transfer functions (TF) as a reliable method for diagnosing of mechanical faults in transformer structure. However, this paper aims to develop the application of TF method in order to evaluate the drying quality of active part during the manufacturing process of transformer. To reach this goal, the required measurements are carried out on 50 MVA 132 KV/33 KV power transformer when active part is placed in the drying chamber. Two different features extracted from the measured TFs are then used as the inputs to artificial neural network (ANN) to give an estimate for required time in drying process. Results show that this new represented method could well forecast the required time. The results obtained from this method are valid for all the transformers which have the same design.

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Authors and Affiliations

Hormatollah Firoozi
Mehdi Bigdeli
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Abstract

This original paper deals with a new approach for the study of behavior in nonlinear regime of a new three-phase high voltage power supply for magnetrons, used for the microwave generators in industrial applications. The design of this system is composed of a new three-phase leakage flux transformer supplying by phase a cell, composed of a capacitor and a diode, which multiplies the voltage and stabilizes the current. Each cell. in turn, supplies a single magnetron. An equivalent model of this transformer is developed taking into account the saturation phenomenon and the stabilization process of each magnetron. Each inductance of the model is characterized by a non linear relation between flux and current. This model was tested by EMTP software near the nominal state. The theoretical results were compared to experimental measurements with a good agreement. Relative to the current device, the new systemprovides gains of size, volume, cost of implementation and maintenance which make it more economical.

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Authors and Affiliations

M. Chraygane
N. El Ghazal
M. Fadel
B. Bahani
A. Belhaiba
M. Ferfra
M. Bassoui
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Abstract

As it is found in the related published literatures, the transfer function (TF) evaluation method is the most feasible method for detection of winding mechanical faults in transformers. Therefore, investigation of an accurate method for evaluation of the TFs is very important. This paper presents three new indices to compare the transformer TFs and consequently to detect the winding mechanical faults. These indices are based on estimated rational functions. To develop the method, the necessary measurements are carried out on a 1.3 MVA transformer winding, under intact condition, as well as different fault conditions (axial displacement of winding). The obtained results demonstrate the high potential of proposed method in comparison with two other well-known indices. Additionally, two important methods for describing TFs by rational functions are studied and compared in this paper.

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Authors and Affiliations

Mehdi Bigdeli
Mehdi Vakilian
Ebrahim Rahimpour
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Abstract

The paper presents theoretical and experimental analyses of a possible effect of the short-circuit forces on the transformer winding. The first part of the paper is focused on creation and activity of the radial and axial forces during a short circuit. It shows dimensions, direction and − of course − the resulting mechanical stress. The presented equation shows basic dependencies of these mechanical forces created in the transformer winding. Finally, the paper presents experimental methods of diagnosing and analysing the effects of short-circuit forces on the transformer winding.

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Authors and Affiliations

Miroslav Gutten
Richard Janura
Milan Šebök
Daniel Korenčiak
Matej Kučera
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Abstract

This paper describes the design and test of a new high-current electronic current transformer based on a Rogowski coil. For better performances, electronic current transformers are used to replace conventional electro-magnetic inductive current transformers based on ferromagnetic cores and windings to measure high-current on the high voltage distribution grids. The design of a new high-current electronic current transformer is described in this paper. The principal schemes of the prototype and partial evaluation results are presented. Through relative tests it is known that the prototype has a wide dynamic range and frequency band, and it can allow high accuracy measurements.

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Authors and Affiliations

Ming Zhang
Kaicheng Li
Shunfan He
Jun Wang
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Abstract

An optimized method of vibration Energy Harvesting is based on a step-down transformer that regulates the power flow from the piezoelectric element to the desired electronic load. Taking into account parameters of the whole system, the “optimal” voltage gain the piezoelectric transformer can be determined where the harvested power is maximized for the actual level of mechanical excitation. Consequently the piezoelectric transformers can be used to boost up the conversion of mechanical strain into electrical power with considerable potential in Energy Harvesting applications. Nowadays however, the most important factor is usage of lead free material for its construction. Additional desired parameters of such ceramics include high value of piezoelectric coefficients, low dielectric losses and reasonable power density. This work for first time proposes a lead free K0.5Na0.5NbO3 (KNN) material implementation for stack type of piezoelectric transformer that is designed for load efficiency optimization of vibration energy harvester.

