2,283 research outputs found
Generalised transformer modelling for power flow calculation in multi-phase unbalanced networks
No full textLow voltage systems are unbalanced networks where a significant share of the users is single-phase connected, so a multi-phase system needs to be considered in order to assess the mutual influence of the different phases. The presence of single-phase unevenly distributed users, leads to unbalances in the power flow on the three phases. This issue is emphasised considering the presence of local single-phase generators. This study presents a generalised method for transformers modelling in any multi-conductor grid representation in order to allow the analysis on unbalanced networks such as low-voltage distribution systems. The method, based on an incidence matrix approach, is proposed to represent any network object involving mutual connections among the phases, once the impedances for each single-phase equivalent circuit are known. Some application examples validate the approach and illustrate how to numerically realise the model
Undesired islanding of MV networks sustained by LV dispersed generators compliant with present grid code requirements
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Use of Rod Compactors for High Voltage Overhead Power Lines Magnetic Field Mitigation
No full textIn the last decades, strengthening the high voltage transmission system through the installation of new overhead power lines has become critical, especially in highly developed areas. Present laws concerning the human exposure to electric and magnetic fields introduce constraints to be considered in both new line construction and existing systems. In the paper, a technique for passive magnetic field mitigation in areas close to overhead power lines is introduced, fully modelled and discussed through a parametric analysis. The investigated solution, which basically consists in approaching line conductors along the span making use of rod insulators, is applicable on both existing and under-design overhead lines as an alternative to other mitigating actions. Making use of a 3-dimensional representation, the procedure computes both positions of phase conductors and forces acting on insulators, towers, conductors and compactors, with the aim of evaluating the additional mechanical stress introduced by the compactors. Finally, a real case study is reported to demonstrate and quantify the benefits in terms of ground magnetic field reduction achievable by applying the proposed solution, in comparison to a traditional configuration. Furthermore, using compactors to passively reduce the magnetic field is simple to be applied, minimally invasive and quite inexpensive as regards to alternative mitigating actions
Influence of electricity pricing models on the daily optimization of residential end-users integrating storage systems
No full textEngaging MV and LV end-users in providing ancillary services to the main grid is a very interesting scenario, in which the traditional interactions between Distribution System Operators and customers are significantly modified. In this work, a novel pricing structure is introduced to investigate how the behaviour of active end-users, including local generation and storage systems, could be influenced. In particular, suitably modifying the unit price of electricity according to the power exchanged at the connection node, a double benefit is directly achievable: on one hand, a substantial reduction of the customer billing cost is possible by optimally sizing and managing a local storage system; on the other hand, from the Distribution System Operator's perspective, the modified end-users behaviour facilitates the network management, since voltage violations and line congestions become less frequent. As a result, without increasing the end-users' costs, the proposed approach is able to opportunely influence their power profiles and to indirectly increase the network hosting capacity
Losses Allocation Methods in Planning and Management of Low Voltage Active Distribution Networks
No full textEffects of Energy Storage Systems Grid Code Requirements on Interface Protection Performances in Low Voltage Networks
No full textThe 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
Impact of Distributed Generation Grid Code Requirements on Islanding Detection in LV Networks
No full textThe 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
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