Wrocław University of Science and Technology
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Application of TSD and SEA methods for measurements of space charge and polarisation in PET electrets
No full textThe step electroacoustic (SEA) and thermally stimulated discharge (TSD) methods were applied for analysis of electret state in corona charged samples. Simultaneous measurements of electric field distribution and current during thermally stimulated discharge allow to get information about real space charge density and quasi-frozen polarisation in a dielectric
Effect of area on surface flashover voltage in vacuum
No full textIt is known that the breakdown voltage in a vacuum insulation system drops with an increase in linear dimension of electrodes and with an increase in the number of insulating spacers bridging the gap. Normally this is explained to be the result of the increase in the number of so-called weak links in the system. The influence of an external capacitance on the flashover voltage of an electrode gap bridged by a spacer was investigated. When a capacitor was connected inside the vacuum chamber near the discharge site in parallel with the gap, it was found that the additional capacitance lowered the breakdown voltage in a manner similar to that observed with an increase in electrode area. This supports the energy explanation of the area effect. A larger external capacitor, far from the discharge site, had no influence on the breakdown voltage
Thermally stimulated currents of Zn-Bi-O thin film arresters
Get PDFCeramic varistors based on zinc oxide have excellent properties as protection devices used in power industry. However, their breakdown voltage, dependent on number of grain boundaries, is too high for use in electronic applications. In this work, performance of micro-devices having varistor-type current-voltage characteristics with low breakdown voltage is reported. The thermally stimulated depolarisation current (TSDC) technique was used to study the dielectric relaxation of the Zn-Bi-0 thin-film arresters. The surface varistor layers were prepared by r.f. magnetron sputtering on nickel support. The TSDC measuring system and cryostat apparatus used in experiment have been described
Neural networks for real-time estimation of parameters of signals in power systems
Get PDFThe purpose of this paper is to present new algorithms and along with them new architectures of analogue neuron-like adaptive processors for online estimation of parameters of sinusoidal signals, which are distorted by higher harmonics and corrupted by noise. For steady-state conditions we have developed neural networks which enable us to estimate the amplitudes and the frequency of the fundamental component of signals. When estimating the basic waveform of currents during short circuits the exponential DC component distorts the results. Assuming the known frequency, we have developed adaptive neural networks which enable us to estimate the amplitudes of the basic components as well as the amplitudes and the time constant of a DC component. The problem of estimation of signal parameters is formulated as an unconstrained optimization problem and solved by using the gradient descent continuous-time method. Basing on this approach we have developed systems of nonlinear differential equations that can be implemented by analog adaptive neural networks. The solution of the optimization problem bases on some principles given by Tank and Hopfield [ 4 ] as well as by Kennedy and Chua. The developed networks contain elements which are similar to the adaptive threshold elements of the perceptron presented by Widrow
A small signal problem and anomalous electric condution in the metal-solid-metal system. Further analytical and numerical results
Get PDFA new approach to a small signal theory is presented. An electrical transport in a discharging capacitor system is analysed. A solid in which there can exist the deep or shallow trapping levels is considered. It is found that the current flow is stimulated by the trapped electrons and that the system can act as an anomalous reservoir of electrical energy (a case of solar cell)
A space-charge problem including trapped positive charge. A case of solar cell
Get PDFA theoretical description of an interior of a solid for space charge is continued. Carrier generation and recombination conditions are considered. On this basis it is found that the metal-solid-metal system can act as a perfect blocking diode. A solar cell problem is discussed
Dyskretne przekształcenie Fouriera
Get PDFDyskretne przekształcenie Fouriera (ang. Discrete Fourier Transform - DFT) jest jedną z dwóch najbardziej popularnych i wydajnych procedur spotykanych w dziedzinie cyfrowego przetwarzania sygnałów. (Drugą jest filtracja cyfrowa.) DFT pozwala nam analizować, badać i syntetyzować sygnały w sposób niemożliwy do wykorzystania przy przetwarzaniu sygnałów ciągłych (analogowych). Pomimo tego, że jest ono obecnie używane w prawie każdej dziedzinie inżynierii, ujrzymy zastosowania dla DFT, pozwalające nadal mu rozkwitać, jako że jego użyteczność staje się coraz szerzej rozumiana. Z tego powodu właściwe rozumienie DFT jest obowiązkowe dla każdego, kto działa w dziedzinie cyfrowego przetwarzania sygnałów
A bipolar space charge problem for solids including a secondary electron emission
Get PDFIn this paper a new mathematical model for a space charge transport through a solid placed between the two electrodes is presented. Using new equations for allowed electron hole transitions, the effect of the light on the electric field distribution and on the shape of current - voltage characteristic is determined. For a space charge distribution some new singular solutions are obtained. Also, some new shapes of current - voltage characteristic with negative resistance are determined. In this paper it is found that the system can act as an n-p-n or p-n or n-n blocking diode
An assessment of ageing of oxide varistors exposed to pulse hazards using dielectric spectroscopy
Get PDFThe common use of zinc oxide varistors has brought about qualitative changes in the overvoltage protection of electronic and electric power equipment. This is due to the special properties of ZnO varistors, mainly the high current-voltage characteristic nonlinearity and the capacity to withstand strong current surges. In service conditions varistors are exposed to the sustained action of constant or variable voltage or momentary overvoltage pulses. As a result varistors may undergo degradation reflected in changes in their current-voltage characteristics. The changes are manifested in an increase in leakage current and are limited to a highly thermally activated low-current region where the performance of the varistor is determined by the parameters of the potential barriers. Thus one can conclude that the degradation is a result of processes leading to the movement of ions and the deformation of the potential barriers. Therefore dielectric spectroscopy (testing of the dielectric response in a wide frequency band) could be useful for the investigation of degradation changes, and so this method is proposed in this paper
Synteza obwodów elektrycznych
No full textSlajdy do wykładu Synteza obwodów liniowych (Obwody i Układy