Network assimilation methodology and sectorization of water distribution systems by graph mining and optimization algorithm

Water Distribution Networks (WDNs) play a vital importance rule in communities, ensuring well-being band supporting economic growth and productivity. The need for greater investment requires design choices will impact on the efficiency of management in the coming decades. This thesis proposes an algorithmic approach to address two related problems:(i) identify the fundamental asset of large WDNs in terms of main infrastructure;(ii) sectorize large WDNs into isolated sectors in order to respect the minimum service to be guaranteed to users. Two methodologies have been developed to meet these objectives and subsequently they were integrated to guarantee an overall process which allows to optimize the sectorized configuration of WDN taking into account the needs to integrated in a global vision the two problems (i) and (ii). With regards to the problem (i), the methodology developed introduces the concept of primary network to give an answer with a dual approach, of connecting main nodes of WDN in terms of hydraulic infrastructures (reservoirs, tanks, pumps stations) and identifying hypothetical paths with the minimal energy losses. This primary network thus identified can be used as an initial basis to design the sectors. The sectorization problem (ii) has been faced using optimization techniques by the development of a new dedicated Tabu Search algorithm able to deal with real case studies of WDNs. For this reason, three new large WDNs models have been developed in order to test the capabilities of the algorithm on different and complex real cases. The developed methodology also allows to automatically identify the deficient parts of the primary network and dynamically includes new edges in order to support a sectorized configuration of the WDN. The application of the overall algorithm to the new real case studies and to others from literature has given applicable solutions even in specific complex situations.

Microgrids and their operations

Interconnection of loads and small size generation forms a new type of distribution systems, the Microgrid. The microgrids can be operated together with the utility grid or be operated autonomously in an island. Thesesmall grids present a new paradigm of the construction of the low voltage distribution systems. The microgrids in the distribution systems can become small, controllable units, which immediately react to the system's changes. Along with that the microgrids can realize the special properties, such as increasing the reliability, reducing losses, voltage sag correction, uninterruptible supplying. The goals of the thesis are to explain the principles of the microgrid's functioning, to clarify the main ideas and positive features of the microgrids, to find out and prove their advantages and explain why they are so popular nowadays all over the world. The practical aims of the thesis are to construct and build a test setup of a microgrid based on two inverters from SMA Technologie AG in the laboratory and to test all the main modes and parameters of the microgrid's operating. Also the purpose of the thesis is to test the main component of the microgrid - the battery inverter which controls allthe processes and energy flows inside a microgrid and communicates with the main grid. Based on received data the main contribution of the thesis consists of the estimation of the established microgrid from the reliability, economy and simplicity of operating points of view and evaluation ofthe advisability of its use in different conditions. Moreover, the thesis assumes to give the recommendations and advice for the future investigations of the built system.

Rovakaira Oy:n keskijänniteverkon kehittämissuunnitelma toimitusvarmuuskriteeristön näkökulmasta

Diplomityössä tavoitteena on etsiä teknistaloudellisimmat ratkaisut sekä tutkia niiden vaikutuksia sähkönjakeluverkoston käyttövarmuuteen ja luotettavuuteen toimitusvarmuuskriteeristön näkökulmasta. Lisäksi työssä esitetään uusi tunnusluku kriteeristön ylityksestä aiheutuvan haitan arvostukseen. Merkittävä osa Rovakaira Oy:n keskijänniteverkosta joudutaan uusimaan lähivuosikymmeninä teknistaloudellisen pitoajan täyttyessä. Verkon uusiminen antaa mahdollisuuden toteuttaa verkkoa nykyisiin vaatimuksiin paremmin sopivilla ratkaisuilla. Kehitysvaihtoehtoina vertaillaan johdon tien varteen siirtoa, maastokatkaisijoiden lisäämistä, pienitehoisten ja päättyvien haarajohtojen korvaamista 1 kV tekniikalla sekä pienoissähköaseman kannattavuutta. Työssä tarkastellaan yksityiskohtaisemmin Sodankylän käyttövarmuuden parantamista sähköasemavian aikana ja alueen kuormituksenkasvuun varautumista.

