Use of rod compactors for high voltage overhead power lines magnetic field mitigation

In 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

Effects of energy storage systems grid code requirements on interface protection performances in low voltage networks

The 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

Generalised transformer modelling for power flow calculation in multi-phase unbalanced networks

Low 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

Voltage Management in Unbalanced Low Voltage Networks Using a Decoupled Phase-Tap-Changer Transformer

The paper studies a medium voltage-low voltage transformer with a decoupled on load tap changer capability on each phase. The overall objective is the evaluation of the potential benefits on a low voltage network of such possibility. A realistic Danish low voltage network is used for the analysis. The load profiles are characterized by using single phase measurement data on voltages, currents and active powers with a 10 minutes resolution. Different scenarios are considered: no tap action, Three-phase coordinated tap action, single phase discrete step and single phase continuous tap action. The effectiveness of the tapping capability is evaluated by comparing the Voltage Unbalance Factor and the voltage levels on the neutral cable

A Novel Unidirectional Smart Charging Management Algorithm for Electric Buses

The difficulty of controlling the charging of electric buses (EBs) and their effects on network demand are discussed in this study. The solutions suggest a call for worldwide, complex infrastructures that manage EVs and EBs equally. Additionally, the Distribution Network (DN) must be prepared for an increased prevalence of reverse power flow caused by widespread distributed renewable generation. This paper focuses exclusively on EBs since they have higher capacity and predictable charging patterns, which makes them more significant for the DN in the context of a transition to complete vehicle electrification and technologies that are mature enough to be hosted. The proposed algorithm employs the Day-Ahead Energy Market (DAEM) in the Smart Charging (SC) to forecast the network operating circumstances. Additionally, the technique makes it possible to facilitate distributed photovoltaic (PV) generation, allowing network demand to be referenced depending on net demand. It also identifies an appropriate individual charger current per vehicle and per-time-step with load-levelling or peak-shaving as its primary goal. The final real demand demonstrates that a coarse correction of the demand is possible. According to the analysis of the DN voltage profile and associated line losses, the ideal node position location of the CS is dependent on PV penetration

Reactive Power Control for Smarter (Urban) Distribution Network Management With Increasing Integration of Renewable Prosumers

Smart cities need to deliver reliable electric energy while utilizing every renewable energy source available in a sustainable manner. Increasing renewable electricity capacity, through Distributed Generation (DG) such as small wind and PV generation, causes difficulties for the distribution network operator (DNO) in sustaining adequate and appropriate power quality across the network. The positive impacts provided by such energy sources can be undermined by voltage increases and voltage balance issues. To overcome these problems, urban distribution networks need to transform ideally into smarter energy networks that can deliver renewable electricity locally, predictably and in a controllable and optimized manner. The research presented here is based on electricity network simulation in an urban context. The main focus is the hosting capacity enhancement of distribution networks, while maintaining power quality, which is ultimately a pre-requisite for increasing prosumer engagement. In this regard, a test-bed representation of a 4-wire low-voltage section of distribution network in Dublin, Ireland is developed in DIgSILENT Power Factory. Several scenarios that consider increasing penetration of renewable prosumers in a smart electricity network context are presented. The results show that STATCOM, in the context of increasing DG integration, can provide continuous voltage support, by supplying or absorbing reactive power and thereby facilitating increased renewable DG contributions for a smarter, greener network

Internal Carotid Artery Occlusive Disease and Polymorphisms of Fractalkine Receptor CX3CR1

Background and Purpose— Fractalkine (FKN), a chemokine expressed by inflamed endothelium, induces leukocyte adhesion and migration via the receptor CX3CR1. The polymorphisms V249I and T280M affect receptor expression and function. The role of FKN in atherosclerosis has been recently demonstrated. The aim of this study was to investigate a possible association between CX3CR1 polymorphisms and increased risk of internal carotid artery (ICA) occlusive disease. Methods— We studied 108 patients consecutively recruited for ICA occlusive disease, 84 of whom underwent operation for carotid endarterectomy, and 204 subjects without ICA occlusive disease (controls). Polymorphic genotypes were determined by polymerase chain reaction and sequencing analysis. Results— The adjusted odds ratio (OR) associated with the presence of the M280 (TM+MM versus TT genotype) was 0.55 (95% CI: 0.29 to 0.99; P =0.037). Therefore, this allele is associated with a reduced risk of ICA occlusive disease. No significant differences were observed in I249 distribution. The frequency of I249 allele was significantly higher in cases of hard plaques, which are considered more stable than soft ones (OR: 0.38; 95% CI: 0.13 to 1.05; P =0.037). Multiple logistic regression analysis using the common risk factors and the I249 and M280 allele variants revealed that the M280 allele was an independent risk factor for ICA stenosis ( P =0.047). Conclusion— The results show that the CX3CR1 M280 is an independent genetic risk factor for ICA occlusive disease and that I249 is involved in the stability of carotid plaques. Even if obtained from a relatively limited patient series, these results might have relevant implications for treatment of ICA stenosis and possibly prevention of carotid related stroke. Further prospective cross-sectional studies are needed to confirm these results

