Wrocław University of Science and Technology
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Assessment of transient disturbances in HV systems with single-phase autoreclosures
Full text linkThis paper proposes some extended method for assessment of transient disturbances in HV system with single-phase autoreclosures. Main efforts are addressed to second arc extinction on the basis of recorded voltage in faulty line in presence of arc. Introduced ideas utilizes recent definitions of time-varying power quality indices. A new contribution of the work is a proposition of characteristic based on local values of odd and even harmonics distortion index
Power Quality in Wind Power Systems
Full text linkWind power generation systems influence power quality in a specific way making important the need for detailed and accurate evaluation of disturbances caused by wind generators. Wind power system can cause sub- and interharmonic components to appear in the spectrum of voltages and currents. The paper shows different aspects of spectrum estimation in power systems, including the doubly fed induction generator (DFIG) connected to low voltage distribution grid. Harmonic distortions caused by wind generator under various operational conditions regarding wind speed, active and reactive power are shown and discussed. Advanced spectral methods (like ESPRIT) are applied to overcome the drawbacks of Fourier based techniques
Model order selection criteria: comparative study and applications
Full text linkA practical application of information theoretic criteria is presented in this paper. Eigenvalue decomposition of the signal correlation matrixbased AIC, MDL and MIBS criteria are investigated and used for online estimation of time varying parameters of harmonic signals in power systems.===PL===Artykuł przedstawia kryteria i porównanie metod redukcji modelu procesu. Przedstawiono i porównano różne kryteria bazujące na dekompozycji macierzy korelacji według wartości własnych: AIC, MDL i MIBS. Porównania dokonano na sygnałach harmonicznych odpowiadających układowi niestacjonarnemu
Trimmed estimators for robust averaging of event-related potentials
Full text linkAveraging (in statistical terms, estimation of the location of data) is one of the most commonly used procedures in neuroscience and the basic procedure for obtaining event-related potentials (ERP). Only the arithmetic mean is routinely used in the current practice of ERP research, though its sensitivity to outliers is well- known. Weighted averaging is sometimes used as a more robust procedure, however, it can be not sufficiently appropriate when the signal is nonstationary within a trial. Trimmed estimators provide an alternative way to average data. In this paper, a number of such location estimators (trimmed mean, Winsorized mean and recently introduced trimmed L{mean) are reviewed, as well as arithmetic mean and median. A new robust location estimator tanh, which allows the data{dependent optimization, is proposed for averaging of small number of trials. The possibilities to improve signal-to-noise ratio (SNR) of averaged waveforms using trimmed location estimators are demonstrated for epochs randomly drawn from a set of real auditory evoked potential data
Plasma Metallization Textiles as Shields for Electromagnetic Fields
No full textThe aim of this paper is electromagnetic testing of innovative shielding textiles in the frequency range from 30 MHz up to 1300 MHz. These new materials were obtained using plasma metallization process. The metallic film was deposited by magnetron sputtering in argon atmosphere from Zn-target on the polypropylene (PP) nonwovens. The microstructure of Zn-films was studied by scanning microscopy (SEM). Obtained metallic layers were characterized by good adhesion to PP and shielding effectiveness (SE) over 50 dB. It was indicated that 3
Time-varying signal parameters for assessment of disturbances in wind energy systems
Full text linkThis paper proposes some extended method for assessment of transient disturbances in wind energy systems. Main efforts are addressed to transient analysis using time-frequency methods coupled with instantaneous characteristic of signal parameters. Introduced ideas utilize smoothed non-parametric time-frequency representations as well as empirical mode decomposition and Hilbert transform. Streszczenie: Artykuł poświęcony jest zagadnieniom oceny zakłóceń w układach energetyki wiatrowej, zwłaszcza analizie stanów przejściowych z wykorzystaniem metod czasowo-częstotliwościowych oraz chwilowych charakterystyk parametrów sygnału. Proponowane rozwiązania wykorzystują wygładzone nieparametryczne transformacje czasowo-częstotliwościowe oraz dekompozycje na mody empiryczne i transformację Hilberta. (Zmienne w czasie parametry sygnału w ocenie zakłóceń układów energetyki wiatrowej
