Study of Grid Code Compliance
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UPTEC-ES12026 Examensarbete 30 hp Augusti 2012 Study of Grid Code Compliance Thanet Wind Farm Malin Sjölund Abstract Study of Grid Code Compliance - Thanet Wind Farm Malin Sjölund Teknisk- naturvetenskaplig fakultet UTH-enheten The trend towards harmonizing grid codes within Europe will increase the demands for grid code Besöksadress: compliance. Wind power is for several reasons not Ångströmlaboratoriet Lägerhyddsvägen 1 comparable to conventional power generation but will, Hus 4, Plan 0 due to large installations, need to show compliance with the grid codes. This thesis is investigating grid Postadress: code requirements as proposed by National Grid (UK) Box 536 751 21 Uppsala and ENTSO-E. Modelling work and simulations have also been performed to investigate the grid code Telefon: compliance of Thanet offshore wind farm in UK. The 018 – 471 30 03 work has been about investigating frequency response Telefax: and fault-ride-through criterion and shows that grid 018 – 471 30 00 codes are fulfilled in Thanet but that the model requires further work. Hemsida: http://www.teknat.uu.se/student Handledare: Urban Axelsson, Ying He Ämnesgranskare: Mikael Bergkvist Examinator: Kjell Pernestål ISSN: 1650-8300, UPTEC ES12 026 Popul¨arvetenskaplig sammanfattning ”Grid Codes” inneb¨arsystemkrav som m˚aste uppfyllas av en produktionsenhet f¨oratt den ska f˚akoppla upp sig p˚aeln¨atet. Anledningen ¨aratt eln¨atet ¨arett stort och viktigt system som det ¨arviktigt att uppr¨atth˚alla stabiliteten p˚a.Stabiliteten p˚aeln¨atet kan framf¨orallt k¨anneteckas av att avbrott inte intr¨affar, alternativt intr¨affar ytterst s¨allan. Men stabilitet inneb¨arocks˚aatt h˚alla frekvens och sp¨anning inom de nominella v¨arden som ¨aruppr¨attade f¨oratt elektrisk utrustning ska kunna fungera utan sv˚arigheter. Vindkraft ¨arhistoriskt sett en liten energik¨alla och har d¨arf¨orinte varit f¨orem˚alf¨or omfattande systemkrav. Detta utifr˚anatt det har resonerats om att vindkraften inte p˚averkat eln¨atet d˚aproduktionen varit liten och eln¨atet starkt. Under senare ˚arhar dock vindkraften sett en enorm utveckling och fr˚anatt ha inneburit sm˚amaskiner p˚a n˚agra hundra kilowatt byggs nu stora parker som omfattar ett hundratal megawatt. Det ¨arav dessa anledningar naturligt att krav p˚aatt uppr¨atth˚alla systemet st¨alls ¨aven p˚avindkraftsparker men det inneb¨arextra kostnader f¨orde som ¨ager vindkraftparkerna. Inom EU finns det ambitioner att harmonisera elmarknaden f¨oratt underl¨atta handel ¨over gr¨anserna. Av denna anledning har ocks˚af¨orfattandet av gemensamma systemkrav p˚ab¨orjats, lett av ENTSO-E (European Network for Transmission System Operators of Electricity). Det ¨artydligt att systemkraven utformas i en riktning s˚aatt de kommer bli mer kr¨avande i framtiden, framf¨orallt f¨orvindkraft eftersom denna energik¨alla p˚am˚anga s¨att skiljer sig fr˚antraditionell. Bland annat ¨arvindkraften intermittent och har inte det naturliga tr¨oghetsmoment som storskaliga synkronmaskiner besitter. Existerande systemkrav idag ¨arutformade utifr˚ansystemets behov. England har tradi- tionellt h˚arda systemkrav och kan anv¨andas som en god referens f¨oranalys av nya f¨orslag. England ¨ardock inte det enda landet som st¨aller krav p˚avindkraften vid anslutning och turbintillverkare blir tvungna att tillgodose l¨osningar f¨orm˚anga olika behov. Thanet offshore vindpark har varit i fokus f¨ordenna studie, parken best˚arav vindtur- biner av typen dubbel-matad asynkrongeneratorer. Reglertekniska l¨osningar har legat i fokus vid studier f¨orhur parken uppfyller systemkrav p˚afrekvensrespons och ”fault- ride-through” kriterier d˚afel simuleras p˚adet ¨overliggande n¨atet. Studien visar att vindparken ¨arkapabel att uppfylla de krav som studerats. Studien p˚avisar dock att modellen som anv¨ants har brister och tolkning av resultaten b¨orta h¨ansyn till detta. 3 Summary In terms of wind farm owner Vattenfall is responsible to ensure grid code compliance of its wind farm Thanet. As Thanet is connecting to UK the grid code to comply with is the one issued by National Grid. The grid codes concerned in this study have been those covering frequency response and fault-ride through. As these disturbances are not convenient to introduce in the real transmission system simulation studies in the software PSS/E have been performed. The study has been covering modelling work, out of an existing model covering the grid connection, as well as simulation studies regarding dynamics. The modelling work has resulted in an aggregated representation of Thanet wind farm and the transmission grid in the connecting point has been expanded and represented in a Thevenin equivalent. The model consists of the connection configuration, including SVC Plus devices, and aggregated wind turbines provided by the wind turbine manufacturer. The wind tur- bines also involves a power plant controller, which is a technique developed for future grid code demands. The simulations assures grid code compliance for Thanet offshore wind farm with re- gards to frequency response and fault ride through for three-pase shortcircuit faults and single-line to ground faults on the overlying network. These simulations are limited to full-load operation. The study also covers summaries of the grid code issued by National Grid and European Network of Transmission System Operator for Electricity (ENTSO-E). It is concluded that future grid codes most certainly will be more demanding for wind farm owners and that technique such as the power plant controller will be required to achieve compliance. 