Frequency response testing of zero-sequence current transformers for mining ground fault protection relays

W polskim górnictwie węgla sieci dystrybucyjne średniego napięcia działają z izolowanym punktem neutralnym. Przekładniki prądowe o zerowej sekwencji są podstawowymi czujnikami, które generują sygnały wejściowe dla przekaźników zabezpieczających przed zwarciem doziemnym. W literaturze problem analizy odpowiedzi częstotliwościowej różnych typów przekładników prądowych był wielokrotnie badany, np. [1] [2], ale jak dotąd nie dotyczy przekładników prądowych o zerowej sekwencji. W ramach pracy przetestowano dwa typy przekładników prądowych o zerowej sekwencji w zakresie od 0,1 Hz do 100 kHz. Przeanalizowano zarówno zmianę stosunku prądu, jak i przesunięcie kątowe między prądem wtórnym transformatora a całkowitym prądem pierwotnym

Frequency response testing of zero-sequence current transformers for mining ground fault protection relays

W polskim górnictwie węgla sieci dystrybucyjne średniego napięcia działają z izolowanym punktem neutralnym. Przekładniki prądowe o zerowej sekwencji są podstawowymi czujnikami, które generują sygnały wejściowe dla przekaźników zabezpieczających przed zwarciem doziemnym. W literaturze problem analizy odpowiedzi częstotliwościowej różnych typów przekładników prądowych był wielokrotnie badany, np. [1] [2], ale jak dotąd nie dotyczy przekładników prądowych o zerowej sekwencji. W ramach pracy przetestowano dwa typy przekładników prądowych o zerowej sekwencji w zakresie od 0,1 Hz do 100 kHz. Przeanalizowano zarówno zmianę stosunku prądu, jak i przesunięcie kątowe między prądem wtórnym transformatora a całkowitym prądem pierwotnym

Comparative Analysis of European and American Standards for Maximum Fault Current Calculations on Medium Voltage Mine Power Networks

Continuous work of mine supplying electrical power networks is a prerequisite to ensure the continuity of the mining process and the safety of its crew. The choice of the appropriate method for calculating short-circuit currents is therefore particularly important in terms of both economic and safety considerations. The methods used are always a compromise between the accuracy of obtained results, computational complexity and availability of data necessary for calculations. The study compares the two most common standards for calculating maximum short-circuit currents - IEC and ANSI/IEEE. The study presents the most important interrelationships that describe the characteristic magnitudes of short-circuit currents for IEC standard and for the ANSI/IEEE standard. This comparison has been done on the basis of novel calculations performed on a typical MV mine network. The results of the calculations showed a high contiguity of the results despite the different methodological assumptions for rotating machines modelling and for determining the equivalent value of resistance and reactance of the network where the fault occurred, and the extent of assumed simplifications

Transcription regulation of restriction-modification system Esp1396I

The convergently transcribed restriction (R) and methylase (M) genes of the Restriction–Modification system Esp1396I are tightly regulated by a controller (C) protein that forms part of the CR operon. We have mapped the transcriptional start sites from each promoter and examined the regulatory role of C.Esp1396I in vivo and in vitro. C-protein binding at the CR and M promoters was analyzed by DNA footprinting and a range of biophysical techniques. The distal and proximal C-protein binding sites at the CR promoter are responsible for activation and repression, respectively. In contrast, a C-protein dimer binds to a single site at the M-promoter to repress the gene, with an affinity much greater than for the CR promoter. Thus, during establishment of the system in a naïve host, the activity of the M promoter is turned off early, preventing excessive synthesis of methylase. Mutational analysis of promoter binding sites reveals that the tetranucleotide inverted repeats long believed to be important for C-protein binding to DNA are less significant than previously thought. Instead, symmetry-related elements outside of these repeats appear to be critical for the interaction and are discussed in terms of the recent crystal structure of C.Esp139I bound to the CR promoter

