Wrocław University of Science and Technology
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Analysis of steady state electric conduction in solid with given functions of carrier mobilities under conditions of collision recombination
No full textThis work presents an analysis of the transport of "hot carriers" of charge in the planar capacitor system. The effect of carrier injection on current-voltage dependence j = j (U) with given carrier mobilities is investigated. It was found that if the boundary functions are quadratic then j ~ U^4, whereas if they are of Schottky type then j(U) can be decreasing function (dU/dj < 0). The condition carrier injection, which make the j ~ U^(3/2), was determined
Electron-ion conductance in the metal-dielectric-metal system with two given boundary conditions. P. 2. Generation-recombination with two mobilities.
Full text linkTransport of free positive charge carriers and of trapped negative charge carriers in a model dielectric is considered. It was found that when recombination processes predominate there is no switching of the current-voltage characteristic
Transient states of electric conduction in solid dielectrics including carrier recombination : 2. Ideal dielectric with deep traps.
Full text linkElectric conduction in a dielectric with deep traps is analysed. The space charge is made up of free electrons, holes and trapped electrons. The effect of injection mechanisms and carrier mobility on time curves of absorption current density is investigated. The problem is solved numerically
Bipolar problem of space-charge in dielectric : II. System with trapping.
Full text linkA model of dielectric with bipolar injection of charge and with trapping taken into account is presented. Charge transport was described by partial differential equations in the system of plane parallel capacitor. The space-time distributions of charge and induction as well as time courses of resorption current were determined. Initial values were found on the basis of stationary state of absorption. In analytical and numerical consideration the theory of partial quasi - linear differential equations was used
Analysis of power quality disturbances using the S-Transform
Full text linkThe method presented in this paper employs recently introduced S-transform which is an important development of STFT with improved properties. Proposed methods allow tracking changes in amplitude and frequency with better precision than STFT and Wigner-Ville transform. Possible applications in diagnosis and power quality problems are targeted. The S-transform outperforms the STFT in that it has a better resolution in phase space giving a fundamentally more sound time frequency representation. Investigations of the representation error show that optimally adjusted S-transform can also outperform the Wigner-Ville transform when dealing with time-frequency representations of the signal. The S- transform is also tested on nonstationary electric signals where it shows excellent tracking capability. These properties show that S-transform can be effectively used for analysis of electric signals, especially when dealing with multi-component time-varying waveforms
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Aspects of Fast Fourier Transform Application for Analysis of Electrical Systems with Wind Generation
Full text linkOne of the most powerful tools in spectral analysis is the Fast Fourier Transform (FFT). Since the sixties it has been successfully installed in many electrical engineering applications. Nowadays, the engineer needs to press a button to get results. Nevertheless, meaningful analysis of measurements requires in-depth knowledge of the FFT algorithms. Sometimes the engineer would be forced to use other spectral analysis tools, e.g. Prony method to obtain satisfactory results. The paper is concerned with educational aspects of FFT. The engineer in spe should be aware of the features and restrictions imposed on FFT and if needed refer to other spectral analysis methods
Application of thermal imaging in electrical equipment examination
Full text linkThe paper states about applying thermal imaging measurement methods to electrical equipment diagnostics. Modern infrared mapping techniques allow to take fast and nonexhausting measurements of devices that are not easy accessible or where measurements are dangerous to humans. Thermography has found it’s principal use in power engineering in diagnostics of electrical apparatus and equipment, mainly transformers and insulators
Statistics of Short-Circuit Signals for Power System Protection Purposes
Full text linkBasic ideas of probability and statistics with application to chosen power system protection problems are presented. Since fault appearance and parameters are of probabilistic nature, calculated distributions of selected short-circuit signals should bring great amount of information useful for protection purposes. Two examples are described how calculated statistics may be used for decision making in a fault detection and classification unit and for effective choice of optimal input signals in an ANN-based out-of-step prediction scheme. The short-circuit cases for determination of needed distributions were obtained performing extensive simulations with use of EMTP/ATP programme