1,721,701 research outputs found
Descrizione del GIS/database implementato: sito di Portoscuso
Full text linkUna delle attività previste nella Fase II del progetto riguardava la costruzione di un database e di un GIS per i dati dei due siti selezionati nella Fase I: Oristano e Portoscuso [Muscas e Cau, 2000, Muscas et al., 2000]. Per il sito di Oristano tale attività è stata realizzata nella Fase II, mentre il ritardo con cui sono stati reperiti i dati relativi al sito di Portoscuso ha comportato lo slittamento di questo lavoro alla Fase III.
Nel presente rapporto viene descritta l’implementazione del GIS/database del sito di Portoscuso. Anche per il sito di Portoscuso, come per Oristano, gli applicativi GIS utilizzati sono stati: ArcInfo e ArcView, entrambi della ESRI [Muscas e Cau, 2000]. In particolare ArcInfo è stato utilizzato per la correzione degli errori, costruzione della topologia e creazione ex novo di nuovi livelli informativi. Il GIS realizzato è stato invece organizzato in un progetto Arcview
Power quality monitoring in modern electric distribution systems
No full textIn electric power systems, there may be disturbances in the supply voltage and the load current drawn by a user. These disturbances happen when the frequency and amplitude are not equal to their corresponding nominal values, when there are non-sinusoidal waveforms, and when there is the presence of negative and zero-sequence components in three-phase systems. Power quality (PQ) is a generic expression used to characterize the disturbances. This paper offers an overview of the methods and instruments currently used in PQ measurements and some research activity to improve the
Dizionarietto zoologico sardo-italiano
No full textCagliari : Tip. Muscas di P. Valdes, 1897
https://galileodiscovery.unipd.it/discovery/fulldisplay?context=L&vid=39UPD_INST:VU1&search_scope=MyInst_and_CI&tab=Everything&docid=alma99000049579020604
Assessment of electric power quality: indices for identifying disturbing loads
No full textThe study aimed at defining parameters capable of assessing, in terms of distortion and unbalance, the quality
of the electric power drawn by the customer: Taking as a starting point the advantages and limitations of the
methods proposed so far in the literature, two new indices are introduced, useful for quantifying the disturbing
characteristics of a load. The efficiency of these indices has been assessed by computer simulations to assess
the applicability of the method to three-wire and four-wire three-phase systems in many realistic situations
A space vector based approach for synchrophasor measurement
No full textThis paper proposes a simple technique to estimate the positive sequence synchrophasor and the frequency of three-phase voltages or currents in power systems. The approach is based on the space vector transformation using a reference frame which rotates at the rated angular frequency ω0 of the power system. All the frequency components are shifted by ω0, so that the positive sequence phasor appear as a very low frequency term. The frequency shift also decreases the ratio between the frequency of the positive sequence phasor and those of the disturbances, so that they can be rejected by using a simple IIR filter thus requiring low computational effort. Then, the magnitude and phase of the phasor as well as its frequency can be easily estimated through an ordinary least square optimization. A proper tuning of the parameters allows the approach to comply with P-class or M-class requirements of the standard IEEE C37.118.1
Influence of sustainable control methods on selected life-history parameters of Planococcus ficus (Hemiptera: Pseudococcidae)
Full text linkPlanococcus ficusis a key pest in the most important grape-growing regions. Its effective chemical control is difficult to achieve owing to its biotic potential and concealed habit. In addition, insecticide applications represent a threat for environment and human health. In this PhD thesis, alternative control techniques to reduceP. ficuspopulations were evaluated. Specifically, the effects of different cover crop management systems as well as of increasing nitrogen fertilization regimes on the life-history parameters of the mealybug were investigated in a commercial vineyard and in a screenhouse, respectively. Moreover, laboratory and field trials were carried out to determine the influence of delayed mating and mating disruption on biological and demographic parameters ofP. ficus. Finally, the potential of the parasitoid Leptomastix dactylopii as a biological control agent against the vine mealybug was evaluated under laboratory conditions. The results obtained show that both ground covers and nitrogen fertilization affect developmental and reproductive parameters of the mealybug. Mating disruption reduced and delayed matings, whereasL. dactylopii successfully developed onP. ficusand showed a performance comparable to that of its preferred host, Planococcus citri (Risso). The results indicate that accurate cultural practices and environmentally friendly control methods may effectively integrate the conventional chemical control againstP. ficus
Comparative analysis between active and passive current transducers in sinusoidal and distorted conditions
No full textHysteresis and eddy currents compensation in current transformers
No full textIn the paper a digital technique for improving the accuracy of instrument current transformers is presented. Since the exciting current can be considered as the main error source, its evaluation can allow the compensation of its detrimental effects to be obtained. The exciting current required by the transformer in every kind of steady state operation can be determined by simply acquiring the secondary current, provided that the examined CT has been preliminarily identified. A simple scalar model for the CTs magnetic core, taking into account saturation as well as hysteresis and eddy currents phenomena, has been implemented in a software compensation routine. This allows us to improve the accuracy in the reproduction of the primary current, in the case of both sinusoidal and distorted current waveforms (provided that DC components are not present).
Many experimental tests, under different practical situations, have been performed. The results clearly show that the proposed technique is able to significantly reduce, in comparison with traditional methods, the errors introduced by current transformers
On the selection of the "best" test waveform for calibration electrical instruments under nonsinusoidal conditions
No full textComparative analysis between active and passive current transducers in sinusoidal and distorted conditions
No full textCurrent measurements are a critical item in the monitoring of modern electrical power plants, since the quantities to be measured often show high harmonic content. The current transducers should therefore guarantee a good accuracy even when they operate with distorted waveforms. In this paper, the behavior of some devices commonly used for current measurement is examined, considering either sinusoidal or distorted conditions. Traditional current transformers, transducers based on the Hall effect, and resistive shunts combined with isolation amplifiers have been considered. The comparison is performed by evaluating a synthetic error index, called composite error, which allows all the main causes of uncertainty (amplitude errors, time shifts, and distortion) to be taken into account.
The proposed investigation aims to find out the main characteristics that make each transducer suitable or unsuitable in different practical situations
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