Wrocław University of Science and Technology
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Power system harmonics estimation using linear least squares method and SVD
No full textThe paper examines the Singular Values Decomposition (SVD) for estimation of harmonics in sinals, in the presence of high noise
Investigations of the field emission current from bismuth ceramic cathodes
Get PDFIn this work the investigations of the emission current from BizSrzBazCu30axn d Bi2Sr2BaCu2Ox ceramic cathodes are presented. Experiments were carried out in the vacuum chamber at pressure within the range of Tr 10-8(10-6 Pa), with DC high-voltage power supply and high-class digital electrometer. Current-voltage and Fowler-Nordheim characteristics for the cathodes superconducting in liquid nitrogen temperature were obtained for various distances between electrodes. Current vs. temperature characteristics were also measured. For some measurements the transparent anode technique was employed in order to provide informations about emission origin point. Emission current was registered for the electron emission originating from a single emission center.Superconducting state did not influence current-voltage dependences. It was observed for superconducting cathodes that emission current abruptly changes in the vicinity of the superconducting transition temperature T,. Emission current was stable and practically constant for the temperatures below T, and became unstable and noisy for the temperatures above T,. Emission current rate depends on the temperature range of the superconducting transition AT,.. Superconducting parameters of the cathodes: critical temperature T,, temperature range of the superconducting transition AT, and critical current density j, were also measured. It was found that sorbtion phenomena on the surface of cathodes during cooling and heating of the electrodes influence emission current values and play major role in the emission phenomena
Effect of Water conductivity on its Pulse Electric Strength
Get PDFThe dependence of the impulse electrical strength of water on conductivity was investigated in non-uniform electric field - point-plate electrode system. The voltage pulses, with the rise time t,=l ps, and time to half-decay tuz= 30 ps, were generated by a Marx bank. Conductivity was varied by the use of different CuSO4 concentrations in distilled water. The voltage and current during the electrical breakdown were recorded by using a pulse voltage divider and current shunt. The dynamic resistance calculated from current and voltage waveforms during electrical breakdown, is also presented. On the basis of these waveforms, the dependencies of the time to breakdown and breakdown voltage on the conductivity for two polarizations of the point electrode are plotted. Investigations made by means of static photography were carried out. It was found that the electrical strength of water depends strongly on the polarity of point electrode and the conductivity of the water. The electrical strength of water decreases, and time to breakdown increases, as water conductivity is increased
Influence of thin layers on static electrification phenomena of materials for power transformers
Get PDFThe static electrification phenomenon is investigated, using a test cell with a rotating metallic disk coated on both sides with thin layers (0,5 and 2 pm) of conducting, semiconducting and insulating materials, obtained by magnetron sputtering. The current characterising the static electrification is studied as a function of the nature of the coating material and the oil, the temperature and the rotating velocity of the disk. Modification of the surface properties has a decisive influence on the static electrification of insulating oils, the sign and the amplitude of the currents are strongly affected
Analysis of double injection in solids: Further results
Get PDFIn this work we further continue to analyse electric conduction with two given boundary conditions. The space charge is formed by free holes and electrons as well as by trapped electrons. We have determined the conditions in which the current-voltage dependence can be strongly nonlinear and discontinuous
Electron-ion conductance in the metal-dielectric-metal system with two given boundary conditions. P. 1. Carrier generation with three mobilities.
Get PDFA dielectric model is considered in which space charge is formed by free carriers of positive and negative charge and trapped negative charge carriers. It was found that a characteristic feature of carriers generation is the switching of the current-voltage characteristic
Power Swing Phenomena and its Detection and Prevention
Get PDFPower Swing which is basically caused by the large disturbances in the power system which if not blocked could cause wrong operation of the distance relay and can generate wrong or undesired tripping of the transmission line circuit breaker. And if not prevented from the generator could cause severe damage to the machine. To prevent unwanted distance or other relay operation during a Power Swing, we did fundamental studies of traditional and advanced detection and prevention methods. Further, we did research on setting of Power Swing Blocking (PSB) scheme to realize real applications
Wavelet Transform Approach to High Impedance Fault Detection in MV Networks
Get PDFApplication of wavelet transform technique to high impedance arcing fault detection in distribution networks is presented. Phase displacement between discrete wavelet coefficients calculated for zero sequence voltage and current signals at natural network frequency is tracked. The developed wavelet based HIF detector has been tested with EMTP-ATP generated signals, proving better performance than traditionally used algorithms and methods. The protection method proposed is efficient, robust and may be used for HIF detection independently of the network neutral point grounding mode
Current Transformer Saturation Detection with Genetically Optimized Neural Networks
Get PDFApplication of the genetic algorithm (GA) for optimization of artificial neural network (ANN) based CT saturation detector is presented. To determine the most suitable ANN topology for the CT state classifier the rules of evolutionary improvement of the characteristics of individuals by concurrence and heredity are used. The proposed genetic optimization principles were implemented in MATLAB programming code. The initial as well as further consecutive network populations were created, trained and graded in a closed loop until the selection criterion was fulfilled. Various aspects of genetic optimization have been studied, including ANN quality assessment, versions of genetic operations etc. The developed optimized neural CT saturation detector has been tested with EMTP-ATP generated signals, proving better performance than traditionally used algorithms and methods