4 Abbrevation List AC Alternating Current DC Direct Current DFIG Double-Fed Induction Generator ENTSO-E European Network of Transmission System Operators for Electricity FRT Fault Ride Through FSM Frequency Sensitive Mode HV High Voltage LFSM Limited Frequency Sensitive Mode LVRT Low Voltage Ride Through MSC Mechanical Switched Capacitor MSR Mechanical Switched Reactor NG National Grid PCC Point of Common Coupling PPC Power Plant Controller TSO Transmission System Operator WTG Wind Turbine Generator 5 Contents 1 Introduction 8 1.1 Background . 8 1.2 Purpose ..................................... 9 1.3 PreviousWork ................................. 9 1.4 Definitions.................................... 11 1.5 Limitations . 12 1.6 ProjectOutline................................. 12 2 Theory 13 2.1 Wind power technology . 13 2.2 Systemstability................................. 14 2.2.1 Frequency control . 14 2.2.2 Fault Ride Through -FRT . 15 2.3 Symmetrical Components and Unbalanced Faults . 15 2.4 PowerPlantController-PPC . 18 3 Grid Codes 19 3.1 National Grid . 19 3.1.1 Frequency Control . 19 3.1.2 Voltage Control . 25 3.1.3 Fault Ride Through . 27 3.2 ENTSO-E.................................... 30 3.2.1 Frequency Control . 30 3.2.2 Voltage Control . 32 3.2.3 Fault Ride Through . 35 4 Model Work 37 4.1 Aggregating Thanet wind farm . 37 4.2 Studyoftheoverlyingnet ........................... 38 4.2.1 Modelforfrequencyresponse . 41 4.2.2 Model for fault studies . 43 4.3 Dynamic Parameter Set-Up . 43 6 5 Frequency Response 45 5.1 HighFrequencyEvents............................. 46 5.2 LowFrequencyEvents ............................. 48 6 Solid Three-Phase Short Circuit Faults 50 6.1 Results from Dynamic Simulation . 50 6.2 Voltage and Current Contribution . 56 6.3 SwingBusBehavior .............................. 57 7 Unsymmetrical Single Line to Ground Fault 60 7.1 Zerosequencedata............................... 60 7.2 Voltage and Current Contributions . 61 7.3 Dynamic Simulation . 63 8 Discussion 67 8.1 GridCodes ................................... 67 8.2 ThanetSimulationModel ........................... 68 8.3 Conclusion and Prospects for Further Work . 71 7 1. Introduction 1.1 Background Grid codes are basically the rules to be followed when connecting generators to the grid. The grid codes within a transmission region are issued by the, for that region, transmis- son system operator (TSO), with the purpose to ensure system stability. As wind power until the end of the nineties was rather small and had small impact on system operation, grid code requirements specially issued for wind power plants are a fairly new concern [1]. With wind power plants growing bigger in size it is reasonable that wind power must be included in the grid codes. Wind power is an intermittent power source by nature though and can therefore not be regarded as a conventional synchronous generation unit. The region for which the Transmission System Operator (TSO) is responsible is nor- mally a country (or part of a country for countries of a greater area). Since the purpose with the grid codes is to sustain system stability, the grid codes will depend on system needs. The grid codes contain power quality requirements as well as system stability requirements, this work will be covering system stability, i.e. frequency response, voltage stability and fault ride through (FRT). At present the grid codes issued by the European TSO:s are individual for the coun- tries. Vattenfall is operating wind power in Germany, UK and Holland as well as in Sweden and is thereby facing different grid codes for the different countries. The grid codes in UK have shown to be technically demanding and are therefore extra cost driving. The European Network of Transmission System Operators of Electricity (ENTSO-E) has been working for a common grid code for the TSO:s operating in Europe. This grid code is under development and this thesis is covering the draft presented in January 2012 [3]. The aim of the ENTSO-E grid code is to harmonize the power market and ensure system stability. With operation in several European countries Vattenfall will be affected by the new regulations and sees interest in discussion regarding the new grid codes. 8 1.2 Purpose This thesis has the main purpose to study grid code compliance for Thanet wind farm UK. Secondly it serves to clarify how different grid codes affect technical solutions and their costs. Theory will be complemented with simulation studies to give a systems perspective and a better understandning for techniques involved in meeting grid code demands.