Wrocław University of Science and Technology
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Spectrum estimation methods for signal analysis in the supply system of DC arc furnace
No full textIn this paper, Prony and root-MUSIC methods are applied for analysis of waveforms from the DC arc furnace supply. Several experiments were performed using non-stationary voltage and current signals. The experiments proved the effectiveness of the applied methods for time-varying spectral analysis
Using Plasma Metallisation for Manufacture of Textile Screens Against Electromagnetic Fields
Full text linkIn this study, a method of the metallisation of polypropylene (PP) nonwovens is presented.The influence of power dissipated in the target on the efficiency of screening a flat electromagnetic wave is discussed. Fabric metallisation was carried out using the standard magnetron sputtering process of Zn-Bi metal targets in argon ambient. A pulse current source with a changing group frequency was used for powering the target. The metallic layers obtained were characterised by good adhesion to PP, with a screening efficiency approaching 45 dB
Platforma zdalnej edukacji „Moodle” – projektowanie kursu komplementarnego
Full text linkW referacie przedstawiono propozycję modyfikacji kursów opracowanych w formie „tradycyjnej”, zmierzającą w kierunku planowania kursów komplementarnych. Kursy komplementarne (blended learning) często w polskich przekładach nazywane są także kursami mieszanymi(autorzy referatu wprowadzają opis: m-kurs). Oba określenia w pełni oddają ideę kształcenia odnoszącego się w odpowiednich proporcjach zarówno do form „tradycyjnych” jak i form szeroko rozumianej edukacji wspomaganej nowoczesnymi środkami przekazu (m.in. multimedia, Internet). Rozważane są zależności pomiędzy kreowanymi formami komplementarnymi i stopniem ich akceptacji przez grupy uczestników (studentów) realizujących zadania według programów dydaktycznych nie tylko obowiązkowych, ale również wybieralnych. Kształcenie ukierunkowane na wykorzystanie nabytej (ale nie „wyuczonej”) wiedzy w zakresie umiejętności diagnozy problemu,innowacyjnego spojrzenia oraz w rezultacie uzyskania rozwiązania postawionego problemu. Propozycja skierowana jest przede wszystkim do pracowników dydaktycznych posiadających wieloletnie doświadczenie w nauczaniu "tradycyjnym" w szkołach wyższych i średnich. Autorzy na podstawie własnych doświadczeń oraz obserwacji środowiska akademickiego próbują przybliżyć podstawowe zasady planowania procesu kształcenia wspomaganego wybranymi zasobami zdalnej platformy edukacyjnej Moodle
Artificial rain test of outdoor long rod insulators
Full text linkDue to the decrease of industrial contamination emission nearly the whole territory of Poland belongs to the pollution class light. As a result, the insulators can have now a very short leakage distance. The long-term tests carried out at Glogow test station show that cylindrical insulators without sheds and with a small diameter can have the specific leakage distance of 0,8 cm/kV which is twice shorter than that recommended by the international standard IEC60815. This is valid not only for silicone rubber insulators but even for porcelain insulators. To understand this surprisingly good performance, the test results of porcelain cylindrical insulators and standard long rod insulators under artificial rain were presented. The influence of water conductivity, shed parameter and inclination angle from the vertical line was also shown
Two Brain Signal (EEG) processing applications
Full text linkTrimmed estimators are a class of robust estimators of data locations which can help to improve averaging of experimental data when: number of experiments is small, data are highly nonstationary, data include outliers. Compromise between median which is very robust but discard too much information and arithmetic mean conventionally used for averaging which use all data but, due of this, is sensitive to outliers. Additional improvement of averaging can be gained by introducing advanced weighting of ordered data. Existing techniques are limited to removing only such part of raw signal which contain no or almost no components of brain origin but rather external artifacts and noise. We found a cluster of AMUSE-decorrelated components which is sensitive to AD. Room for improvement in ranking and selection of optimal (significant) components
Detection of Short Transients and Interruptions using the Hilbert Transform