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Authors and Affiliations

L. Kozielski
K. Feliksik
B. Wodecka-Duś
D. Szalbot
S. Tutu
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Abstract

In this study a group of selected transformation kinetics equations is applied to describe the isothermal ferritic transformation in austempered ductile iron (ADI). A series of dilatometric tests has been carried out on ADI at different temperatures. The obtained experimental data are utilized to determine the parameter values of the considered kinetic equations. It is found that the transformation kinetics models by Starink, Austin and Rickett are substantially more effective at describing the ferritic transformation in ADI than the much celebrated Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. Furthermore, it is demonstrated that evaluating the kinetic parameters using the least squares method instead of calculating them from vastly used formulas can significantly improve the accuracy of the JMAK model’s predictions.

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Authors and Affiliations

C. Suchocki
D. Myszka
K. Wasiluk
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Abstract

The article is a review of the book edited by Krzysztof Brzechczyn, The Paths of Transformation. Theoretical Approach and Empirical Descriptions, Poznań 2003.
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Authors and Affiliations

Mariusz Weiss
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Abstract

“Isolation would be most unfortunate. We would be doing science in our own company, completely indifferent to what is happening outside our own universe. This would be totally self-destructive and I hope it will never happen,” says Professor Michał Głowiński in an interview with Grzegorz Wołowiec, titled “A Time Unexpected,” a fragment of which is presented below.

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Authors and Affiliations

Mochał Głowiński
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Abstract

Dr. Artur Obłuski of the University of Warsaw tells us about research into political, social, and religious transformations in Sudan in the Middle Ages, the present-day importance of archaeological discoveries, and the meaning of the word “UMMA.”

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Authors and Affiliations

Marcin Obłuski
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Abstract

On 16 July 2019, another significant amendment to the provisions of the Act on the transformation of the right of perpetual usufruct to land built-up for residential purposes into the ownership title to that land was introduced. The purpose of this research paper is to analyse the influence of the amendments to the regulations on the scope of the real properties subject to the transformation of perpetual usufruct into ownership, to identify the problems and to assess the status of the implementation of the transformation process in practice. The conducted research has resulted in the presentation of the structure of land on the example of a selected city, in particular with reference to real estate let into perpetual usufruct for residential purposes. The author has also determined the status of the implementation of the transformation process in practice as well as the problems hindering the issuance of certificates for all transformed properties within the statutory period. The progress of the transformation process in a given area depends, inter alia, on the scope of real properties subject to this transformation, the requirement to perform additional analyses, including those regarding non-compliance of the legal and factual state of the property, and the assessment of the existence of public aid and related payments. This study is a continuation of the earlier research, extended by the effects of the regulations introduced in July 2019, as well as by the assessment of the progress in the transformation process in practice.

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Authors and Affiliations

Anna Trembecka
ORCID: ORCID
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Abstract

This paper examines how Latvian communities abroad reacted to and were influenced by a change of the first magnitude in the political life of their homeland, namely, the proclamation of the Republic of Latvia on November 18, 1918. News of the proclamation, first of all, necessitated diaspora Latvians choosing attitudes towards the new phenomenon, which highlighted the political pre‑dispositions of the different groups within the diaspora. Polarisation of opinions was followed shortly by a wave of activities both in support of and against the new Republic. These activities included gathering financial resources for war victims and state institutions in Latvia, public relations campaigns in diaspora host countries, political lobbying etc. The establishment of the Republic of Latvia also profoundly influenced and intensified the internal formation processes within the diaspora. A marked increase of activity is observable in all fields of engagement that are characteristic of an active ethno‑national diaspora: the internal organisational structure was further developed; contacts with the homeland intensified; mutual links between geographically distant diaspora groups became closer. The great political changes in the homeland gave the Latvian diaspora the push necessary to fully develop and become an active ethno‑national diaspora.
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Authors and Affiliations

Kristīne Beķere
1
ORCID: ORCID

  1. University of Latvia
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Abstract

Demand for energy and resources has been growing as a result of population growth and increased consumption to the point where all the scientific evidence shows we are bumping up against fundamental planetary boundaries on which our civilizations depend. In new EASAC report trends that lead calls for “transformative” change, with a focus on some of the systemic and structural failures that are driving our current unsustainable development has been discussed.
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Authors and Affiliations

Rajmund Michalski
1

  1. Instytut Podstaw Inżynierii Środowiska PAN w Zabrzu

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