Metal-support interaction and charge distribution in ceria-supported Au particles exposed to CO

Understanding how reaction conditions affect metal-support interactions in catalytic materials is one of the most challenging tasks in heterogeneous catalysis research. Metal nanoparticles and their supports often undergo changes in structure and oxidation state when exposed to reactants, hindering a straightforward understanding of the structure-activity relations using only ex situ or ultrahigh vacuum techniques. Overcoming these limitations, we explored the metal-support interaction between gold nanoparticles and ceria supports in ultrahigh vacuum and after exposure to CO. A combination of in situ methods (on powder and model Au/CeO2 samples) and theoretical calculations was applied to investigate the gold/ceria interface and its reactivity toward CO exposure. X-ray photoelectron spectroscopy measurements rationalized by first-principles calculations reveal a distinctly inhomogeneous charge distribution, with Au+ atoms in contact with the ceria substrate and neutral Au0 atoms at the surface of the Au nanoparticles. Exposure to CO partially reduces the ceria substrate, leading to electron transfer to the supported Au nanoparticles. Transferred electrons can delocalize among the neutral Au atoms of the particle or contribute to forming inert Auδ− atoms near oxygen vacancies at the ceria surface. This charge redistribution is consistent with the evolution of the vibrational frequencies of CO adsorbed on Au particles obtained using diffuse reflectance infrared Fourier transform spectroscopy

Diagnostics of a ladle furnace transformer after damage repair

The paper presents results of diagnostic tests of a ladle furnace transformer conducted after damage repair, before putting the ladle to operation. In the tests, the waveforms of voltages and currents were recorded digitally on the primary and secondary side of the transformer in no-load as well as in under-load state. Additional temperature measurements of the transformer casing during its operation, conducted with an infrared camera, are also presented. The recorded data were numerically processed. The results made it possible to assess condition of the transformer components (core, windings and casing), indicate hazards and formulate operation recommendations

Analysis of load and losses in converter transformers of electric drives

Electric converter drives are nonlinear loads that produce higher harmonics of current. To reduce their influence on quality of electric energy in a power network, medium and high power drives are fed from separate converter transformers. The secondary current of these transformers are non-sinusoidal due to properties of converters and, sometimes, the supply voltage is also distorted. A non-sinusoidal current and voltage with significant content of higher harmonics result in additional power losses and heating of a transformer. As a result, due to thermal effects, the transformed power has to be reduced in comparison to nominal power specified for a linear load. The article deals with analysis of load and losses of transformers feeding frequency converters and controlled rectifiers of steelworks drives. Necessary reductions of transformers nominal power due to non-sinusoidal load current are determined on the basis of harmonic spectra of recorded waveforms of voltages and currents

Variable frequency drives of overhead crane with gripper

The paper describes the structure and properties of the overhead crane drives. They allow the movement of the transported item in three axes: x (driving the bridge), y (driving the trolley) and z (lifting - lowering). Drive systems are equipped with squirrel cage induction motors powered by frequency converters. Control of the crane is supported with PLC. The temporal waveforms of the basic quantities of electro-mechanical drives for lifting and lowering the weight and during its horizontal transport along the x and y axis are presented. DriveWindow software tool was used to record the signals. This software is dedicated to the parameterization and monitoring of the ABB drive systems.W artykule opisano struktury i właściwości napędów mechanizmów suwnicy chwytakowej. Umożliwiają one przemieszczenie transportowanego elementu w trzech osiach: x (jazda mostem), y (jazda wózkiem) oraz z (podnoszenie - opuszczanie). Układy napędowe wyposażone są w silniki asynchroniczne klatkowe zasilane z przemienników częstotliwości. Sterowanie pracą suwnicy wspomagane jest sterownikiem PLC. Zamieszczono przebiegi czasowe podstawowych wielkości elektromechanicznych dla napędów suwnicy przy podnoszeniu i opuszczaniu ciężaru oraz podczas jego transportu poziomego wzdłuż osi x i y. Do rejestracji przebiegów wykorzystano oprogramowanie narzędziowe DriveWindow dedykowane do parametryzacji oraz monitorowania pracy przekształtnikowych układów napędowych firmy ABB

Selected problems of reactive power compensation and higher harmonics filtering in modernized converter drives

The paper deals with requirements that have to be met in design and modernization of electric converter drives. Technical issues connected with compensation of the reactive power and filtering of higher harmonice of the current, occurring during implementation and operation of the drives, are described using selected examples. One of the problems is increase of the voltage distortion at buses of a medium voltage switching station due to mismatch between the LC filter parameters and the current harmonic spectrum after replacing controlled DC drives of the bar rolling mill with squirrel cage motors with frequency converters. Negative effect of the idle run current compensation circuit of a new dry transformer on valve switching in the controlled rectifier after replacing old oil transformers is also described. Diagrams of supply circuits, waveforms of currents and voltages as well as harmonic spectra illustrating discussed problems are presented and conclusions and recommendations are formulated

Experimental measurements of parameters and characteristics of the arc furnace electrodes hydraulic drive

