Wrocław University of Science and Technology
Repozytorium Eny Politechnika WrocławskaNot a member yet
431 research outputs found
Sort by
Time-frequency analysis of non-stationary three phase signals
Get PDFNew method of observation and diagnosis of inverter-fed induction motor drives is developed and tested. Unsymmetrical conditions concerning the machine impedances or valves operation are reflected in the spectrum of the current space- phasor. We estimate the spectrum of the space-phasor with the help of the Wigner-Ville distribution (WVD) and we obtain its time-frequency representation with excellent time and frequency resolution. The proposed method is tested with nonstationary multiple- component signals occurring during the fault operation of inverter-fed drives and transmission lines. Copyright © 2002 IFA
Real-Time Parameter Estimation of Signals in Converter Fed Drives using Adaptive Neural Networks
No full textFrequency converter-fed induction motor drives were simulated using the EMTP-ATP (Electromagnetic Transients Program - Alternative Transients Program) The aim of the simulation investigations is to develop a feasible method for drive visualisation and for diagnosis of different unsymmetrical operations. Visualisation of a converter-supplied drive by means of modal space phasors is a very useful and compact observation and diagnosis method. Fast and exact estimation of the frequency of distorted voltages and currents at the motor input enables to obtain stationary space-phasors and to determine an appropriate sampling window for a DFT analysis. For this purpose an adaptive neural network is proposed. Computer simulation results confirm the validity and performance of the proposed method
DGA system utilising semiconductor gas sensors
Get PDFThermal and electric faults developing inside transformers lead to the generation of gaseous products dissolving in the insulating oil. Chromatographic analysis of the gas products composition and concentration (DGA) is a routine procedure used in test and maintenance of the transformers. Unfortunately DGA is rather a laboratory method and cannot be applied in the field during the transformers exploitation. The research aimed at working out a portable system for fast, introductory DGA analysis by means of semiconductor gas sensors. DGA procedures, test system construction and efficient gas extraction methods as well as the results of various oil sample tests are discussed. Unexpected impact of the extraction method on the sensor response is also mentioned
RBF and SVM Neural Networks for Power Quality Disturbances Analysis
Get PDFThis paper presents classification results of different power quality disturbances. SVM and RBF neural networks are considered as appropriate classifiers for power quality issues, however SVM networks show better performance. Simulation of disturbed signals by parametric equations enabled the assessment of signal parameters influence on classification rate. Positive results encouraged further research. Model of supply system suffering from sags was simulated. Independent from line length and sag duration the classifier was set to recognize different sag types. The idea of space phasor was applied to obtain distinctive patterns from three phase system. Wavelet transform was used to find the beginning of sags. Positive classification results were obtained
Time-domain temperature variations of a composite insulator surface exposed to arc discharges
Get PDFIn this paper, a system of equations is presented, which describes time-dependent temperature variations for a dielectric surface exposed to an arc discharge. The formulas are derived for a circular(as well as any-shape)region interacting with the arc discharge. The final set of equations makes it possible to convert temperature values, measured at some depth beneath the sample surface which is exposed to the arc heating, to the corresponding surface temperature values. The theoretical results are verified by measurements according to the IEC 61621 test method, and numerical calculations are done for an epoxy composition that is used in composite insulator manufacturing
Time-Frequency Analysis of Distorted Electric Signals using a Complex Space-Phasor
Get PDFWe consider applying non-parametric and parametric methods for calculation of time-frequency representation of non-stationary electric waveforms. Space phasor is applied as a complex representation of 3-phase signals and visualization of the spectrum of positive and negative-sequence components. We compare the uncertainty of measurements using described time-frequency representations, as well as a widely used Fourier techniques. Proposed methods allow tracking instantaneous frequency as well as magnitude of non-stationary signals in power systems. Possible applications in diagnosis and power quality area are targeted
Electric insulation for energy-saving equipment
Get PDFEquipment is labelled as energy-saving if it requires less energy during its manufacture and operation. A reduction in energy consumption in the manufacture of large electrical machines and equipment can be obtained by reducing their dimensions with their power preserved. To achieve this, new insulating materials characterized by high thermal conductivity must be used to increase the capacity to carry away the heat generated in the windings. This paper presents a technique of obtaining insulating composites with increased thermal conductivity, results of tests on composites and the use of these materials in highpower electric machines and for the production ofHV insulators with increased resistance to surface discharges
Dyskretna transformacja Fouriera
Get PDFCelem wiczenia jest przeprowadzenie analizy widmowej sygnałów okresowych za pomocą szybkiego przekształcenia Fouriera (FFT
Transient states of electric conduction in solid dielectric including carrier recombination : 1. Ideal dielectric without traps
Get PDFA model of a dielectric in which the charge carriers are electrons and holes is considered. The flow of charge is described by the Gauss equation, the continuity equation and an equation for the kinetics of carrier recombination. The boundary conditions are determined on the basis of the investigated mechanisms of injections of charge carriers from the electrode into the dielectric. The effect of injection mechanisms, carrier mobility and recombination coefficient on time curves of absorption intensity is investigated. The problem is solved numerically
Dydaktyczne aspekty projektowania wirtualnego w kształceniu na odległość
Get PDFW referacie przedstawiono doświadczenia i sugestie dotyczące wprowadzania do programów dydaktycznych elementów kształcenia na odległość (e-learning) w zakresie wspomagania kursów uruchamianych w formie tradycyjnej (blended learning), nazywanych często w polskich przekładach kursami komplementarnymi lub mieszanymi. W szczególności rozważane są zależności pomiędzy kreowanymi formami komplementarnymi i stopniem ich akceptacji przez grupy uczestników (studentów) realizujących zarówno zadania według programów dydaktycznych obowiązkowych jak i wybieralnyc