Search results for "tecnica"
showing 10 items of 2886 documents
Different Measurement Setup Configurations for Space Charge test in Mini Cable Specimens with the PEA Method
2019
Under DC stress, the space charge accumulation is believed one of the most responsible of dielectrics ageing. For this reason, due to the increase of the HVDC transmission, a recommendation has been proposed. The latter want to introduce the space charge measure, with the PEA method, in cable specimens during the prequalification or type tests. Considering the several issues related to this kind of measures the aim of the proposed work is find a measurement setup for mini cable specimens which is able to provide a clear and clean space charge profile. Therefore, different tests have been made in this work. In particular, the length of the cable specimen, the width of the pulse electrodes, a…
A new approach to calibrate the thermal conditions in space charge measurements on HVDC mini-cables
2019
The PEA method is currently widespread used for space charge measurements in mini-cables in order to qualify the behavior of semicon-dielectric-semicon compound under electric and thermal stress. The main goal of this research is to quantitatively evaluate the relationship between the thermal boundary conditions applied to cables or mini-cables and the maximum local electric field due to the accumulated space charge. Hitherto, several research groups have obtained thermal gradients over the dielectric's radius heating the conductor by Joule effect due to an induced current. In this paper, a numerical approach is offered to calibrate the heat exchange boundary conditions to apply to a sample…
A Dynamic Electrical Scheme for the optimal reconfiguration of PV modules under non-homogeneous solar irradiation
2012
This paper presents a strategy for the maximization of the output power of photovoltaic (PV) systems under non homogeneous solar irradiation by means of automatic reconfiguration of the PV arrays layout. The innovation of the proposed approach is the employment of a simple Dynamic Electrical Scheme (DES), allowing a large number of possible modules interconnection, to be installed between the PV generator and the inverter. The models of the PV generator and of the DES have been realized and simulated with Simulink (Dynamic System Simulation for MATLAB). The attained experimental results appear to be quite interesting in terms of the attainable benefit in power and thus energy terms. The lim…
Influenza del coefficiente di poisson sul comportamento in compressione di colonne composte acciaio-calcestruzzo a sezione circolare
2009
In the paper an analytical model able to predict the whole compressive response of stub CFT subjected to uniaxial compression is presented and discussed. Cases examined re-ferred to member with circular cross-section having length 400 mm and diameter ranging be-tween 88.9 and 457 mm and wall thickness between 6 and 8 mm. Two steel grades of 275 and 460 MPa yielding stress were examined and four concrete grades were investigated (20, 28, 40 and 45 MPa). The proposed model take into account of the variable confined pressures exercised by steel wall on concrete core and of the biaxial state of stresses induced in steel wall. The model was verified both in term of load-shortening curves with da…
On the volumetric response of a compacted clay subjected to wetting and drying cycles
2009
Experimental evidence on the volumetric response of a compacted clay was collected in controlled suction oedometric tests, with the aim to assess the volumetric response of this soil when subjected to wetting and drying cycles. The overall soil behaviour seems mainly to depend on the double structural arrangement observed in the compacted specimens. Selected results are presented and discussed focusing on the influence of the stress history on the volumetric response. Test results are simulated by a double-structure suction-dependent elasto-plastic constitutive model, in which the mechanical response is related to micro and macrostructural deformations and their mutual interactions. The pro…
RC Columns Strengthened with Steel Angles and Battens: Experimental Results and Design Procedure
2013
In this paper, an analytical model for the design of axially loaded strengthened RC columns with steel angles and battens is presented. Cases of directly loaded and not directly loaded steel angles are considered. The model considers the contribution in confinement pressures caused by transverse battens and steel angles and the contribution in terms of the load-carrying capacity of steel angles subjected to axial force and the bending moment. An experimental investigation on the compressive behavior of eight short, confined, RC columns externally strengthened with steel angles and steel battens with various pitches was carried out, and has been utilized as support for the analytical model. …
Caratterizzazione geotecnica del comporportamentodi una grande frana in argille varicolori in Sicilia
2014
Si illustrano le misure degli spostamenti e delle pressioni neutre raccolte in un paio d’anni di osservazione del comportamento di un esteso corpo di frana in una formazione di argille varicolori in Sicilia. L’analisi delle misure raccolte indica che la riattivazione riguarda zone distinte del corpo di frana, nelle quali gli spostamenti si sviluppano con velocità e direzioni differenti. L’evoluzione degli spostamenti è manifestamente dipendente dalle condizioni climatiche, dal momento che essi aumentano al crescere delle pressioni interstiziali, a loro volta regolate dalle piogge, e rallentano nella stagione secca, spesso senza annullarsi del tutto. Analisi a ritroso effettuate in una delle…
MONTAGNE. CRISI DI GIUDIZIO E PROSPETTIVA
2012
Un'armatura territoriale di insediamenti numerosi a presidio della montagna, già robustamente strutturati e in sintonia con la natura del territorio, entra adesso in crisi. Quali strategie, e su quali piani, occorre mettere in campo per frenare e invertire la rotta del calo demografico e dell'abbandono?
Design and Performance Evaluation of a High Power-Density EMI Filter for PWM Inverter-Fed Induction-Motor Drives
2016
This paper presents the design of an electromagnetic interference (EMI) filter for a low-voltage high-current induction-motor drives supplied by dc power grids. In order to effectively design the EMI filter, a suitable common-mode/differential-mode (CM/DM) separation technique has been used. Due to the high operating currents, the software-based separation technique using time-domain measurements has been applied. The proposed technique allows the CM and DM sections of the EMI filter to be properly selected in a more economical way, i.e., without the need of a dedicated hardware or costly radio frequency (RF) instrumentation. The design has been done according to a power-density criterion. …
Genome-wide analysis of Italian sheep diversity reveals a strong geographic pattern and cryptic relationships between breeds
2014
Summary Italy counts several sheep breeds, arisen over centuries as a consequence of ancient and recent genetic and demographic events. To finely reconstruct genetic structure and relationships between Italian sheep, 496 subjects from 19 breeds were typed at 50K single nucleotide polymorphism loci. A subset of foreign breeds from the Sheep HapMap dataset was also included in the analyses. Genetic distances (as visualized either in a network or in a multidimensional scaling analysis of identical by state distances) closely reflected geographic proximity between breeds, with a clear north–south gradient, likely because of high levels of past gene flow and admixture all along the peninsula. Sa…