Wrocław University of Science and Technology
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Methods of Determining Internal Parameters of Varistor Model
Get PDFZnO varistors are semiconductor devices with highly nonlinear current-voltage characteristic and are widely used as devices for overvoltage protection. Varistor applications range from the use of small varistors to protect electronic components to large varistors for protection of power systems. This paper presents proposed model of ZnO varistor and methodology of its mathematical analysis and simulation. The mathematical analy-sis of the proposed model makes it possible simulate the current trace on a nonlinear element
Resistance of Silicone Rubber High Voltage Insulation to Leakage Current in Modified Inclined Plane Test
Get PDFIn this paper results of investigations of resistance to leakage currents of two different silicone rubbers subjected to a modified inclined plate test are presented. The modification of the experiment consisted in a change of the sample’s inclination angle and in feeding a moistening solution to the upper surface of the sample. The main aim of the modification was to create laboratory test conditions as close to the ones observed in reality as possible
Instantaneous Frequency Calculation Using Wigner Distribution
Get PDFThis paper introduces two-dimensional methods of observation and diagnosis of non-stationary signals in electrical engineering as well as its further application in instantaneous frequency calculation. The investigations are carried out on two levels: firstly, two-dimensional representations are obtained applying Wigner Distribution, then local frequency moments are calculated to achieve one-dimensional characteristics of instantaneous frequency. It is shown that such characteristic preserves information about the nonstationarity in time domain and can be used for detection and duration of transient states
Voltage fluctuation assessment with application of neural networks
Get PDFThe paper presents a contribution to voltage fluctuation assessment. The importance of automated power quality assessment, especially voltage fluctuation, is firstly shown. The SVM network is then introduced and considered as an appropriate tool for classification issues. The feature extraction for SVM classifier is done with application of space phasor. Disturbed signals were generated using a model build in Matlab. Finally, the results of classification of disturbed signals are presented
Proceedings of the Int. Conference "7th EEEIC International Workshop on Environment and Electrical Engineering"
No full textOut-of-Step Protection with AI Methods
Get PDFIn the paper the results of investigations on the application of Artificial Intelligence (AI) methods to the out-ofstep (OS) protection of synchronous machines are presented. The main efforts have been focused on development of new Artificial Neural Network (ANN) based and mixed protection techniques which should ensure better (faster and more secure) detection of generator loss of synchronism. The designed AI-based OS protection schemes have been thoroughly optimised and tested with EMTP-generated case signals. Wide robustness analysis as well as comparison with chosen standard OS detection method have also been performed
Modeling of overhead transmission lines with line surge arresters for lightning overvoltages
Get PDFLightning is one of the most significant source of overvoltages in overhead transmission lines. The lightning overvoltages could lead to failure of the devices connected to the transmission line. A fundamental constraint on the reliability of an electrical power transmission system is the effectiveness of its protective system. The role of the protective system is to safeguard system components from the effects of electrical overstress. Surge arresters are an important means of lightning protection in distribution systems. Therefore, it is necessary to analyze influence of such overvoltages in order to applying the line surge arrester for improving the reliability of transmission line system. The method used to analyze the increase in voltage due to lightning was done by using the ATP/EMTP software This paper is aimed at analyzing the lightning performance improvement of a transmission line after installing line surge arresters
Impact of environmental conditions in West Europe, Poland and Algeria on outdoor insulators performance and selection
Get PDFThis paper presents the data of environmental conditions in France, Germany, Poland and Algeria. The trends in industrial contamination were given, especially of dust, SO2, NOx, rainfall and acidity. The large improvement, especially decrease of dust deposit density in Europe, should be taken into account during selection of insulator according to IEC Publication 60815. On the other hand the natural contamination in Algeria (Sahara dust or see salt) is a dominating factor in this country, therefore no changes here are expected
Switching Vacuum Arc in a Pulsed Transverse Magnetic Field
Get PDFAn experimental analysis of the vacuum arc behavior in a pulsed transverse magnetic field with amplitudes up to 120 mT and frequency of 900 Hz is presented in the paper. The arc was produced between Cu contacts during the switching off operation of the current half-wave of amplitude 500 A and frequency of 30 Hz, so that the circuit parameters had rather moderate values which are easy to obtain in a vacuum switch. The presented results are a part of work which aims to examine the possibilities of using transverse magnetic fields to force a current interruption in vacuum. The analysis was performed using high-speed photography (2000 frames/s) and a shielded Langmuir probe. The results obtained show that the plasma movement and the displacement of the arc in the oscillatory magnetic field proceed according to the Lorentz force acting on ions. This arc displacement is in accordance with the retrograde motion known from the literature, which is opposite to that resulting from the Amperian force. Arc voltage increases of up to about 80 V were observed during the magnetic field action, but the current flow remained undisturbed
Thermally stimulated current in high resistivity Cd0.85Mn0.15Te doped with Indium.
Get PDFCharge carrier traps in Cd(0,85)Mn(0,15)Te doped with indium were studied using thermally stimulated current measurements. The investigations were performed in temperatures ranging from 100 to 300 K. Four peaks in the current spectrum were identified. From the initial rise method and the best fit of the spectrum to the theoretical model, the activation energies and the relaxation parameters for the corresponding traps were determined