All customers connected to a public electricity network, whether generators or consumers, must comply with agreed technical requirements. Electric networks rely on generators to provide many of the control functions, and so the technical requirements for generators are unavoidably more complex than for demand customers. These technical requirements are termed 'Grid Codes'.
The technical requirements governing the relationship between generators and system operators need to be clearly defined. The introduction of renewable generation has often complicated this process significantly, as these generators have physical characteristics that are different from the directly connected synchronous generators used in large conventional power plants. In some countries, a specific grid code has been developed for wind farms, and in others the aim has been to define the requirements as far as possible in a way which is independent of the power plant technology.
The technical requirements within grid codes and related documents vary between electricity systems. However, for simplicity the typical requirements for generators can be grouped as follows:
• Tolerance - the range of conditions on the electricity system for which wind farms must continue to operate;
• Control of reactive power - often this includes requirements to contribute to voltage control on the network;
• Control of active power - often this includes requirements to contribute to frequency control on the network;
• Protective devices; and
It is important to note that these requirements are often specified at the Point of Common Coupling (PCC) between the wind farm and the electricity network. In this case, the requirements are placed at wind farm level, and wind turbines may be adapted to meet these requirements. It is also possible for some requirements to be met by providing additional equipment, as for example for FACTS devices.
One of these new connection requirements regarding wind energy is fault ride-through capability. In the past, wind generators were not allowed to remain connected to the utility when voltage at the PCC fell below 85 %, forcing their disconnection even when the fault happened far from the wind farm (Jauch et al, 2007; Rodriguez et al, 2002). That is the reason why, in grids with significant wind energy penetration, the voltage dip and the subsequent wind farm disconnections would create an important stability problem.
Therefore, it is important to check the compliance with Grid Codes. The Spanish Wind Energy Association has developed the document "Procedure for Verification Validation and Certification of the Requirements of the OP 12.3 on the Response of Wind Farms in the Event of Voltage Dips (PVVC) (AEE, 2007), and the German Fördergesellschaft Windenergie und andere Erneuerbare Energien the document "Technical Guidelines for Power Generating Units. Part 8. Certification of the electrical characteristics of power generating units and systems in the medium., high- and highest-voltage grids"(FGW-TG8) (FGW, 2009) that describes the procedures to certify wind power installations according their corresponding Grid Codes.
The Compliance with Grid Codes can be checked by means of in-field test or by simulation of validated models. This chapter describes the procedure to verify wind installations according PVVC and FGW-TG8. Section 2 lists the most outstanding international Grid Codes, section 3 describes the fault ride through solutions of the different wind turbine types. Section 4 describes the fault ride through certification procedure, section 5 the voltage dip test, section 6 the model validation according to PVVC and FGW-TG8. Section 7 the wind farm verification according to PVVC.
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