Wrocław University of Science and Technology
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Automatic Fault Classification in Power Electronics Using Time-Frequency Distribution and Neural Networks
Full text linkA new method of fault analysis and detection by signal classification in frequency converters is presented. The Wigner-Ville time frequency distribution is used to produce the representation of the signal and the probabilistic neural network as a classifier. The accuracy and robustness of the proposed method is investigated on signals obtained during the different fault mode operations of the industrial frequency converter
Analysis of non-stationary electric signals using the S-transform
Full text linkPurpose – The purpose of this paper is to compare the accuracy of tracking the amplitude and frequency changes of non-stationary electric signals. Design/methodology/approach – Short-time fourier transform (STFT) and S-transform algorithms were applied to analyze non-stationary signals originating from switching of capacitor banks in a power system. Findings – The S-transform showed possibilities of sharp localization of basic component, and allowed improvement of tracking dynamism the transient components in comparison to STFT. Practical implications – S-transform is a better tool for the analysis non-stationary waveforms in power systems and its properties can be used for diagnostic and power quality applications. Originality/value – The dynamic tracking of the changes in time and frequency of real-like signals originating from a power system were investigated in this paper
Nonlinear regression applied for power quality disturbances characterization in grids with wind generators
Full text linkThe impact of wind generation on the electrical system should be assessed to figure out potential hazards to system operation and deterioration of power quality indices. In this paper signal processing algorithms has been applied to analyse switching transients within wind generation units. Nonlinear regression method and Prony model were applied to determine transients’ parameters for various operation modes of the wind generator. Both methods delivered quite satisfactory results, but the regression method was prone to local minima
Rozwój bibliotek cyfrowych i repozytoriów elektronicznych na Dolnym Śląsku w latach 2004-2008
Full text linkW referacie przedstawiono biblioteki cyfrowe i repozytoria elektroniczne funkcjonujące na Dolnym Śląsku w latach 2004-2008. Scharakteryzowano ogólnie ich zawartość i wielkość, zaprezentowano standardy i systemy zarządzania kolekcjami cyfrowymi oraz omówiono uwarunkowania prawne towarzyszące zarządzaniu zasobami cyfrowymi. Wskazano możliwości wykorzystania kolekcji cyfrowych w badaniach naukowych realizowanych w regionie. DEVELOPMENT OF DIGITAL LIBRARIES AND ELECTRONIC REPOSITORIES IN LOWER SILESIA IN YEARS 2004-2008 In following elaboration were presented digital libraries and electronic repositories operating in Lower Silesia region in years 2004-2008. General description of character and size of their collections was presented, as well as standards and methods of digital collections management and juridical aspects of this management. Potential of usage of digital collections in regional scientific researches was describe
Changes of space charge profiles in PET electrets after thermally stimulated discharges
No full textBehaviour of electric changes in the PET film has been investigated under the condition of partial discharging at higher annealing temperatures. The PET electrets corona-charged at room temperature and 440 K were investigated. The step electro-acoustic method was used for the measurement of space-charge distributions. The highest surface charge densities were obtained after negative corona charging at 440 K
Varistor performance of nanocrystalline Zn-Bi-O thin films prepared by reactive RF magnetron sputtering at room temperature
Full text linkThe Zn–Bi–O films were deposited by reactive radio frequency magnetron sputtering in oxygen atmosphere from ZnBi alloy target (wt. ratio Zn:Bi=9:1) on glass substrate at room temperature. The XRD patterns show that the films deposited on tin-doped indium oxide/glass substrates were nanocrystalline. The microstructure of Bi-doped ZnO films was studied by scanning electron microscopy in combination with energy dispersive X-ray spectroscopy. All the obtained layers had varistor-type non-linear current–voltage (I–V) characteristics with low breakdown voltage varying from few tenths of a volt to few volts
Electrochemical gas sensors can make DGA a portable screening procedure
Full text linkDissolved Gas Analysis (DGA) in its classical chromatography-based laboratory approach has become a routine procedure for testing and assessment of power transformer condition. New measurement practice employing novel gas sensing devices can yet help in making DGA simpler and migrating it into the field
Field emission current from high-Tc ceramic cathodes
Full text linkIn this work the result of emission phenomena investigations are presented. Experiments were conducted for high Tc, superconducting ceramics YBaCuO and BiPbSrCaCuO. Fowler- Nordheim characteristics and the current-temperature dependencies were observed for superconducting and non-superconducting cathodes. It was noticed that the emission current value abruptly changed in the vicinity of the critical temperature. All measurements were done in a vacuum chamber at l0-6 Pa. X-ray diffraction analysis and scanning electron microscopy examination of the ceramic electrodes were performed also
Möglichkeiten für einen digitalen Leitungsdifferentialschutz mit Symmetrischen Komponenten
Full text linkEin neues Verfahren für den digitalen Leitungsdifferentialschutz wird vorgestellt. Der Schutz vergleicht die Zeitvorgänge der Symmetrischen Strom-Mitkomponenten am Leitungsein- und -ausgang. Die Symmetrische Mitkomponente wird nach dem SD4c-Algorithmus aus vier aufeinanderfolgenden Abtastwertetripeln ermittelt. Die ersten Untersuchungsergebnisse werden gezeigt. Durch zusätzliche Ermittlung der orthogonalen Zeitfunktion nach dem SD4s-Algorithmus ist es möglich, phasenunabhängige Ansprechzeiten unter einer halben Periode zu erreichen. ___ A new method for a digital line differential protection is presented. The protection cornpares the time function of the symmetrical positive-sequence component at the input and output of a transmission line. The symmetrical positive-sequence component is calculated according to SD4c-algorithm from four successive sampled triplets. The first results of investigation are shown. Additional determination of the orthogonal time function according to SD4salgorithm enables to obtain phase-independent operating time of iess than half a period
Domains of existence and physical properties of the 2201-and 2212-type structure phases on Bi203-SrO-CaO-CuO quaternary system
Full text linkThe domains of existence of the 2201- and 2202-type structures in solid solutions of the Bi,O,SrO-CaO-CuO quaternary system are investigated from the powder x-ray diffraction, density and resistive transition measurements. It is shown that the general formula of Torardi should not be identified as describing fixed stoichiometry of Bi-based compounds but as a code according to which the unit cells are to be constructed. We have also shown that the composition of the investigated phases can vary within some region of homogeneity. The 2201-type structure acts as a matrix for the formation of new phases by addition of some quantities of calcium and copper, which are known as 80 K and 110 K superconductors. The influence of oxygen on the properties of Bi-based compounds is also evaluated