1,721,082 research outputs found
On the Distribution of Lightning Current among Interconnected Grounding Systems in Medium Voltage Grids
Full text linkThis paper presents the results of a first investigation on the effects of lightning stroke on medium voltage installations’ grounding systems, interconnected with the metal shields of the Medium Voltage (MV) distribution grid cables or with bare buried copper ropes. The study enables us to evaluate the distribution of the lightning current among interconnected ground electrodes in order to estimate if the interconnection, usually created to reduce ground potential rise during a single-line-to-ground fault, can give place to dangerous situations far from the installation hit by the lightning stroke. Four different case studies of direct lightning stroke are presented and discussed: (1) two secondary substations interconnected by the cables’ shields; (2) two secondary substations interconnected by a bare buried conductor; (3) a high voltage/medium voltage station connected with a secondary substation by the medium voltage cables’ shields; (4) a high voltage/medium voltage station connected with a secondary substation by a bare buried conductor. The results of the simulations show that a higher peak-lowering action on the lighting-stroke current occurs due to the use of bare conductors as interconnection elements in comparison to the cables’ shields
Evaluation of the optimal renewable electricity mix for Lampedusa island: The adoption of a technical and economical methodology
Full text linkWorldwide, the majority of small islands not connected to the main grid is still dependent on fossil fuels. From an economic and environmental point of view, this condition is no more sustainable given the high costs for electricity generation and the high level of pollutant emissions. Furthermore, the dependence on fossil fuel represents a risk for the security of the supply of several small developing Countries since they are obliged to import those resources from foreign Countries. The introduction of renewable energy sources in small islands represents a valid solution to solve these problems. In this context, the paper investigates the case of Lampedusa, a small Italian island whose electrical power system is currently totally supplied by diesel power plants. In the paper, the authors investigate the transition toward an economically and technically feasible generating system based on solar, wind and sea wave plants, to achieve specific targets of decarbonization. Commercial technologies are adopted for the exploitation of solar and wind sources, while sea wave plants are based on an innovative device, currently under development at the University of Palermo. A mathematical model is proposed to find the optimal energy mix that can satisfy a fixed share of annual electricity production from renewables, considering the Levelized Cost of Electricity. Finally, the proposed solution is analyzed in order to check the dynamic stability of the power system. The paper shows that, for replacing the 40% of the current electricity demand of Lampedusa, an optimal energy mix comprising 1509 kW from photovoltaic plants, 2100 kW from wind turbines and 640 kW from wave energy converters is needed. In this way, the actualized cost for the electricity production could be reduced to 0.260 €/kWh from the current value of 0.282 €/kWh
Fault Diagnosis On Photovoltaic Modules By Thermographic Analysis With Drone Support
No full textAs part of the energy transition needed to combat climate change, photovoltaic systems are taking on an increasingly important role, with a considerable rise in the number of systems installed. This makes it necessary to find quick and reliable ways of performing inspections aimed at ensuring their proper operation, with the highest possible level of production. The amount of electricity that such plants manage to provide can, in fact, decrease due to simple shading, for the presence of deposits and debris on the modules, or, in the worst case scenario, due to a fault. The techniques used to carry out monitoring and surveying the operating status of a plant can be different. The most commonly used methods are visual inspection, I-V characteristic survey, and thermographic inspection. The latter, when carried out with the help of drones, allows inspections to be realized in a very short time and is the subject of study in this paper, in which an inspection carried out at a 999 kWp photovoltaic plant installed in Sicily and the use of the PSO algorithm to identify the optimal position of the drone are described
Grid Stability Improvement Using Synthetic Inertia by Battery Energy Storage Systems in Small Islands
No full textIn this paper, the synthetic inertia need of the small island of Pantelleria in the Mediterranean Sea is assessed. Firstly, the optimal renewable energy mix able to minimize the Levelized Cost of Energy for the generation system of the island is evaluated, considering the yearly load demand and the characteristics of the local natural resources. The optimal energy mix introduces in the island a quota of power generation with static power converters interfaced to the grid that could jeopardize the security of the system if not suitably controlled. Therefore, the inherent inertial response of the diesel generators of the system is calculated hour by hour for each month of one year, considering the new schedule of the generators for various cases characterized by different percentages of production from the optimum renewable energy mix. Finally, the rated power and capacity of a battery energy storage system is calculated in order to compensate the reduction of the inertial response in the power system thanks to a suitable synthetic inertia control. The calculation is done by considering the maximum allowed frequency nadir in case of a disturbance. For each scenario, the maximum disturbance is also assessed with and without synthetic inertia. The results are compared with those obtained in a previous study on the same island where batteries were used for different purposes
Performance Optimization of a Residential Microgrid Balancing Economic and Energy Issues
Full text linkMicrogrids are currently seen as the future of power generation and distribution systems. This paper illustrates the optimization of the operation stage of the main components of a microgrid supplying the final demands for electricity, heating and cooling of a residential district. The optimization was performed with reference to four seasonal standard days and optimizing the operating costs or the primary energy use. The electricity production from a photovoltaic system and a combined heat and power (CHP) satisfies the local electricity demand. The heating demand is fulfilled with a gas-fired boiler, a CHP, a solar thermal collector and a reversible heat pump that is employed also for the cooling demand together with an absorbtion chiller. Moreover, a storage system for each demand is also included. The optimization model is formulated through a mixed-integer linear programming approach and implemented in MATLAB. The results show a reduction of costs ranging between about two and four times and a reduction of primary energy use between about two and five times with respect to the traditional scenario (electricity and gas from the grid)
Time Series Bootstrap for Renewable Energy Analysis in Power Grid Optimization
No full textAs renewable energy becomes an increasingly important factor in electricity generation, accounting for the variability of its primary sources (such as wind speed and solar irradiation) is essential in energy grid design and power system analysis. In this context, simulating time series of renewable energy sources that reflect the characteristics of the original data helps understanding the impact of this variability on grid performances. A moving block bootstrap procedure is applied to generate time series for wind speed, solar irradiation, or temperature with hourly frequency, preserving temporal dependencies and addressing inherent seasonal trends. The approach allows simulation-based analysis of the impact of critical scenarios on different electric microgrids
On the Interconnections of HV-MV Stations to Global Grounding Systems
No full textThe interconnection of grounding systems of HV-MV stations via the armors of medium voltage cables, is herein analyzed to verify the effects on touch voltages in ground-fault conditions. The major contributions of this paper are two: the analysis of the impact of an HV ground-fault on a global grounding system (GGS), and the analysis of the parameters that may affect safety due to the interconnection between HV-MV stations and the GGS. The authors have analyzed cases when the connection of an HV-MV station to a GGS improves safety, and then may introduce hazards under ground-fault conditions. Two main issues are herein discussed: 1) the transfer of dangerous voltages to substations, due to ground-faults occurring at the HV-MV station; and 2) the reduction in the magnitude of the ground potential rise caused by ground-fault conditions at substations, due to the connection of their ground grids to the HV-MV station's grounding system. This paper, by examining various grid configurations, demonstrates that in some instances the inclusion of HV-MV stations in the GGS may reduce the level of protection against touch voltages, and that this depends on the following elements: the number of MV lines fed by the faulted station, the number of MV-LV substations per line, the value of the ground resistance of the substations, and the distance between the substations. This paper has practical relevance for both utilities distribution systems and industrial facilities supplied by the MV power grid
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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