Electrical Networks of Corpower Wave Farms Economic Assessment and Grid Integration Analysis of Voltage
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DEGREE PROJECT IN ELECTRICAL ENGINEERING, SECOND CYCLE, 30 CREDITS STOCKHOLM, SWEDEN 2017 Electrical Networks of CorPower Wave Farms Economic Assessment and Grid Integration Analysis of Voltage NIERAJ RAJ KUMAR BHARATHI KTH ROYAL INSTITUTE OF TECHNOLOGY SCHOOL OF ELECTRICAL ENGINEERING Electrical Networks of CorPower Wave Farms Economic Assessment and Grid Integration Analysis of Voltage NIERAJ RAJ KUMAR BHARATHI Supervisors Ryan O’Donnell and Jéromine Maillet CorPower Ocean Mohammad Nazari Royal Institute of Technology, Stockholm Examiner Lennart Söder Royal Institute of Technology, Stockholm Master of Science Degree Project in Electric Power Systems at the School of Electrical Engineering Royal Institute of Technology Stockholm, Sweden, November 2017. Abstract On the path towards the commercialisation of wave energy, there are still certain developmental challenges to be tackled by industry and academia. One of these challenges is the grid integration of wave farms along with the development of the offshore electrical networks for the farms. These networks are distinct from those of offshore wind farms on certain features – connection layouts, electrical interface equipment (subsea connectors), power ratings and cable lengths amongst many others. These differences apart from some challenges unique to wave farms make the corresponding research attractive. CorPower Ocean AB has been developing a 250 푘푊 point-absorber type Wave Energy Converter (WEC) and the thesis investigates the afore-mentioned challenges with a stage- wise analysis of wave farms comprising the CorPower WECs. Prior research on electrical networks for CorPower WECs is limited and in this regard the objective is to gain a preliminary insight into the electrical architecture of a pre-commercial wave farm. Furthermore, the entire study is based at the wave test site of the European Marine Energy Centre (EMEC). Analysis of network architecture and operational constraints resulted in 4 network variants for the farm ratings of 2 푀푊 and 10 푀푊. Three of the variants are applied to a 2 푀푊 farm and are subjected to a varied analysis after which the standout variant is chosen for subsequent modelling and analysis in the form of a 10 푀푊 farm. The comparative analysis includes an investigation into the capital expenditure (CAPEX), the associated cost uncertainty, technology readiness level (TRL) of the electrical components and network efficiency. Dynamic modelling and simulation of the networks is then performed on DIgSILENT PowerFactory to provide the network efficiency and voltage quality parameters including step voltage change, operational voltage limits and voltage flicker. The voltage quality of the modelled networks at the connection point are largely found to be compliant to the UK Distribution Code, applicable at the EMEC site. But, the same could not be said for the results at some of the internal points of the electrical networks of the wave farms as the voltage levels at certain terminals were found to be on the higher side. From the results of the thesis, a greater understanding of the compatibility of variants for a 2 푀푊 farm and 10 푀푊 farm of 250 푘푊 point-absorber WECs, has been obtained. Overall, it is believed that the thesis has contributed to the growing reservoir of information on offshore electrical networks of wave farms and the corresponding grid integration issues. i Sammanfattning På vägen mot kommersialisering av vågenergi finns det fortfarande vissa utvecklingsutmaningar som måste hanteras av industrin och akademin. En av dessa utmaningar är grid integrationen av våg farmar tillsammans med utvecklingen av de offshore elnäten för gårdarna . Dessa nätverk skiljer sig från de vindkraftverk som finns på vissa områden - anslutningslayouter, elektrisk gränssnittsutrustning (subsea-kontakter), effektvärden och kabellängder bland många andra. Dessa skillnader förutom vissa utmaningar som är unika för våg farmar gör att motsvarande forskning attraktiv. CorPower Ocean AB har utvecklat en punktabsorberande Wave Energy Converter (WEC) på 250 푘푊 och avhandlingen studerar på de ovan nämnda utmaningarna med en stegvis analys av våg anläggningar som omfattar CorPower WEC. Tidigare forskning på elnät för CorPower WEC är begränsad och målet är att få en preliminär inblick i den elektriska arkitekturen hos en kommande kommersiell våggård. Dessutom är hela studien baserad på vågtestplatsen för European Marine Energy Center (EMEC). Analys av nätverksarkitektur och operativa begränsningar resulterade i 4 nätverksvarianter för gårdarna på 2 MW och 10 푀푊. Tre av varianterna appliceras på en 2 푀푊 gård och utsätts för en varierad analys varefter den utmärkbara varianten väljs för efterföljande modellering