Acoustic emission from BiSrCaCuO superconducting samples
Full text linkThe aim of the paper was to show if the acoustic emission (AE) signals from BiSrCaCuO ceramic superconductors appear during normal state–superconductivity transition. These AE signals were previously observed from YBaCuO-type superconducting materials. The BiSrCaCuO samples were prepared and characterised. The resistance–temperature and current–voltage characteristics of these samples were measured. The critical temperature and critical current density were estimated. AE was measured from samples with and without current flow. The AE signals during sample temperature rise were observed at temperature near the critical value
Hygroscopic properties of natural pollutants on silicone rubber surfaces
Full text linkThe aim of this research is to determine whether hydrophilic and hygroscopic particulate pollutants on glass and silicone insulator surfaces maintain their electrical and water absorption properties, once low molecular weight siloxanes have migrated through the pollution layer. Surface conductivity measurements were performed on glass and silicone rubber plates (HTV and RTV) under conditions of extremely high humidity. Test dusts from the Sahara and Negev Deserts, from Glogow insulator pollution test station (Poland), fly-ash and also standard kaolin were applied in a laboratory to virgin glass and rubber plates. It was found that the value of the surface conductivity measured on the HTV silicone rubber is similar to that on virgin glass. This is true even after time is allowed for possible hydrophobicity transfer to the applied hygroscopic pollution dust. Surface conductivity on RTV silicone rubber with dusts, applied two weeks earlier, was 30% to 60% lower than on a freshly polluted sample. Surface conductivity measured at 100% humidity, increases, where the final surface conductivity depends on the dust type, yet is considerably lower than the surface conductivity measured on a sample wetted by a sufficient amount of water
Influence of High Voltage Insulator on Pollution Flashover Voltage
No full textResults of pollution flashover voltage measurements and optical observation obtained for high voltage insulators placed in the vertical and the horizontal positions are presented. H was found that the well known difference between flashover voltages measured in tests of insulators placed in these positions was a function of the mean contaminant thickness and the uniformity of layer distribution on the insulators. On the basis of measurements of the ESDD conducted on insulators subjected to prolonged, natural contamination, their self-cleaning, in the vertical and horizontal positions, was determined
EEG filtering based on blind source separation (BSS) for early detection of Alzheimer's disease
Full text linkObjective: Development of an EEG preprocessing technique for improvement of detection of Alzheimer’s disease (AD). The technique is based on filtering of EEG data using blind source separation (BSS) and projection of components which are possibly sensitive to cortical neuronal impairment found in early stages of AD. Method: Artifact-free 20 s intervals of raw resting EEG recordings from 22 patients with Mild Cognitive Impairment (MCI) who later proceeded to AD and 38 age-matched normal controls were decomposed into spatio-temporally decorrelated components using BSS algorithm ‘AMUSE’. Filtered EEG was obtained by back projection of components with the highest linear predictability. Relative power of filtered data in delta, theta, alpha1, alpha2, beta1, and beta 2 bands were processed with Linear Discriminant Analysis (LDA). Results: Preprocessing improved the percentage of correctly classified patients and controls computed with jack-knifing cross-validation from 59 to 73% and from 76 to 84%, correspondingly. Conclusions: The proposed approach can significantly improve the sensitivity and specificity of EEG based diagnosis. Significance: Filtering based on BSS can improve the performance of the existing EEG approaches to early diagnosis of Alzheimer’s disease. It may also have potential for improvement of EEG classification in other clinical areas or fundamental research. The developed method is quite general and flexible, allowing for various extensions and improvements. q 2004 Published by Elsevier Ireland Ltd. on behalf of International Federation of Clinical Neurophysiology