Downloaded from orbit.dtu.dk on: Dec 20, 2017 Switching overvoltages in offshore wind power grids Arana Aristi, Ivan; Nielsen, Arne Hejde; Holbøll, Joachim; Jensen, Kim Høj; Sørensen (fratrådt), Troels Publication date: 2011 Document Version Publisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Arana Aristi, I., Nielsen, A. H., Holbøll, J., Jensen, K. H., & Sørensen (fratrådt), T. (2011). Switching overvoltages in offshore wind power grids. Kgs. Lyngby: Technical University of Denmark (DTU). 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PhD Thesis, November 2011 Iván Arana Aristi Switching overvoltages in off- shore wind power grids. Measurements, modelling and validation in time and frequency domain. PhD Thesis, November 2011 Switching overvoltages in offshore wind power grids. Measurements, modelling and validation in time and frequency domain. Author(s): Iván Arana Aristi Supervisor(s): Joachim Holbøll, Arne Hejde Nielsen, Troels Stybe Sørensen and Kim Høj Jensen Department of Electrical Engineering Centre for Electric Technology (CET) Technical University of Denmark Elektrovej 325 DK-2800 Kgs. Lyngby Denmark www.elektro.dtu.dk/cet Tel: (+45) 45 25 35 00 Fax: (+45) 45 88 61 11 E-mail: [email protected] Release date: December 2011 Class: 1 (public) Edition: First edition Comments: This report is part of the requirements to achieve PhD in Electri- cal Engineering at the Technical University of Denmark. The report represents 30 ECTS points. Rights: © Iván Arana Aristi, 2011 2 Introduction Con amor para mi familia que está, que se fué y que vendrá. 3 Introduction 4 PREFACE The present PhD thesis is submitted as part of the requirements for achieving the Danish PhD degree at the Department of Electrical Engineering, Electric Components at the Technical University of Denmark. The research has been conducted from the 1 Decem- ber 2008 to the 30 November 2011. This thesis shows the main results of the work made as part of the Industrial PhD project "Overvoltages and protection in offshore wind power grids" supported by the Danish Ministry of Science, Technology and Innovation, project number 08-041566. Firstly, I would like to thank my academic and industrial supervisors for their guidance and encouragement during the entire period of the project; Associate Professor Joachim Holbøll and Associate Professor Arne Hejde Nielsen from the Department of Electrical Engineering at DTU; Lead Specialist Troels Stybe Sørensen from the Electrical Systems at DONG Energy Renewables and Development Engineer Kim Høj Jensen at Siemens Wind Power R&D. Secondly, I would like to thank my colleagues from DONG Energy, since thanks to them I felt part of the Department right from the beginning: Lukasz Kocewiak, Ole Holmstrøm, Jan Okholm, David Taus Johnsen, Jesper Hjerrild and Asger Jensen. I would like to thank specially my Manager, Søren Ranneries, for his support and help during these three years. During the project I was involved with different Offshore Wind Farm projects at DONG Energy on different stages of design, construction and operation. I would like to extend my gratitude to the people that helped me in Nysted Offshore Wind Farm, Gunfleet Sands Offshore Wind Farm, Avedøre Offshore Wind Farm, Burbo Bank Offshore Wind Farm, Walney Offshore Wind Farm, Anholt Offshore Wind Farm and London Array Offshore Wind Farm. I would like to express my gratitude as well to Assembly Line Manager, Carsten Mad- sen, at Siemens Wind Power in Brande for his help and support during the measure- ments of different components in Brande. 5 Introduction I received extensive support from the people at the High Voltage Laboratory and Work- shop at DTU. I would like to thank Freddie Fahnøe, Jens Chr. Jensen, and specially Flemming Juul Petersen for their help, patience and understanding. Different cooperation with international research centres, universities and companies were started along these three years, and thanks to these people the work reported here has been enriched; Bjørn Gustavsen from SINTEF in Trondheim, Rosemary King from Alstom in Stafford, Hans Kristian Høidalen from NTNU in Trondheim, Andrzej Holdyk from DTU in Kgs. Lyngby, Alvaro Hernandez from Siemens AG in Erlangen, Unnur Stella Gudmundsdottir from Energinet.dk in Fredericia, Peter Werelius from Megger in Täby, and Sadegh Mir Ghafourian from The University of Manchester in Manchester. In particular, I would like to thank SINTEF and Siemens AG for their enriching support during my stay in Trondheim and Erlangen, respectively. Thanks to Peter Weinreich-Jensen from Siemens A/S in Ballerup, for having made it possible for me to start communication