och analys i form av en 10 푀푊 gård. Den jämförande analysen innefattar en undersökning av kapitalkostnaderna (CAPEX), associerad kostnadsosäkerheten, teknologis mognadsgrad (TRL) för de elektriska komponenterna och nätverkseffektiviteten. Dynamisk modellering och simulering av nätverket utförs sedan på DIgSILENT PowerFactory för att tillhandahålla nätverkseffektivitet och spänningskvalitetsparametrar inklusive stegspänningsbyte, driftsspänningsgränser och spänningsflimmer. Spänningskvaliteten hos nätverket vid anslutningspunkten är i stor utsträckning befunnit att överensstämma med den brittiska distributionskoden, som är tillämplig på EMEC- platsen. Detsamma kunde inte sägas om resultaten på några av de inre punkterna i elnätens våg farmar, eftersom spänningsnivåerna vid vissa terminaler befanns vara på det högre sidan. Av avhandlingens resultat har en större förståelse erhållit för varianternas kompatibilitet för en 2 푀푊 gård och 10 푀푊 gård med 250 푘푊 punktabsorberande WEC. Generellt är det troligt att avhandlingen har bidragit till den växande information om offshore elnät av våg farmar och motsvarande grid integrationsfrågor. ii Acknowledgments I would first like to thank CorPower Ocean AB for giving me the opportunity to write my thesis in the very interesting field of grid integration of wave energy. It is exciting to learn from and contribute towards a new and rapidly growing field of technology that could one day become one of the major sources of energy on the planet. More importantly, I want to express my gratitude to Dr. Ryan O’Donnell, my supervisor at CorPower Ocean who has been a pillar of guidance and support through the duration of the thesis. He has always been available for correspondence and our detailed discussions on several topics has been invaluable for the work performed in this report, apart from enabling me to tackle the broad variety of topics seen in the thesis. Then, I would like to thank Jéromine Maillet, Project Manager at CorPower Ocean for her continued guidance and for her penchant for encouraging me to always put the results of the work in a larger context. Then, I would like to thank Dr. Mohammad Nazari who has been my supervisor at KTH, for his critical support at various stages of the thesis, ultimately helping me reach my final goal. I would also like to thank Professor Lennart Söder for agreeing to be my examiner, and for the evaluation and constructive feedback provided on the thesis. Finally, I want to thank my family and friends, both near and far from Stockholm. They have been a constant source of unfailing support and motivation right through the duration of this thesis. iii Table of Contents Chapter 1 - Introduction .............................................................................. 1 Challenges of Wave Energy .............................................................................................. 1 1.1 Wave Energy Converter .......................................................................... 1 1.1.1 Types of Devices .................................................................................................... 2 1.1.2 CorPower Ocean .................................................................................................... 3 1.2 Thesis Background .................................................................................. 5 1.2.1 Objectives .............................................................................................................. 6 1.2.2 Network Variants ................................................................................................... 6 1.3 Power System Simulations ...................................................................... 7 1.3.1 DIgSILENT PowerFactory ..................................................................................... 7 1.4 Thesis Outline .........................................................................................8 Chapter 2 - Wave Farm Electrical Architecture ....................................... 9 2.1 European Marine Energy Centre Test Site .......................................... 10 2.2 Wave Energy Converter Design ............................................................ 11 2.2.1 Typical Power Ratings ........................................................................................... 11 2.2.2 Electrical Design of CorPower .............................................................................. 11 2.3 Wave climate ..........................................................................................12 2.4 Components of the Electrical Network of a Wave Farm ..................... 15 2.4.1 Cables .................................................................................................................... 15 2.4.2 Electrical Interface Equipment ...........................................................................