20 kV ilmajohtoverkon maakaapeloinnin vaikutus maasulkusuojaukseen ja loistehotaseeseen

Sähkömarkkinalakimuutokset ovat ohjanneet useita verkkoyhtiötä muuttamaan investoin-tistrategioitaan. Kiristyneet toimitusvarmuusvaatimukset edellyttävät useilta verkkoyh-tiöiltä aiempaa suurempaa panostusta jakeluverkon kehittämiseksi. Toimitusvarmuusvaa-timusten täyttäminen edellyttää myös merkittäviä muutoksia verkkoyhtiöiden käyttämiin verkostotekniikoihin. Suurhäiriöille alttiita ilmajohtoja muutetaan verkkoyhtiöissä totuttua nopeammalla aikataululla maakaapeleiksi tiukentuneiden toimitusvarmuusvaatimusten täyttämiseksi. PKS Sähkönsiirto Oy:n 20 kV sähköverkko on ollut suurimmalta osalta avojohtoverkkoa jossa toimitusvarmuus ei ole nykyisellään muuttuneen sähkömarkkinalain asettamalla ta-solla. Tämä on johtanut verkostostrategian luomiseen, jossa yhtenä toimena toimitusvar-muuden lisäämiseksi vaaditulle tasolle on avojohtolinjojen korvaaminen maakaapeleilla. Maakaapelointien nopea rakennusaikataulu tuo monia haasteita verkkoyhtiöille. Maakaa-pelointien korkea maasulkuvirran ja loistehon tuotto verrattuna avojohtoverkkoon tulee huomioida yhtiössä verkkoa rakennettaessa. Tässä diplomityössä selvitetään PKS Sähkönsiirto Oy:n verkostostrategian mukaisten maakaapelointien vaikutuksia sähköverkolle. Työssä on arvioitu tavoiteverkon mukaisten maakaapeleiden aiheuttamaa maasulkuvirran ja loistehon tuoton tasoa. Tulosten perusteel-la on tehty johtopäätökset mihin verkkoyhtiön on kiinnitettävä huomioita kaapelointeja suunnitellessa ja toteuttaessa.

Time-series-based maximization of distributed wind power generation integration

Energy policies and technological progress in the development of wind turbines have made wind power the fastest growing renewable power source worldwide. The inherent variability of this resource requires special attention when analyzing the impacts of high penetration on the distribution network. A time-series steady-state analysis is proposed that assesses technical issues such as energy export, losses, and short-circuit levels. A multiobjective programming approach based on the nondominated sorting genetic algorithm (NSGA) is applied in order to find configurations that maximize the integration of distributed wind power generation (DWPG) while satisfying voltage and thermal limits. The approach has been applied to a medium voltage distribution network considering hourly demand and wind profiles for part of the U.K. The Pareto optimal solutions obtained highlight the drawbacks of using a single demand and generation scenario, and indicate the importance of appropriate substation voltage settings for maximizing the connection of MPG.

Evaluating distributed time-varying generation through a multiobjective index

In the last decade, distributed generation, with its various technologies, has increased its presence in the energy mix presenting distribution networks with challenges in terms of evaluating the technical impacts that require a wide range of network operational effects to be qualified and quantified. The inherent time-varying behavior of demand and distributed generation (particularly when renewable sources are used), need to be taken into account since considering critical scenarios of loading and generation may mask the impacts. One means of dealing with such complexity is through the use of indices that indicate the benefit or otherwise of connections at a given location and for a given horizon. This paper presents a multiobjective performance index for distribution networks with time-varying distributed generation which consider a number of technical issues. The approach has been applied to a medium voltage distribution network considering hourly demand and wind speeds. Results show that this proposal has a better response to the natural behavior of loads and generation than solely considering a single operation scenario.

