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    Wyświetlanie 1-7 z 7
    Tytuł:
    Modelling of synchronous generators for the analysis of frequency transients above 1 Hz/s
    Autorzy:
    Assenkamp, Alf
    Powiązania:
    https://bibliotekanauki.pl/articles/2135729.pdf
    Data publikacji:
    2022
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    control system
    distributed energy systems
    frequency support
    generator model
    RoCoF
    synchronous generators
    synchronous machines
    Opis:
    Large synchronous generators are of high importance for the stability of power systems. They generate the frequency of the system and stabilize it in case of severe grid faults like trips of large in-feeders or loads. In distributed energy systems, in-feed via inverters will replace this generation in large parts. Modern inverters are capable of supporting grid frequency during severe faults by different means on the one hand. On the other hand, higher Rates of Change of Frequency (RoCoF) after incidents need to be accustomed by future systems. To be able to analyse the RoCoF withstand capability of synchronous or induction generators, suitable models need to be developed. Especially the control and excitation system model need enhancements compared to models proposed in standards like IEEE Std 421.5. This paper elaborates on the necessary modelling depth and validates the approach with example results.
    Źródło:
    Archives of Electrical Engineering; 2022, 71, 3; 687--700
    1427-4221
    2300-2506
    Pojawia się w:
    Archives of Electrical Engineering
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The dual of Besov spaces on fractals
    Autorzy:
    Jonsson, Alf
    Wallin, Hans
    Powiązania:
    https://bibliotekanauki.pl/articles/1289891.pdf
    Data publikacji:
    1995
    Wydawca:
    Polska Akademia Nauk. Instytut Matematyczny PAN
    Opis:
    For certain classes of fractal subsets F of $ℝ^n$, the Besov spaces $B_α^{p,q}(F)$ have been studied for α > 0 and 1 ≤ p,q ≤ ∞. In this paper the Besov spaces $B_α^{p,q}(F)$ are introduced for α < 0, and it is shown that the dual of $B_α^{p,q}(F)$ is $B_{-α}^{p',q'}(F), α ≠ 0, 1 < p,q < ∞, where 1/p + 1/p' = 1, 1/q + 1/q' = 1.
    Źródło:
    Studia Mathematica; 1994-1995, 112, 3; 285-300
    0039-3223
    Pojawia się w:
    Studia Mathematica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Capability of synchronous machines to ride through events with high ROCOF
    Autorzy:
    Assenkamp, Alf
    Kreischer, Christian
    Kulig, Stefan
    Powiązania:
    https://bibliotekanauki.pl/articles/140451.pdf
    Data publikacji:
    2019
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    ROCOF
    under-excitation protection
    turbo-generator
    low-inertia grids
    Opis:
    The transition of power grids to implement large amounts of nonsynchronous renewables reduces the inertia in the power system. Therefore, the rate of change of fre- quency (ROCOF) after a fault of given energy is higher in low inertia grids than in grids with mainly synchronous machines operating. Standard faults for the design of existing synchronous machines assume fixed frequency grids, in which an electrically close fault happens. It is not tested, if the machines can ride through transient disturbances with high ROCOF. For ROCOF values of up to 1 Hz/s as foreseen for the upcoming grid code of the Republic of Ireland and up to 2 Hz/s for Northern Ireland, a thorough verification, if generators are capable to ride through such events is necessary. For this study, ROCOF frequency traces provided by the transmission system operators (TSOs) of Ireland were first benchmarked with a full-grid model and in a second step impressed on a model of generators connected to the power grid via a step-up transformer to study transient stability and nonlinear response of the generator. This paper focusses on the ability of nine different synchronous machines to stay connected to the transmission system during severe ROCOF events without losing synchronism.
