Grid Integration: Requirements for Wind Turbines

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Grid Integration: Requirements for Wind Turbines

  1. 1. The requirements for wind turbines and services for grid code complianceIntroductionThe advancement in offshore wind power technology has led to larger turbines and largerwind farms being deployed throughout Europe. Where previously wind farms had beenthought of as single distributed power generators, they must now be considered as integralcomponents of the overall energy supply system, and be subject to the same regulations asother types of power generation.The European Wind Energy Association (1) estimates that by 2020 between 14.4% and 16.7% of the EU’s electricity supply will be sourced from wind energy, both on land andoffshore. The European Commission’s energy strategy for Europe (2) suggests that up to12% of this will be supplied by offshore wind farms.Due to the increase in the size of wind farms, and the requirement of Europe’s TSO’s(Transmission System Operators) to integrate them into the network, grid code compliancerules have been implemented to ensure that offshore wind farms contribute to the system,and behave in the same way as conventional generators. Before connection to the grid,wind turbines and wind farms must certify that they comply with regulations surroundingfrequency dependant active power supply (frequency control), Voltage control – bothsteady state and dynamic, Voltage dependant reactive power injection and absorption, andfault ride through stability.While the European grid as a whole must undergo rapid redevelopment to access andintegrate offshore wind power, the responsibility of turbine manufacturers and wind farmconstruction companies is to ensure that their equipment, when connected, has a positiveimpact on the overall system.----------------------------------------------------------------------------------------------------------------------------- IQPC GmbH | Friedrichstr. 94 | D-10117 Berlin, Germany t: +49 (0) 30 2091 3330 | f: +49 (0) 30 2091 3263 | e: eq@iqpc.de | w: www.iqpc.de Visit IQPC for a portfolio of topic-related events, congresses, seminars and conferences: www.iqpc.de
  2. 2. Source: EWEAGrid code requirements for wind turbines and wind farmsThe European Wind Energy association is working towards the harmonisation of grid codecompliance across Europe, and in late 2009 issued the first template for a generic grid code(3) format for wind power plants. The organisation is in continued collaboration with the EUand with Europe’s TSO’s to develop a fully continental-wide harmonised grid code. Some ofthe practical requirements for wind farms are discussed in detail below.ToleranceWhen connected to the transmission network, wind farms must show the capability tooperate within defined parameters of minimum and maximum voltage and frequency.Voltage parameters are usually referred to as ‘steady state’ values, but short term valuesincorporating a wider range may also apply for limited periods in adverse circumstances.Minimum and maximum frequency is a continuous value range, but again there are severalshort term ranges acceptable for short periods in extreme cases.In systems that have a high level of wind power integration, it is to be expected that thewind farm will continue to operate throughout system failures, at very low voltage levels.The grid code requirements for this fault ride through (FRT) situation can vary depending onthe network, and in the case of some wind farms it is more viable to install additionalequipment to ensure compliance.----------------------------------------------------------------------------------------------------------------------------- IQPC GmbH | Friedrichstr. 94 | D-10117 Berlin, Germany t: +49 (0) 30 2091 3330 | f: +49 (0) 30 2091 3263 | e: eq@iqpc.de | w: www.iqpc.de Visit IQPC for a portfolio of topic-related events, congresses, seminars and conferences: www.iqpc.de
  3. 3. Reactive power controlReactive power production and consumption is a utility of power generation plants that windfarms must also comply with. Often voltage dependant, the wind farm must be able tocontrol its power production or absorption to maintain a set level of voltage, which enablesnetwork operators to control the voltage passing through their systems. There may be ruleswithin the grid code that regulate the speed of response and the accuracy of these controls.Some wind turbine manufacturers are able to produce turbine designs that fulfil thesecriteria, and wind farms as a whole may be able to meet the requirements with a highquality SCADA system. Usually the voltage is measured at the point of common coupling,although other locations may be specified depending on the connecting grid and itsregulations. As wind power is such a variable energy source, it may prove more viable insome cases to introduce additional control equipment to achieve these standards.Active power controlActive power control could, in the purest sense, be viewed as wastage for a wind turbine,but it is a vital component of the control of a network for all types of power generators.Active control is the ability to reduce power output to suit the requirements of the system.Conventional systems can offset the power output reduction with the saving in fuel thusmaking economic sense. As wind is a free source of energy, any reduction in power is a lossof energy, and system operators are encouraged to use this as a last resort measure whencontrolling networks.Wind turbines use different methods of power control; a pitched turbine can reduce powerby adjusting the pitch of the blades, whereas stall-regulated turbines can contribute to thepower reduction of the wind farm as a whole if individual turbines are shut down. Neither isthe most accurate in real terms, and some grids implement a capping system whereby awind farm, or group of wind farms, must maintain power output below a certain level at all----------------------------------------------------------------------------------------------------------------------------- IQPC GmbH | Friedrichstr. 94 | D-10117 Berlin, Germany t: +49 (0) 30 2091 3330 | f: +49 (0) 30 2091 3263 | e: eq@iqpc.de | w: www.iqpc.de Visit IQPC for a portfolio of topic-related events, congresses, seminars and conferences: www.iqpc.de
  4. 4. times. In more complex scenarios a cap may require that power output is held at a fixedlevel below the full unrestrained power output possible if utilising full wind speed.To integrate into the network, some grids require that wind farms also control ramp rates ofpower output when wind power increases, or when failed turbines are returned to service.This is so the demand on other generators within the system can be managed moreeffectively.Where wind power is a major contributor to a system, there may also be regulationsrequiring the wind farm to contribute to frequency control. By increasing power outputwhen the frequency is low and decreasing it under high frequency, the wind farm can helpto maintain system frequency levels. Want to learn more about grid integration of offshore wind energy? Visit our download centre for more articles, white papers and interviews: http://bit.ly/grid-offshore-windReferences(1) http://www.ewea.org/index.php?id=196(2) http://ec.europa.eu/energy/publications/doc/2011_energy2020_en.pdf(3) http://www.ewea.org/fileadmin/ewea_documents/documents/publications/091127_GGCF_Final_Draft.pdf(4)http://library.abb.com/global/scot/scot232.nsf/veritydisplay/50fab2bdc45be270c12572ea0050ae66/$File/STATCOM%20Technology%20for%20Wind%20Parks%20to%20Meet%20Grid%20Code.pdfFurther referenceshttp://www.ewea.org/fileadmin/ewea_documents/documents/publications/position_papers/091210_EWEA_Harmonising_Europes_GCs_for_the_Connection_of_Wind_Power_Plants.pdfhttp://www.wind-energy-the-facts.org/en/part-2-grid-integration/chapter-5-grid-connection-requirements/grid-codes-and-essential-requirements-for-wind-power-plants/grid-codes-and-essential-requirements-for-wind-power-plants.html----------------------------------------------------------------------------------------------------------------------------- IQPC GmbH | Friedrichstr. 94 | D-10117 Berlin, Germany t: +49 (0) 30 2091 3330 | f: +49 (0) 30 2091 3263 | e: eq@iqpc.de | w: www.iqpc.de Visit IQPC for a portfolio of topic-related events, congresses, seminars and conferences: www.iqpc.de

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