Wrocław University of Science and Technology
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Parametric Spectral Estimation for Power Quality Assessment
Get PDFThe authors show that the use of highresolution spectrum estimation methods instead of Fourier-based techniques can improve the accuracy of measurement of spectral parameters of distorted waveforms encountered in power systems, in particular the estimation of the power quality indices (such as harmonic and interharmonic groups and subgroups). The comparison of the frequency and amplitude estimation error, based on numerical simulations is presented. Presentation of selected power quality indices is then followed by comparison of estimation error in the case of application of FFT-based algorithms and parametric methods. Investigated waveforms are typical for dc arc furnace plant. MUSIC and ESPRIT high-resolution methods are used to analyze waveforms in a supply system of a DC arc furnace
Carrier generation and the switching phenomenon: further theoretical description
Get PDFIn this paper the problem of the current flow between the two electrodes is further continued. The steady state of solid electric conduction with the two boundary conditions is analysed. The space charge is defined by free holes and electrons as well as by trapped electrons. As the interactions between free carriers, carrier generation is assumed. Under these conditions, it was found that the current-voltage characteristics can be discontinuous. The shape of these curves can be of 'S' or 'N' type
Electrochemical gas sensors can supplement chromatography-based DGA
Get PDFShortening a time gap between oil sampling and its analysis as well as a rapid and correct interpretation of dissolved gas analysis (DGA) results are crucial for effective screening of faulty transformers in predictive-oriented equipment maintenance. Introductory DGA performed quickly by means of a developed portable analyzer, fitted with electrochemical gas sensors, can supplement classical chromatography-based DGA contributing to a correct and rapid transformer fault interpretation. Examples of unusual data mining for sensor-based DGA are also presented
Analyse nicht stationärer Signale in Energiesystemen
Get PDFKlassische Methoden der Spektralanalyse von diskret abgetasteten Signalen mit vielen spektralen Anteilen basieren meistens auf der Fourier-Transformation. Die Abschätzung der Frequenzanteile des Signals mittels der Scheitelwerte des Spektrums hat aber verschiedene Nachteile. Die Länge des Fensters und die Phase der Spektralanteile im Signal beeinflussen das Ergebnis, auch wenn kein Rauschen vorhanden ist. Wir präsentieren hier eine andere Vorgehensweise. Die Frequenzanalyse wir mit Hilfe der Wigner – Ville – Distribution (WVD) durchgeführt. Die so gewonnene Zeit – Frequenz-Darstellung hat eine sehr gute Auflösung sowohl im Zeit - als auch im Frequenzbereich. Die gleiche Aufgabe der Zeit-Frequenzdarstellung wird mit der Min-Norm (Unterraummethode) Methode realisiert. Die Genauigkeit und die Abhängigkeit der Ergebnisse von der Phase des Signals wurden untersucht und mit der Frequenzanalyse der FFT verglichen. Die angesprochenen Methoden wurden auch mit nicht stationären, zusammengesetzten Signalen getestet. Als Beispiel dieser Art der Signale wurden die Verläufe aus stromrichtergespeisten Antrieben und eines Kurzschlusses im Übertragungsnetz genommen
The effect of a metallic particle near a spacer on flashover phenomena in SF6.
Get PDFThis paper presents a study of the flashover mechanism initiated by metallic particles in SF6 gas. Using a high-speed Imacon photographic camera it was established that a metallic particle near the insulator surface plays an important role in flashover development. The influence of the particle on flashover development depends on the pressure of the SF6 gas. At atmospheric pressure, the flashover was always initiated at a point on the particle farthest from the nearest electrode. At high pressures, it was found that breakdown develops from the electrode of relative positive polarity in the form of a leader. The velocity of the discharge crossing the gap increases exponentially when the distance between the particle and the insulator surface decreases
Effect of arc current on properties of composite insulators for overhead lines
Get PDFResults of power arc tests carried out on composite insulators for 110 kV overhead lines are analyzed. The effect of arcing on the basic electrical and mechanical parameters of the tested insulators is examined. Results of pre- and post-arc electric strength tests as well as those of thennomechanical and mechanical tests carried out on insulators subjected to the power arc test are presented
Neural networks for real-time estimation of parameters of signals in power systems
Get PDFFast determination of parameters of the fundamental waveform of voltages and currents is essential for the control and protection of electrical power systems. Most of the known digital algorithms are not fully parallel, so that the speed of processing is quite limited. New parallel algorithms, which can be implemented by analogue adaptive circuits employing some neural networks principles, are proposed. The problem of estimation is formulated as an optimization problem and solved by using the gradient descent method. Algorithms based on the least absolute value, the minimax, the least-squares and the robust leastsquares criteria are developed and compared. The networks process samples of observed noisy signals (voltages or currents) and give as a solution the desired parameters of signal components. Extensive computer simulations confirm the validity and performance of the proposed algorithms and neural network realizations. The proposed methods seem to be particularly useful for real-time, high-speed estimation of parameters of sinusoidal signals in electrical power systems
A current flow problem for amorphous solids : A case of weak and mean electric fields
Get PDFA space charge transport problem for a planar capacitor system is presented. For a solid placed between two electrodes it is assumed that the carrier generation and recombination processes are independent of an external electric field. Some singular cases of the current flow trough the system are considered. It is found that the system can act as an almost perfect blocking diode (or a voltage stabiliser), and also, it is found that the negative differential resistance is a singularity of space charge transport through the system
Elektrotechnika Teoretyczna. Analiza układów nieliniowych
No full textUkłady z elementami rezystancyjnymi, łukiem, elektrycznym, dławik, obwody magnetyczne, ferrorezonans, transformator nieliniowy, obwody nieliniowe indukcyjno pojemnościowe, układy samowzbudne
Neural networks for real-time estimation of the basic waveforms of voltages and currents encountered in power systems
Get PDFAn electronic artificial neural network architecture is presented for estimating the parameters of a sine wave distorted by a DC exponential signal and corrupted by noise. In the proposed approach a finite set or sampled data from noisy measurements is used to implement Lp-norm. The standard least-squares (L2 -norm) criterion is considered as a special case. Mathematical algorithms are presented in detail and associated architectures of analogue artificial neural networks are proposed. Extensive computer simulations are used to demonstrate the validity and performance of the proposed algorithms and neural network realizations. The proposed methods seems to be particularly useful for real-time, high-sped and low-cost estimations of parameters of sinusoidal signals