Phd Thesis Nuno Silva Final V3
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Alternative design strategies of distribution systems A thesis submitted to Imperial College London For the degree of Doctor of Philosophy by Nuno Filipe Gonçalves da Silva Department of Electrical and Electronic Engineering Abstract In contrast with traditional approaches based either on the analysis of a small specific area or on idealistic networks, the proposed methodology determines optimal network design policies by evaluating alternative planning strategies on statistically similar networks. The position of consumers influences the amount of equipment used to serve them. Therefore, simple geometric models or randomly placed points used in previous researches are not adequate. Using an algorithm based on fractal theory, realistic consumer sets are generated in terms of their position, type and demand to allow statistical evaluation of the cost of different design policies. In order to systematically deal with the problem of determining justifiable network investments, the concept of economically adapted distribution network was investigated and applied in the context of a loss-inclusive design promoting efficient investment policies from an overall social perspective. The network’s components are optimized, after yearly load flow calculations, based on the minimum life-cycle cost methodology, balancing annuitised capital investments and maintenance costs against the cost of system operation. Evaluating the cost of each particular design over statistically similar networks allows statistically significant conclusions to be drawn. The main results include the optimal number of substations for typical urban and rural LV, HV and EHV distribution systems, network costs (investment, purchasing and maintenance) and losses as well as the sensitivity of optimal network design to future energy prices and cost of equipment. The impact of the increasing amount of microgeneration on networks has not been fully addressed to date. There have not been clustering problems in existing networks as a result of customers choosing to install microgenerators, either as a new device or as a replacement of a previous heating system. The operation of microgeneration connected to the distribution network can cause statutory voltage limits, recommended voltage unbalance levels and switchgear fault ratings to be exceeded. However, there are a range of distribution network designs and operating practices and thus the impact will vary accordingly. The operation of distribution networks is approached considering the existence of single or three-phase loads and microgeneration. This would however cause the network to be unbalanced and hence, traditional methods that consider a three-phase balanced system would provide misleading results. Every residential daily load’s behaviour shows rapid shifts from “load valleys” to high peaks due to the random and frequent “switch on/off” of appliances. Modelling each load individually will reveal problematic operating conditions which were not considered when using a smooth load profile. Thus, each and every domestic load was represented by a different load profile and the impact on losses was evaluated. Relating losses, voltages, currents and load unbalance ratio leads to conclusions about the way how to optimise the network with DG. The aim was to investigate and develop methodology for evaluation of the long-term loss-inclusive optimal network design strategies and to determine the effect of the penetration of microgeneration, such as CHP and PV, in realistic distribution networks and optimal network planning. The need for reinforcement of network components will depend on the level of generation and on the extent to which reverse power flows occurs. In most parts of the network, microgeneration exports will not be sufficient to result in any need for network investment. However, if the network was to be planned accounting with DG, capital investment scenarios are presented and compared to existing networks trying to accommodate clusters of microgeneration. Declaration No portion of the work referred to in this thesis has been submitted in support of an application for another degree or qualification of this or any other university, or institution of learning 6 Acknowledgements First and foremost, I would like to express my deepest gratitude to my supervisor Professor Goran Strbac for making my PhD a uniquely enriching experience. This thesis is the result of a challenging, exciting and stimulating process. My supervisor’s expertise, experience, and brilliant ideas were crucial for every step along the way. He entrusted me a considerable responsibility from the very beginning and honestly believed in my commitment to fulfilling his expectations. I will never be able to thank him enough, but I will continue to try to honour his effort through very hard work. Doing my PhD within the Control & Power Group at Imperial College and the Manchester Centre for Electrical Energy (MCEE) has been a privilege. It made this experience much more productive, interactive and stimulating. This thesis greatly benefited from access to a large network of internal and external fellows. I am extremely grateful to Dejan Melovic, Danny Pudjianto, Predrag Djapic, Gan Chin Kim and all colleagues that contributed for the successful completion of this research. A special word of gratitude to Alexandre Pais da Silva, Cristiano Marantes, Manuel Castro, Rohan Choudhary, Salvador Acha and Sebastien Grenard for being more than colleagues and becoming genuine friends providing me with encouragement and guidance. I would like to acknowledge the financial support of Fundação para a Ciência e a Tecnologia (FCT). Furthermore, I would also like to thank Professor Nick Jenkins from The University of Manchester as well as Professor Peças Lopes, Professor Manuel Matos and Professor Vladimiro Miranda from the University of Porto. They all played an important role in my university education and continuously encouraged and supported my research in various ways. Finally, and very importantly, I would like to thank Marlene for being always there for me when I most needed. Her encouragement, support and dedication made it all easier. I want to pay a very special tribute to my parents and sister who will always be my roots and the solid basis of each of my achievements, thanks for being role models for me and always encourage my career development. 7 Table of contents Abstract ...............................................................................................................................................3 Declaration ..........................................................................................................................................5 Acknowledgements .............................................................................................................................7 Table of contents.................................................................................................................................8 List of figures.....................................................................................................................................12 List of tables ......................................................................................................................................18 Publications .......................................................................................................................................19 Glossary .............................................................................................................................................21 1. CHAPTER INTRODUCTION ............................................................................................................................23 1.1. Overview.................................................................................................................................23 1.2. System losses ..........................................................................................................................25 1.3. Distribution network design....................................................................................................27 1.4. Distributed generation.............................................................................................................28 1.5. Scope, objectives and research challenges..............................................................................30 1.6. Thesis structure .......................................................................................................................32 1.7. Key findings and contributions of the thesis...........................................................................35 2. CHAPTER GENERIC DISTRIBUTION NETWORK MODEL .....................................................................37 2.1. Overview.................................................................................................................................37 2.2. Optimal design policy of distribution networks......................................................................39 2.3. Research to determine the optimum electricity distribution network design policy....................................................................................................................................40 2.4. Model of generic distribution network....................................................................................42 2.5. Generation of realistic distribution networks ..........................................................................45