The document discusses the requirements for wind turbines and wind farms to comply with European grid codes as offshore wind power increases its contribution to the energy supply. As wind farms get larger, they must be integrated into the transmission network and behave similarly to conventional power plants. Grid code compliance regulations ensure wind farms contribute stability and respond appropriately to changes in voltage and frequency. Specific requirements addressed include operating within defined voltage and frequency ranges, providing reactive power control, engaging in active power control including ramp rate limits, and assisting with frequency control. Harmonizing grid codes across Europe will help increase wind power integration onto the grid.

1. The requirements for wind turbines and services for grid
code compliance
Introduction
The advancement in offshore wind power technology has led to larger turbines and larger
wind farms being deployed throughout Europe. Where previously wind farms had been
thought of as single distributed power generators, they must now be considered as integral
components of the overall energy supply system, and be subject to the same regulations as
other 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 and
offshore. The European Commission’s energy strategy for Europe (2) suggests that up to
12% 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 compliance
rules 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 surrounding
frequency dependant active power supply (frequency control), Voltage control – both
steady state and dynamic, Voltage dependant reactive power injection and absorption, and
fault ride through stability.
While the European grid as a whole must undergo rapid redevelopment to access and
integrate offshore wind power, the responsibility of turbine manufacturers and wind farm
construction companies is to ensure that their equipment, when connected, has a positive
impact on the overall system.
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2. Source: EWEA
Grid code requirements for wind turbines and wind farms
The European Wind Energy association is working towards the harmonisation of grid code
compliance 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 EU
and with Europe’s TSO’s to develop a fully continental-wide harmonised grid code. Some of
the practical requirements for wind farms are discussed in detail below.
Tolerance
When connected to the transmission network, wind farms must show the capability to
operate within defined parameters of minimum and maximum voltage and frequency.
Voltage parameters are usually referred to as ‘steady state’ values, but short term values
incorporating 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 several
short 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 the
wind 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 on
the network, and in the case of some wind farms it is more viable to install additional
equipment to ensure compliance.
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3. Reactive power control
Reactive power production and consumption is a utility of power generation plants that wind
farms must also comply with. Often voltage dependant, the wind farm must be able to
control its power production or absorption to maintain a set level of voltage, which enables
network operators to control the voltage passing through their systems. There may be rules
within 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 these
criteria, and wind farms as a whole may be able to meet the requirements with a high
quality 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 its
regulations. As wind power is such a variable energy source, it may prove more viable in
some cases to introduce additional control equipment to achieve these standards.
Active power control
Active 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 thus
making economic sense. As wind is a free source of energy, any reduction in power is a loss
of energy, and system operators are encouraged to use this as a last resort measure when
controlling networks.
Wind turbines use different methods of power control; a pitched turbine can reduce power
by adjusting the pitch of the blades, whereas stall-regulated turbines can contribute to the
power reduction of the wind farm as a whole if individual turbines are shut down. Neither is
the most accurate in real terms, and some grids implement a capping system whereby a
wind farm, or group of wind farms, must maintain power output below a certain level at all
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t: +49 (0) 30 2091 3330 | f: +49 (0) 30 2091 3263 | e: eq@iqpc.de | w: www.iqpc.de
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4. times. In more complex scenarios a cap may require that power output is held at a fixed
level 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 of
power 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 more
effectively.
Where wind power is a major contributor to a system, there may also be regulations
requiring the wind farm to contribute to frequency control. By increasing power output
when the frequency is low and decreasing it under high frequency, the wind farm can help
to maintain system frequency levels.
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References
(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/STATC
OM%20Technology%20for%20Wind%20Parks%20to%20Meet%20Grid%20Code.pdf
Further references
http://www.ewea.org/fileadmin/ewea_documents/documents/publications/position_papers/091210_EWEA_Har
monising_Europes_GCs_for_the_Connection_of_Wind_Power_Plants.pdf
http://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
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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