with Friedemann Augsburger, Manager of the team ―System Integration & Grid Access‖ (E T PS EN 14) at Siemens AG in Erlangen. In this team, I was kindly received in 2010 for three months and the whole team made me feel very welcome during my time with them. Personally, I am very happy to have many friends around the world and in Copenhagen. You are too many to be named, thank you for making these years unforgettable. I want to express all my gratitude to my father Javier, mother Patricia, sisters Lucia and Teresa and aunt Enriqueta. Thank you for always believing in me, I could never have made it so far without your support as a family. You will always be in my heart even if I will not be so close to you – geographically. To all my relatives from the Monterrey and Mexico City, thank you for making me feel always close to you and being a large united family. Finally, the most important person in my life is my wife Esperanza. Thank you for be- ing supportive in these years. You have shared with me every moment, good and bad, in this PhD journey; and every time I had problems you were reassuring and caring. This would not have been achieved without you. I will always be there for you. Kgs. Lyngby, November 2011 Iván Arana Aristi 6 ABSTRACT Switching transients in wind turbines, the collection grid, the export system and the ex- ternal grid in offshore wind farms, during normal or abnormal operation, are the most important phenomena when conducting insulation coordination studies. However, the recommended models and methods from international standards and guidelines are in- sufficient to take into account considering the special conditions in offshore wind farms. This thesis focuses on the improvement of models and methods used in specialized elec- tromagnetic transient programs. In this thesis, an introduction to offshore wind farm electrical systems and the topic of transients is given in Chapter 1. In Chapter 2 it is described how the component and sub-system models are developed and used from an applied point of view, where com- mon and detail models are mentioned. In Chapter 3 results from frequency domain measurement on transformers and cables are presented. In Chapter 4 results from time domain measurements and simulations of switching operations in offshore wind power grids are described. Specifically, switching operations on a single wind turbine, the col- lection grid, the export system and the external grid measured in several real offshore wind farms are shown together with simulation results. Switching operations in offshore wind power grids can be simulated with different elec- tromagnetic transient programs. Different programs were used in the project and com- pared results are included in Chapter 4. Also in Chapter 4 different models were used in the same program, and in several switching operations sensitivity analysis was made. General models and methods to study switching transient overvoltages in offshore wind farms have been shown in this work. These models and methods are valid for all off- shore wind farms, or other systems to be analysed. As long as the required frequency domain measurements are performed in the appropriate components, the information used is correct and the system is created in a suitable simulation tool. The general method used to validate and create detailed models was proven to be very powerful and efficient. This method is also valid for all offshore wind farms, or other systems to be analysed. Once this method has been completed, the predictive simula- tions can be performed with certainty. 7 Introduction The specific method to adapt FRA measurements for transformer wide band modelling proposed in [54] was used successfully in 100kVA, 4MVA and 120MVA transformers. Based in the positive sequence voltage ratio comparison from different wind farm trans- former, it was concluded that the first resonance frequency from low to high voltage side is around 10kHz. This frequency match the low-frequency-end of the frequency range for natural frequencies on large transformer windings according to [52]. On the other hand, after the positive sequence voltage ratio comparison from different wind turbine transformer, it was concluded that the first resonance frequency in some transformers, from low to high voltage side are within range of the frequency range for natural frequencies on medium transformer windings according to [52]. It was found that some of the resonance frequencies from the offline diagnostics of transformers based on SFRA measurements, match the positive sequence voltage ratio resonance frequencies from low to high voltage side.