Carregamento ótimo de veículos elétricos considerando as restrições das redes de distribuição de média tensão

Pós-graduação em Engenharia Elétrica - FEIS

Controle de tensão e reativos em redes de distribuição de energia elétrica

Pós-graduação em Engenharia Elétrica - FEIS

Real-Time Voltage Regulation in Power Distribution System Using Fuzzy Control

Two different fuzzy approaches to voltage control in electric power distribution systems are introduced in this paper. The real-time controller in each case would act on power transformers equipped with under-load tap changers. Learning systems are employed to turn the voltage-control relays into adaptive devices. The scope of this study has been limited to the power distribution substation, and the voltage measurements and control actions are carried out on the secondary bus. The capacity of fuzzy systems to handle approximate data, together with their unique ability to interpret qualitative information, make it possible to design voltage-control strategies that satisfy the requirements of the Brazilian regulatory bodies and the real concerns of the electric power distribution companies. Fuzzy control systems based on these two strategies have been implemented and the test results were highly satisfactory.

Dimensioning DC-voltage capacitor for a DC-distribution system and dynamic analysis

Technical analysis of Low Voltage Direct Current (LVDC) distribution systems shows that in LVDC transmission the customer voltage quality is higher. One of the problems in LVDC distribution networks that converters both ends of the DC line are required. Because of the converters produce not pure DC voltage, but some fluctuations as well, the huge electrolytic capacitors are required to reduce voltage distortions in the DC-side. This thesis master’s thesis is focused on calculating required DC-link capacitance for LVDC transmission and estimation of the influence of different parameters on the voltage quality. The goal is to investigate the methods of the DC-link capacitance estimation and location in the transmission line.

Location of single line-to-ground faults on distribution feeders using voltage measurements

This paper proposes a dedicated algorithm for lation of single line-to-ground faults in distribution systems. The proposed algorithm uses voltage and current phasors measured at the substation level, voltage magnitudes measured at some buses of the feeder, a database containing electrical, operational and topological parameters of the distribution networks, and fault simulation. Voltage measurements can be obtained using power quality devices already installed on the feeders or using voltage measurement devices dedicated for fault location. Using the proposed algorithm, likely faulted points that are located on feeder laterals geographically far from the actual faulted point are excluded from the results. Assessment of the algorithm efficiency was carried out using a 238 buses real-life distribution feeder. The results show that the proposed algorithm is robust for performing fast and efficient fault location for sustained single line-to-ground faults requiring less than 5% of the feeder buses to be covered by voltage measurement devices. © 2006 IEEE.

Voltage regulator modeling for the three-phase power flow in distribution networks

In this paper a three-phase power flow for electrical distribution systems considering different models of voltage regulators is presented. A voltage regulator (VR) is an equipment that maintains the voltage level in a predefined value in a distribution line in spite of the load variations within its nominal power. Three different types of connections are analyzed: 1) wye-connected regulators, 2) open delta-connected regulators and 3) closed delta-connected regulators. To calculate the power flow, the three-phase backward/forward sweep algorithm is used. The methodology is tested on the IEEE 34 bus distribution system. ©2008 IEEE.

Power Oscillation index - A tool for investigation into unbalance phenomena in the distribution Networks

Unbalance and harmonics are two major distortions in the three-phase distribution systems. In this paper an investigation into unbalance phenomena in the distribution networks using instantaneous space vector theory, is presented. Power oscillation index (POI) and effective power factor (PFe) are calculated in the network nodes for several unbalance loading conditions. For system analysis a general power flow algorithm for three-phase four-wire radial distribution networks, based on backward-forward technique, is applied. Results obtained from several case studies using medium and low voltage test feeder with unbalanced load, are presented and discussed. © 2010 Praise Worthy Prize S.r.l. - All rights reserved.

