Wrocław University of Science and Technology
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Effect of Voltage Harmonics Content on Arrester Diagnostic Result
Get PDFDiagnoses of HV arresters are usually based on an analysis of total leakage current harmonics. The fact that the harmonics content in the supply voltage can be a source of errors is seldom taken into account when routine diagnostic measurements are made. In this paper the effect of harmonics in the voltage signal on the diagnostic result is analysed using Matlab computer simulations
Performance of polymer concrete insulators under light pollution
Get PDFAbstract: This paper deals with polymer concrete, a highly filled composite material as a low cost alternative to porcelain outdoor insulators. A review of earlier laboratory and field tests of PC insulators was given. The insulators were produced according to the technology developed in the USA 30 years ago. The 20 kV support insulators were installed at a distribution power line and exposed to mechanical and electrical stress 8 years ago. The insulators made from polymer concrete are also investigated at Glogow, pollution test station under 75 kV operating voltage. The highest leakage current of 27 mA was measured under the short specific leakage distance of 1,9 cm/kV (phase to ground voltage). Our tests confirm that these insulators can be applied under light pollution condition, that means, in nearly whole territory of Poland and neighbouring countries
Correction of Current Transformer Transient Performance
Get PDFIf a current transformer (CT) saturates while transforming the heavy primary current, in each period, there are sections when the magnetic core is unsaturated and transformation is correct, and when it is saturated, it causes enormous errors. The key to correct the errors is to detect instants of saturation and moments when the saturation ends. This paper presents simple and efficient methods of doing that. In addition, it shows the way how to predict up to three samples after saturation with the acceptable degree of accuracy, thus artificially expanding the unsaturated section. It may substantially facilitate operation of protective devices. The ultimate solution of the problem is to estimate the values of the fundamental frequency component amplitude and the decaying dc component in each period. This paper presents the method of doing that on the ground of four consecutive samples taken during the unsaturated section. If the primary current consists of the fundamental and dc exponential components only, the accuracy of the method is excellent. Neglecting contamination of the current signal with harmonics and noise, it is possible to reconstruct the CT primary current based on the measured values of fundamental and dc components
CT saturation correction based on the estimated CT saturation time constant
Get PDFA new method for CT saturation correction is presented that is based on an on-line estimation of the CT magnetizing inductance. The approach adopted is based on numerical solution of the differential equation, which describes the saturated current transformer. The correction procedure proposed has been tested with EMTP-ATP signals proving to be an effective tool for primary current reconstruction
Application of silicone coatings on porcelain insulators in Poland, a case study
Get PDFSilicone coatings have been used to improve insulating properties of outdoor insulators under polluted conditions for over 30 years. In Poland this method was used for the first time in 1995. This paper presents Polish experiences and analyzes the usefulness of such coatings. Changes in pollution emission and their influence on outdoor insulation performance were taken under consideration
Studies of Epoxy Spacers Subjected to Internal and External Partial Discharge and SF6 Byproducts
No full textIhe reliability of gas insulated switchgear (GIS) has generally been good. However, because of the complexities involved in servicing the enclosed components, maintenance and repair times can rapidly become a serious handicap affecting substation availability, particularly at the higher voltage levels, because of the importance of high reliability of GIS for system security at the higher voltages, there is a concern over the long term ageing characteristics of GIS. Several long term ageing mechanisms have been identified. While bulk failure by electrical treeing of solid dielectrics is a recognized ageing phenomenon, failures linked to long term ageing of spacer surfaces are also coming to the fore; however the corresponding mechanism is poorly understood. Corona discharge, exposure to corrosive SF6 decomposition by-products, and particle contamination can all contribute to the surface failure mechanism(s). The objective of the present study is to develop a better understanding of this failure mechanism, to probe the effects of localized corona discharges on filled epoxies and to characterize the early phases of the internal and external surface degradation process
Zaawansowane metody analizy widmowej sygnałów elektrycznych
No full textI argue in my dissertation that the use of modern high-resolution spectrum estimation methods, such as Min-Norm, Wigner-Ville distribution and combination of these with higher-order statistics (cumulants), provide more possibilities of analysis of highly distorted electrical signals than known methods of spectrum estimation based on Fourier transform. High-resolution spectrum estimation method, such as Min-Norm combined with the use of higher-order statistics could be effectively used for parameter estimation of distorted signals. A new method of visualization of frequency converter supplied drives by means of a static space-phasor was developed as a compact observation and diagnosis method. Statistical properties (estimation error) of the investigated methods for different multi-component signals were analyzed. Spectrums of the space-phasor and of the real-valued signals have been investigated under different operation conditions using the Min-Norm method , Wigner-Ville distribution and power spectrum
On some spectrum estimation methods for analysis of non-stationary signals in power systems. Pt. 1. Theoretical Aspects. & Pt. 2. Numerical Applications
No full textPart I Frequency power converters and arc furnaces generate a wide spectrum of harmonic components and interharmonics. Representation of signals in time and frequency domain has been of interest in signal processing areas for many years, especially taking in the limelight time-varying non-stationary signals. Standard tools of harmonic analysis based on the Fourier transform assume that only harmonics are present and the periodicity intervals are fixed, while periodicity intervals in the presence of interharmonics are variable and very long. In this paper the Prony method was tested for this purpose and a novel approach for the analysis of power nonstationary signals, based on the “subspace” methods, is proposed: the “rootMusic” harmonic retrieval method which is an example of highresolution eigenstructure-based methods. Both methods can allow an accurate and useful estimation of power quality indices as well as of the interharmonic frequencies with their changes in time. This paper, which reports the theoretical aspects of these methods, is a companion paper to a paper of the same title, Part II, in which the numerical aspects of the proposed spectrum estimation methods are analysed using non-stationary voltage and current waveforms in a supply system of a dc arc furnace. Part II This is a companion paper to a paper of the same title, Part I, in which the theoretical aspects of some spectrum estimation methods for analysis of non-stationary voltages and currents in power systems with nonlinear loads are analysed. In particular, the Prony model and rootMusic method are taken into account. In this paper, numerical applications of the methods presented in Part I are discussed, in order to illustrate their implementation problems and practical applications. To investigate the methods, several experiments were performed using non-stationary voltage and current waveforms in a supply system of a dc arc furnace. For comparison, similar experiments were repeated using the Short-Time Fourier Transform. The comparison proved the effectiveness of the new methods; however, their computational efforts can be much more complex. Conclusions and recommendations are made concerning the framework of each method
Zastosowanie programu Matlab wraz z analizatorem SigLab w badaniach laboratoryjnych filtrów analogowych
Get PDFW opracowaniu przedstawiono możliwość wykorzystania pakietu SigLab do bezpośredniego wyznaczania charakterystyk filtrów analogowych. Przedstawiono metodę pomiaru charakterystyk amplitudowo-fazowych laboratoryjnego modelu filtru selektywnego RC za pomocą wirtualnego instrumentu pomiarowego VSS wchodzącego w skład pakietu SigLab. Sformułowano dydaktyczny, pomocniczy program pozwalający na symulację i modelowanie charakterystyk amplitudowo-fazowych filtrów w pakiecie Matlab