Electrical Transmission Systems for Large Offshore Wind Farms
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ELECTRICAL TRANSMISSION SYSTEMS FOR LARGE OFFSHORE WIND FARMS A THESIS SUBMITTED TO CARDIFF UNIVERSITY FOR THE DEGREE OF D octor of Philosophy Rosemary Louise King February 2011 UMI Number: U567155 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI U567155 Published by ProQuest LLC 2013. Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 For Abigail A b s t r a c t The large area required for an offshore wind farm along with its location results in extensive cable systems with a large number of radial feeders and step-up transformers. These transmission systems are very different to traditional onshore networks. Offshore wind farms above around 100MW capacity and over 20km from shore will have either AC or DC transmission, at above 132 kV. The capital costs were compared for AC and DC submarine transmission in order to find a break-even point. Over the lifetime of the wind farm, the cost of losses, maintenance and constrained energy was important. A loss-load factor was determined to enable a quick estimation of the annual cost of losses. Suitable models for the simulation of switching transients in offshore wind farms were identified. Simulations of Nysted offshore wind farm were compared with measurements provided by DONG Energy. A Vacuum Circuit Breaker model was developed and validated against the measurements. It was required in order to represent pre-strikes which caused successive waves and increased the overvoltage. The input data for the cable model was validated by examining the cable charging current and propagation speed of the transients. It was shown that the actual insulation thickness and semiconductor thickness of the cable were each 1mm thicker than that stated in the manufacturer’s data sheets. Simulations of switching transients were carried out in EMTP-RV. Overvoltages in offshore wind farms ranged from temporary over voltages to very fast front transients. Transient Recovery Voltages of the offshore circuit breakers exceeded IEC 62271 requirements in some situations. The disconnection of an array following a single phase fault at a wind turbine produced the most severe overvoltages, exceeding IEC 60071 requirements. The overvoltages in the array remained at a very serious level until the wind turbines stopped generating. D e c l a r a t io n D e c l a r a t io n This work has not previously been accepted in substance for any degree and is not concurrently submitted in candidature for any degree. Signed .....................(candidate) Date: 24/02/2011 S t a t e m e n t 1 This thesis is being submitted in partial fulfilment of the requirements for the degree of PhD. Signed .....................(candidate) Date: 24/02/2011 S t a t e m e n t 2 This thesis is the result of my own independent work/investigation, except where otherwise stated. Other sources are acknowledged by explicit references. S igned A k .....................(candidate) Date: 24/02/2011 S t a t e m e n t 3 I hereby give consent for my thesis, if accepted, to be available for photocopying and for inter-library loan, and for the title and summary to be made available to outside organisations. Signed (candidate) Date: 24/02/2011 4 A cknowledgements First and foremost I would like to express my sincere gratitude to my supervisor, Prof. Nick Jenkins. His guidance, encouragement and advice were essential to this work. I would like to thank Prof. Manu Haddad and Dr. Janaka Ekanayake for their help and advice. I would also like to thank Dr. Bieshoy Awad, Dr. Ahmed Shafiu, Mr. Alvaro Hernandez Manchola, Mr. Ivan Arana and Mr. Fabian Moore for the useful discussions we had. I would like to acknowledge the financial support during my PhD studies from ALSTOM GRID Research and Technology Centre, BP Alternative Energy and Cardiff University. I am very grateful for the support and suggestions from Dr. Angelo Amorelli and Dr. Sandra Eager at BP Alternative Energy. I would also like to acknowledge the advice and support from Dr. Liangzhong Yao, Mr. Harmeet Kang and Dr. Jean-Louis Rasolonjanahary at ALSTOM GRID Research and Technology Centre. I am very grateful to DONG Energy, who kindly supplied data from an offshore wind farm which was used in this thesis. I would like to express my gratitude to Dr. Troels Sorensen at DONG Energy. His feedback was of great importance to this work. I would like to thank all my friends whose advice and encouragement were of great importance to my work. I would like to thank Gnanasambandapillai