Wrocław University of Science and Technology
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431 research outputs found
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Energy saving materials and technologies, nanomaterials, smart materials
No full textThe progress of technology has given us more precise, energy-saving and less expensive manufacturing technologies that can make an unprecedented diversity of new products. Nanotechnology offers a new range of products that are cleaner, stronger, lighter and more. The new class of modem materials have appeared. Nanomaterials have found very new applications. Nanocomposites, polymeric nanocomposites, polymer-ceramic nanocomposites have a number of improved physical properties. This article shows review of tendency in modem advanced materials including smart and active materials
Hygroscopic properties of pollutants on silicone rubber surface
Get PDFSilicone rubber when contaminated by dust has the ability to transfer the hydrophobicity through pollutants. Water on the polluted silicone rubber forms separate droplets. It is a unique advantage of this material. However, the pollution layer on silicone rubber absorbs moisture at high air humidity similar to the pollutants on the glass surface. Under high timidity conditions the surface conductivity on heavy polluted (ESDD and DDD in the range of 0,1 mg/cm2 ) silicone insulators increases to the value in the range a few uS. This leads to dry band formation, arcing and possible surface erosion. The surface conductivity on the silicone rubber contaminated a week earlier by NaCl without bentonite is very small, in the range of 0,1 uS. The surface conductivity of 6 uS was measured on similarly polluted porcelain sample. The pure sea salt pollution is not dangerous for silicone insulators
Analysis of traction system time-varying signals using ESPRIT subspace spectrum estimation method
Get PDFAuxiliary static converters in transportation power systems generate not only characteristic harmonics but also non characteristic harmonics and interharmonics. Representation of signals in time and frequency domain has been of interest in signal processing areas for many years, especially taking in the limelight time-varying non-stationary signals. Standard tools of harmonic analysis based on the Fourier transform are not suitable for analysis in this case. In this paper the ESPRIT method was tested for this purpose that allows an accurate and detailed estimation of parameters of currents in the power supply of auxiliary devices in traction systems, also interharmonic frequencies with their changes in time
Changes on Insulator Surface under the Influence of Strong Electric Field in Vacuum
No full textThe measurements of flash-over voltages on solid insulation, placed in vacuum have shown the initial flash-over occur at voltages considerably lower than this obtained after multiple flash-over. It can be proved that the initial flash-over voltage increase is mainly connected with gas desorption from the insulator electrodes surfaces. As the surface is being cleaned of gas particles the insulator sparking voltage is increasing, hence the energy of particles bombarding the insulator surface is also increasing
Application of higher-order spectra for signal processing in electrical power engineering
Get PDFIn power spectrum estimation, the signal under consideration is processed in such a way, that the distribution of power among its frequency is estimated and phase relations between the frequency components are suppressed. Higher order statistics and their associated Fourier transforms reveal not only amplitude information about a signal, but also phase information. If a non-Gaussian signal is received along with additive Gaussian noise, a transformation to higher order cumulant domain eliminates the noise. These are some methods for estimation of signal components, based on HOS. In the paper we apply the MUSIC method both for the correlation and the 4th order cumulant, to investigate the state of asynchronous running of synchronous machines and the fault operation of inverter-fed induction motors. When the investigated signal is distorted by a coloured noise, more exact results can be achieved by applying cumulants
Harmonics and interharmonics estimation using advanced signal processing methods
Get PDFModern frequency power converters generate a wide spectrum of harmonic components · In some cases, large converter systems generate not only characteristic harmonics typical for the ideal converter operation, but also a considerable amount of non-characteristic harmonics and interharmonic
Evaluation of compensation devices of DC arc furnaces using advanced spectrum estimation methods
Get PDFSpectral representation of waveform distor-tions has been of great interest in power systems for many years since the disturbing loads generate a wide spectrum of components which deteriorate the quality of power supply. When spectral components are time-varying in amplitude and/or in frequency – such as in presence of arc furnaces and adjustable speed drives - high resolution methods should be applied due to their capability of cap-ture these changes in time. In this paper the Prony and ESPRIT high-resolution methods are used to analyse simulated non-stationary waveforms in a supply system of a DC arc furnace. The analysis has been completed before and after the inclusion in the system of several compensa-tion devices (STATCOM, Active Filter, Passive Filter and a hybrid of STATCOM and Active Filter). The main con-clusion of the paper is that Prony and ESPRIT methods are useful tools also for the control system design; in fact, they allow capturing time variations of spectra compo-nents better than most usual techniques such as Fourier-based methods
New solution to the problem of bipolar injection in insulator and semiconductor devices. Solids with an arbitrary distribution of defects
Get PDFA problem of the bipolar space charge transport between the anode and the cathode is presented. The space charge is formed by free electrons and holes as well as by trapped electrons. I1 was found that interactions bctwecn carriera can be described by tne n ( p ) relationships. Also, it was found that there exist the conditions in which the metal-solid metal system can act as an n-p or p-n blocking diode. Ohm, Fowler-Nordheim, Schottky and Child's law are obtained
Analiza sygnałów okresowych metodami statystyk wyższych rzędów
Get PDFCelem pracy jest zbadanie przydatności zastosowania statystyk czwartego rzędu (kumulantów) do estymacji widma wybranych sygnałów spotykanych w elektrotechnice. Praca zawiera dokładny opis teoretyczny zastosowanych metod estymacji widma: maksymalnego prawdopodobieństwa (ML), Pisarenki, MUSIC i minimum normy (MN). Przedstawiono ideę zastosowania statystyk wyższych rzędów w miejsce macierzy korelacji będącej zwykle podstawą powyższych metod estymacji widma. W części doświadczalnej przedstawiono wyniki estymacji widma sygnałów odkształconych, dyskusję nad zaletami i wadami poszczególnych metod oraz możliwe obszary zastosowań statystyk wyższych rzędó