W artykule przedstawiono wyniki pomiarów parametrów i charakterystyk regulacyjnych hydraulicznego napędu elektrod pieca łukowego AC dużej mocy. Opisano układ sterowania i regulacji położenia elektrod z siłownikami hydraulicznymi. Do bezpośredniego pomiaru położenia elektrod pieca użyto laserowych czujników odległości, podłączonych do komputera pomiarowego. Wyznaczono charakterystyki położenia i prędkości elektrod dla różnych stanów pracy oraz pokazano dynamiczne przebiegi czasowe ruchu elektrod w różnych fazach wytopu. Sformułowano wnioski dotyczące nastaw w układzie sterowania elektrod pieca.The article presents the results of measurements of the parameters and characteristics of the hydraulic control of electrodes of high power AC arc furnace. The control and positioning system of the electrodes with hydraulic actuators has been described. Laser distance sensors connected to the measuring computer were used for the direct measurement of the position of AC furnace electrodes. The control signals for the electromagnetic valves were also measured. DasyLab and Matlab software were used for the data acquisition and analysis. The position and speed characteristics of the electrodes for various operating states have been determined. Dynamic characteristics of the electrodes movement in the various melting phases are shown. Conclusions on settings in the furnace electrodes control system were formulated

Asymmetry of the linear speed of multi-motor controlled DC drive

The paper presents the structure and properties of the unit comprising several groups of multi-motors DC drives. The unit drives the transport line of molded steel band. Each drive group is controlled by the SCR rectifier in armature circuits. Excitation circuits of the group of motors are powered from a single semicontrolled rectifier with additional resistors to set the individual excitation currents. The result of technological conditions associated with hydraulic clamp, geometrical deviations of drive rollers, thermal conditions and elasticity of the band is the occurrence of asymmetric linear velocity that determine specific defects of the slabs. Linear speeds of transport rollers were calculated using encoders to measure the speed of motors and programs DasyLab and MATLAB. Asymmetry of the linear speeds of rollers was determined. The summary and conclusions are presented at the end of the paper.Artykuł przedstawia strukturę i właściwości zespołu wielosilnikowych napędów grupowych DC transportującego formowane pasmo metalu. Każda z grup napędowych jest sterowana przekształtnikiem tyrystorowym od strony obwodu tworników. Obwody wzbudzenia silników grupy są zasilane z jednego prostownika półsterowanego z dodatkowymi rezystorami do indywidualnego ustawiania prądów wzbudzenia. Rezultatem uwarunkowań technologicznych związanych z dociskiem hydraulicznym, niedoskonałością geometryczną rolek napędowych, warunkami termicznymi i plastycznością pasma jest występowanie asymetrii prędkości liniowych, które determinują określone wady półproduktu. Wykorzystując enkodery do pomiaru prędkości obrotowej silników i rolek transportowych oraz programy DasyLab i MATLAB obliczono wartości prędkości liniowych, na podstawie których określono stopień asymetrii prędkości liniowych rolek. W końcowej części artykułu przedstawiono podsumowanie i wnioski

Improvement of energy efficiency as a result of modernization of the rolling mill's drive system

The article presents a method for calculating power losses in drive systems with converter systems. Calculation was made on the example of a rolling mill originally driven by a DC motor supplied from a thyristor converter, and after modernization with asynchronous motor controlled by a frequency converter. Passive L-C filter was used on the supply side in both systems. The power loss analysis includes the nonsinusoidal currents in the electrical installation including the transformer and medium voltage cables. Power values and harmonic currents were calculated in the power system of the mill drive systems on the basis of computer measurements. The calculations made it possible to estimate electrical power losses in the rolling mill system.Artykuł przedstawia metodę określenia strat mocy w układach napędowych z układami przekształtnikowymi. Obliczenia wykonano na przykładzie walcarki napędzanej pierwotnie przez silnik prądu stałego zasilany z przekształtnika tyrystorowego, a po modernizacji przez silnik asynchroniczny sterowany przemiennikiem częstotliwości. W obu układach po stronie sieci zasilającej zastosowano pasywny filtr L-C. W analizie strat mocy uwzględniono niesinusoidalny przepływ prądu w elementach instalacji elektrycznej obejmującej transformator oraz kable średniego napięcia. Na podstawie pomiarów komputerowych obliczono wartości mocy oraz zawartości wyższych harmonicznych prądów w systemie zasilania układów napędowych walcarki. Wykonane obliczenia umożliwiły oszacowanie strat mocy i energii elektrycznej w układzie walcarki

Application of DriveWindow software for diagnostics of operating conditions of AC and DC drives

The paper deals with practical applications of the DriveWindow software to electric drive technology. This software tool is designed for setting up, monitoring and controlling drives fed from ACS and DCS series converters. Benefits from implementation and operation of electric drive systems are shown on example of selected facilities on a metal plate processing line. Example waveforms of electromechanical quantities in dynamic states of AC and DC drives, recorded using the DriveWindow software during research and start-up works, are presented

Influence of high power DC converter drives on operating parameters of induction machines

In the paper we determined the content of higher harmonics in medium voltage supplying power units of hoisting machines on the basis of measured voltage and current signals. Next a procedure for calculation of voltage harmonic factor HVF is presented as well as its influence on real efficiency of induction motors fed from the same voltage source. There are also presented results that make possible calculation of the HVF factor with respect to load factor and applied reactive power compensation as well as higher harmonics filters