Ramtharan, Nolan Calio, Yan He, Haziah Hamid and Carlos Ugalde for their support. I am also very grateful to Chidinma Agwu, Shazia Mughal, Sarah Williams, Alison Moses, Kate Herbert, Claudia Stem, Nadia Sebai, Yin Tsang, Sara Brumwell, Rebecca Broadhead, Tracey Rous, Leigh Neilan, Karen Di Piazza, Claire Banford and Helen Shaw for their friendship and encouragement. I would like to thank my family for all their love and encouragement. My parents, Jean and Andrew King, have provided help and support in a myriad of ways, including encouraging my interest in science and engineering and supporting my ideas and study. I would like to thank my sister, Jenny King, for being very supportive. To my fiance Martin Urban, thank you for your encouragement, your patience and for the useful discussions. Finally, I would like to thank my daughter, Abigail, for reminding me that there are more important things in life than a PhD thesis. Her joy was contagious, even during tough times in the PhD pursuit. 5 L is t o f P ublications King, R., Moore, F., Jenkins, N., Haddad, A., Griffiths, H., Osborne, M., “ Switching transients in offshore wind farms - impact on the offshore and onshore networks ”, International Power Systems Transients Conference (IPST2011), Delft, the Netherlands, June 14-17, 2011 Chukaluri, E. K., Barker, C., King, R., “A study on some of the important aspects related to feasibility of HVDC grid ”, CIGRE International Symposium “The Electric Power System of the Future - integrating supergrids and microgrids”, Bologna, Italy, September 13-15, 2011 King, R., Yao, L., Kang, H., Rasolonjanahary, J. L., Jenkins, N., “Transient Recovery Voltages in Offshore Wind Farms ”, 9th International Workshop on Large Scale Integration of Wind Power and on Transmission Networks for Offshore Wind Farms; Quebec City, Quebec, Canada, October 18-19, 2010; ISBN: 978-3-9813870- 2-5; Publisher: Energynautics Gomis-Bellmunt, O., Liang, J., Ekanayake, J., King, R., Jenkins, N., “Topologies of multiterminal HVDC-VSC transmission for large offshore wind farms”, Electrical Power Systems Research; Article in Press; Accepted; 8 Sept 2010, Available online; 27 Oct 2010; DOI: 10.1016/j.epsr.2010.09.006; Publisher: Elsevier Ltd King, R., Ekanayake, J. B., “Harmonic modelling of offshore wind farms”, IEEE PES General Meeting “Power Systems Engineering in Challenging Times”, Minneapolis, Minnesota, USA, July 25-29, 2010; Organiser: IEEE King, R., Jenkins, N., “ Switching Transients in Large Offshore Wind Farms”, 7th International Workshop on Large Scale Integration of Wind Power and on Transmission Networks for Offshore Wind Farms, Madrid, Spain, May 26-27, 2008; ISBN: 978-3-9813870-0-1; Publisher: Energynautics 6 C o n t e n t s C o n t e n t s Abstract........................................................................................................................ 3 Declaration ...................................................................................................................4 Acknowledgements...................................................................................................... 5 List of Publications ...................................................................................................... 6 List of Tables ..............................................................................................................12 List of Figures.............................................................................................................14 1. Introduction ....................................................................................................... 21 1.1. Offshore Wind Energy ................................................................................. 21 1.2. Offshore wind farms ......................................................................................21 1.2.1. Offshore Wind Farms in the UK ........................................................... 22 1.3. Transmission options for large offshore wind farms .................................. 23 1.3.1. Medium Voltage AC Transmission......................................................24 1.3.2. High Voltage AC Transmission .............................................................24 1.3.3. HVDC Transmission ............................................................................. 26 1.4. Research Objective ........................................................................................ 27 1.4.1. Main Objectives of the Thesis .................................................................. 27 1.4.2. The