The role of alkane coordination in C–H bond cleavage at a Pt(II) center

The rates of CFormula H bond activation for various alkanes by [(N–N)Pt(Me)(TFEd3)]+ (N Formula N = ArFormula NFormula C(Me)Formula C(Me)Formula NFormula Ar; Ar = 3,5-di-tert-butylphenyl; TFE-d3 = CF3CD2OD) were studied. Both linear and cyclic alkanes give the corresponding alkene-hydride cation [(N–N)Pt(H)(alkene)]+ via (i) rate determining alkane coordination to form a CFormula H {sigma} complex, (ii) oxidative cleavage of the coordinated CFormula H bond to give a platinum(IV) alkyl-methyl-hydride intermediate, (iii) reductive coupling to generate a methane {sigma} complex, (iv) dissociation of methane, and (v) beta-H elimination to form the observed product. Second-order rate constants for cycloalkane activation (CnH2n), are proportional to the size of the ring (k ~ n). For cyclohexane, the deuterium kinetic isotope effect (kH/kD) of 1.28 (5) is consistent with the proposed rate determining alkane coordination to form a CFormula H {sigma} complex. Statistical scrambling of the five hydrogens of the Pt-methyl and the coordinated methylene unit, via rapid, reversible steps ii and iii, and interchange of geminal CFormula H bonds of the methane and cyclohexane CFormula H {sigma} adducts, is observed before loss of methane

Catalytic Alcoholysis of Tetramethylsilane via Pt-Mediated C−H Bond Activation

Tetramethylsilane reacts with 2,2,2-trifluoroethanol (TFE) in the presence of a cationic platinum(II) catalyst [(NN)PtMe(TFE)]+ (NN = 1,2-bis(3,5-dimethylphenylimino)butane). Catalytic Si−C bond heterolysis results in the formation of the trimethylsilyl ether, Me_3SiOCH_2CF_3, accompanied by liberation of one equivalent of methane. Preliminary experiments suggest that a rate-determining C−H bond activation precedes rapid attack by solvent at silicon to yield the silyl ether product and regenerate the active platinum methyl cation

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Ve své nynější tvorbě - diplomové práci - se zabývám vytvořením co nejefektivnějšího orientačního systému v reálném prostoru Gynekologicko-porodnické kliniky VFN v Praze. Tato práce je jakýmsi završením mého studia na Fakultě designu a umění Ladislava Sutnara Západočeské univerzity v Plzni. Pokusil jsem se v ní zhodnotit své dosavadní znalosti i zkušenosti z oboru Grafický design a 3D design.ObhájenoIn my current work - diploma thesis - I deal with the creation of the most effective orientation system in the real space of the Gynecology and Obstetrics Clinic of the General Hospital in Prague. This work is a kind of completion of my studies at the Faculty of Design and Art of Ladislav Sutnar University of West Bohemia in Pilsen. I tried to evaluate my current knowledge and experience in the field of Graphic Design and 3D Design

Transcription regulation of restriction-modification system Esp1396I

The convergently transcribed restriction (R) and methylase (M) genes of the Restriction–Modification system Esp1396I are tightly regulated by a controller (C) protein that forms part of the CR operon. We have mapped the transcriptional start sites from each promoter and examined the regulatory role of C.Esp1396I in vivo and in vitro. C-protein binding at the CR and M promoters was analyzed by DNA footprinting and a range of biophysical techniques. The distal and proximal C-protein binding sites at the CR promoter are responsible for activation and repression, respectively. In contrast, a C-protein dimer binds to a single site at the M-promoter to repress the gene, with an affinity much greater than for the CR promoter. Thus, during establishment of the system in a naïve host, the activity of the M promoter is turned off early, preventing excessive synthesis of methylase. Mutational analysis of promoter binding sites reveals that the tetranucleotide inverted repeats long believed to be important for C-protein binding to DNA are less significant than previously thought. Instead, symmetry-related elements outside of these repeats appear to be critical for the interaction and are discussed in terms of the recent crystal structure of C.Esp139I bound to the CR promoter