1,720,968 research outputs found
Analysis of ΔP - ΔQ Area of Uncontrolled Islanding in Low-Voltage Grids With PV Generators
No full textUndesired islanding of MV networks sustained by LV dispersed generators compliant with present grid code requirements
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Effects of average power factor management in distribution systems with dispersed generation
No full textElectrical systems are inevitably affected by power losses, mainly due to the current flowing through lines and transformers. Currents depend on end-users' power absorption and are strictly related to the overall power factor, resulting from loads, compensating units and distributed generation. The power factor management has a great influence on network power losses and voltage profiles along distribution lines. In the past, before the distributed generation diffusion, the network losses minimization could be obtained by requiring a high average power factor to end-users, evaluating the parameter on the bill period. Differently, nowadays the power factor management for active users is requiring different rules, since the previous statement is no longer valid. The paper investigates inconsistences between local generation and present power factor requirements in the Italian context. Considerations about sizing compensating devices are introduced, in accordance with the recent evolution of connection codes. Losses are compared considering different reference power factors, local generation amount and generators' connection topologies. Results are verified basing on data from meters installed in distribution networks
Effects of Energy Storage Systems Grid Code Requirements on Interface Protection Performances in Low Voltage Networks
Full text linkThe ever-growing penetration of local generation in distribution networks and the large diffusion of energy storage systems (ESSs) foreseen in the near future are bound to affect the effectiveness of interface protection systems (IPSs), with negative impact on the safety of medium voltage (MV) and low voltage (LV) systems. With the scope of preserving the main network stability, international and national grid connection codes have been updated recently. Consequently, distributed generators (DGs) and storage units are increasingly called to provide stabilizing functions according to local voltage and frequency. This can be achieved by suitably controlling the electronic power converters interfacing small-scale generators and storage units to the network. The paper focuses on the regulating functions required to storage units by grid codes currently in force in the European area. Indeed, even if such regulating actions would enable local units in participating to network stability under normal steady-state operating conditions, it is shown through dynamic simulations that they may increase the risk of unintentional islanding occurrence. This means that dangerous operating conditions may arise in LV networks in case dispersed generators and storage systems are present, even if all the end-users are compliant with currently applied connection standards
Combined effects of distributed generation grid code requirements on the transient behaviour of islanded systems
No full textNational and internationals grid codes define the connection rules for passive and active users, guaranteeing the electrical power system stability and safety. Recently, the increasing diffusion of Distributed Generators from Renewable Energy Sources, mainly interfaced through electronic converters, has called for a drastic review of traditional approaches to distribution network operation. As a consequence, new regulating functions, aiming to support network stability by regulating local units power flows, have been defined, and others are under investigation. The paper discusses the role of existing and proposed stabilizing actions in terms of unintentional islanding identification, according to the Low Voltage interface protection characteristics
Impact of Distributed Generation Grid Code Requirements on Islanding Detection in LV Networks
Full text linkThe recent growing diffusion of dispersed generation in low voltage (LV) distribution networks is entailing new rules to make local generators participate in network stability. Consequently, national and international grid codes, which define the connection rules for stability and safety of electrical power systems, have been updated requiring distributed generators and electrical storage systems to supply stabilizing contributions. In this scenario, specific attention to the uncontrolled islanding issue has to be addressed since currently required anti-islanding protection systems, based on relays locally measuring voltage and frequency, could no longer be suitable. In this paper, the effects on the interface protection performance of different LV generators’ stabilizing functions are analysed. The study takes into account existing requirements, such as the generators’ active power regulation (according to the measured frequency) and reactive power regulation (depending on the local measured voltage). In addition, the paper focuses on other stabilizing features under discussion, derived from the medium voltage (MV) distribution network grid codes or proposed in the literature, such as fast voltage support (FVS) and inertia emulation. Stabilizing functions have been reproduced in the DIgSILENT PowerFactory 2016 software environment, making use of its native programming language. Later, they are tested both alone and together, aiming to obtain a comprehensive analysis on their impact on the anti-islanding protection effectiveness. Through dynamic simulations in several network scenarios the paper demonstrates the detrimental impact that such stabilizing regulations may have on loss-of-main protection effectiveness, leading to an increased risk of unintentional islanding
Emergency generators for supplying islanded MV networks
No full textIn order to increase network resilience, Distribution System Operators are evaluating different remedial actions against extreme events that lead to long interruptions. This paper evaluates the technical solutions for deploying an emergency generator (EG) supplying an islanded Medium Voltage (MV) network. The paper identifies the minimum technical requirements and different neutral grounding arrangements that can be adopted. Taking into account the maximum size of the mobile generators available in the market, evaluation results show that supplying a section of a distribution network could be done only if cable length is lower than 5 km and maximum load is less than 0.5 MW
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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