Wrocław University of Science and Technology
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The idea of surface recombination in analysis of bipolar-charge transport in metal-dielectric-metal configuration with a thick dielectric
Get PDFA problem of the boundary-condition formulation in the analysis of space bipolar-charge transport in a planar capacitor at constant supply voltage was developed. Influence of surface charge on electric conductivity in the system was investigated. Absorption-current densities j(t) and surface-charge densities qs(t) as functions of time on the interface surfaces between dielectric and metal have been obtained
Relations n(p) between positive and negative charge carrier concentrations in conditions of bimolecular recombinations
Get PDFA model of dielectric with positive and negative charge carrier is presented. The trapped charge is omitted. Electric conductivity is analysed in steady state at constant voltage. It is demonstrated that in conditions of external electric field the carrier concentrations may satisfy the law of mass action np = const
The effect of generation-recombination processes and of injection mechanism on current-voltage dependences in the metal-dielectric-metal system : II. Carrier recombination
Get PDFA dielectric model in which electrons and holes are the charge carriers was studied. The space charge is formed by free electrons and holes as well as by trapped electrons. Carrier recombination with two trapping states in steady state and at constant voltage was considered in the assumed dielectric model. The considerations refer to the flat capacitor system. The charge injection mechanisms were described by the function of current density and field intensity at the electrodes. The effect of injection mechanisms in conditions of carrier recombination on current-voltage relations was investigated
Bipolar problem of space-charge in dielectric : I. System without trapping.
Get PDFA model of a dielectric with bipolar injection of charge in the form of a plane parallel capacitor is presented. Space and time distributions of charge and induction as well as time courses of the resorption current were determined. The resorption state is described by partial differential equations. Initial conditions were determined on the basis of the stationary state of absorption. The theory of partial quasi - linear differential equations was used in the analytical and numerical considerations
Optimal Sizing of Fixed Capacitor Banks Placed on a Distorted Interconnected Distribution Networks by Genetic Algorithms
Get PDFIn this paper, the optimal sizing of fixed capacitor banks problem in a distorted interconnected distribution system is formulated and solved by a Genetic Algorithm (GA) solution technique to minimize the cost of power production and capacitor banks under the constraints include voltage limits , sizes of installed capacitors and Total Harmonic Distortion (THD), the algorithm is applied on IEEE 30-bus test system and the results are given for different cases: Light and heavy harmonic cases. Computer simulation shows that the harmonic components affect the optimal capacitor sizing
The Perceived Power Quality Way as New Frontier of Relationships between Customers and Producers
Get PDFThe description of perceived power quality state of art is presented. The necessity to satisfy a constant demand of quality in the electric energy field is faced presenting the procedure that should be followed to safeguard the economic interests of the electric energy customers is pointed out with the remarkable byproduct to increase the diffusing of the Knowledge of the electric energy by customers
New power quality indices
Get PDFThe author shows that the use of high-resolution spectrum estimation methods instead of Fourier-based techniques can improve the accuracy of measurement of spectral parameters of distorted waveforms encountered in power systems, in particular the estimation of the power quality indices (such as inter/harmonic groups and subgroups). The comparison of the frequency and amplitude estimation error, based on numerical simulations is presented. Presentation of selected power quality indices is then followed by comparison of estimation error in the case of application of FFT-based algorithms and parametric methods. Investigated waveforms are typical for dc arc furnace plant. MUSIC and ESPRIT high-resolution methods are used to analyze waveforms in a supply system of a DC arc furnace
Analysis of influence of power quality disturbances using a neuro-fuzzy systems
Get PDFThe authors propose an automated neuro-fuzzy system approach (with neural network subsystem) to power quality assessment incorporating equipment susceptibility patterns. The system is expected to handle dependencies between superposition of different disturbances and specific devices’ susceptibility to disturbances. Two neural network architectures were applied: a well known radial-basis neural networks for automatic rules’ generation and a neuro-fuzzy system for overlaid disturbances influence modeling. Proposed approach can help to predict damages or abnormal functioning of devices and implement adequate countermeasures
Influence of Partial Discharges on ZnO Varistors
Get PDFThe varistors used in HV overvoltage limiters are constantly exposed to operating voltage and environmental hazards and also to transient hazards associated with, among others, overvoltages or pollution. Pollution exposures and the associated partial discharges (PD) are a major problem in the operation of overvoltage limiters. The discharges degrade the electrical properties of varistors which results in an increase in the conduction current active component below the varistor continuous operation voltage. This may lead to loss of thermal stability. To determine the effect of partial discharges on the varistor elements in HV overvoltage limiters, the service exposures were simulated on single varistors in laboratory conditions
Pollution behaviour of insulators with spiral shaped sheds
Get PDFThe paper reviews the experimental investigation of the performance of insulators with spiral shaped sheds under laboratory and field conditions. The study carried out in different countries and author’ own measurements are presented. It was shown that the pollution flashover voltage of spiral shaped insulators is lower than that of insulators with standard sheds. The poorer performance of spiral shaped insulators is caused by the formation of non-uniform surface layer along the leakage path