EVS-EN 61400-21:2008

This part of IEC 61400 includes:
•definition and specification of the quantities to be determined for characterizing the power quality of a grid connected wind turbine;
•measurement procedures for quantifying the characteristics;
•procedures for assessing compliance with power quality requirements, including estimation of the power quality expected from the wind turbine type when deployed at a specific site, possibly in groups.
The measurement procedures are valid for single wind turbines with a three-phase grid connection. The measurement procedures are valid for any size of wind turbine, though this part of IEC 61400 only requires wind turbine types intended for PCC (Point of Common Coupling) at MV or HV to be tested and characterized as specified in this part of IEC 61400.
The measured characteristics are valid for the specific configuration and operational mode of the assessed wind turbine type only. Other configurations, including altered control parameters that cause the wind turbine to behave differently with respect to power quality, require separate assessment.
The measurement procedures are designed to be as non-site-specific as possible, so that power quality characteristics measured at for example a test site can be considered valid also at other sites.
The procedures for assessing compliance with power quality requirements are valid for wind turbines with PCC at MV or HV in power systems with fixed frequency within 1 Hz, and sufficient active and reactive power regulation capabilities. In other cases, the principles for assessing compliance with power quality requirements may still be used as a guidance.
This part of IEC 61400 is for testing of wind turbines, though it contains information that may also be useful for testing of wind farms.
NOTE This part of IEC 61400 uses the following terms for system voltage:
– low voltage (LV) refers to Un  1 kV;
– medium voltage (MV) refers to 1 kV < Un  35 kV;
– high voltage (HV) refers to Un > 35 kV