Influence of a MV/LV voltage-regulating transformer on the maximal share of distributed generation

V diplomskem delu je predstavljena ena izmed možnih rešitev pri problemu prenapetosti v distribucijskem omrežju, ki je posledica vključevanja vedno večjega števila razpršenih virov. Trendi na področju energetike nakazujejo, da se fosilna goriva poskuša nadomestiti z obnovljivimi viri energije. S tem je prisotnost razpršenih virov v omrežju vse večja, ti pa so praviloma blizu odjemalca, na distribucijski strani omrežja. Razpršena proizvodnja ima veliko pozitivnih strani – prenosne poti od proizvajalca do odjemalca se skrajšajo, posledično so manjše izgube. Krajše poti pomenijo tudi manjše posege v okolje, problemi pa nastajajo, ko v omrežju ni velike porabe in razpršeni viri obratujejo z nazivnimi vrednostmi, kar povzroči spremembo smeri pretokov moči. Nove razmere zamajejo napetostni profil, kar ogroža celoten elektroenergetski sistem. Omrežja ob izgradnji niso bila načrtovana, da bi sledila tem trendom, zato so potrebne nadgradnje omrežja, da bi ob vsem, kar prihaja, odjemalcem še naprej nudili kar se da zanesljivo in kakovostno dobavo električne energije. Opisan problem se lahko rešuje z ojačitvami prenosnih poti, novimi metodami regulacije porabe bremen in regulacije proizvodnje razpršenih virov. Ena izmed možnosti, ki bi težave lahko rešile, je tudi vgradnja SN/NN regulacijskih transformatorjev, ki bi stopnjo napetosti lahko spreminjali tudi med obremenitvijo. Obravnava slednjega je tema diplomskega dela. Prva poglavja so namenjena kratki predstavitvi razpršenih virov in vpliva, ki jih ima njihovo priključevanje v omrežje na porast napetosti. Opisana sta tudi model in delovanje pametnih omrežji. Ob številnih omejitvah, s katerimi se srečujemo pri vzdrževanju starih in gradnji novih členov elektroenergetskega sistema, postajajo nujna nadgradnja prihodnosti. Rezultati simulacij so uporabni samo v primeru, ko lahko pričakujemo, da se bodo stanja, ki smo jih simulirali, ob podobnih razmerah ponovila tudi v realnosti. V ta namen se z računalniškimi programi sprogramira ekvivalentni model omrežja, na katerem se izvaja simulacije. Omrežje je zmodelirano z Open DSS simulacijskim orodjem, ki v povezavi s programom MATLAB olajša izvajanje analize in podajanje rezultatov. Način modeliranja, simuliranja in analiziranja je v celoti tudi opisan. Z vsemi nepredvidljivimi dejavniki, ki vplivajo na razmere v omrežju, je pri simuliranju za dobre končne ugotovitve potrebno uporabiti statistične metode. V delu je opisana in uporabljena metoda Monte Carlo, ki z velikim številom ponovitev simulacije in z naključnimi vrednostmi spremenljivk poda najboljši približek realnemu stanju. V zadnjih poglavjih sledi opis in rezultat simulacij, ki so izvedene za razmere, ko v omrežje dodajamo razpršene vire. Prikazana je primerjava razmer omrežja, ko iz srednjenapetostnega na nižjenapetostni nivo prehajamo preko transformatorja, ki ne more regulirati napetostne stopnje pod obremenitvijo in ko imamo na istem mestu regulacijski transformator, ki to lahko počne. Uporabljeni sta dve vrsti regulacijskega transformatorja – regulatorji prvega preverjajo napetost na NN zbiralki transformatorja, regulatorji drugega pa na vseh vozliščih v omrežju. Na koncu so vsi rezultati prikazani še grafično in dodatno pojasnjeni z ugotovitvami.This dissertation seeks to present one of the possible solutions in relation to distribution network overload, which is a consequence of multiple distributed power sources. Recent trends in power industry indicate the increased use of renewable energy sources in relation to fossil fuels. Consequently, the presence of distributed generation in a distribution network is growing, which are usually closer to the consumer, on the distribution side of the network. The distributed generation has brought a lot of advantages, including, the shorter transmissions from manufacturer to consumer, which minimised the power loss in transmission. Shorter transmissions also lessened the impact on the environment. Problems occur when the distributed generation produces a lot of energy but the usage is minimal, all combined reverse the direction of power flow. The new conditions shake the voltage profile, endangering the entire electric power system. The current distribution networks haven\u27t been designed for the recent trends. Therefore, to ensure the constant reliable and quality supply of energy for the consumers, the distribution networks need an upgrade. The above-described problem can be solved by reinforcing the transmissions lines, using the new regulation methods for consumption reducing the burden on the electric grid and distributed sources regulation. However, another possible solution is the integration of SN/NN regulatory transformers. It also enables the monitoring of voltage stability/rate during the system load. The latter is the main focus of this dissertation. The first chapters focus on introducing the distributed sources and how the integration of distributed sources affects distribution networks in relation to voltage increase. Furthermore, it describes the smart distribution grids model and its operations. The maintenance of the old distribution networks and the construction of the new electric distribution networks lead to numerous limitations and issues. Therefore, the smart grids are becoming a necessity. This dissertation only presents the simulated results that would most likely correspond to the results produced in the »real world« under similar conditions. Using the proper computer programmes we can programme the equivalent software-based distribution model network simulations. The software-based distribution model network has been programmed using the Open DSS simulation tool, which in comparison to MATLAB program, facilitates fairly accurate and simple data analysis and data presentation. The whole programming process, simulation procedures, and data analysis are also described in the following chapters. In order to reach reliable findings, due to a high number of unpredictable factors influencing the network, the simulation process required the use of statistical methods. This dissertation uses the Monte Carlo method. Basically, the high number of simulation repetitions, the addition of random variables, produces the best possible »real world« approximation. Last chapters focus on describing and analysing simulation results, produced while loading the distribution network by integrating distributed power sources. It compares and demonstrates the transmission between medium and low voltage distribution network with the transformer that does not have regulatory ability and with the transformer that does have a regulatory ability – regulatory transformer. The regulatory transformer has two types of monitoring systems. The first monitors the voltage on the NN regulatory transformers collector whereas the second monitors all distribution network intersections. The final chapter graphically displays all above – generated results