1,720,960 research outputs found
Heatwaves and Duration of Distribution System Faults: A Comparison of Different Indexes
No full textThe temperature increase challenges both humans and infrastructures. In particular, one of the most evident phenomena is the rising of the number of high temperature periods (i.e., heat waves), whose severity, measured in terms of duration, results being higher than in the past. Heat waves affect, among others, the underground urban distribution system, with a rising of the faults of its constitutive elements (i.e., cables, cable joints and terminals). Recognizing when heat waves happen becomes hence important, for introducing new strategies for the improvement of the distribution system resilience. For this reason, this paper compares the performance of two different heat wave indicators, and calculates a covariance matrix between them and the fault duration. The results show that the Excess Heat Factor presents better performance than the Index of Heatwave, both in terms of heatwave period identification and in terms of correlation
European electricity market zone reconfiguration considering large penetration of RES
No full textL'abstract è presente nell'allegato / the abstract is in the attachmen
Statistical Analysis of Reliability in a Real Urban Distribution System
No full textUnderground cables are generally used in urban Medium Voltage systems. In the last years, the cable lines appeared to be more fragile than expected, with an increase of the number of faults, especially in the warmest periods of the year with the occurrence of heat waves. This paper, starting from actual data gathered in urban areas, aims to verify the existence of a relation between the number of faults and the temperature increase, to understand the possible limitations in using the classical reliability hypotheses to study the probability distributions of the time between faults. The results indicate the presence of critical periods with remarkable discrepancy between the empirical probability distributions and the exponential distribution used in the classical reliability analysis
Performance Assessment of Electricity Market Zones Reconfiguration: the Italian Case
No full textFrom January 2021, the configuration of the electricity market zones in Italy has changed, which prompts us to question whether modifying the existing bidding zone structure would effectively contribute to achieving the goals of enhancing competition and efficiency in the market mechanism. To assess the influence of different Italian zonal configurations on the market performance, we have devised a set of evaluation indicators that encompass various aspects. These indicators are conceived to allow the comparison among different market dispatch mechanisms such as the "pure economic dispatch"and the "network constrained dispatch with nodal representation", as well as the "network constrained dispatch with zonal representation". By comparing the two Italian bidding zone configurations existing in 2020 and 2021, respectively, the performance of such configurations is analysed and compared. The calculation results reveal that the implemented reconfiguration has yielded increased social surplus and reduced congestion costs. In contrast to that of 2020, the configuration implemented in 2021 enables enhanced market efficiency and increased market liquidity, particularly during the summer
Allowing Large Penetration of Concentrated RES in Europe and North Africa via a Hybrid HVAC-HVDC Grid
Full text linkRenewable energy sources (RESs) and electricity demand are not evenly distributed geographically across Europe. Thus, harvesting the wind energy from the north and solar energy from the south and delivering them to the demand in central Europe is a more viable solution. However, the present High-voltage alternating current (HVAC) transmission grids have been sometimes congested; thus, High-voltage direct current (HVDC) provides another possibility along the existing HVAC infrastructure. In this paper, we propose a hybrid HVAC-HVDC grid, allowing a large penetration of concentrated RES in Europe and North Africa. More specifically, the HVDC network is constructed to transfer wind and hydro electricity from northwestern Europe and solar electricity from north Africa, while the HVAC network is used to distribute electricity within each country or among adjacent areas. To quantitatively evaluate the feasibility and relevant performances, multiple dimensions of indicators are designed. Employing several European energy scenarios up to 2050, the performances of the proposed HVAC-HVDC infrastructure are analyzed and compared. The calculation results show that compared with the pure HVAC grid, the integrated HVAC-HVDC grid can significantly reduce greenhouse gas emissions and pollutants, leading to a further reduction in the number of deaths from air pollution. In addition, the HVAC-HVDC grids can accommodate a higher penetration of RES without causing infeasible power flows
A Framework for Assessing Electricity Market Performance under Different Bidding Zone Configurations
Full text linkImproper configuration of bidding zones can lead to market efficiency losses, hinder the integration of renewable energy sources (RESs), and reduce grid security. To evaluate the impact of different bidding zone configurations on market performance, we developed a multi-dimensional evaluation framework containing a series of indicators covering aspects of market efficiency, grid security, and sustainability. These indicators facilitate the comparisons among different market dispatch mechanisms. To validate the proposed framework, the reconfiguration of the Italian bidding zones has been applied to a simplified Italian grid model to compare the market performance under different bidding zone configurations. The simulation results indicate that the implemented reconfiguration has led to enhanced market efficiency and security in the Italian power system. However, the reconfiguration shows a comparatively lower reduction in greenhouse gas (GHG) emissions, suggesting a weaker sustainable performance
Dynamic Decoupling-Based Convex-Concave Programming for Optimal Power Flow in Asymmetric Bipolar DC Distribution Networks
No full textOptimal power flow (OPF) plays a crucial role in addressing asymmetric operational problems of bipolar direct current distribution networks (DCDNs). However, the effectiveness of existing OPF models applied to bipolar DCDNs exhibits sensitivity to the problem type, underlying assumptions, and choice of objective functions. Hence, this paper proposes a dynamic decoupling-based convex-concave programming (CCP) framework to formulate an OPF model, aiming for a more rational impact across diverse applications in asymmetric operational bipolar DCDNs. More specifically, the coupled power between poles and ports of bipolar DCDNs is analyzed in detail, leading to the derivation of decoupled pole-to-ground equivalent circuits without relying on any preliminary assumption. Subsequently, the OPF problem of the equivalent circuits is formulated via CCP, involving the introduction of a cutting plane through difference-of-convex inequalities to limit the feasible region of the traditional OPF based on second-order cone programming, thereby diminishing dependence on exact relaxation conditions. Finally, a solution method is proposed to dynamically correct both the decoupled equivalent circuits and the cutting plane. The numerical results indicate that this method effectively addresses power optimization problems with a non-strictly monotonic objective function. Furthermore, it exhibits scalability, showcasing its applicability to large-scale radial bipolar DCDNs
Market zone configuration under collusive bidding among the conventional generators and renewable energy sources in the day-ahead electricity market
No full textThe European cross-zonal day-ahead (DA) electricity market is transitioning to the flow-based market coupling model for market clearing. With the increasing integration of renewable energy sources (RESs), market participants have opportunities for collusive bidding, resulting in decreased social welfare (SW). Thus, this paper is the first to propose an approach to configure the market zone (MZ) considering collusive bidding among conventional generators (CGs) and RESs in the DA market. Specifically, a bi-level model is developed to analyze collusive bidding among the CGs and RESs. Then, multi-dimensional market performance indices are used to determine the critical branches (CBs), on which the configuration of MZs is based. Finally, test 6-bus and simplified European systems are used to demonstrate the validity and merit of the proposed approach. Our simulation on the 6-bus system shows that when compared with the initial zonal market (ZM), the SW of the optimized ZM increased by 18 %, while the re-dispatch surrogate cost decreased to 0. Also, the penetration of RESs improved by 12 %, which guarantees the development of RESs
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
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