Analysis of the Dielectric Behavior of Distribution Insulators Under Non-Standard Lightning Impulses Voltages

Overhead distribution lines are often exposed to lightning overvoltages, whose waveforms vary widely and can differ substantially from the standard impulse voltage waveform (1,2 - 50). Different models have been proposed for predicting the strength of insulation subjected to impulses of non-standard waveforms. One of the most commonly used is the disruptive effect model, for which there are different methods for the estimation of the parameters required for its application. This paper aims at evaluating the dielectric behavior of medium voltage insulators subjected to impulses of non-standard waveforms, as well as at evaluating two methods for predicting their dielectric strength against such impulses. The test results relative to the critical lightning impulse flashover voltage (U50) and the volt-time characteristics obtained for the positive and negative polarities of different voltage waveforms are presented and discussed.

Development and characterization of a distributed measurement system for the evaluation of voltage quality in electric power networks

The research activity carried out during the PhD course in Electrical Engineering belongs to the branch of electric and electronic measurements. The main subject of the present thesis is a distributed measurement system to be installed in Medium Voltage power networks, as well as the method developed to analyze data acquired by the measurement system itself and to monitor power quality. In chapter 2 the increasing interest towards power quality in electrical systems is illustrated, by reporting the international research activity inherent to the problem and the relevant standards and guidelines emitted. The aspect of the quality of voltage provided by utilities and influenced by customers in the various points of a network came out only in recent years, in particular as a consequence of the energy market liberalization. Usually, the concept of quality of the delivered energy has been associated mostly to its continuity. Hence the reliability was the main characteristic to be ensured for power systems. Nowadays, the number and duration of interruptions are the “quality indicators” commonly perceived by most customers; for this reason, a short section is dedicated also to network reliability and its regulation. In this contest it should be noted that although the measurement system developed during the research activity belongs to the field of power quality evaluation systems, the information registered in real time by its remote stations can be used to improve the system reliability too. Given the vast scenario of power quality degrading phenomena that usually can occur in distribution networks, the study has been focused on electromagnetic transients affecting line voltages. The outcome of such a study has been the design and realization of a distributed measurement system which continuously monitor the phase signals in different points of a network, detect the occurrence of transients superposed to the fundamental steady state component and register the time of occurrence of such events. The data set is finally used to locate the source of the transient disturbance propagating along the network lines. Most of the oscillatory transients affecting line voltages are due to faults occurring in any point of the distribution system and have to be seen before protection equipment intervention. An important conclusion is that the method can improve the monitored network reliability, since the knowledge of the location of a fault allows the energy manager to reduce as much as possible both the area of the network to be disconnected for protection purposes and the time spent by technical staff to recover the abnormal condition and/or the damage. The part of the thesis presenting the results of such a study and activity is structured as follows: chapter 3 deals with the propagation of electromagnetic transients in power systems by defining characteristics and causes of the phenomena and briefly reporting the theory and approaches used to study transients propagation. Then the state of the art concerning methods to detect and locate faults in distribution networks is presented. Finally the attention is paid on the particular technique adopted for the same purpose during the thesis, and the methods developed on the basis of such approach. Chapter 4 reports the configuration of the distribution networks on which the fault location method has been applied by means of simulations as well as the results obtained case by case. In this way the performance featured by the location procedure firstly in ideal then in realistic operating conditions are tested. In chapter 5 the measurement system designed to implement the transients detection and fault location method is presented. The hardware belonging to the measurement chain of every acquisition channel in remote stations is described. Then, the global measurement system is characterized by considering the non ideal aspects of each device that can concur to the final combined uncertainty on the estimated position of the fault in the network under test. Finally, such parameter is computed according to the Guide to the Expression of Uncertainty in Measurements, by means of a numeric procedure. In the last chapter a device is described that has been designed and realized during the PhD activity aiming at substituting the commercial capacitive voltage divider belonging to the conditioning block of the measurement chain. Such a study has been carried out aiming at providing an alternative to the used transducer that could feature equivalent performance and lower cost. In this way, the economical impact of the investment associated to the whole measurement system would be significantly reduced, making the method application much more feasible.