Analysis of capacitance to ground formulas for different high-voltage electrodes

Stray capacitance can seriously affect the behavior of high-voltage devices, including voltage dividers, insulator strings, modular power supplies, or measuring instruments, among others. Therefore its effects must be considered when designing high-voltage projects and tests. Due to the difficulty in measuring the effects of stray capacitance, there is a lack of available experimental data. Therefore, for engineers and researchers there is a need to revise and update the available information, as well as to have useful and reliable data to estimate the stray capacitance in the initial designs. Although there are some analytical formulas to calculate the capacitance of some simple geometries, they have a limited scope. However, since such formulas can deal with different geometries and operating conditions, it is necessary to assess their consistency and applicability. This work calculates the stray capacitance to ground for geometries commonly found in high-voltage laboratories and facilities, including wires or rods of different lengths, spheres and circular rings, the latter ones being commonly applied as corona protections. This is carried out by comparing the results provided by the available analytical formulas with those obtained from finite element method (FEM) simulation, since field simulation methods allow solving such problem. The results of this work prove the suitability and flexibility of the FEM approach, because FEM models can deal with wider range of electrodes, configurations and operating conditions.Peer ReviewedPostprint (published version

Simplification and cost reduction of visual corona tests

Peer ReviewedPostprint (author's final draft

Transient thermal modelling of substation connectors by means of dimensionality reduction

This paper proposes a simple, fast and accurate simulation approach based on one-dimensional reduction and the application of the finite difference method (FDM) to determine the temperatures rise in substation connectors. The method discretizes the studied three-dimensional geometry in a finite number of one-dimensional elements or regions in which the energy rate balance is calculated. Although a one-dimensional reduction is applied, to ensure the accuracy of the proposed transient method, it takes into account the three-dimensional geometry of the analyzed system to determine for all analyzed elements and at each time step different parameters such as the incremental resistance of each element or the convective coefficient. The proposed approach allows fulfilling both accuracy and low computational burden criteria, providing similar accuracy than the three-dimensional finite element method but with much lower computational requirements. Experimental results conducted in a high-current laboratory validate the accuracy and effectiveness of the proposed method and its usefulness to design substation connectors and other power devices and components with an optimal thermal behavior.Postprint (published version

Comparative study of AC and positive and negative DC visual corona for sphere-plane gaps in atmospheric air

Due to the expansion of high-voltage direct current (HVDC) power systems, manufacturers of high-voltage (HV) hardware for alternating current (ac) applications are focusing their efforts towards the HVDC market. Because of the historical preponderance of ac power systems, such manufacturers have a strong background in ac corona but they need to acquire more knowledge about direct current (dc) corona. Due to the complex nature of corona, experimental data is required to describe its behavior. This work performs an experimental comparative analysis between the inception of ac corona and positive and negative dc corona. First, the sphere-plane air gap is analyzed from experimental data, and the corona inception voltages for different geometries are measured in a high-voltage laboratory. Next, the surface electric field strength is determined from finite element method simulations, since it provides valuable information about corona inception conditions. The experimental data obtained are fitted to an equation based on Peek’slaw,whichallows determining the equivalence between the visual corona surface electric field strength for ac and dc supply. Finally, additional experimental results performed on substation connectors are presented to further validate the previous results by means of commercial high-voltage hardware. The results presented in this paper could be especially valuable for high-voltage hardware manufacturers, since they allow determining the dc voltage and electric field values at which their ac products can withstand free of corona when operating in dc grids.Peer ReviewedPostprint (published version

Analysis and mitigation of stray capacitance effects in resistive high-voltage dividers

This work analyzes the effects of the parasitic or stray distributed capacitance to ground in high-voltage environments and assesses the effectiveness of different corrective actions to minimize such effects. To this end, the stray capacitance of a 130 kV RMS high-voltage resistive divider is studied because it can severely influence the behavior of such devices when operating under alternating current or transient conditions. The stray capacitance is calculated by means of three-dimensional finite element analysis (FEA) simulations. Different laboratory experiments under direct current (DC) and alternating current (AC) supply are conducted to corroborate the theoretical findings, and different possibilities to mitigate stray capacitance effects are analyzed and discussed. The effects of the capacitance are important in applications, such as large electrical machines including transformers, motors, and generators or in high-voltage applications involving voltage dividers, conductors or insulator strings, among others. The paper also proves the usefulness of FEA simulations in predicting the stray capacitance, since they can deal with a wide range of configurations and allow determining the effectiveness of different corrective configurations.Peer ReviewedPostprint (author's final draft

Qué ves cuando las ves: Las mafias italianas en los paisajes lingüísticos de la Ciudad de Buenos Aires

