WG 21 - TC 88/WG 21

IEC TS 61400-21-4:2025 specifies a uniform methodology, defining measurement, testing and assessment procedures of electrical characteristics of wind turbine components and subsystems, as basis for the verification of the electrical capabilities of wind turbines and wind turbine families.
This document includes the following aspects:
- definitions of test bench, subsystems and interface;
- definitions of system requirements for the test bench to perform relevant measurements (grid strengths, short circuit power, THD, …);
- measurement procedures for quantifying the electrical characteristics;
- test and measurement procedures for verifying and validating the electrical characteristics of components and subsystems in relation to grid compliance requirements;
- procedures for the transferability of the component and subsystem test results, measured at the test bench, to WT product families;
- documentation requirements and validation procedures of components, subsystems and wind turbines.
The results of the measurements and assessments of the wind turbine components and subsystems will be used as input for the verification of electrical capabilities as described in IEC 61400-21-1 and for the validation and verification of the electrical simulation models for wind power plants (WPP) as described in IEC 61400-27.

IEC 61400-21-2:2023 defines and specifies the quantities that are determined to characterize the electrical characteristics of grid-connected power plants (PPs).
This document defines the measurement and test procedures for quantifying the electrical characteristics as basis for the verification of compliance of PPs. This document defines a uniform functionality test and measurement procedure for the power plant controller (PPC), as a basis for the unit test of the power plant controller.
This document defines the procedures for assessing compliance with electrical connection requirements, including the aggregation methods for power quality aspects such as voltage variations, flicker, harmonics and interharmonics. This document defines the procedures for measurement and fault recording, for example for the verification of power plant electrical simulation models in relation to undervoltage and overvoltage ride-through events.

IEC 61400-21-1:2019 includes:
· definition and specification of the quantities to be determined for characterizing the electrical characteristics of a grid-connected wind turbine;
· measurement procedures for quantifying the electrical characteristics;
· procedures for assessing compliance with electrical connection requirements, including estimation of the power quality expected from the wind turbine type when deployed at a specific site.
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 connection to an electricity supply network to be tested and characterized as specified in this part of IEC 61400.
This first edition cancels and replaces the second edition of 61400-21 published in 2008. This edition includes the following new items with respect to 61400-21:
a) frequency control measurement;
b) updated reactive power control and capability measurement, including voltage and cos φ control;
c) inertia control response measurement;
d) overvoltage ride through test procedure;
e) updated undervoltage ride through test procedure based on Wind Turbine capability;
f) new methods for the harmonic assessment.

IEC 61400-21:2008 covers the 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; and procedures for assessing compliance with power quality requirements, including estimation of the power quality expected from the wind turbine type. The main changes with respect to the previous edition deal with interharmonics and current distortions (
This publication is of high relevance for Smart Grid.