Full text linkIn electrical energy power networks, disturbances can cause problems in electronic devices so their monitoring is fundamental in Power Quality. In this paper we address the problem of disturbances estimation by using the Hilbert Transform (HT). It is employed as an effective technique for tracking the voltage waveforms in electrical distribution systems. The mathematical simplicity of the proposed technique, compared with the commonly used algorithms from the literature, renders them competitive candidate for the on-line tracking of disturbances. The accurate tracking of the HT facilitates its implementation for the control of disturbances mitigation devices. Simulation results are provided to verify the tracking capabilities of the algorithm and this has been tested under different conditions: voltage dip with phase jump, noise and frequency changes shows that the Hilbert Transform can be used as a valid methodology for this type of phenomena
Internal Arcing Test on Polluted High Voltage Surge Arresters
Full text linkA test to prove the performance of extremely non-uniform polluted single unit metal oxide (MO) and gapped arresters (SiCA) is presented. The test procedure used represents the worst case condition which can occur especially under a small wetting rate and at severe polluted arrester housings. The resulting temperature increase of metal or silicon carbide varistors was measured. Internal partial discharges or internal arcing during the test were also investigated. Currents, power dissipation, voltage distribution along varistors and pollution layer and lightning sparkover voltage were measured or have been calculated
Modern spectral analysis of non-stationary signals in electrical power systems
Full text linkA novel approach to harmonic and interharmonic analysis, based on the “subspace” methods, is proposed. Min-norm harmonic retrieval method is an example of high-resolution eigenstructure-based methods. The Wigner-Ville representation was also tested for time-frequency analysis of electric signals. The high-resolution methods do not show the disadvantages of the traditional tools and allow exact estimation of the interharmonic frequencies. To investigate the methods several experiments were performed using real and simulated signals, current waveforms at the output of a simulated frequency converter, shunt reactor compensated transmission lines, and compensated AC arc furnace installation. For comparison, similar experiments were repeated using the FFT. The comparison proved the superiority of the new methods
Performance of parametric spectrum estimation methods
Full text linkW pracy przedstawiono porównanie dokładności wyznaczania częstotliwości i amplitudy składowych sygnałów harmonicznych odkształconych przy pomocy parametrycznych metod estymacji widma: MUSIC i ESPRIT. Miarą dokładności jest błąd średniokwadratowy estymacji określonego parametru dla wielu symulowanych przebiegów. Przebiegi testowe są charakterystyczne dla zagadnień spotykanych w elektroenergetyce, stąd otrzymane wyniki mogą być zastosowane w praktyce, umożliwiając optymalny dobór parametrów tych metod obliczeniowych. Jako praktyczny przykład zastosowania metod MUSIC i ESPRIT przedstawiono wyznaczanie wskaźników jakości energii. Uzyskano ponad 50% wzrost dokładności po zastąpieniu algorytmu opartego na DFT (dyskretnym przekształceniu Fouriera) parametrycznymi metodami podprzestrzeni. ========Introduction The quality of voltage waveforms is nowadays an issue of the utmost importance for power utilities, electric energy consumers and also for the manufactures of electric and electronic equipment. The proliferation of nonlinear loads connected to power systems has triggered a growing concern with power quality issues. The inherent operation characteristics of these loads deteriorate the quality of the delivered energy, and increase the energy losses as well as decrease the reliability of a power system [4]. The methods of power quality assessment in power systems are almost exclusively based on Fourier Transform. The crucial drawback of the Fourier Transform-based methods is that the length of the window is related to the frequency resolution. Moreover, to ensure the accuracy of Discrete Fourier Transform, the sampling interval of analysis should be an exact integer multiple of the waveform fundamental period [3]. Parametric spectral methods, such as ESPRIT or MUSIC [5] do not suffer from such inherent limitations of resolution or dependence of estimation error on the window length (phase dependence of the estimation error). The resolution of these methods is to high degree independent on signal-to-noise ratio and on the initial phase of the harmonic components. The author argues that the use of high-resolution 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 [4]. The paper is composed as follows: After the short description of parametric methods (ESPRIT and MUSIC), the comparison of the frequency and amplitude estimation error, based on numerical simulation is presented. Next part presents basics of selected power quality indices (harmonic sub/groups), followed by comparison of estimation error in the case of application of FFT-based algorithms and parametric methods