En este trabajo interrogamos las referencias visuales a las mafias italianas en los paisajes lingüísticos en la Ciudad de Buenos Aires a través de un enfoque discursivo y etnográfico. Mediante el análisis de los rasgos temáticos, retóricos y enunciativos que diversas superficies textuales que circulan en espacios presenciales y/o virtuales presentan, así como de ciertas ausencias significativas, buscamos problematizar el sentido común visual que modela nuestras percepciones, tanto individuales como colectivas, sobre el fenómeno mafioso. Por la proliferación y la tendencia a la espectacularización que asumen las formas de visibilización analizadas redundarían en un no ver nada, que tiende a naturalizar una interpretación poco informada, cuando no abiertamente sesgada, que paradójicamente oculta más de lo que muestra.In this article we question the visual references to the Italian mafias in the linguistic landscapes in the City of Buenos Aires, through a discursive and ethnographic approach. By analyzing the thematic, rhetorical and enunciative features deployed by the textual surfaces that circulate in public and/or virtual spaces, as well as some significant absences, we aim at problematizing the visual common sense that shapes our individual and collective perceptions on mafia. Due to the proliferation of those visualities and their tendency to spectacularization of the phenomenon of mafias, they would result in a «gaslighting» which tends to naturalize a poorly informed (if not openly biased) interpretation, which paradoxically hides more than what it shows.Fil: Balsas, María Soledad. Universidad Nacional de la Matanza. Departamento de Derecho y Ciencia Politica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Capelli, Francesca. Universidad Nacional de la Matanza. Departamento de Derecho y Ciencia Politica; Argentin

First report outside Eastern Europe of West Nile virus lineage 2 related to the Volgograd 2007 strain, northeastern Italy, 2014

open11noWest Nile virus (WNV) is a Flavivirus transmitted to vertebrate hosts by mosquitoes, maintained in nature through an enzootic bird-mosquito cycle. In Europe the virus became of major public health and veterinary concern in the 1990s. In Italy, WNV re-emerged in 2008, ten years after the previous outbreak and is currently endemic in many areas of the country. In particular, the northeastern part of Italy experience continuous viral circulation, with human outbreaks caused by different genovariants of WNV lineage 1, Western-European and Mediterranean subcluster, and WNV lineage 2, Hungarian clade. Alongside the WNV National Surveillance Program that has been in place since 2002, regional surveillance plans were implemented after 2008 targeting mosquitoes, animals and humans.openRavagnan, Silvia; Montarsi, Fabrizio; Cazzin, Stefania; Porcellato, Elena; Russo, Francesca; Palei, Manlio; Monne, Isabella; Savini, Giovanni; Marangon, Stefano; Barzon, Luisa; Capelli, GioiaRavagnan, Silvia; Montarsi, Fabrizio; Cazzin, Stefania; Porcellato, Elena; Russo, Francesca; Palei, Manlio; Monne, Isabella; Savini, Giovanni; Marangon, Stefano; Barzon, Luisa; Capelli, Gioi

A genetic algorithm optimized fractal model to predict the constriction resistance from surface roughness measurements

The electrical contact resistance greatly influences the thermal behavior of substation connectors and other electrical equipment. During the design stage of such electrical devices, it is essential to accurately predict the contact resistance to achieve an optimal thermal behavior, thus ensuring contact stability and extended service life. This paper develops a genetic algorithm (GA) approach to determine the optimal values of the parameters of a fractal model of rough surfaces to accurately predict the measured value of the surface roughness. This GA-optimized fractal model provides an accurate prediction of the contact resistance when the electrical and mechanical properties of the contacting materials, surface roughness, contact pressure, and apparent area of contact are known. Experimental results corroborate the usefulness and accuracy of the proposed approach. Although the proposed model has been validated for substation connectors, it can also be applied in the design stage of many other electrical equipments.Postprint (author's final draft

Feasibility study on thermal energy harvesting for low powered electronics in high-voltage substations

Electronic devices combining sensors, wireless communications, and data processing capability allow easing predictive maintenance tasks in many applications. This paper applies this approach in power connectors for high-voltage electrical substations, which are transformed into smart connectors. Such connectors are often linked to tubular aluminum bus bars, whose temperature increases due to the Joule losses generated by the combined effect of the electrical resistance and the electric current. Since the human intervention must be minimized, an energy harvesting system is required to supply the electronics of the smart connectors. To this end, a thermoelectric module (TEM) is used to transform heat power into electrical power. Since the voltage provided by the TEM is very low, a suitable power converter is used to supply the electronics of the smart connector. This work analyzes the effect of the various parameters that affect the power generated by the TEM when placed on a substation bus bar. Experiments have been carried out by placing a TEM with different configurations on different types of bus bars for diverse operating conditions.Peer ReviewedPostprint (published version

Low-cost online contact resistance measurement of power connectors to ease predictive maintenance

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting /republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other worksWith the increasing use of sensors and wireless communication systems, predictive maintenance is acquiring more and more importance to assess the condition of in-service equipment. Predictive maintenance presents promising cost savings, as it allows minimizing unscheduled power systems faults, which can have very costly and catastrophic consequences. Early stage detection of power system failure requires acquiring, monitoring, and periodically analyzing the condition of the elements involved, such as high-voltage power connectors, since they are critical devices which are often located in key points of power systems. This paper proposes a low-cost online system to determine the contact resistance of high-voltage direct current (dc) and alternating current (ac) power connectors, to determine their health condition in order to apply a predictive maintenance plan. The contact resistance is considered as a reliable indicator of the connector's health condition. However, it cannot be directly measured, and the applied strategy differs between dc and ac power systems. The experimental results show a maximum uncertainty of 4.5%, thus proving the accuracy and feasibility of the approach presented in this paper, since the proposed limit of acceptable resistance increase is 20%. This approach can also be applied to many other power systems' elements.Postprint (author's final draft