    Źródło:
    Archives of Electrical Engineering; 2019, 68, 2; 325-339
    1427-4221
    2300-2506
    Pojawia się w:
    Archives of Electrical Engineering
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Real or Not, Doesn’t Matter, As Long As You Are Hot: Exploring the Perceived Credibility of an Instagram Virtual Influencer
    Autorzy:
    Awdziej, Marcin
    Plata-Alf, Dagmara
    Tkaczyk, Jolanta
    Powiązania:
    https://bibliotekanauki.pl/chapters/2049048.pdf
    Data publikacji:
    2022-05-15
    Wydawca:
    Akademia Leona Koźmińskiego w Warszawie
    Opis:
    The following study aimed to check whether or not the knowledge regarding the fact that an influencer is a fictional/virtual character affects their perceived credibility. The research is of a pioneering nature, as the virtual influencer phenomenon is just developing. When conducting the study, we wanted to find out whether or not the knowledge regarding the virtual influencer differentiates the assessment of their credibility in relation to its three dimensions: attractiveness, trust towards them and their expertise. In order to meet the objectives of the study, our own experimental research was conducted (246 management students were recruited for the study). The research findings confirm that when it comes to assessing the source credibility, it is irrelevant whether recipients know (or not) if the character that they come in contact with is virtual or real.
    Źródło:
    Extending Boundaries.The Impact of the Digital World on Consumers and Marketing; 33-46
    9788366502062
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Petrology of nepheline syenite pegmatites in the Oslo Rift, Norway: Zr and Ti mineral assemblages in miaskitic and agpaitic pegmatites in the Larvik Plutonic Complex
    Autorzy:
    Andersen, Tom
    Erambert, Muriel
    Larsen, Alf Olaf
    Selbekk, Rune S.
    Powiązania:
    https://bibliotekanauki.pl/articles/127623.pdf
    Data publikacji:
    2013
    Wydawca:
    Polskie Towarzystwo Mineralogiczne
    Tematy:
    alkaline rocks
    nepheline syenite pegmatite
    agpaitic rocks
    zirconium minerals
    titanium minerals
    Oslo Rif
    Opis:
    Agpaitic nepheline syenites have complex, Na-Ca-Zr-Ti minerals as the main hosts for zirconium and titanium, rather than zircon and titanite, which are characteristic for miaskitic rocks. The transition from a miaskitic to an agpaitic crystallization regime in silica-undersaturated magma has traditionally been related to increasing peralkalinity of the magma, but halogen and water contents are also important parameters. The Larvik Plutonic Complex (LPC) in the Permian Oslo Rift, Norway consists of intrusions of hypersolvus monzonite (larvikite), nepheline monzonite (lardalite) and nepheline syenite. Pegmatites ranging in composition from miaskitic syenite with or without nepheline to mildly agpaitic nepheline syenite are the latest products of magmatic differentiation in the complex. The pegmatites can be grouped in (at least) four distinct suites from their magmatic Ti and Zr silicate mineral assemblages. Semiquantitative petrogenetic grids for pegmatites in log aNa2SiO5 – log aH2O – log aHF space can be constructed using information on the composition and distribution of minerals in the pegmatites, including the Zr-rich minerals zircon, parakeldyshite, eudialyte, låvenite, wöhlerite, rosenbuschite, hiortdahlite and catapleiite, and the Ti-dominated minerals aenigmatite, zirconolite (polymignite), astrophyllite, lorenzenite, titanite, mosandrite and rinkite. The chemographic analysis indicates that although increasing peralkalinity of the residual magma (given by the activity of the Na2Si2O5 or Nds component) is an important driving force for the miaskitic to agpaitic transition, water, fluoride (HF) and chloride (HCl) activity controls the actual mineral assemblages forming during crystallization of the residual magmas. The most distinctive mineral in the miaskitic pegmatites is zirconolite. At low fluoride activity, parakeldyshite, lorenzenite and wöhlerite are stable in mildly agpaitic systems. High fluorine (or HF) activity favours minerals such as låvenite, hiortdahlite, rosenbuschite and rinkite, and elevated water activity mosandrite and catapleiite. Astrophyllite and aenigmatite are stable over large ranges of Nds activity, at intermediate and low water activities, respectively.
    Źródło:
    Mineralogia; 2013, 44, 3/4; 61-98
    1899-8291
    1899-8526
    Pojawia się w:
    Mineralogia
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-7 z 7

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