Voltage Control for Unbalanced Low Voltage Grids Using a Decoupled-Phase On-Load Tap-Changer Transformer and Photovoltaic Inverters

This paper presents modeling and analysis of the potential benefits of joint actions of a MV/LV three-phase power distribution transformer with independent on-load tap-changer control on each phase and photovoltaic inverters provided with reactive power control capability, in terms of accommodating more renewable generations in the LV grid. The potential benefits are investigated in terms of voltage unbalance reduction and local voltage regulation. 24-hours root-mean-square dynamics simulation studies have been carried out with timestep of 1 second using 10-mins resolution consumption and production profiles. A totally passive real Danish low voltage distribution network is used for the grid topology as well as for the characterization of loads profiles, while the production ones are empirically defined under assumptions in scenarios with different level of photovoltaic penetration and grade of unbalance

Centralized OPF in Unbalanced Multi-Phase Neutral Equipped Distribution Networks Hosting ZIP Loads

The Optimal Power Flow (OPF) model for low voltage active Distribution Networks (DNs), which are equipped with neutral conductors, requires an explicit representation of both phases and neutral conductors in its formulation to obtain complete information about the state variables related to these conductors. In this regard, a centralized OPF relaxation based on semi-definite programming is presented in this paper for neutral-equipped DNs hosting ZIP loads and neutral-ground impedance, and contain a significant level of unbalance. The major restriction in the development of an OPF model for these networks is the coupled power injection across the conductors which is successfully handled by deriving the explicit active and reactive power injections for each conductor through a network admittance matrix-based approach. The shortcomings of existing voltage magnitude-based technique for the modelling of ZIP loads are comprehensively reported and a novel complex voltage variable-based approach is proposed which successfully incorporates ZIP loads in the developed multi-phase OPF relaxation. For the handling of constant current load, a modelling approach based on the first-order-Taylor series is introduced as well. Furthermore, the impact of the application of Kron reduction approach on the global optimal solution of single- and multiple-point grounded DNs is discussed in detail. Three metrics, eigenvalue ratio, power mismatch and cumulative normalized constraint violation, are utilized to evaluate the exactness of proposed relaxation. Simulations, carried out on several medium and low voltage DNs, show that the proposed relaxation is numerically exact under several combinations of ZIP load parameters and a reasonable range of grounding impedance value for both time-varying and extreme system loading scenarios irrespective of the degree of unbalance in a network

Micro Market based Optimisation Framework for Decentralised Management of Distributed Flexibility Assets

Continuously changing electricity demand and intermittent renewable energy sources pose challenges to the operation of power systems. An alternative to reinforcing the grid infrastructure is to deploy and manage distributed energy storage systems. In this work, a micro-energy market is proposed for smart domestic energy trading in the low-voltage distribution systems in the context of high penetration of photovoltaic systems and battery energy storage systems. In addition, a micro-balancing market is proposed to address the congestions due to unforeseen energy imbalance. Centralised and decentralised management strategies are simulated in real time, based on generation and demand forecasts. In addition, electric vehicles are also simulated as potential storage solutions to improve grid operation. A techno-economic evaluation informs key stakeholders, in particular grid operators on strategies for a sustainable implementation of the proposed strategies. The results show that the micro-energy market reduces the energy cost for all grid users by 4.1-20.2, depending on their configuration. In addition, voltage deviation, peak electricity demand and reverse power flow have been reduced by 12.8, 7.7 and 85.6 respectively, with the proposed management strategies. The micro-balancing market has been demonstrated to keep the voltage profile and thermal characteristic within the set limit in case of contingency