Wrocław University of Science and Technology
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Concentration of a-terpineol and (2-dodecanoyloxyethyl)trimethylammonium bromide required for prevention of air bubble coalescence in aqueous solutions.
Full text linkFlotation is a widely used process in mineral pro cessing. It utilizes different reagents including, collectors and frothers. It was proposed by Cho and Laskowski to use th e so-called critical coalescence concentration (CCC) for characterization of flotation frothers. In this paper the CCC values were determined for α -terpineol, which is widely used as a frother in laboratory flotation tests, and for (2-dodecanoyloxyethyl)trimethylammonium bromide (DMM-11) which represents a broad family of reagents known as chemodegr adable cationic surfa ctants. The CCC for α -terpineol was found to be 0.16 mmol/dm 3 while for DMM-1, depending of the procedure of approximation, between 0.06 and 0.14 mmol/dm 3
Pollution flashover of single unit metal oxide arresters
No full textFlashover voltage of uniform and non-uniform polluted metal oxide arresters and their porcelain housings without internal parts was measured
Degradation of metal oxide varistors caused by electrical stresses
No full textThe degradation of ZnO elements under AC or DC operating voltage and impulse current is described
Application of the Prony Method for Compensation of Errors in Distance Relays
Full text linkIn this paper we propose an application of the Prony method as a filtering technique for distance relays. First, an overview of the Prony method is presented, then the distance relay model and the impact of non-filtered frequency components such as interharmonics and subharmonics by application of typical digital filters in the operation of the distance relay is shown. We apply a solution using Prony method as a filtering technique applied to distance relay algorithms. Finally, an analysis of the proposed algorithm using simulated signals is evaluated to validate the proposed distance relay algorithm in reach error and operation time of the relay, a distorted characteristic of the Mho distance relay is shown in the impedance plane
Error Compensation in Distance Relays Caused by Wind Power Plants in the Power Grid
Full text linkThis article presents the Prony method as a filtering technique for distance relays. First, the effect of non-filtered frequency components generated by Wind Power Plants in distance relays is evaluated in a simplified model of a doubly fed induction generator, resulting in an error of apparent impedance measurement. Then, the effects of non-filtered frequency components for typical distance relay are presented. The error in apparent impedance measurement is evaluated in reach and operation time of the relay; a distorted characteristic of the mho distance relay is shown in the impedance plane. Finally, Prony method as a filtering technique is implemented as a solution of the apparent impedance measurement error, and the simulated case and a real fault event are evaluated to validate the proposed distance relay algorithm. Thus the asynchronous frequency components of voltage and current signals are identified and filtered, as a result the performance of the distance relay is enhanced
Analysis of Sub-Harmonics in Power Systems
Full text linkWith a wide range of power electronics-related applications in power systems, harmonic currents are increasing at an alarming rate which has greatly deteriorated the power quality in electrical power networks. Moreover, some of electronic controlled equipments used in power systems, such as power converters, produce sub-harmonics, a type of waveform distortion, which can severely degrade the power system performance. Therefore, they must be closely monitored. Moreover, Fast Fourier Transform cannot accurately analyse waveforms containing sub-harmonics because the synchronization of the sampling procedure to sub-harmonics is practically infeasible. The detection of sub-harmonics requires an approach different from that used for harmonics analysis. In most analysis methods the voltage waveform is expected to be a pure sinusoid with a given frequency and amplitude. Standard tools of harmonic analysis based on the Fourier transform assume that only harmonics are present in the investigated signal and the periodicity intervals are fixed, while periodicity intervals in the presence of inter-harmonics and sub-harmonics can be variable and very long. A novel approach to analysis of non stationary signals, based on the “subspace” methods, is proposed. “Root-Music” harmonic retrieval method is an example of high resolution eigenstructure-based method
Assessment of Power Quality in Wind Power Systems
Full text linkWind power generation systems influence power quality in a very specific manner creating the requirements for detailed and correct analysis of disturbances caused by wind generators. Wind power system cause sub- and interharmonic disturbances within the spectrum of voltages and currents. The paper shows alternative method of spectrum estimation in power systems, tested on the system with the doubly fed induction generator (DFIG) connected to low voltage distribution grid. Advanced spectral estimation algorithm (ESPRIT) are applied to overcome the drawbacks of Fourier-based techniques
EM Shielding – Theory and Development of New Materials
Full text linkIn recent years we can observe rapid increase in the number of sources which generate the electromagnetic (EM) fields (like radio broadcasting, television, radio communication, cellular telephony), continuously extending range of applied frequencies and increasing power generated by those sources. The contemporary requirements of civilization lead to the necessity of applying more and more effective methods for shielding of electromagnetic fields, which take into account the specificity of modern devices and systems and the health of people living and working in the vicinity of these fields. Therefore, the choice of suitable materials for the shields and their appropriate arrangement have an essential meaning. Nowadays, one of the most dynamically developing areas of application for the new materials is the electromagnetic compatibility, more precisely development new materials for electromagnetic fields shielding. Content: Chapter 1 The basics of the electromagnetic shielding Janina Pospieszna Chapter 2 Electromagnetic shielding of lightweight and flexible composites Mariusz Ozimek, Maciej Jaroszewski, Jan Ziaja and Wiesław Wilczyński Chapter 3 Conducting polymers for electromagnetic interference (EMI) shielding Mahnaz M. Abdi, Anuar Kassim, Mehdi Jonoobi and Lim Hong Ngee Chapter 4 Polymer based nanocomposites for electromagnetic interference (EMI) shielding Veena Choudhary, S.K. Dhawan and Parveen Saini Chapter 5 Effects of changes of permissible values of the magnetic field intensity in the environment on the scope of protecting against the health effects of the 50 Hz electromagnetic fields Marek Szub
Effect of acid rain on outdoor insulators
Full text linkThis paper gives an overview of the acid rain problem in Europe, Poland and the Polish province of Silesia. The relationship between pH and water conductivity is shown. Different reactions between acid rain and particles are presented. Effects of temperature on the conductivity of H2SO4 solutions were studied. Finally, pollution flashover voltages and leakage currents on a model insulator that was contaminated with H2SO4 and other solutions were measured
HV on-site testing on cables by alternating voltage of variable frequency
Full text linkFrequency-tuned resonant test systems are, meanwhile, state-of-the-art for on-site testing and diagnostics on high-voltage plastic-insulated cables. The paper describes the basic idea and relations of this particular type of test systems. After experience with several commissioned systems, the technical data, especially the specific weight and the performance have been further optimised. A specially adapted diagnostic technique has been developed for the application together with test systems of variable fre-quency. Basic research on cable samples with different failures has obviously qualified AC voltage near to the power fre-quency to be the optimum test voltage wave shape. Resulting from these it is logical to apply this test voltage shape also on medium-voltage cable systems. An example is also introduced in this paper